BULLETIN
OF MARINE
SCIENCE, 27(3):
400-422, 1977
COMMENTS ON THE WATER VASCULAR SYSTEM, FOOD
GROOVES, AND ANCESTRY OF THE
CLYPEASTEROID ECHINOIDS
Thomas
F. Phelan
ABSTRACT
Schemes for distribution of wat~r vessels in adoral, ambital, and petaloid regions of
the ambulacra are described. In the adoral and ambital region three basic patterns are
described. All three function as connections between the accessory tube foot ampullae and
the radial water vessels. Lobe-like expansions or side spurs of the radial water vessels
connect to the accessory tube foot ampullae in genera of the suborder Laganina. Simple
unbranching lateral water vessels connect to the accessory tube foot ampullae in genera of
the suborder Clypeasterina.
Complex branching lateral water vessels were observed in
genera of the suborder Scutellina. Accessory tube feet help collect food and are closely
associated with the food grooves. Four schemes of lateral water vessel and accessory
tube foot distribution within petaloid areas are described, two observed in petals composed of primary plates only, and two observed in petals with primary and demiplates.
The respiratory tube foot/ampulla
system of Del/draster excentricus is comparcd with
the suckered tube foot/ampulla system of the regular urchin Strongylocentrotus purpuratus.
The ampullae of both systems are flattened, and very thin walled. Fluid constantly circulates between tube foot and ampulla.
Un flattened bulbous ampullae were observed on the accessory tube feet and buccal
tube feet of clypeasteroids and the buccal tube feet of the regular urchin S. purpura/us.
These bulbous ampullae connect to the respective tube feet through single pores.
The greatly expanded ambulacral columns and adoral interruption of interambulacral
columns are considered closely related to the development of the accessory tube foot
system in clypeasteroids.
These expanded ambulacra and the adjacent regions of the
interambulacra which support accessory tube feet are considered phyllodes and homologous
to the more recognizable but less expansive phyllodes of the cassiduloids.
Some characters are common to the cassiduloids and clypeasteroids strongly suggesting
a cassiduloid ancestry for the clypeasteroids. Among these are a monobasal apical system,
respiratory pores between petal plates, the shape of lantern pyramids, buccal tube feet
on basicoronal plates, expansion of the ambulacra forming phyllodes, and single pore
supported tube feet adoral to the petals.
Most previously published works that
mention accessory tube feet are limited to
accessory pore distribution, tube foot activity, and histology. In this paper I intend to
describe the several schemes of water vessel
distribution and the functional relationship
of accessory tube feet to food grooves where
present.
Comments on the increase in number of
accessory tube feet and lateral water vessels
relative to plate growth are limited as the
processes by which this is accomplished is
not yet fully understood. This study is con-
tinuing on the plates of Dendraster excentricus.
Less extensive comments are given on
the respiratory tube feet/ampullae and the
ampullae of buccal tube feet. The relationship of accessory tube feet to expanded ambulacral columns and the recognition of
these and portions of some interambulacra
as phyllodes lead to the comments on the
ancestry of clypeasteroids. Many of my
ideas on the relationship of clypeasteroids
to cassiduloids had as their source my close
association with Porter M. Kier.
400
PHELAN:
WATER
VASCULAR
MATERIALS
The echinoids listed below were studied
for this work. Throughout the text generally
only the generic name is used because this
paper is primarily concerned with principles
rather than systematic descriptions.
Echinocyamus
sp. USNM ] 406 (3 specimens). Jacksonaster fudsiyama (Doederlein)
USNM 34]96 (l specimen), Heliophora
orbiculus
(Linnaeus) USNM 40043 (1
specimen), Clypeaster subdepressus (Gray)
USNM E578 (2 specimens). C. rosaceus
(Linnaeus)
(l specimen), Pel/aster zelandiae (Gray) USNM EI0140 (1 specimen), Encope michelini Agassiz (5 specimens), E. aberrans Martens (2 specimens).
Mellita quinquiesperforata
(Leske) (2 specimens), Dendraster excentricus (Eschscholtz)
(3 specimens from San Francisco Bay, 15
specimens from off Coos Bay, Oregon).
Echinarachnius parma (Lamarck) (3 specimens). Strongylocentrotus purpuratus Stimpson (6 speci mens) .
The specimen of the second species listed
above (Jackson aster fudsiyama)
is catalogued as Laganum fudsiyama Doederlein
but due to the shape and position of the periproct and large size of the first post-basicoronal plates in interambulacrum 5, I feel
more comfortable referring it to the genus
Jacksonaster.
This is of little significance
though as the water vessel scheme for serving the accessory tube feet is most likely
similar in all the laganids.
Definition of Terms
The Lovenian system based on columns of
plates is used in this paper to define the
boundaries of the ambulacra and interambulacra. Clypeasteroids commonly have
tube feet in the interambulacra. To avoid
confusion the distribution of tube feet is not
used as the basis for establishing the boundaries of the ambulacra. Throughout this
paper, plate sutures are referred to by name
and four terms of direction or position are
commonly used. These are defined as: interradial Slltllre, a midline (meridional) su-
SYSTEM
OF ECHINOIDS
401
ture between two columns of interambulacral
plates; adradial suture, a suture on the boundary between an ambulacrum and an interambulacrum; perradial suture, a midline
(meridional) suture between two columns of
ambulacral plates; adapical suture, the transverse (horizontal) suture on the adapical
edge of a plate in a column; adoral suture,
the transverse (horizontal) suture on the
adoral edge of a plate in a column; adapical/adoral sutures, the transverse (horizontal) sutures of a column of plates. The
adoral suture of one plate is the adapical
suture of the adjacent older plate of that
column; adapical, a direction or position toward the apical system following the course
of the column of plates; adoral, a direction
or position toward the mouth following the
course of the column of plates; adradial, a direction or position toward the perradial suture; abradial, a direction or position away
from the perradial suture. Note: The
adradial sutures are on the adradial edges of
the interambulacra, but are on the abradial
edges of the ambulacra.
THE
MADREPORITE,
TUBE
FEET,
AND
AMPULLAE
Madreporite
The apical system of clypeasteroids is
monobasal, there is a single large genital
plate. This plate also serves as the madreporite. The development of this plate is quite
varied among the clypeasteroids. The complexity of the madreporite parallels the complexity or sophistication of other test characters such as internal supports, food
grooves, and pore pairs (e.g. simple round
non-conjugate or elongate conjugate and
partitioned). Ontogenetic changes occur in
the madreporite concurrently with development of other test characters. In many
genera with simple test characters, fossil and
Recent, a single pore in the madreporite is
common (e.g. Echinocyamus).
More sophisticated forms have a few more pores.
Some genera have pores in little grooves
(e.g. Laganum).
Clypeasteroids with highly
402
BULLETIN OF MARINE SCIENCE, VOL. 27, NO.3,
sophisticated tests commonly have a large
star shaped madreporite with hundreds of
pores (e.g. Encope) .
Primary Tube Feet
1977
g
rtf
The first tube feet to develop on all
echinoids are the five primary tube feet
present at metamorphosis Hyman, 1955:
511, figs. 219a,b). Respiratory tube feet
have been called primary tube feet by some
authors, but to avoid confusion with the five
tube feet present at metamorphosis they are
called respiratory tube feet in this study.
Respiratory Tube Feet
The petaloid area of each ambulacrum is
the most conspicuous external feature associated with tube feet in c1ypeasteroids. The
pore pairs in the petals are situated between
plates and not within plates as is common
with other echinoids. The pore pairs at the
distal ends of the petals of some genera are
within plates (e.g. Jacksonaster). The petal
pore pairs serve respiratory tube feet. The
outer (abradial) pore is subdivided or partitioned in many genera (Fig. 1A).
Respiratory tube feet have no suckers, are
flattened in an adapicaljadoral direction but
transversely elongated in spanning the respiratory pore pairs. The ampullae which serve
respiratory tube feet are similarly flattened.
They taper slightly as they extend into the
perivisceral coelom. The blind ends of the
ampullae were attached to the gonads in
"ripe" specimens of Clypeaster, Mellita, and
Dendraster. They are probably also attached
to the gonads in many other genera.
Nichols (1959:551 and 1961:177) reported a complete lack of ampullae on the
respiratory tube feet of Echinocyamus pusi/Ius (Muller). However, ampullae were found
on the respiratory tube feet of all clypeasteroids with preserved tissue that were examined in this study including specimens of
Echinocyamus sp. (USNM 14046) from
Unalaska, Alaska.
There is a continuous circulation of
coelomic fluid through the ampullae and tube
Fig. I. (A) Dendr(/ster excentriclls, respiratory
tube foot (rtf) has division for circulating fluid
(arrows), and a globular tip (g) on the finger-like
protuberance above the outer pore, flattened ampulla (a) with out pouchings (op). The inner edgc
of the ampulla is at the inner pore. The ampullac
for the accessory tube feet (atf) are in a cavity in
the stereom near the radial water vesscl (r). (B)
Strongylocentrotus
purpuratus, the tube foot (tf)
has a partition near its base, the ampulla (a) is
flattened, interconnections between ampullae sides
form passageways for the circulating fluid (arrows). The inner edge of the ampulla is between
the inner pore and the radial watcr vessel (r).
Both figures are diagrammatic.
feet. The fluid enters the tube foot through
the outer (abradial) pore and returns to the
ampulla through the inner (adradial) pore.
The flow of coelomic fluid can be determined by observing the movement of coe10mcytes past a given point.
PHELAN:
WATER
VASCULAR
I observed
this circulating
fluid in
Dendraster
excentricus
(Eschscholtz)
and
compared it with that of the regular echinoid Strongylocentrotus
purpuratus Stimpson. The current in both species moved in
the same direction and seemed to flow at
the same rate. In D. excentricus a respiratory ampulla has two broad flattened
sides. These sides have out pouchings which
increase the surface area (Fig. lA).
S.
purpuratus also has ampullae with flattened
sides. There are several rows of connections
between the two sides of each ampulla. The
circulating fluid was observed flowing between these rows (Fig. ] B). The inner edge
of an ampulla is between the radial water
vessel and the inner pore. In D. excentricus
and other clypeasteroids examined the inner
edge of each ampulla was at the inner pore.
A comparison
between the tube foot and
ampulla of D. excentricus and S. purpuratus
is shown diagrammatically
in Fig. 1.
I observed very little action of the ampullae in S. purpuratus even though the tube
feet were active. The most noticeable activity was the constant current circulating between the ampullae and tube feet. I did not
observe any fluid entering the tube foot
through the inner pore. The current in this
pore was always from the tube foot to the
ampulla. I believe it is to facilitate this circulating current that echinoids have two
pores for some tube feet. Apparently
this
circulating current was present even in early
Paleozoic echinoids since they have a pair of
pores for each tube foot.
Externally there is a finger-like protuberance of the respiratory tube foot above the
outer (abradial)
pore on D. excentricus.
The protuberance
terminates with a small
hollow globular tip (Fig. lA).
When I
touched the tip of a protuberance
with a
barbed broach the tube foot immediately retracted and the surrounding
broad tipped
spines closed protectively
over the entire
respiratory tube foot. The response to touch
was not conducted on other areas of the tube
foot.
Similar protuberances
were not seen on
SYSTEM OF ECHINOIDS
403
the respiratory tube feet of Encope michelini.
I have not observed the respiratory tube feet
of live specimens of other c1ypeasteroids under the microscope.
MacBride (1909: 544547, fig. 242) described and figured the
respiratory
tube feet of Echinarachnius
parma and reported suckers at their tips.
The globular tip on a respiratory tube foot
of D. excentricus is not a sucker.
Buccal Tube Feet
Some c1ypeasteroids have buccal tube feet.
An un flattened bulbous ampulla serves each
tube foot, through a single pore in the
peristomial edge of each basicoronal ambulacral plate.
There are 10 plates, each with a buccal
tube foot, on the peristomial membrane of
many regular echinoids.
Nichols (] 961 :
161) termed these tube feet "peristomials"
and reported they had no ampullae.
The buccal tube feet/ampullae
(peristomials) of the regular urchin Strongylocentrotus purpuratus were studied for comparison
with the buccal tube feet/ampullae
of the
dypeasteroids.
I found the buccal tube
feet of S. purpuratus to have fusiform shaped
ampullae.
Accessory
Tube Feet
Thousands
of very small single pores
which serve suckered accessory tube feet are
distributed throughout the ambulacra of dypeasteroids.
These pores are difficult to see
with the unaided eye.
In some genera the accessory tube feet
are distributed
from the adapical end of
the petals to the peristomial edge of the test.
In other genera the accessory tube feet are
distributed widely in the interambulacra
as
well.
The histology of the accessory tube feet
and ampullae of Echinocyamus pusillus was
described by Nichols (1959:542-547,
figs.
2-5) . The external appearance of the accessory tube feet of four species is given below.
Clypeaster rosaceus (Fig. 2) has relatively
404
BULLETIN
I
':~,:\.~~':/::;.;:':'<
~~.. -.
:~.~
"":1.0'
OF MARINE SCIENCE,
60#
VOL. 27, NO.3,
,
A
.. .. ..
"0
1977
."
i:., .........•. _
'0 :'~.\':~;.'~~':"
,.~
Figure 2. Terminal end of an accessory tube foot
of Clypeasler rosacel/s.
large accessory tube feet. The diameter of
the terminal knob including the prominent
sheath is some 144 j.tm. A diaphragm some
36 ftm in diameter is at the tip. On fixed
specimens it protrudes some 6 ftm. The
accessory tube feet of C. rosaceus are considerably larger than those of Echinocyamus
described by Nichols (1959:542-545, figs.
2,3) but many of the features are quite similar.
On Dendraster excentricus, Encope michelini, and Mellita quinquiesperjorata there
are longer accessory tube feet (retracted
state) in the areas immediately bordering the
food grooves than elsewhere except for the
large diameter accessory tube feet in the
food grooves near the peristome. The long
tube feet bordering the food grooves of D.
excentricus are about twice the diameter of
those commonly found in the food grooves,
remote from food grooves on the adoral surface, and in the petals. The terminal knobs
~
Figure 3. Terminal ends of accessory tube feet
of Dendraster excelltricl/s showing the changes in
shape of tip. (A) Terminal knob closed concealing
most of the conical tip. (B) Terminal knob par-
B
15J.l
I----i
c
tially withdrawn from conical tip. (C) Terminal
knob fully withdrawn from conical tip. In this
position the conical tip is very prominent.
PHELAN:
WATER VASCULAR SYSTEM OF ECHINOIDS
·"':::!:}':;:~ft
'.
.,
••
'
•
..
••••
.'
,
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••••
0°
• ~
~.",,;c.~··b,
·~\''':''',,\/·i)·.··_~i.·
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0
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.... .
:
• ."
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Figure 4. Terminal
of Encope michelini.
-;'
.~
••••
~
:::
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::
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'0,'
°0
i
end of an accessory tube foot
of the larger tube feet near the peristome
and bordering the food grooves of D. excentricus are some 120 p'm in diameter. The
common smaller tube feet have terminal
knobs some 60 to 72 p'm in diameter.
Live specimens of D. excentricus were
readily available for study and considerable
time was spent observing tube foot activity.
The accessory tube feet extend slowly with
a waving motion then retract very rapidly.
The terminal knobs of the accessory tube
feet appeared capable of altering their shape.
Sometimes a very prominent conical tip
extended beyond the terminal knob and
again it would be difficult to detect. Serial
sections 6 p'm thick were made on numerous
accessory tube feet to determine the nature
of these changes. Unsectioned accessory
tube feet were also photographed at various
angles to help in this determination. It was
found that the conical tip was always present
but was only prominent when the dense terminal knob was withdrawn from around it
(Fig. 3A-C).
405
A diaphragm or depression is not apparent on the tip of the terminal knob of the
accessory tube feet of Encope michelini or
Mellita quinquiesperjorata. The capability
of these tube feet to lift relatively large shell
fragments could indicate that some form of
sucker tip is present. The research cine films
produced by Kier in 1972 show closeup
views of this activity. The shape of the
terminal knob of the accessory tube feet of
Encope and Mellita is very similar so only
that of E. michelini is illustrated (Fig. 4).
The diameter and height of the terminal
knob of accessory tube feet from several
selected positions on E. michelini are given
below.
a. Submarginal not in a food groove: diameter 60 p'm, height 48 p.m.
b. Main branch of a food groove: diameter
72 p'm, height 60 p.m.
c. Near peristome in perradial portion of
food groove: diameter 120 p'm, height
72 p.m.
The diameter and height of the terminal
knob of the tube feet from several positions
on M. quinquiesperjorata were measured.
a. Main branch of a food groove: diameter
84 p'm, height 60 ,.,.m.
b. Remote from a food groove: diameter 84
p'm, height 60 p.m.
c. Near peristome in perradial portion of a
food groove: diameter 132 p'm, height 84
p.m.
The ampullae of the accessory tube feet
are variable in shape and size. Those of live
specimens of D. excentricus were observed
(Fig. 5). They are almost cylindrical except
for a constriction where attachment is to
the lateral water vessel. The blind ends of
the ampullae were spherical and all had a
globular cluster of coelomocytes in the spherical tip. The shape of the ampullae gradually
changed somewhat after fixation in 70%
ethyl alcohol. The spherical shape of the
blind end was lost. The globular mass of
coelomocytes in each ampulla broke up.
They fragmented and the parts drifted about
BULLETIN OF MARINE SCIENCE, VOL. 27, NO.3,
406
I
25 JJ
]977
Figure 6. Simple perradial food grooves (fg).
Grooves of this type are found in the laganids,
Clypeaster, and Fel/aster but those of Pcl/aster extend over the ambitus to the apical system.
are ingested for the attached organic material. In other genera such as Dendraster,
organic material and little sand is ingested.
Food Grooves
Figure 5. Accessory tube foot ampulla of Delldraster excclltricus, the finely stippled area in the
spherical blind end and cylindrical portion represent masses of coelomocytes in the fluid. Lateral
water vessel added to show position only. It was
not in the photograph.
in the ampullae. While alive the spherical
blind ends had a dark appearance due to the
color of the cluster of coelomocytes.
RELATIONSHIP BETWEEN WATER VESSELS,
ACCESSORY TUBE FEET, AND FOOD GROOVES
OF THE AMBITUS AND ADORAL SURFACES
Accessory tube feet help collect food or
food bearing material (sand grains) and pass
it toward the mouth. In genera such as
Clypeaster, Mellita, and Encope, sand grains
A food groove is a furrow on the external
surface of the test of an echinoid leading
toward the peristome. Particles bearing organic material and free organic material are
passed to the mouth along the food grooves.
In some genera accessory tube feet are
abundant within and around the food
grooves. In other genera few or no accessory tube feet occur within the food grooves
but are abundant in surrounding areas.
Food grooves with accessory tube feet commonly have an abundance of glassy tubercles
which bear no appendages. The glassy
tubercles and accessory tube feet extend in a
series beyond the point where the food
groove ceases to be a furrow.
There are two basic kinds of food grooves
with many intermediate types. The perradial
food groove (Fig. 6) is the simplest form
and the polyfurcating food groove the most
complex (Fig. 13).
The basic perradial food groove is a
simple unbranching furrow lying along the
PHELAN:
WATER VASCULAR SYSTEM OF ECHINOIDS
perradial suture between two columns of ambulacraL plates. Each radial water vessel lies
along a perradial suture on the interior of
the test. The water vessel is separated from
the suture by other radial systems such as
the radial nerve. There are obstacles to overcome in supplying accessory tube feet directly in the perradial food groove due to the
position of the radial systems. This problem
has been solved in different ways which will
be discussed later in this section.
Adorally the polyfurcating food groove
has a very short section lying on the perradial
suture ncar the peristome. Beyond this short
section the food groove divides into two
main branches. Each branch extends along
the growth centers of a column of ambulacral
plates. There are commonly many side tributaries to each main branch and additional
fllrcations near the ambitus. The main
branches and tributaries tend to cross plate
sutures at nearly right angles. The major
portion of a polyfurcating food groove is remote from the internal position of the radial
systems. This provides unobstructed access
for connections between the internal lateral
water vessels and the accessory tube feet in
the food grooves. Service to the accessory
tube feet in the short perradial portion near
the mouth must overcome the same difficulties noted for the simpLe perradial food
groove. This wiLLbe discussed later in this
section.
PoLyfurcating food grooves provide a
greater network of food gathering channels
to the mouth than perradial food grooves.
The fibulariids lack food grooves and have
the simplest scheme in the clypeasteroids.
Radial Water Vessels with Side Lobes
or Spurs
The fibulariid Echinocyamus has relatively
broad radial water vessels for its small size.
Accessory tube foot ampullae are in a band
on each side of the radial water vessel on
the basicoronal ambulacral plates. There is
a lobe-like expansion of the radial water vessel onto each younger ambulacral plate (Fig.
7). A band of accessory tube foot ampullae
407
lmm
Figure 7. Radial water vessel (r) of EchillocyaII1US showing the lobes (I) tbat serve the accessory
tube foot ampullae.
Position of ampullae indicated by large dots, peristome (p), ambitus of test
(t) .
border each lobe except on its adoral side
(side closest to the peristome). The pore
pattern of the exterior adoral surface reflects
the position of accessory tube foot ampullae.
Nichols (1959 :fig. 4a) shows the connection of an accessory tube foot/ampulla to
the radial water vessel. The internal surface
of the adoral plates of the test is sculptured
in such a way that the position of the radial
water vessel and side lobes is evident even on
denuded specimens. This is well illustrated
in Durham (1966b:469, fig. 360 5c). The
exterior accessory pore pattern reflecting the
radial water vessel shape for E. pusillus is
shown in Durham (1966b:469, fig. 360
5b). The pore pattern of the basicoronal
and first few post-basicoronal plates of Durham (1966b:455, fig. 340 2) and Nichols
(1959:541, fig. Ib) is inaccurate.
The accessory pores in Echinocyamus are
in bands parallel to the perradial suture on
basicoronal plates. At the ambitus the bands
of pores are at right angles to the perradial
suture. The bands of pores between these
two positions are transitional in position and
BULLETIN OF MARINE SCIENCE, VOL. 27, NO.3,
408
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Figure 8. View of the internal surface of a portion of a test of Jacksonaster fudsiyama showing
radial water vessel (r) with one side spur (sp) on
the adoral edge of each post-basicoronal ambulacral plate. There is a dense band of accessory tube
foot ampullae (stippled area) along the sides of
the radial water vessel and side spurs. Dashed
lines are plate sutures.
are in more or less arcs. The accessory pores
between the ambitus and the petaloid areas
are on the adapical plate sutures (between
ambulacral plates of a column).
Middle Eocene fibulariids apparently also
had these lobes on the radial water vessels
to serve accessory tube feet. Note the accessory pore patterns of Echinocyamus hi-
1977
sexus Kier (1968: 19, fig. 21) and Leniechinus herricki Kier (1968: pI. 1, fig. 4).
The Iaganids and fibulariids are members
of the suborder Laganina. The genus Jacksonaster (a laganid) has simple unbranching
perradial food grooves that extend from the
peristome partway to the ambitus (Fig. 6).
The radial water vessels and dense bands
of accessory tube foot ampullae of Jacksonaster (Fig. 8) are very similar to those of
Echinocyamus. The radial water vessels
have long blind ending side spurs. One spur
lies along the adoral edge of each post-basicoronal plate. There are no side spurs on
the basicoronal plates, only a dense band
of accessory tube foot ampullae on each side
of the radial water vessel as in Echinocyamus. On each post-basicoronal ambulacral
plate the accessory ampullae are in a continuous band along the side of a radial water
vessel and one side and tip of a spur. No
ampullae are connected to the side of the
spur that lies near the adoral plate suture
(Fig. 8).
There is an abundance of accessory tube
feet in the perradial food grooves of Jacksonaster. The test is thin at the perradial
sutures because internally the radial systems
lie in a groove on each perradial suture. The
accessory tube foot ampullae close to each
radial water vessel connect to the tube feet in
a perradial food groove by passing obliquely
through the test.
The side spurs are not directly opposite
each other (Fig. 8) due to the offset nature of the ambulacral plates on each side
of the perradial sutures. This is because the
basicoronal plates are of unequal length.
The offset position of the side spurs allows
for an uninterrupted series of accessory tube
feet in the food grooves.
I do not consider the lobes of Echinocyamus or the side spurs of Jacksonaster true
lateral water vessels. They are broad and
flattened like the radial water vessels.
Simple Lateral Water Vessels
Clypeaster and Fellaster (suborder elypeasterina) have simple systems of true lat-
PHELAN:
WATER
VASCULAR
SYSTEM
OF ECHfNOJDS
409
mm
.
'
.
"
,.
'"
,"
.,'
.....
~~Iw\'
I-----l
Imm
Figure 9. View of internal surface of a portion of
some adoral ambulacral plates of Clypeaster subdepressus showing radial water vessel (1'), lateral
water vessels (lwv) and position of accessory
pores/ampullae
(a). Some lateral water vessels
lie across plate sutures (dashed lines).
eral water vessel distribution. Many lateral
water vessels connect the accessory tube feet
of each plate to a radial water vessel.
Clypeaster has the simpler system of the
two. The lateral water vessels lie on the internal surface of the plates commonly parallel to the adapical and adoral plate sutures.
A few lateral water vessels lie across adoral
or adapical plate sutures and serve accessory
tube feet/ampullae of two ambulacral plates.
Some lateral vessels lie across adradial sutures and serve accessory tube feet/ampullae
of an ambulacral and an interambulacral
plate (Fig. 9). I have not observed branching of these simple vessels. In some species
(e.g. C. rosaceus) the stereom partially or
completely closes over many lateral water
vessels. Many accessory tube foot ampullae
are connected to each lateral water vessel.
All ampullae observed were connected to the
adapical side of the vessels. No accessory
tube foot ampullae were observed directly
connected to a radial water vessel. The number of lateral water vessels and accessory
tube feet on a plate increases as a plate expands with growth, but the processes by
which this is accomplished is not yet fully
understood.
'i\fg
Figure 10. External view of an adoral area of
test of Clypeaster sllbdepresslls showing a portion
of the food groove (fg) and perradial suture (ps).
Notch on each accessory pore points in an adoral/
ad radial direction where lateral water vessels are
at right angles to a perradial suture. Note the
absence of accessory pores in the perradial food
groove.
Clypeaster
has simple perradial food
grooves that almost reach the ambitus. Accessory tube feet are numerous and extensive
on either side of the food grooves (Fig. 10).
Only near the ambitus were accessory tube
feet observed within the food grooves. Internally the radial systems lie in a groove
along each perradial suture.
There are many lateral water vessels on
each ambulacral plate on the oral surface of
Fellaster but their pattern is slightly more
complex than in Clypeaster. On the internal
surface of the basicoronal plates the lateral
water vessels lie at an angle toward the
peristome. In the area of the post-basicoronal plates, lateral water vessels are inclined
slightly toward the ambitus. If these vessels
branch it is not commonly. I have not observed it. The number, position, or branching of bands of accessory tube feet/pores on
the exterior surface does not reflect the number, position, or branChing of the lateral
water vessels. The exterior surface pattern
of accessory pores is accomplished by realignment of the pores as they pass to the
exterior surface of the test (Fig. 11). The
center of the exterior surface of a third or
410
...--.:::..::::::
.:::::
::--..---. --........
I
BULLETIN
.... _
." ~
-
OF MARINE
SCIENCE,
VOL. 27, NO.3,
1977
......•..
~_
-.-.·_..;o·c;·o.o·.o;;·~·~oti~·····~·
.
---~=~:=-::~:-::~~~!~;_::~:
...•.•.••.......
........
..••..•..••••
-'
•••.•.•••••.•••••
.-....
..··~~
....•... -........
..-.....
.
.J....
..
.-.
..
-
...
.. .
•.••.•• ,ri" •.••.••••••••••••·•••.•••••.
.......
••..•
p
/
/.
..•.
/~
••••••••
M"
.•.......•..
1 mm
i-=---l
Figure 11. Fellaster zelandiae, rows of accessory
pores (stippled bands) on a portion of an adoral
ambulacral
plate. Circles representing
tubercles
are drawn around
one point of branching
Figure 12. Echinarachnius pari/ill, with long sections of its food grooves on the perradial sutures,
after Durham (1955).
(omitted
elsewhere).
Number, position, and branching of
pore bands do not represent number, position, and
branching of lateral water vessels. Food groove
(not shown) is to the right. Pcristome is in direction of arrow (p).
fourth postbasicoronal plate commonly has
at least one band of accessory pores with
several branches but on the interior, the
lateral vessels are unbranching and parallel
to each other. The lateral water vessels do
not extend into the immediate regions of the
adradial sutures. The distal ends of the vessels are in microcanals. I have been unable
to determine if the ampullae are connected
to the water vessels in a set pattern as in
Clypeaster.
Lateral water vessels and accessory tube
feet become more numerous as plates expand
with growth but it is not fully understood
how this is accomplished.
The unbranching food grooves of Fellaster
lie along the perradial sutures from near the
apical system to the peristome. No accessory
tube feet were observed directly in the food
grooves. The accessory tube feet are in
bands leading toward the food grooves.
Fellaster is so similar to Arachnoides that
the description given here for Fellaster probably applies equally to Arachnoides.
Complex Lateral Water Vessels
The genera of the suborder Scutellina have
complex schemes of lateral water vessel dis-
tribution. Four genera were represented in
the material studied. Echinarachnius has
basically the same scheme as the other three
studied but it is poorly developed. It seems
transitional between the simpler schemes of
Clypeaster and Fellaster, and the complex
schemes of Dendraster, Encope, and Mellita.
Echinarachnius has a major portion of
each food groove on a perradial suture (Fig.
12). Branching only occurs in the region
near the ambitus. Dendraster, Encope, and
Mellita have complex polyfurating food
grooves (Fig. 13). There are accessory tube
feet within the food grooves throughout their
length in the four genera.
Since Echinarachnius seems to possess the
most primitive scheme of the four genera it
is described first. Internally each radial
water vessel descends from the water vascular ring to an elevated stereom structure
(perradial septum) on the perradial suture
between two basicoronal ambulacral plates.
Beyond the slope of the perradial septum
each radial water vessel is supported on a
slight ridge which extends along the perradial suture. There are pits aU along the
sides of each perradial septum and also along
the sides of each perradial ridge. These
pits provide access to the perradial food
groove for lateral water vessels and ampullae
serving accessory tube feet.
Many lateral water vessels branch from
a radial water vessel to serve the accessory
tube feet of each plate. In the central cavity
PHELAN:
WATER
VASCULAR
SYSTEM
411
OF ECHINOIDS
Figure 13. Ellcopl' michelilli, with complex polyfurcating food grooves. Mellila and Leodia have
similar food grooves, after Phelan (1972).
of the test (area without internal supports
and macrocanals) the lateral water vessels
tend to curve toward the peristome (Figs.
14, 15) and extend about halfway across
each plate toward the adradial suture.
Branching occurs, but most of it is limited
to short side branches on long vessels. The
vessel nearest the adapical suture of a first
post-basicoronal plate is described as an example. The long lateral vessel extends at an
angle toward the peristome. It has numerous
short branches on the adapical side of the
vessel. Each of these short branches serves
only two, three, or four accessory tube
feet/ampullae. Ampullae may be attached to
either side of a lateral water vessel.
Throughout the plate many of these short
branches from long lateral vessels lead toward the adapical, adoral, and adradial
sutures (Figs. 14, 15). This seems to be a
slight development of the scheme so highly
developed in Dendraster, Encope, and Mellita.
The lateral water vessels near the ambitus
(area where food grooves branch) tend to
be straighter, branch, and lie across entire
plates. Some vessels extend into interambulacral plates.
.••••
1 mm
----I
•..1
I
Figure 14. Echillarac/Illius parma, adapicalfadradial portion of first post-basicoronal ambulacral
plate showing position of lateral water vessels
(Iwv) and accessory pores (a). Radial water vessel is at right (r). Dotted lines indicate plate sutures.
New lateral water vessels, ampullae, and
tube feet are added to plates as they grow,
but the process by which they are added is
not fully understood.
Dendraster has polyfurcating food grooves
(Fig. 16). A short portion of each lies on a
perradial suture near the peristome. A main
branch of each food groove extends down
the middle of a column of ambulacral plates
(through successive growth centers). There
are many side tributary grooves and additional branches especially near the ambitus
of the test. The food grooves are most devoloped in ambulacra I and V, least developed in III. Food grooves of the posterior
region extend onto the adapical surface.
Internally each radial water vessel descends
from the water vascular ring to a perradial
412
BULLETIN
OF MARINE
SCIENCE,
VOL. 27, NO.3,
1977
1 mm
-- -fl
I
I~
I
I
I
I
I
I
I
I
I
I
I
,
I
I
Figure 15. Echinarachnius parma, adoral/adradial
corner of a second post-basicoronal
ambulacral
plate showing distribution of lateral water vessels
(lwv) and accessory pores (a).
Radial water
vessel (r) at left. Dotted lines indicate plate sutures.
Figure 16. Dendraster excentricus with differentially developed polyfurcating food grooves. The
anterior food grooves are poorly developed. The
posterior food grooves are highly developed. Many
of the posterior grooves extend onto the adapical
surface.
septum as in Echinarachnius. Beyond the
slope of the perradial septum each radial
water vessel lies in a perradial groove.
There are many pits on each side along the
base of each perradial septum. These provide access to tube feet in the perradial portion of the food grooves. The portion of a
perradial suture not occupied by a food
groove has few or no accessory tube feet.
This is also the condition in Encope (Durham, 1966b:456, fig. 341 Ib).
Internally, lateral water vessels on postbasicoronal plates lie in open channels or
microcanals, depending upon the degree of
stereom development.
Lateral vessels leave the radial water vessel
at nearly right angles and extend to a point
directly above a food groove (Fig. 17). At
this point the lateral water vessels turn and
lead toward the adradial suture (suture between ambulacral
and interambulacral
plates). On the abradial side of the plate
(near the adradial suture) the lateral vessels
branch extensively.
At the adoral and adapical ends of a plate
there is a slight difference in distribution.
The lateral water vessels send branches to-
ward the adoral and adapical plate sutures
respectively and continue branching until
they terminate.
The result of this scheme of distribution
is that lateral water vessels are always extending toward the growing edges of the
plate and continually adding ampullae and
tube feet. Water vessels extending from
ambulacral plates onto interambulacral
plates especially in the posterior regions repeat a modified form of this distribution
scheme on interambulacral plates.
Accessory tube foot ampullae are very
close to the lateral water vessels. They are
attached to either side of these vessels.
Work is progressing on Dendraster to
learn how lateral water vessels and accessory
tube feet are added to plates as they expand
with growth.
Echinoids such as Encope, Mellita, and
Leodia with notches or lunules in the ambulacra have an obstacle to overcome in serving
accessory tube feet closer to the ambitus than
the inner limits of notches or lunules. The
arc in a radial water vessel between its adoral
and adapical portions lies internally to the
inner limits of an ambulacral notch or lunule.
PHELAN:
WATER VASCULAR SYSTEM OF ECHINOIDS
413
Figure 18. Leodia sexiesperforata (Leske), outline of test and lunule positions, (A) area where
radial water vessels are in contact with ambulacral
plates, (B) larger area remote from radial water
vessels where many ambulacral and interambulacral plates are served by lateral water vessels which
branch from each radial water vessel at the inner
ends of ambulacrallunules.
4 mm
Figure 17. Dendraster excentricus, view of internal surface of test at adapicaljadradial
corner of
a first post-basicoronal
ambulacral plate and the
adoral/ad radial portion of a secondpost-basicoronal ambulacral plate showing pattern of open channels (oc) which provide passageways for lateral
water vessels. More than one vessel is present in
some channels. Each vessel branches extensively.
The ends of vessels lead toward the growing edges
of the plates. Some channels are covered or partially covered. Radial water vessel (r) is at left.
Dashed lines indicate position of plate sutures.
In Leodia the area of the adoral surface
beyond the inner ends of the ambulacral
lunules is greater than the central area (Fig.
18). Lateral water vessels serving the areas
beyond the inner limits of notches and
lunules commonly cross several plates to
serve accessory tube feet remote from the
radial water vessels in genera such as Leodia,
Encope, and Mellita.
Lateral water vessel distribution within
plates adjacent to the radial water vessel is
very similar to that of Dendraster (Fig. 19).
The following description is based on dis-
sections of Encope but with minor changes
applies also to Leodia and Mellita.
Internally near the peristome each radial
water vessel descends into the microcanal
network of the adoral plates. There is a
short elongate opening in the stereom above
each radial vessel near the peristome. This
opening does not extend beyond the tips of
the lantern wings. The stereom between
microcanals and the exterior surface is very
thin, therefore the connecting vessels between the ampullae and the tube feet are
quite short. The stereom is so thin in
Encope michelini that where microcanals
cross food grooves there is actually a little
hump in the interior of the microcanals. This
permits easy service to an abundance of accessory tube feet within the food grooves.
The main branches of the food grooves
and many tributary grooves extend into the
region beyond the inner ends of ambulacral
notches and lunules. Internally from the
inner end of each ambulacral notch or lunule, very broad lateral water vessels branch
from a radial water vessel. These vessels
pass through microcanals commonly crossing
BULLETIN
414
OF MARINE SCIENCE,
VOL. 27, NO.3,
1977
5 mm
r
\
-------
5 mm
Figure 19. Encope michelini, microcanal pattern
within an adoral ambulacral plate. Radial water
vessel (r) at left. More than one lateral water
vessel commonly occupies each microcanal (me).
Lateral water vessels lead toward growth center
of the plate, turn and lead toward growing edges
of plate. Water vessels branch profusely.
several plates, branch into numerous other
microcanals, and serve accessory tube feet in
the ambital region beyond the inner ends of
notches and lunules (Fig. 20). Water vessel
distribution within plates of this region is
basically the same as that described for Dendraster with water vessels leading toward
the growing edges of each plate. Accessory
tube feet and vessels are added as plates
grow.
The microcanals may serve additional
functions other than as passageways for
lateral water vessels as some microcanals extend into areas not supplied with water vessels.
Rotulina
The single specimen of Heliophora orbiculus (Linnaeus) available for study was a
dry test completely lacking tissue. It was inadequate for any determination of the water
vessel distribution in the suborder Rotulina.
The food grooves are polyfurcating with a
main branch extending along the growth
centers of each column of ambulacral and
--\
Figure 20. Encope michelini, microcanal network
which serves long lateral water vessels whieh leave
radial vessel (r) at inner edge of ambital notch.
Microcanals
which serve only individual plates
omitted from drawing.
interambulacral plates. No small tributary
grooves were observed leading into the main
branches. The food grooves extend onto the
finger-like extensions along the posterior ambitus formed by deep notching along perradial, ad radial, and interradial sutures.
Throughout the food grooves in ambulacra and interambulacra there are numerous
pores indicating they are supplied with accessory tube feet.
RELATIONSHIP
ACCESSORY
BETWEEN
TUBE
FEET,
AND FOOD GROOVES
WATER
PETALOID
VESSELS,
PLATES,
OF THE ADAPICAL
SURFACE
Accessory tube feet of the margin and
adapical surface help collect food as do
those of the adoral surface. They also lift
sand, shell fragments, algae, and other material from the substrate and working in conjunction with spines pass it over the adapical
surface. The particles may be for covering or
the product of burrowing. Kier produced
research cine films in both normal and time
lapse photography showing this activity.
Kier and Grant (l965:pl. 4-7) show several species carrying a wide variety of material including dead echinoid tests and show
several species covering themselves with
sand in the process of burrowing. Nichols
PHELAN:
WATER
VASCULAR
SYSTEM
OF ECHINOIDS
415
Petals with Primary Plates only
lmm
rp
..
Figure 21. Echinaracl/llius parma, internal view
of the adapical end of a petal showing accessory
pores (a). Note that no accessory pores are located in the poriferous zones (pz) of the respiratory pores (rp). Petal is composed of simple primary plates.
(1959:539-540) describes the covering and
burrowing activity of Echinocyamus pusillus.
Poriferous Zone
No accessory tube feet were observed in
the poriferous zones of the respiratory tube
feet (Figs. 2], 24B) I have looked for this
condition and have not observed it on any
specimen studied.
Petaloid Plates
There are two basic petaloid plate arrangementsin the c1ypeasteroids. One is a column
of simple primary plates in each half ambulacrum (Fig. 21). The other has a column of
primary plates in each half ambulacrum
which are narrow in the region of the respiratory tube feet. Here demiplates alternate
with primary plates (Fig. 24B). There are
more complex arrangements of demiplates
in some fossil clypeasteroids. For details of
these see Durham (1955 :fig. 27a-c).
Echinarachnius has this plate arrangement
and is used for the first description. The
lateral water vessels, pores for accessory
tube feet, and respiratory tube feet lie along
the sutures between ambulacral plates. The
lateral water vessels and accessory pores arc
slightly to the side of some sutures or lie
across a suture at a slight angle. There is
only one lateral water vessel along each suture and it serves both accessory tube feet
and a respiratory tube foot (Fig. 21). The
youngest plates observed accommodating accessory tube feet were approximately the
sixth to eighth from the terminal plate. All
plates adoral to this point had accessory tube
feet.
I have observed living populations of
Echinarachnius parma while diving off Cape
May, New Jersey. They did not burrow or
cover themselves. The accessory tube feet
of the petals probably primarily serve in
collecting food. There was little or no sand
in the intestinal tract.
MacBride (]909:545) reported that the
accessory tube feet of E. parma are present
in all plates, ambulacral and interambulacral,
on the adapical surface. This is inaccurate.
E. parma has accessory tube feet in both
ambulacral and interambulacral plates at and
near the ambitus on the adapical surface similar to many c1ypeasteroids. There are no
accessory tube feet in the interambulacral
plates between the petals of E. parma. One
of his figures of E. parma (MacBride, 1909:
fig. 242 a,b) is misidentified. The figured
specimen is Dendraster excentricus.
MacBride (1909:546) observed E. parma
in comparatively shallow water on a sandy
bottom and described them as nearly but
not quite buried in sand.
Stanley and James (1971 :pI. 1:figs. b,
c; pI. 2: figs. a-c; pI. 3: figs. d, e) photographed living populations of E. parma on
the ocean floor. Most of the sand dollars
are on the surface of the substrate. In
several photographs a few are partially
buried as MacBride reported.
416
BULLETIN OF MARINE SCIENCE, VOL. 27, NO.3,
1977
3mm
Figure 22. Dendraster excentricus, internal view
of posterior petal (I). Radial water vessel depicted
by dotted zone (rr) along the perradial suture.
Pseudopores (c) leading to cavities for accessory
tube foot ampullae adjacent to the radial water
vessel (r). Outer pairs of pores are for respiratory
tube feet (rp).
Dendraster excentricus (Eschscholtz) of
the Pacific coast also ingests little sand.
Accessory tube foot distribution is very
closely related to food groove development
on the adoral surface. The anterior petal
(III) has very few accessory tube feet.
Most of these are near the distal end of
the petal. The anterior adoral food grooves
are poorly developed. The posterior paired
petals (I and V) have an abundance of accessory tube feet throughout their length.
The posterior food grooves are highly developed and extend onto the adapical surface. A series of glass]y tubercles from
within the distal end of each petal leads down
each column of ambu]acra] plates and enters
a food groove. Each series of glassy tubercles has a band of accessory tube feet in
the same pathway.
The anterior paired petals (II and IV)
also reflect the poorly developed anterior
and well developed posterior adoral food
grooves. The anterior half of these petals
(lIb and IVa) have fewer accessory tube
feet than the posterior half (lla and IVb).
I think this distribution in relation to food
groove development strongly reflects the
food gathering function of the accessory
tube feet. (See Durham, 1966:269.) I have
observed live specimens of Dendraster and
only the anterior portion was buried in the
substrate. In Dendraster the accessory tube
feet seem to function more for feeding than
Figure 23. D. excelltricus, cross section along suture between plates of one half petal showing
pselldopore and cavity (c) for accessory tube feet,
and respiratory pores (rp).
Note partitions in
outer (abradial) pore.
burrowing. The accessory tube feet collect
particles of organic material suspended in the
water and also pick up food particles from
the substrate. The collected material is
passed to the mouth along the food grooves.
The interior surface of petals I and V appears to have a triple series of pores in each
column of ambulacral plates. Only the two
outer series are pores for the respiratory
tube feet. The innermost series are pseudopores. They lead to cavities in the plates to
accommodate the ampullae of accessory tube
feet (Figs. lA, 22, 23). These cavities are
less developed on petals II and IV and virtually absent on petal III.
The plates with cavities for accessory
tube foot ampullae have a different system
of lateral water vessel distribution than occurs in Echinarachnius. The accessory tube
feet/ampullae are served by separate vessels
from those serving respiratory tube feet.
Two lateral water vesse]sleave the radial
water vessel at approximately the same point.
Some of these connections appear to be
branching of a single vessel very near the
radial water vessel. One lateral water vessel
leads along the suture to the ampulla of a
respiratory tube foot. The other vessel descends immediately into the cavity to serve
the ampullae of the accessory tube feet.
Petals with Primary and Demiplates
The lateral water vessels do not lie along
plate sutures in clypeasteroids with altern at-
PHELAN: WATER VASCULAR SYSTEM OF ECHINOIDS
417
101m
f------l
rp
.
~
~
~r·p··~"··~·.
:\
~
B
Figure 24. Clypeasler subdepressus, (A) internal
view of the adapical end of a petal showing, by
the course of accessory tube foot pores (a), how
some lateral water vessels lie across plate sutures.
The junctions of the lateral water vessels with a
radial water vessel are on plates more remote from
the apical system than the plates where the distal
ends of the lateral vessels connect to respiratory
tube foot ampullae; respiratory tube foot/ampullae pores (rp). Radial water vesscllies along perradial suture (s). (B) Internal view of mid-petal
area showing, by course of accessory tube foot
pores, the position of the two lateral water vessels
on each plate. Accessory tube foot pores do not
extend into the poriferous zone (pz) of the respiratory tube feet. Petals arc composed of primary
and demiplates.
ing primary and demiplates. Clypeaster and
have this alternation of primary
and demiplates. Two lateral water vessels
lie on the internal surface of each primary
plate. Each terminates at the inner pore of
a respiratory tube foot in contact with that
plate (Figs. 24B, 26, 27). Two respiratory
tube feet are in contact with each primary
plate. At the middle and distal ends of the
petals some primary plates have an additional lateral water vessel which serves only
accessory tube feet. The lateral vessels
serving respiratory tube feet also serve accessory tube feet. The ampullae for the accessory tube feet are attached to the adapical
side of the lateral water vessels of Clypeaster.
It is undetermined on Fellaster. As plates
grow new ampullae and accessory tube feet
are added to the lateral water vessels. On
Clypeaster
subdepressus
(Gray) and the
number of ampullae on a single vessel was
observed to be nearly equal to the number
of growth lines on the plate served.
Internally in Clypeaster
subdepressus
Fellaster
4 mm
Figure 25. Clypeaster subdepressus, exterior surface of the adapical portion of a petal. Large
black pores are respiratory pores (rp). Concentric
circles are sunken tubercles and areoles.
The
small ring around the adapical portion of each accessory pore (ap) is a depression formed of
small pits in the stereom to which the accessory
tube foot is attached.
some petals examined had lateral water vessels lying across sutures between primary
plates of a column. At the proximal end of
a petal with this condition, the connections
of lateral water vessels to the radial water
vessel is at plates more remote from the
apical system than the plates to which these
vessels connect to respiratory ampullae.
These vessels serve accessory ampullae
on more than one plate. Figure 24A is a
drawing of plates with this condition. The
tissue was removed from the stereom prior
to photographing the plates. The course of
the lateral water vessels was along the rows
of accessory pores.
In the large mid-petal region some lateral
water vessels lie across plate sutures. The
two or three vessels on each primary plate
commonly lie almost parallel to the sutures
between plates of the column (adapical and
adoral plate sutures). Figure 24B is a
drawing of plates on which the accessory
pores lie in two rows nearly parallel to the
adapicaljadoral plate sutures. The photograph for the drawing was made after the
tissue was removed from the stereom.
BULLETIN
418
OF MARINE
11 mml
SCIENCE,
VOL. 27, NO.3,
I
ap
1977
I11Ill
....
- - -.!.
-~ .
.
- ~-.......•....
"-
...........................
...................... "'-
-,
-
-,
-
-
'-.
--- ............... ..............
--
.
,- -
.
- ..- -.
.
Figure 26. Fellasler zelandiae, internal view of a
portion of a petal showing the position of the
lateral vessels by position of accessory pores (ap).
Pores are more numerous than can be shown at
this low magnification.
Petals are composed of
primary and demiplates.
Accessory pores are in rows on the interior surface of the petals. The pores do
not pass straight through the stereom to the
exterior but pass through at various angles.
The result is a random arrangement of pores
on the exterior surface (Fig. 25).
The lateral water vessels of Pel/aster also
align parallel to the sutures between ambulacral plates. At the adapical end of the petal
there are two lateral vessels on each primary
plate. There are a few plates in the middle
of the petals with an additional vessel. At
the distal end of a petal, most primary plates
have three lateral water vessels-two serving
respiratory and accessory tube feet and one
serving only accessory tube feet. The accessory pores on the interior surface of each
primary plate are in alignment with the
lateral water vessels (Fig. 26). The pores
realign in passing through each plate. On the
exterior surface of each primary plate there
is a series of diagonal rows of accessory
pores. The diagonal rows of adjacent plates
align more or less giving the appearance of
continuous rows. The diagonal bands of accessory tube foot pores cross several plates
in an adoraljadradial direction and terminate
at the edge of a perradial food groove (Figs.
27, 28). Each food groove extends from
Figure 27. Fellasler zelandiae, semi-block diagram of section of a petal. Dashes on surface indicate position of adapical and adoral plate sutures
(ps). Food groove (not shown) is toward the left.
Circles represent tubercles (t). Water vessels (less
ampullae) are drawn in at right to indicate their
position parallel to plate sutures. Each water vessel serves half of the accessory tube feet of each
plate (except on plates with three vessels). The
pores on the internal surface of the plates are
aligned along the water vessels. The oblique lineation on surface results from variable inclination
of pores passing through to the exterior surface of
plates. The scale applies only to the external surface.
near the apical system to the peristome.
There are no tube feet in the food grooves.
The diagonal bands of accessory tube feet
are separated by diagonal bands of large
and small spines and tubercles. This condition results in the so-called "combed" areas
of Fellaster and Arachnoides.
EXPANSION
INTERRUPTED
OF
AMBULACRAL
INTERAMBULACRAL
PLATES
AND
COLUMNS
Clypeasteroid ambulacral plates commonly widen near the distal end of the
petaloid area. The ambulacral columns are
commonly wider than the interambulacral
columns at the ambitus (Fig. 29A). On
the adoral side expanded post-basicoronaJ
ambulacral plates commonly interrupt the
PHELAN:
WATER
VASCULAR
SYSTEM
419
OF ECHTNOIDS
lmm
0-··..
'-'0
0""0
".Uo
)
••••
0
".',00
O· "; 0
00
:
V
;
OU"-"OU
ps
"0 0oq,,'"
00,;
~-dO-Og600000~'
0 ".
0
00~::~o(----~~-~.•.
?Ro
~?o 0,00!
:,
O·..
§;O"O~·-~~;.~;~oo----\,0 0,o~c;:~'O:'~8
(
0....
0.···0
000 ",,0'9
•.••••
00
0
) ••.•.••.•
,'..~o
n ...
"
""
'
0°,·,
0
0941 ~.,,-
fg
r
{l'j"r\
ap
Figure 28. Fe/laster zealandiae, small section of
the perradial portion of the petal, accessory tube
foot pores lead in an adoraljadradial
direction toward the food groove (fg). Dotted lines indicate
position of plate sutures (ps). Note the absence
of accessory tube foot pores in the food groove.
columns of interambulacral plates (Fig.
29B). For additional information see Durham (1955:figs. 17,21-25).
I believe the
great expansion of the ambulacra is related
to the increased food gathering capacity afforded by a broad distribution of accessory
tube feet.
H the clypeasteroids evolved from the
juvenile stage of a cassiduloid (discussed
later in this paper) the tendency for expanded ambulacral plates may have preceded the development of true accessory
tube feet. The phyllodes of cassiduloids are
formed by an expansion of post-basicoronal
plates which support specialized feeding tube
feet. Late in the Cretaceous these tube feet
evolved from the two pore to single pore
forms (Kier, 1962:chart 2). Accessory tube
feet are also served by a single pore. Cassiduloid tube feet between the phyllodes and
the petals also evolved into the single pore
form.
The large areas served by accessory tube
feet on clypeasteroids are truly phyllodes in
my opinion. They fit the broad definition of
the term as used by Kier (1974: 20). The
accessory tube feet are so small that these
clypeasteroid phyllodes are not as readily
recognized as they are on other echinoids.
Figure 29. Dendraster excenlricus, expansion of
ambulacra (stippled) beyond the petals, (A) adapical view, (B) adoral view. Note interrupted interambulacrum 5. Individual plates are not shown.
FEATURES
SUPPORTING
ANCESTRY
THE
CASSIDULOID
OF CLYPEASTEROIDS
Kier (1974:88) has raised doubts that
any clypeasteroid has yet been found in the
Cretaceous.
The clypeasteroids evolved
rapidly once established. During the middle
Eocene most genera had some simple unsophisticated test characters such as a single
pore in the madreporite, poorly defined
petals, simple round non-conjugate pore
pairs, slightly developed or no internal supports, ovid test, and a lack of food grooves.
Genera
with some
of these
simple
characters
are Fibularia, Echinocyamus, Lenita, Leniechinus, and Pentedium. Many of these simple characters are common in juveniles of
genera with highly sophisticated test characters. Some middle Eocene genera had developed a relatively high degree of sophistication. Periarchus had pores distributed
throughout the madreporite, food grooves,
internal supports, and petal pore pairs with
elongate outer pores. The clypeasteroid record is poor earlier than the middle Eocene.
I believe the simple test characters of many
middle Eocene species support the hypothesis that clypeasteroids evolved from the juvenile stage of their ancestor. Nichols (personal communication, 1976) stated that
small size does not necessarily suggest
neotenic derivation from a juvenile. It is
not genetically difficult to alter the size of
BULLETIN OF MARINE SCIENCE, VOL. 27, NO.3,
420
an animal, whatever its origin. Most middle
Eocene clypeasteroids were relatively small.
Whether this is a factor of their neotenic
derivation is not known.
The fibulariids are apparently the most
primitive of the c1ypeasteroids based on test
characters. One of these is a very juvenile
level of madreporite development. It is common for sexually mature fossil and Recent
fibulariids to have a single madreporite pore.
Only one pore is present in the madreporite
in the earliest stage of development in echinoids (Hyman, 1955:470). This is the hydropore from the larval stage. This does not
necessarily
indicate
a cassiduloid
ancestor
but it is a strong juvenile feature representing
a level at or near metamorphosis.
Some interesting changes were taking
place within the cassiduloids as the Cretaceous ended. Many of these changes resulted in features common to cassiduloids and
clypeasteroids. The cassiduloids developed
a monobasal apical system (Kier, 1962:
chart 1). An exception is the Apatopygidae
(Kier, 1974:33, Fig. 28c). Clypeasteroids
also have a monobasal apical system. The
double pore tube feet beyond the petals of
cassiduloids evolved into the single pore
form (Kier, 1962, chart 1). The accessory
tube feet of clypeasteroids each have a single
pore. The respiratory tube foot pores shifted
from within plates to between plates (on the
suture) on cassiduloids.
Clypeasteroids
have their respiratory tube foot pores similarly located between plates. Cassiduloids
developed single pore buccal tube feet, one
on each basicoronal ambulacral plate (Kier,
1962: chart 2). Many genera of clypeasteroids have a single pore buccal tube foot
on each basicoronal ambulacral plate.
Recent immature cassiduloids a few millimeters in length are known to have a low
profile lantern with large wings unlike the
erect lantern of regular and holectypoid
echinoids. The lantern of immature cassiduloids is very similar to the lantern of oligopygoids and clypeasteroids (Kier, 1974:51-56,
figs. 56a-d).
The oligopygoids probably
also evolved from the immature stage of a
1977
cassiduloid. The juvenile cassiduloid has the
same basicoronal plate arrangement and
lantern support structure as the oligopygoids
(Kier, 1974:59-61).
The absence of compasses in the clypeasteroids has been explained as due to
the absence of gills and a nonseparation of
the lantern from the main coelomic cavity of
the test (Nichols, 1962:69) (Kier, 1974:
56). Another possibility is that the clypeasteroids evolved from the juvenile stage
of a cassiduloid. Compasses never fully develop in cassiduloids. All ossicles of the
lantern except the compasses are formed before an echinoid
passes
through
metamor-
phosis (Hyman, 1955:496). It could be that
the absence of compasses and presence of
a lantern in the clypeasteroids and oIigopygoids is related to the juvenile level of development at which these orders evolved
from their respective cassiduloid ancestors.
Compasses were present in echinoids early in
the Paleozoic Era prior to the development
of echinoid gills. The lantern of a clypeasteroid is not enclosed within a loose fitting
peripharyngeal membrane as in the regular
echinoids, but close examination reveals the
lantern is effectively sheathed in close fitting
membranes.
CONCLUSIONS
The ampullae of pore pair supported tube
feet have many features in common, even
comparing the respiratory tube foot ampullae of clypeasteroids with the ampullae of
regular urchins. Both ampullae are flattened.
Fluid constantly circulates between tube feet
and ampullae. Both ampullae have facilities
for distribution of the current, and very thin
walls.
Specialized bulb shaped ampullae somewhat like those of asteroids are found in
echinoids where the pore pairs have evolved
into a single pore. Examples are the ten buccal tube feet or peristomials of regulars and
the buccal tube feet and accessory tube feet
of clypeasteroids.
The complex water vessel network serving
PHELAN: WATER VASCULAR SYSTEM OF ECHINOIDS
accessory tube feet tends to parallel development of the food grooves. This is evident on
Dendraster where the anterior food grooves
are poorly developed and those of the posterior are highly developed. The fibulariids,
which lack food grooves, have simple lobes
on the radial water vessels to serve accessory
tube feet. Laganids have perradial food
grooves and accessory tube feet are served by
bands of ampullae along the sides of the
radial water vessels and blind ending side
spurs. Clypeaster and Fellaster have perradial food grooves and simple lateral water
vessels, many for each ambulacral plate.
Echinarachnius
has a long segment of each
food groove on a perradial suture but many
tributary branches near the ambitus of the
test. There are many lateral water vessels
for each plate, some with short branches
which tend to lead toward the growing edges
of the plate. Encope, Me/lita, and Dendraster have polyfurcating food grooves and
many lateral water vessels for each plate.
The lateral water vessels repeatedly branch
leading toward the growing edges of the
plates and even send long vessels into interambulacral plates. In clypeasteroids with
true lateral water vessels, new vessels are
added, older vessels lengthened, and additional accessory tube feet/ampullae formed
as the plates grow.
The lateral water vessels that serve respiratory tube feet commonly also serve accessory tube feet. Some plates within the petals
have lateral vessels which serve only accessory tube feet. Lateral water vessels in the
petals commonly are parallel to adapicalj
adoral plate sutures regardless of the pattern
of. pores on the exterior surface (e.g. F ellaster) . The accessory tube foot ampullae
are within cavities in the plates in the petals
of Dendraster. No accessory tube feet were
observed within the poriferous zones of the
respiratory tube feet.
The great lateral expansion of ambulacral
plates and adoral interruption of interambulacral columns is believed closely related to
the development of the accessory tube foot
system. They provide a broad food gathering
421
capability. These expanded areas are considered phyllodes and homologous to those
of the cassiduloids. They possibly have not
been previously recognized as phyllodes due
to the near microscopic size of the structures
of the test that accompany the abundant
minute accessory tube feet.
Numerous features are common to the
cassiduloids and clypeasteroids, strongly suggesting that the cassiduloids are ancestral to
clypeasteroids. Many middle Eocene clypeasteroids have juvenile characters possibly
supporting the hypothesis that the clypeasteroids evolved from sexually mature juvenile
cassiduloids. The absence of compasses and
possession of a lantern in clypeasteroids are
also suggested as juvenile features supporting
neotonic derivation of the clypeasteroids
from the cassiduloids.
ACKNOWLEDGMENTS
I thank Wyatt Durham, David Nichols, Porter
M. Kier, and Carol Wagner Allison for critically
reading the manuscript and offering excellent suggestions; the staff of the Oregon Institute of Marine Biology, Paul P. Rudy and Robert C. Terwilliger for providing laboratory facilities, Jean Hanna
and Kim Baxter for assistance in laboratory techniques; POrter M. Kier for providing encour"agement and information.
Specimens for study were
provided by Maureen Downey, Wyatt Durham,
Porter M. Kier, Klaus Ruetzler, J. Ross Wilcox,
and the staff of the Oregon Institute of Marine
Biology. I thank my wife, Kathleen Phelan for
typing the manuscript.
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---.
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---.
1966b. Clypeasteroids.
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DATE ACCEPTED:
July 21, 1976.
Oregon Institute
Charleston, Oregon 97420.
ADDRESS:
of Marine
Biology,