INTEGR. COMP. BIOL., 43:542–548 (2003)
Visual Ecology and Functional Morphology of Cubozoa (Cnidaria)1
MELISSA M. COATES2
Hopkins Marine Station, Department of Biological Sciences, Stanford University, Ocenview Boulevard, Pacific Grove,
California 93950
INTRODUCTION
The class Cubozoa (Werner, 1975) is the smallest
class within the phylum Cnidaria with only: one order
(Cubomedusae), two families (Carybdeidae and Chiropdropidae), seven genera, and roughly two dozen
species. In spite of this small size there is a lack of
consensus on the naming and description of species.
As a result the reader will notice different spellings of
genera, for example Charybdea xaymacana (Conant,
1898) vs. Carybdea sivickisi (Hoverd, 1985) depending on the choice of the author who described that
species. For this review I have chosen to hold to the
spellings of the original authors.
Originally grouped as an order within the class
Scyphozoa, the Cubozoa were elevated to class status
once research revealed the magnitude of the differences between this and other cnidarian groups (Werner,
1973; Werner et al., 1976). Berger (1900) first noticed
the physiological intermediacy of the cubomedusae between the scyphomedusae and hydromedusae. Although they share traits with the scyphozoans (rhopalia
that come in multiples of four) and hydrozoans (possession of a nerve-ring), cubozoans also possess traits
found in neither of the two other medusoid classes.
These include complete metamorphosis from polyp to
medusa (Werner, 1971, 1973; Arneson and Cutress,
1976; Laska-Mehnert, 1985), box-shaped exumbrella
(in most species, Tripedalia cystophora being a notable exception), and, complex lensed camera-type eyes
(Berger, 1898).
The eyes are located on the rhopalia, marginal sense
organs which hang from the bell on stalks and are
weighted down by a statolith. The function of the
statolith is not known and it has been proposed as both
a gravity-sensing organ and as a weight to keep the
eyes oriented in the same direction regardless of body
orientation (Berger, 1900). On each rhopalium there
are two lensed eyes (large complex eye and small complex eye), an identical pair of pit-shaped ocelli (pit
eyes), and an identical pair of slit-shaped ocelli (slit
eyes) (Fig. 1A). There is one rhopalium on each side
of the box-shaped bell, four in all. These alternate with
a single tentacle, or a group of tentacles, at each corner
of the bell (Fig. 1B). This makes four rhopalia per
medusa, six eyes per rhopalium, a total of twenty-four
eyes. What are the cubomedusae doing with all this
visual hardware?
Nilsson and Pelger (1994) predict that eye evolution
responds rapidly to lifestyle changes (see also Darwin,
1872). This implies that visual needs shape eye design
much more than phylogenetic position. Therefore, it is
useful to look at lifestyle differences between the cubozoans and other cnidarians and to ask: what is the
need for complex eyes? Is this need driven by ecological imperatives unique to cubomedusae (among Cnidaria)?
VISUAL ECOLOGY: INTERACTIONS BETWEEN AN
ORGANISM AND ITS ENVIRONMENT MEDIATED BY
VISUAL INFORMATION
Ecology is the study of interactions of animals with
their environment. While this is often the study of energy or nutrients moving through a system, information is an equally important component of the environment. Information is collected, dispersed, processed, created, and hidden by organisms in countless
ways. The question becomes: with what sensory information do cubomedusae interact with their environment? How could that information enable the cubomedusae to succeed by encoding cues about location,
habitat, obstacles, foods, mates, and so forth? Compared with the open ocean, kelp forests, mangroves,
and coral reefs are similar near-shore environments in
1 From the Symposium Comparative and Integrative Vision Research presented at the Annual Meeting of the Society for Integrative and Comparative Biology, 4–8 January 2003, at Toronto, Canada.
2 Present address: Melissa Coates c/o Department of Cell and Organism Biology, Lund University, Helgonavägen 3, Lund, Sweden,
223 62; e-mail: [email protected]
542
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SYNOPSIS. Jellyfish belong to one of the oldest extant animal phyla, the Cnidaria. The first Cnidaria appear
in the fossil record 600 million years ago, preceeding the Cambrian explosion. They are an extremely
successful group present in all marine environments and some freshwater environments. In contrast to many
animal phyla in which vision is a primary sense Cnidarians do not, generally, employ image forming eyes.
One small class stands alone: the Cubozoa. Cubomedusae are commonly known as box jellyfish. They possess
image forming eyes (Coates et al., 2001) which certainly evolved independently from other metazoans. Cubomedusae therefore offer a unique perspective on the evolution of image forming eyes. This literature
review collects, into one place, what is known about: the multiple eye types of box jellyfish, cubomedusan
life history and ecology, and the sensory and neural systems of box jellyfish. Here I discuss how these features
set cubomedusae apart from scyphomedusae and hydromedusae. Knowledge in these areas is sparse; the
work done to date inspires increased efforts.
CUBOZOAN VISION
543
terms of obstacles in the water column. These obstacles all present low frequency visual information.
These near-shore environments are the prefered habitat
of cubozoan species (Table 1).
Cubomedusae exhibit many light mediated behaviors (Conant, 1898; Berger, 1900; Barnes, 1966; HartTABLE 1.
Species
Charybdea grandis (Charybdea
alata var grandis)
Charybdea xaymacana
Charybdea alata
Charybdea marsupialis var
xaymacana
Charybdea aurifera
Charybdea punctata
Charybdea rastonii
wick, 1991; Hamner et al., 1995; Matsumoto, 1996;
Stewart, 1996; Coates and Thompson, 2000). For example, Chironex fleckeri avoids dark obstacles in a
tank and in the wild (Hamner et al., 1995) and can
also orient to the light of a match (Barnes, 1966). Tripedalia cystophora rapidly swims away from dark ob-
Summary of cubozoan species with reported habitats.
Environment
Location
Exposed shores
Anaa Island, Pacific Ocean
Surface, calm, shallow water
Kingston Harbor, Jamaica; Bermuda
Puerto Rico
Near-shore, near bottom during
the day
Near-shore
Not noted
Not noted
Surface, shallow water, sandy
beaches, inlets
Tortugas, Florida
Tortugas, Florida
Mangareva Harbor; Honolulu
Harbor; Misaki Biological Station; Southern and Western
Australia
Australia; New Zealand
Puerto Rico; Southern California
Carybdea sivickisi
Carybdea marsupialis
Coral reefs, near-shore in bays
Near-shore, mangrove channels,
kelp forests
Tripedalia cystophora
Mangrove swamps
Kingston Harbor, Jamaica;
Puerto Rico
Tripedalia binata
Tamoya haplonema
Chiropsalmus quadramanus
Chiropsalmus quadrigatus
Mangroves at high tide
Near-shore
Near-shore
Within 1 m of beach in calm
water
Within 1 m of beach in calm
water
Near-shore, sandy beaches
Northern Australia
East Coast, US
East Coast, US
Australia
Chironex fleckeri
Unidentifed cubomedusae:
‘‘Morbakka’’ and ‘‘Irukandji’’
Australia
Australia
Reference
Agassiz and Mayer (1902); Light
(1921)
Conant (1898); Bigelow (1938)
Bigelow (1918); Arneson and
Cutress (1976)
Bigelow (1918)
Mayer (1900)
Mayer (1900)
Bigelow (1909); Yatsu (1917);
Fenner and Williamson
(1987); Matsumoto (1996)
Hoverd (1985); Hartwick (1991)
Studebaker (1972); Arneson and
Cutress (1976); Larson (1976);
Larson and Arneson (1990)
Conant (1898); Arneson and Cutress (1976); Piatigorsky et al.
(1989); Stewart (1996)
Moore (1988)
Larson and Arneson (1990)
Larson and Arneson (1990)
Barnes (1966)
Barnes (1966); Southcott (1956);
Hartwick (1991)
Barnes (1966); Southcott (1967);
Fenner et al. (1985)
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FIG. 1. A. A schematic diagram of the rhopalium. The large and small complex eyes lie along the medial line while the pit and slit ocelli
are paired laterally. B. Drawing of Tripedalia cystophora courtesy of F. Sommer. Note that T. cystophora is unusual among cubozoans in
having a rounded, not box-shaped bell. Each medusa has four rhopalia located around the margin of the bell (arrows) which alternate with
the four groups of tentacles. The complex eyes point toward the center of the bell.
544
MELISSA M. COATES
jects and is attracted to light shafts in the water (personal observation; Coates and Thompson, 2000). Presumably the eyes of the sensory clubs mediate these
behaviors based on the visual information they extract
from the environment.
The ocelli
The ocelli come in two shapes, pits and slits, and
are paired symmetrical to the medial line of the rhopalium (Fig. 1A). The ocelli are formed by invagination of the surface epithelium (Conant, 1898). The distal portions of the epithelial cells lining the invaginations are heavily pigmented (Berger, 1900; Ng, 1974).
Berger (1900) and Conant (1898) found only one type
of cell in these invaginations (as did Laska and Hündgen, 1982) while they mention that earlier authors
(Schewiakoff, 1889; Claus, 1878) found two. The invaginated cells are photoreceptors (Yamasu and Yoshida, 1976). There is a refracting secretion in the space
of this invagination presumably protecting the photoreceptor cells (Conant, 1898; Berger, 1900; Yamasu
and Yoshida, 1976).
The camera-type eyes are similar in morphology to
those of vertebrates and cephalopods
The complex eyes are made up of a cornea, cellular
lens, possibly a vitreous space (see below) and a retina
with pigmented cells (Conant, 1898; Berger, 1898).
The similar morphology to that of other camera-type
eyes, vertebrates and cephalopods, suggests a similar
function (Pearse and Pearse, 1978). Apart from size
differences, the large and small complex eyes are similar in morphology. In Carybdea marsupialis the large
eye is 350–400 mm in diameter while the small eye
has a diameter of 250–300 mm. The lens diameter is
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CUBOMEDUSAE POSSESS THREE DISTINCT TYPES OF
EYES
Cubomedusae have six eyes located on each of the
four rhopalia. The eyes can be separated into three
distinct types: camera-type eyes, slit shaped ocelli, and
pit shaped ocelli (Fig. 1A). All three eye types possess
ciliated photoreceptors (Yamasu and Yoshida, 1976;
Laska and Hündgen, 1982). Although the earliest reports of cubomedusae all mention these three eye
types, often the number of ocelli present ranged from
one to several (Haeckel, 1879; Agassiz and Mayer,
1902). Haake (1887, as reported by Berger [1900])
claimed that the simple lateral ocelli (pit and slit eyes)
were present in young Charybdea rastonii, but absent
in the adults. We know this to be incorrect from more
recent descriptions of this species; the ocelli are present in both the young and the adults (Matsumoto,
1996). In fact all species on which current research
has focused (Carybdea sp.—Satterlie, 1979; Mackie,
1999; Tripedalia cystophor—Laska and Hu ¨ndgen,
1982; Stewart, 1996; Coates and Thompson, 2000;
Chironex fleckeri—Hamner et al., 1995; Carybdea
rastonii—Matsumoto, 1996) have the six eyes (two of
each type) described here.
150 mm in both eyes (Martin, 2002). Although there
is some variation in eye size between cubozan species,
the complex eyes are always roughly on this same order of magnitude.
The cornea is made up of flattened cells continuous
with the epithelium of the rhopalium (Berger, 1898).
All authors seem to be in agreement with this interpretation. The lens is cellular but the ‘interior lacks
nuclei, cell walls, and protoplasmic structure’ (Berger,
1900). Berger also noted that the degree of cellularization of the interior of the lens varied with lens size,
smaller lenses being more cellular. This difference
holds between small and large eyes within a specimen,
and between eyes of smaller and larger (younger and
older) specimens. The lens is ectodermal in origin
(Berger, 1900) and biconvex and heterogeneous.
Mackie (1999) assumes this is a graded index of refraction lens. The crystallin proteins are novel (Piatigorsky et al., 1989, 1993). The lens is surrounded
closely by a capsule which may be a secretion from
the lens cells (Berger, 1900). Ng (1974) refers to this
capsule as a vitreous humor, believing its position and
function synonymous to that of the vertebrate eye.
Earlier authors report the presence of a large vitreous body beteween the lens and the retina (Schewiakoff, 1889; Conant, 1898). Conant (1898) reported what
he termed ‘prism cells’ in this body which possess a
central fiber and concluded that they were extensions
of the retinal cells. Berger (1900) clarifies this by proposing that the retina and the vitreous body are histologically different parts of the same structure (see
also Laska and Hündgen, 1982). The term retina is
thus used for both taken together, while vitreous body
refers only to the vitreous portion of the retina. It is
important to note that this implies there is no space
between the lens and the retina, with the receptive segments of the photoreceptors extending all the way to
the lens, as suggested by more recent authors (Laska
and Hündgen, 1982; Pearse and Pearse, 1978; Satterlie, 2002). In this way Berger divided the retinal cells
into three topographical regions or zones: the vitreous
zone (vitreous body of other authors), the pigmented
zone, and the nuclear zone. Martin (2002) still claims
the presence of a vitreous space, although a much
smaller one than earlier authors.
Schewiakoff (1889, as reported by Conant, 1898)
held that there are two types of cells in the retina of
both the large and small complex eyes, called pigment
and visual cells. Conant (1898) himself could not distinguish two types of cells in the retina. Berger (1900)
found three distinct cell types in the large complex
eye, which he termed: prism cells and pyramid cells
(both presumed sensory), and long pigment cells (presumed structural). Here, he draws an analogy between
the prism and pyramid cells and the rods and cones of
vertebrates. However, he found only one type of cell,
the prism cell, in the small complex eye (Berger,
1900). Ng (1974) reports four types of cells in the
retina of the large complex eyes: long and short pigmented cells, and type A and B receptor cells. Laska
CUBOZOAN VISION
and Hündgen (1982) report three types of cells in the
large, and two in the small, complex eyes. The number
and type of cells reported in the retina differ largely
from author to author and it is not useful to go into
the details of each of the cell types beyond this. Rather
I will say this is an area where careful revisitaiton will
lead to much clarification. Obviously there is conflicting information here and not all these descriptions can
be accurate. This variation likely comes from collection, fixation, or microscopy techniques all of which
have improved greatly since these earliest descriptions.
The Photoreceptors
NERVOUS SYSTEM ORGANIZATION
In 1898, Conant recognized the presence of the
nerve ring as distinguishing cubomedusae from scyphomedusae. The nerve ring connects between the
rhopalia and the pedalia (points of attachment of the
tentacles) (Conant, 1898; Laska and Hündgen, 1984).
The nervous system can be divided into three functional parts: the sensory clubs or rhopalia, the conducting nerve ring, and the motor nerve net underlying
the subumbrellar epithelium (Conant, 1898; Passano,
1982). In the course of the nerve ring there are several
sets of ganglia: four radial ganglia situated where the
nerve ring branches to connect to the rhopalia and four
pedal ganglia situated where the nerve ring sends off
nerves to the tentacles (Conant, 1898; Laska and
Hündgen, 1984).
The rhopalia are filled with nerve fibers and cell
bodies, referred to as a rhopalial ganglion. This ganglion fills most of the space between the sensory organs and the extension of the gut which enters the
rhopalium (Conant, 1898; Ng, 1974; Laska and
Hündgen, 1984). There are two groups of large multipolar ganglion cells, one above each pit ocelli. The
area between and behind the small complex eye is
filled with a large group of network cells (Berger,
1900). The tissue directly below the retina is composed of ganglion cells and nerve fibers (Conant,
1898; Berger, 1900). These form synaptic connections
(Laska and Hündgen, 1982) via interneurons to the
rhopalial ganglion cells (Yamasu and Yoshida, 1976).
Removing the rhopalia completely leads to a cessation of swimming (Berger, 1900). Satterlie (1979,
2002) has shown that the swim pacemaker cells reside
in the rhopalial ganglia. Unfortunately, due to the location of these pacemaker cells, and the close association of the rhopalial ganglia with the eyes, it is impossible to do the desired experiment of removing the
rhopalial ganglion and leaving the eyes and swimming
behavior intact. If this experiment were possible I
would predict that removing the rhopalial ganglion
cells would eliminate a behavioral response to light
even if the eyes and the swim system remained unharmed. It is my opinion that the location of the rhopalial ganglion cells leaves them poised to sort information encoded by the eyes and to dictate appropriate
behavioral responses.
Cephalization may not be appropriate for a radially
symmetrical animal
It is easy to be biased by bilateral symmetry and
assume that a centralized nervous system is necessary
for any integrative nervous system function. However,
this may not only be unnecessary but actually detrimental in a radially symmetrical animal, where sensory input comes from several directions. Spencer and
Arkett (1984) have suggested, based on work in the
hydromedusae Polyorchis, that: 1) ‘‘the nerve-rings
constitute the central nervous system of hydrozoan jellyfish and that the condensation of neuronal networks
into ring structures is the maximum degree of localization that can be tolerated, bearing in mind the integrative mechanisms used,’’ 2) ‘‘networks of identical
neurones are the radiates’ equivalent of identifiable,
paired neurones in the CNS of bilateral protostomes’’
and 3) ‘‘rather than cephalic condensation . . . the hydromedusae have distributed their ganglia throughout
the outer nerve-ring so as to match the distributed arrangement of mulitcellular sense organs such as the
ocelli.’’ These ideas are supported by other authors for
a host of cnidarian groups (Passano, 1976; Satterlie,
2002; Mackie, 2002). These arguments hold for the
cubomedusan nervous system as well.
The function of the nervous system is to sense the
environment and respond appropriately (Satterlie and
Nolen, 2001). Cubomedusae have their sensory systems located around the margin of the bell where they
can receive information from all directions. They have
their integrative centers (rhopalial ganglia) concentrated near these sensory inputs (Satterlie, 1979; Satterlie
and Spencer, 1979; Laska and Hündgen, 1984). It is
known that the swim pacemakers located in the rhopalial ganglia communicate with eachother via the
nerve ring (Sattelie and Nolen, 2001). These rhopalial
ganglia presumably sort this information and then distribute it to the appropriate effectors, the swim musculature, via the distributed nerve net of the subumbrella. Distributed sense organs make the most sense
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The photoreceptors of cubozoans, and all cnidarians,
are ciliary with the 912 arrangement of microtubules
(Yamasu and Yoshida, 1976). They are made up of a
receptive outer segment, a pigmented layer, and a nuclear layer. Many microvilli extend from the central
cilium (Yamasu and Yoshida, 1976) and these are
thought to be involved in primary photoreception
(Laska and Hündgen, 1982; Takasu and Yoshida,
1984). The photoreceptors themselves contain the
screening pigment (Laska and Hündgen, 1982). Martin
(2002) reports that the outer segments possess stacks
of parallel membranes which form discs similar to vertebrate rod cells. These cells contain many mitorchondria and vesicles (Martin, 2002). An axon leaves from
the nuclear side. Connections from these photoreceptors lead to the rest of the nervous system through
interneurons (Laska and Hündgen, 1982).
545
546
MELISSA M. COATES
in a radially symmetric organism (Satterlie and Spencer, 1987; Satterlie, 2002).
Satterlie and Nolen (2001) have shown that the reduction to only four swim pacemakers in cubomedusae, compared to the higher multiples of four seen in
scyphomedusae, represents a partial of centralization
of the cubozoan nervous system. These swim pacemakers are located in the rhopalia and allow for rapid
responses to asymetrical stimuli (Satterlie and Nolen,
2001). This accounts for the agile swimming ability
and rapid directional changes seen in cubomedusae
(Satterlie and Nolen, 2001). Could this be in response
to visual information?
FOR THE ROLE OF THE
IN A BOX JELLYFISH
COMPLEX EYES
Lenses not only focus light but they also increase
light capture. Some authors have suggested that this
may be the sole purpose of the complex eyes (Laska
and Hündgen, 1982; Stewart, 1996). However, there
are no known examples of animals that employ this
strategy (Nilsson, personal communication). Another
idea that has been put forth is that the complex eyes
allow for orientation to luminescent prey at night
(Pearse and Pearse, 1978). Matsumoto (1996) suggests
that vision is primarily involved in feeding and reproduction (see also Pearse and Pearse, 1978; Martin,
2002). These two tasks can also be carried out with
chemoreception. Several authors have suggested some
sort of near-sighted view of small objects inside the
bell (Berger, 1898; Conant, 1898; Pearse and Pearse,
1978; Laska and Hündgen, 1984; Stewart, 1996; Matsumoto, 1996) because of the inward orientation of the
eyes. However, viewing small objects inside the bell
is also unlikely. The optics of the lenses of both the
large and small complex eyes show long focal lengths
(Coates et al., 2001). This means the lens acts as a
low pass filter. A low pass filter removes high spatial
frequency image information (such as small objects)
before that information reaches the retina. This leaves
only low frequency image information (larger objects
such as mangrove roots) for the retina to detect. This
will be the ideal use for the complex eyes. A low pass
filter will give enough information to avoid obstacles
in the water. Also, transparency of the bell allows for
possibly unencumbered view of the outside world
(Stewart, 1996). Meaning that the inward pointing orientation of the complex eyes will not restrict the field
of view to objects within the bell.
THE LIFE HISTORY AND ECOLOGY OF THE
CUBOMEDUSAE DIFFERS FROM OTHER MEDUSAE
Most medusae are open ocean drifters
Most medusae are found far from shore and are
planktonic, at the mercy of the currents and not capable of swimming against them (Graham et al.,
2001). In many areas it is uncommon to see medusae
near shore unless they have been swept in by changing
currents and tides. Often in these cases, medusae are
washed up on shore and die.
Cubomedusae are neritic, often living in complex
near-shore habitats such as mangrove swamps
A note on taxonomy: the number and descriptions
of species has changed many times over the years
(Haeckel, 1879; Mayer, 1910; Bigelow, 1918, 1938;
Stiasny, 1930; Kramp, 1961; Uchida, 1970) and there
is a great need to revisit this issue to form some consensus. For the discussion below, however, I am interested in conveying the typical habitat of the cubomedusae. To this end I will use the species names and
spellings used by the authors who collected and remarked on the habitat of a certain cubozoan.
Cubomedusae are near-shore species, usually tropical or sub-tropical (Werner, 1973). Agassiz and Mayer
(1902) found one individual, Carybdea grandis in a
trawl that came from a depth of 300 fathoms during
the expedition of the ‘Albatross,’ 1899–1900. This
may have contributed to the early misconception that
cubomedusae were deepsea animals. However, the
very next day they found a swarm of mature adults
very near the surface off Anaa Island.
Reports of cubomedusae date back more than 200
years (Linne, 1758). While the exact habitats are not
always recorded, we are beginning to get a sense of
their natural history, and they appear to prefer nearshore habitats, such as mangroves, kelp forests, coral
reefs, and sandy beaches (Table 1).
The cubozoan Tripedalia cystophora actively swims
near the surface during the day (Conant, 1898; Stewart, 1996), maintaining position among the mangrove
roots without damaging its delicate body. Cubozoans
are agile swimmers (Stewart, 1996) and voracious
feeders (Larson, 1976).
DISCUSSION
By bringing together all the work of previous authors, whether it be on life history or nervous system
function, a picture emerges that details the interactions
of cubozoans with their environments. From this picture it is now possible to make predictions about vision
in the Cubozoa.
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PREVIOUS IDEAS
Noteably, all epipelagic, midwater, and deepsea medusae have very simple, reduced, or absent ocelli. For
example, all species in the order Narcomedusae lack
ocelli (Mayer, 1910). Species of narcomedusae are
found from the surface down to depths greater than
1,000 m (Raskoff, 2001). While we think of jellyfish
as predators, their method of food capture more closely
resembles fishing than hunting. Beyond predator and
prey locations, or conspecific interactions, the open
ocean offers little environmental visual information.
Still, with simple ocelli, openwater medusae perform
phototactic behaviors. For example, Aurelia aurita
(Scyphozoa) navigates by sun-compass (Hamner et al.,
1994). Many hydrozoan species perform large vertical
diel migrations, which may bring individuals together
in spawning aggregations (Mills, 1983). Even with
large migrations, open ocean jellyfish rarely encounter
obstacles in their environments.
CUBOZOAN VISION
SUPPOSITION: SPATIAL VISION ALLOWS FOR
EXPLOITATION OF PRODUCTIVE NEAR-SHORE HABITATS
BY CUBOZOANS
As seen in Table 1, all known species of cubomedusae are found in near-shore habitats. Have the eyes
of the cubomedusae allowed them to expand into this
ecological niche?
Presupposition: medusae are soft, delicate, and
easily damaged by obstacles in the water column
Presupposition: vision is a useful way to detect
objects at a distance
Chemoreception lacks the resolution needed to
avoid obstacles. Mechanoreception will not give information on a time scale which leaves the medusae
able to respond; once contact is made the damage has
been done. Given the right resolution, spatial vision
will allow for detection and avoidance of obstacles.
Counter-supposition: cubozoan eyes represent
evolution gone wild, form without function
Gerhart and Kirschner (1997) propose that the cubozoan eyes shows how far form can go without function; citing the lack of a brain as evidence against the
usefulness of these eyes. In fact, most skepticism about
the image forming capabilities of the box jellyfish eye
comes in this form: what good is an image without the
nervous ability to interepret it (Nilsson and Pelger,
1994; Darwin, 1872)? Mackie (1999) is quick to point
out the under appreciation of, and in fact often misinformation concerning, the cnidarian nervous system
(see also Passano, 1976; Mackie, 2002; Satterlie,
2002). Everyone agrees that cnidarians can respond to
mechanical and chemical stimulation, should visual information be fundamentally different?
Although cubomedusae are a somewhat neglected
group more is being learned about them all the time.
When compared to other meduseae we see sophisticated eye design, complex nervous systems, and a
unique ecological niche. Bringing together the knowledge of previous researchers we are poised to explore
the role of vision in the Cubozoa.
ACKNOWLEDGMENTS
I would like to thank Jamie Theobald for support,
advice, and useful discussion, as well as Stuart
Thompson and Dan-Eric Nilsson. I thank Caren Braby
and Christian Reilly for careful reading of this manuscript as well as the two anonymous reviewers.
Thanks to Mason Posner for inviting me to participate
in the symposium. Thanks to Mason Posner, Todd
Oakley, and Sonke Johnson for organizing the symposium.
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For many years these beautiful creatures were incompletely described because what came up in plankton nets was often severely damaged. Improved collecting techniques increased knowledge over the past
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an animal with such a delicate body survive a nearshore habitat, where obstacles form effective walls?
Cubomedusae live in such environments but they must
have some way to keep from colliding with such obstacles.
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