Phylum Porifera - Sponges

• Mostly marine, but include some freshwater inhabitants; usually found attached to the substratum in shallow or deep water.

• They are

sessile

; permanently attached to the substrate • Obtain their food by

filter feeding

General Morphology

• The internal cavity is called the

atrium

or

spongocoel

• Water is drawn into it through a series of

incurrent pores

or

dermal ostia

present in the body wall into a central cavity and then flows out of the sponge through a large opening at the top called the

osculum

Body layers

1. The

pinacoderm -

an outer layer of flattened cells called

pinacocytes

2. An inner lining containing flagellated cells

(choanocytes) -

draw water in through the pores and move out through the osculum; also trap food particles that are suspended in the water.

• The water current is also used for gas exchange, removal of wastes, and release of the gametes 3. Between the pinacodern and the choanocytes is a gelatinous material called

amoeboid cells Archaeocytes mesohyl

are amoeboid cells that ; contains several different kinds of wandering cells called phagocytize food particles; they can also undergo differentiation to form other cells, including cells that produce spicules and gametes

The Skeleton

In the mesohyl is the skeleton composed of tiny pointed structures made of silica or calcium carbonate called protection

spicules.

These structures act as an internal scaffolding, but also function in Among some sponges the skeleton consist of

spongin fibers

made of collagenous material; found in many of the commercial sponges

Types of Sponges (Canal Systems)

A. Asconoid Sponges

• Simple vaselike structure • This stucture puts limitations on size; (increase in volume without a corresponding increase in the surface area of the choanocytes)

Types of Sponges (Canal Systems) cont.

B. Synconoid Sponges

• The flagellated choanocyte layer has undergone folding forming finger like projections • There is a single osculum but the body wall is more complex, with water being received through incurrent canals, which pass it along to radial canals through to the spongocoel • Results in an increase in the surface area which allowed sponges to increase in the size

Types of Sponges (Canal Systems) cont.

C. Leuconoid Sponges

• No atrium; several small chambers in which choanocytes are located • There is a whole series of incurrent canals leading to the choanocyte chambers; water is discharges through excurrent canals • The leuconoid sponges exhibit a significant increase in surface area and are, therefore, among the largest sponges

Sponge Reproduction

• Most are

hermaphroditic parenchymula larvae

or

monoecious

• Sperm leaves a sponge via the osculum, and enters a sponge by the currents generated from the choanocytes.

Fertilized eggs develop into ciliated free-swimming larvae called • Sponges can reproduce asexually by .

fragmentation

• Many of the freshwater sponges can produce asexual bodies called

gemmules ,

aggregations of cells that are enclosed in hard outer covering containing spicules

Sponge Taxonomy

Class Calcarea (Calcispongidae)

• Only sponges that possess spicules composed of calcium carbonate. • Spicules are straight or have 3-4 rays, and do not have hollow axial canals. • Today, their diversity is greatest in the tropics, predominantly in shallow waters

Taxonomy cont.

Class Hexactinellida

(

Hyalospongiae)

• Glass sponges; characterized by siliceous spicules consisting of six rays intersecting at right angles • Widely viewed as an early branch within the Porifera

Taxonomy cont.

Class Demospongiae

• Greater than 90 percent of the 5,000 known living sponge species are demosponges.

• Demosponge skeletons are composed of spongin fibers and/or siliceous spicules • Siliceous spicules with one to four rays not at right angles, All members express the leuconoid body form

Yellow sponge growing on a wall on a Caribbean reef.