I. Classes
 Classification is based on the skeletal structure
 There are four different classes:
1. Calcarea
 Spicules made of calcium carbonate
 Usually smaller sponges that are tubular or vase-shaped
2. Demospongiae
 Most common class
 Spicules can be made of silica, or spongin, or both
 Often brightly colored
3. Hexactinellida
 Often referred to as glass sponges
 Have six-rayed spicules made of silica in a lattice
formation
 Mainly found in deep, cold waters
4. Sclerospongiae
 Skeleton consists of silica, spongin, and calcium carbonate
 Usually found in dark tunnels in coral reefs
II. Structure
 Osculum: large opening at the top of the sponge through which waer and
waste flow out of the sponge
 Atrium: the central cavity of the sponge, also called the spongocoel
 Choanocyte: also called collar cells. They line the inner cavity of the
sponge. They have a sticky, funnel-shaped collar and a flagellum. They
digest food particles and are also involved in sponge reproduction by
catching floating sperm.
 Spicule: form the sponge skeletons and are there for support and to deter
predators.
 Ostia: tiny pores found all over the body of a sponge that let water into the
sponge. Singular is ostium.
 Amoebocytes: store, digest and transport food, excrete wastes, secrete
skeleton and also may give rise to buds in asexual reproduction.
 Pinacocyte: flattened cell which comprises the outer surface of the sponge.
Can be expanded or contracted at their margins to allow the whole animal
to alter its size slightly. At the base the pinacocytes secrete collagen,
which anchors the sponge to its substrate.
 Pinacoderm: single layer of pinacocyte cells that separate the inner cellular
region and external environment
 Mesohyl: the gelatinous matrix within a sponge. The mesohyl resembles a
type of connective tissue. The mesohyl is composed of the following
main elements: collagen, fibronectin-like molecules, galectin, and a minor
component, dermatopontin. Provides the platform for specific cell
adhesion as well as for signal transduction and cellular growth.
 There are three different body types:
1. Asconoid
 Are tube shaped
 Have radial symmetry
 Most primitive and simplistic in structure
 Have size limits due to the problem of water flow
2. Syconoid
 Sponges can get bigger because there is greater surface area
 Are vase shaped
 Have radial symmetry
3. Leuconoid
 Have no radial symmetry and are irregular in shape
 May attain large sizes due to even more surface area
 Most hydrologically efficient due to the lack of spongocoel
III. Unique Characteristics
 Simplest multicellular animal with no body systems
 Have no tissues or organs
 Have unspecialized cells that can move throughout the body and transform
into other types
 Mostly sessile animals
 Can produce toxins that prevent other sessile organisms from growing on
or near them.
 Able to suffer damage. Because the cells are not linked in a tissue it is
possible for them to be separated and then come together again.
 When invaded, gray cells produce a chemical that stops movement of
other cells in the affected area, preventing the intruder from using the
sponge's internal transport systems. If the intrusion persists, the grey cells
concentrate in the area and release toxins that kill all cells in the area.
IV. Habitat
 99% of all sponges live in salt water
 Generally found in shallow waters where there are more nutrients
 Grow better in unpolluted water so their pores don’t clog
 They form flattened or rounded shapes in water with strong currents, but
in still waters can grow into tall and often tree-like structures
 Majority attach themselves to any suitable surface such as rocks, hardshelled animals or seaweeds. Some are able to attach to sediment with a
root like structure.
V. Feeding
 Filter-Feeding
o The central cavity is lined with choanocytes (a.k.a. collar cells)
o Each collar cell has an undulating flagellum that creates a current
of water, which causes water to enter through the sponge's pores,
circulate in the chambers, and flow into the central cavity.
o Microscopic plants and animals and organic debris that are brought
in with the water are drawn to the collar cells, where they are
engulfed and then ingested.
o The incoming water currents also bring oxygen to the cells.
o After water circulates in the central cavity, it passes out through a
large opening, the osculum, to dispel carbon dioxide and other
waste products discharged by the cells.
 Carnivorous Sponges
o Usually found deeper in the ocean, where the current lacks
nutrients
o Have hook-shaped spicules, called anisochelae, that grab
crustaceans floating by
o Grow on a stalk, so are usually slightly taller
o After a day, cell movement and growth covers the hooked animal,
and after a few days the animal is completely ingested.
VI. Reproduction
 Asexual
o Budding
 Ends of the branches constrict until the ends fall off and
regenerate into new individuals
o Gemmulation
 Food enriched cells surrounded by a protective coating
 Two chitinous layers (the internal one being
delicate and the external tougher)
 A pneumatic coat that is thick and filled with air
pockets to create buoyancy
 This egg like structure is called a gemmule
 More common in freshwater
 Used to endure harsh conditions, such as drought or
freezing temperatures
 Sexual
o Both hermaphroditic (producing both sperm and egg cells) and
dioecious (producing only sperm or egg cells) species exist
o Sperm and egg cells develop spontaneously within sponge walls
from transformed sponge cells. Sperm cells leave through the
oscula and excurrent water columns and enter other sponges
through the ostia and incurrent water columns.
o After fertilization, the embryos develop within the body wall until
the larval stage
o At the larval stage, they break off and are carried to the open
water, where, after a short free-swimming existence, the sponge
larvae settle and attach to a desired surface and grow into an adult
sponge