Sponges Loosely Organized Animals

The lineage leading to modern sponges separated from the lineage leading to all other animals very early during animal evolu tion. The difference between pro tist colonies and simple multicellu lar animals is that the animal cells are differentiated and their activities are coordinated. However, sponge cells do not form true organs.

(c) Coelomate

Coelomate Animals

(c) Coelomate

Earthworm

Acoelomates do not have enclosed body cavities.

Pseudocoelomates have a cavity lined with mesoderm on the outer side, but no mesoderm surrounds the internal organs.

Earthworm

Earthworm Mesoderm

Coelomate body cavities have mesoderm on both the outer side and surrounding internal organs.

Gut (endoderm) Internal organ Peritoneum (mesoderm)

Coelom Muscle (mesoderm)

Ectoderm

Coelomate body cavities have mesoderm on both the outer side and surrounding internal organs.

Water, carrying food particles, enters through many small pores.

Water flows through the sponge's body and exits through a large opening, the osculum.

Water, carrying food particles, enters through many small pores.

Water flows through the sponge's body and exits through a large opening, the osculum.

Coelomate Body Plan

The inner wall is studded with specialized feeding cells called choanocytes.

32.4 The Body Plan of a Simple Sponge The flow of water through the sponge is shown by blue arrows. The inner body wall is studded with choanocytes, a type of specialized feeding cell that may be a link between animals and colonial protists (see Figure 28.28).

The inner wall is studded with specialized feeding cells called choanocytes.

32.4 The Body Plan of a Simple Sponge The flow of water through the sponge is shown by blue arrows. The inner body wall is studded with choanocytes, a type of specialized feeding cell that may be a link between animals and colonial protists (see Figure 28.28).

Sponges (phylum Porifera, from the Latin, "pore bearers"), the simplest of animals, are sessile: They live attached to the substratum and do not move about. The body plan of all sponges—even large ones, which may reach more than a meter in length—is an aggregation of cells built around a water canal system. Feeding cells called choanocytes line the inside of the internal chambers. These cells, with a collar of microscopic villi and a single flagellum, bear a striking re semblance to choanoflagellates (see Figure 28.28). By beating their flagella, choanocytes cause the surrounding water to flow through the animal. The water, along with any food particles it contains, enters by way of small pores and passes into the water canals, where food particles are captured by the choanocytes. Water then exits through one or more larger openings called oscula (Figure 32.4).

Between the thin epidermis and the choanocytes is another layer of cells, some of which are similar to amoebas and move about within the body. A supporting skeleton is also present, in the form of simple or branching spines, called spicules, and often an elastic, complex, network of fibers. A few species of sponges are carnivores that trap prey on hook-shaped spicules that protrude from the body surface. Sponges also have an extracellular matrix, composed of collagens, adhesive glycoproteins, and other molecules, that holds the cells together. This molecular adhesion system may also be involved in cell-cell signaling.

Thus, sponges are functionally more complex than a superficial look at their morphology might suggest. Nonetheless, sponges are loosely organized. Even if a sponge is completely disassociated by being strained through a filter, its cells can reassemble into a new sponge.

Most of the 5,500 species of sponges are marine animals; only about 50 species live in fresh water. Sponges come in a wide variety of sizes and shapes that are adapted to different movement patterns of water (Figure 32.5). Sponges living in intertidal or shallow subtidal environments, where they are subjected to strong wave action, hug the substratum. Many sponges that live in calm waters are simple, with a single large osculum on top of the body. Most sponges that live in slowly flowing water are flattened and are oriented at right

Choanocytes Electron Microscopy

32.5 Sponges Differ in Size and Shape (a) Glass sponges are named after their glasslike spicules, which are formed of silicon. (b) The purple tube sponge is typical of many simple marine sponges. (c) This predatory sponge uses its hook-shaped spicules to capture small prey animals.

(c) Asbestopluma sp.

(a) Euplectella aspergillum (b) Aplysina lacunosa

(c) Asbestopluma sp.

32.5 Sponges Differ in Size and Shape (a) Glass sponges are named after their glasslike spicules, which are formed of silicon. (b) The purple tube sponge is typical of many simple marine sponges. (c) This predatory sponge uses its hook-shaped spicules to capture small prey animals.

angles to the direction of current flow; they intercept water and the prey it contains as it flows past them.

Sponges reproduce both sexually and asexually. In most species, a single individual produces both eggs and sperm, but individuals do not self-fertilize. Water currents carry sperm from one individual to another. Asexual reproduction is by budding and fragmentation.

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Responses

  • Tanja
    How water moves through a sponge?
    8 years ago
  • VIHTORI
    Does barrel sponge have coelomate?
    8 years ago
  • alan
    Why sponges have loosely organized cells?
    3 years ago
  • MADOC
    Do sponges and poriferns are coelomate?
    3 years ago

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