Lecture 8
PHYLUM PORIFERA
Kingdom Animalia (animals)
Phylum Porifera (sponges)
Class Calcarea
Class Demospongiae
Class Hexactinellida
KINGDOM ANIMALIA
1. PHYLUM PORIFERA (sponges)
Name: Porifera means "pore-bearing". Exterior covered by tiny pores.
Chief characteristics: Globular, cylindrical, conical or irregular shape. Interior may be
hollow or filled with branching canals. Solitary or colonial. Skeletal elements are called
spicules, and they may be separate or joined. Composition may be calcareous, siliceous
or organic material called spongin. Fossil sponges are common in the floor tiles of the
Fernbank Museum of Natural History in Atlanta.
Geologic range: Cambrian to Recent.
Mode of life: Attached to the sea floor. Most are marine.
Astraeospongia, fossil
sponge
from
the
Middle
Silurian
of
Tennessee, 420 my.
About
5
cm
in
diameter.
Living
sponge,
aquarium at Skidaway
Institute
of
Oceanography,
Georgia
Jurassic fossil sponge
in the Solnhofen
Limestone, floor tiles,
Fernbank Museum of
Natural History,
Atlanta, GA.
Transverse section.
Jurassic fossil sponge
in the Solnhofen
Limestone, floor tiles,
Fernbank Museum of
Natural History,
Atlanta, GA.
Longitudinal section
through several
sponges in a cluster.
Note openings at top.
Jurassic fossil sponge
in the Solnhofen
Limestone, floor tiles,
Fernbank Museum of
NaturalHistory,
Atlanta, GA.
Longitudinal section.
Note opening at top.
The Porifera, more usually called SPONGES, are sessile aquatic animals with the simplest
structure found in the many-celled animals. They are mainly marine, and live in all depths of
water. Sponges are often encrusting, and may be of irregular shape, but in many the body has
a definite form, e.g. bowl- or vase-shaped with approximate radial symmetry. The skeleton is
internal, and may be organic (spongin as in bath sponges), siliceous (opaline silica) or
calcareous (calcite).
In its simplest form, the body is sac-shaped (fig.136a). The wall is perforated by small
pores leading by a system of canals to a central cavity which is lined by special cells,
flagellate collar cells. A current of water, initiated by the beating of the flagellae, is drawn
through the pores into the central cavity where the collar cells remove food (microorganisms) and oxygen. The water is passed out by one or more large openings (OSCULUM, -
l), on the upper surface (fig. l36a).
The body wall consists of an inner and outer layer sandwiching a jelly-like substance with
cells which secrete the units (SPICULES) of which the skeleton is composed. The spicules vary
in shape but are usually symmetrical (fig.136f-m). They may remain discrete and thus
separate on the death of the animal, or they may be united to form a rigid structure, in which
case forms with calcareous or siliceous spicules may be preserved entire.
Some common fossils
Siphonia (fig. l36c,d). The skeleton is tulip-shaped and was attached by a stalk. Minute
surface pores lead to a system of canals which traverse the thick wall, some in a radial
direction and others parallel to the outer surface (fig. 136d). Siliceous. Middle Cretaceous to
Tertiary.
Mode of life
Sponges are gregarious, living for the most part in relatively clear water. They are found at
all depths from the littoral zone down to abyssal depths. Modern calcareous forms are usually
restricted to coastal waters less than 100 m deep while siliceous sponges range into deeper
water to about 300 m though a few of these are characteristically found in cold water below
1000 m.
136 Morphology of the sponges.
a, longitudinal section through a simple type of sponge to illustrate the general structure of
the body; b, enlarged view of collar cells, c -d, tulip-shaped sponge (d, longitudinal section
showing the system of radial and vertical canals; the latter lead into the central cavity), e,
vase-shaped sponge, f-m, various types of spicules. (Arrows indicate the incurrent and
excurrcnl flow of water.)
137 A calcareous sponge. Raphidonerna, Lower Greensand, Lower
Faringdon, Berks.
Cretaceous,