THE PHYLUM PORIFERA

THE SPONGES

 

INTRODUCTION

Sponges are among the most unusual animals

because of lifestyle and appearance originally thought they were plants; especially since some are green due to commensal algae

are primarily marine, mostly in shallower waters along coast

are sessile and attached to either the substrate or submerged objects- occasionally on other animals such as crabs

are the most primitive metazoans and have neither true tissues or organs

 

MORPHOLOGY

Have 4 very loosely differentiated cells:

Pinacocytes- outer cells covering sponge; equivalent of epiderm

Porococytes- cells which line the pores of the sponge; through which water is drawn

Choanocytes- similar to choanoflagellates; collared cells with flagella which create water current and collect food matter or sticky contractile collar; may also produce sperm.

Amoebocytes- amoeba-like cells found throughout the sponge; store, digest and transport food, excrete wastes, secrete skeleton and also may give rise to buds in asexual reproduction; there are several different types:

Large Amoebocytes- distribute food to other cells of sponge; move by way of pseudopods

Archeocytes- undifferentiated sponge cells that can give rise to more differentiated cells such as pinacocytes, porocytes or oocytes.

Scleroblasts- produce spicules; two types

Calcoblasts- make calcium carbonate spicules

Silicoblasts- make silicious spicules

SPONGE TYPES

There are 3 basic architectural types of sponges

Asconoid- most primitive and simplistic in structure

have radial symmetry

are tube shaped

 

There are two basic openings in the sponge:

Ostia- or incurrent pores that open into a central cavity called the spongocoel; it is lined with choanocytes or collar cells

Osculum- the opening of the spongocoel to the outside; this is the opening by which water leaves the sponge

the asconoid imposes definite size limits to sponges due to the problem of water flow

the spongocoel contains such a large volume of water that it is hard to push it our rapidly

there just are not enough choanocytes

 

Syconoid Sponges-

this is the next level of complexity in sponge architecture; it is derived from the asconoid structure except the walls are invaginated- allowing for greater surface area over which water can pass.

typically vase shaped like the asconoid sponges

 

radial symmetry

the syconoid structure helps to rectify some of the water movement problem by increasing the surface area and decreasing the spongocoel volume- so there are more choanocytes to water volume

these sponges able to get bigger than asconoid

 

Leuconoid Sponges- This is the highest level of complexity in sponges;

have lost radial symmetry and are very irregular in shape and may attain large sizes

they arise from syconoid sponges in which the invaginated canals are even further invaginated and folded to from small flagellated chambers

further increase in surface area makes these sponges highly efficient in moving and filtering water

spongocoel is gone except for canals that lead to the osculum- or there may be a series of excurrent openings

the largest sponges are leuconoid types because they have eliminated the spongocoel so that all the water entering the sponge is moved through small canals all lined with flagella

is the most hydrologically efficient method

 

HIGHER CLASSIFICATION OF SPONGES

there are 4 classes of sponges:

Calcarea

found in shallow coastal waters

all are marine

 

Hexactinellida - glass sponges

chiefly live in 500-1000 meter depth

are syconoid sponges

all are marine

 

Demospongiae

spicules are silicious if present otherwise skeleton is made of spongin or both

variously shaped some are huge

all are leuconoid

all but two families are marine- Spongillidae and Metaniidae- are freshwater with about 300 freshwater species; in North America are about 27 species in 11 genera (most belong to Spongillidae)

this is the group from which we get our commercial sponges

Sclerospongiae

have silicious spicules and spongin

also have an outer covering composed of calcium carbonate

are leuconoid sponges

 

REPRODUCTION

Sexual Reproduction

gametes formed by amoebocytes

there are both hermaphroditic and dioecious species; most freshwater species are dioecious

most hermaphroditic species produce eggs and sperm at different times so they do not self fertilize

sperm is released into environment via osculum and is brought in by another sponge via ostia

fertilization takes place in parent sponge

zygote is expelled - called an amphiblastula larva or parenchymula larva, it is planktonic when it reaches a certain size it drops to bottom and begins to develop

 

 

 

Asexual Reproduction

two types

1. Budding- fragmentation of body wall, buds appear as outgrowth on sides of sponge

when they reach a certain size they drop off and settle to bottom to form a new sponge

2. Gemmules- occurs only in freshwater sponges

gemmules are groups of food laden amoebocytes that deposit a hard covering of spicules around them

formation is triggered by environmental conditions such as decreased temperatures

they allow the sponge to pass the winter or periods of drought

after which the outer covering breaks open and a new sponge develops

 

OSMOREGULATION

no special organs

main waste is ammonia- it is removed by water currents within the sponge

ECOLOGY

Substrate Preference

most sponges prefer hard substrate such as rocks, plants or logs

some able to live on soft substrates (S. lacustris) such as mud, and is commonly found on muddy substrates of lakes

 

Nutritional Ecology

All are filter feeders; Choanocytes produce currents that transport water in and out of sponges; Amoebocytes distribute food throughout sponge

many have algae symbionts, which makes them green- these supply organic carbon and oxygen to host sponge, sponge supplies habitat and carbon dioxide to algae

 

Biotic Interactions

may compete with other sponges for available substrate

Interaction with other animals:

Spongillaflies - (Neuroptera; Sisyridae)- require sponges to exist

Ceraclea - (Trichoptera; Leptoceridae)- some species feed on sponges and are found only in association with them.

 

 

Collection and Preservation

For positive identification sponges must be collected when there are gemmules present- usually in the late fall or winter; gemmoscleres are especially important in identification.

may be either dried or stored in alcohol

preparation for identification involves the digestion of tissues in concentrated nitric acid to release spicules; spicules are then washed and concentrated and mounted permanently on slides with permount or canadian balsam

spicules are used for genus and species level identification

 

 

Classification

Two families in North America:

Spongillidae- this contains most species found in North America; including the most common species- Spongilla lacustris. Many species have very limited distribution (see text).

Metaniidae- two North American species; both belong to the genus Corvomeyenia; caroliniensis is known only from one site in South Carolina, the other, everetti, is known from the eastern part of the US and Canada