Sealife guideThe marine sponges

The phylum of marine sponges includes 3 classes and is close to 10,000 species.

These different classes are primarily characterized by the nature of their skeleton: calcareous, siliceous or made of spongin alone:

the demosponges
the glass sponges or hexactinellids
the calcareous sponges or calcarea

Sponges are considered the simplest multicellular animals or metazoans: they lack a nervous system, digestive tract and circulatory system.

Sponges are sedentary and live attached to a substrate, sometimes mobile, like a crab's shell or a hermit crab's shell.

Taxonomy

Common name: Sponge
French name: Eponge, porifére, spongiaire
Scientic name: Porifera
Class: 3 classes
- the demosponges
- the glass sponges or hexactinellids
- the calcareous sponges or calcarea

Range

Marine sponges are found in all the seas and oceans of the planet.

Habitat

Marine sponges are benthic, sedentary animals that live attached to a substrate, sometimes mobile, like a hermit crab's shell.

Marine sponges can be found at all depths.

Description

Marine sponges come in various colors and shapes: encrusting, perforating, shrub-like, ball-shaped, cup-shaped, 'brain coral'-like, tube-shaped, vase-shaped or barrel-shaped for the larger ones.

A vase-shaped marine sponge

Sponges have the ability to adapt their shape to the current conditions and the nature of the substrate.

The structure of all sponges is based on an aggregate of cells that form 'small bags'.

This sac-like structure has a wall, more or less complex depending on the presence or absence of a network of peripheral water circulation canals, consisting of 2 membranes:

the external membrane or ectoderm
and the internal membrane or endoderm

These two membranes are separated by a gelatinous layer reinforced by spicules. The chemical composition of the spicules determines the sponge's family classification.

The cells constituting the external membrane are called pinacocytes, while those of the internal membrane are called choanocytes and are responsible for reproduction.

The surface of the external wall is perforated by inhalant pores. Through these pores, seawater enters to supply a central cavity, either directly or indirectly through a large network of canals that communicate with chambers containing choanocytes before draining into the central cavity.

The central cavity is called the atrium and opens to the outside through an opening called the osculum, which allows seawater to be expelled.

The complexity of seawater circulation through the wall has led to a classification into 3 types of sponges:

the Ascon type characterizes sponges with a simple wall
the Sycon type characterizes sponges with a wall featuring a simple network of peripheral water circulation canals
the Leucon type characterizes sponges with a wall featuring a complex network of peripheral water circulation canals

The different types of sponges: Ascon, Sycon, and Leucon

The wall of this bag is also perforated due to the presence of perforated cells or porocytes distributed across its entire surface, allowing water to enter inside.

Food chain

Diet

Unable to move to capture their food, sponges must bring it to them through a system of water circulation and filtration.

The sponge constantly filters seawater to feed

Water is inhaled through the pores, then filtered and expelled through the osculum. The sponge is capable of filtering several thousand times its own volume of water per day.

The mobile flagellated cells called amoebocytes, which line the entire internal wall of the sponge, ensure the distribution of nutrients among all the cells.

Predators

The main predators are nudibranchs, starfish, some fish and sea turtles.

Reproduction

Several types of reproduction can be observed in sponges:

sexual reproduction: sponges are hermaphrodites and both male and female gametes are released at the level of the choanocytes.
reproduction by budding: a fragment of the sponge detaches to give birth to a new sponge.

Did you know ?

The natural bath sponge you find in stores is actually the skeleton of a demospong.

Tips for observing

Identify the numerous openings
Observe the shape of the sponge

Be careful of the formation of air pockets above caves or cavities, which are fatal for encrusting sponges covering the ceiling.

Diver's Guide

The phylum of marine sponges includes 3 classes: demosponges, glass sponges and calcareous sponges, totaling 10,000 species.

The most well-known sponge to the general public is the demospong whose skeleton is sold as a natural bath sponge.

Some marine sponges to discover

Venus flower basket
(Euplectella aspergillum)

Compressed purse sponge
(Grantia compressa)

Yellow sponge Clathrina
(Clathrina clathrus)

Orange-red encrusting sponge
(Crambe crambe)

Rred boring sponge
(Cliona delitrix)

Stony sponge
(Petrosia ficiformis)

Yellow tube sponge
(Aplysina fistularis)

Azure vase sponge
(Callyspongia plicifera)

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