Brachiopods superficially resemble bivalve mollusks

Brachiopods (phylum Brachiopoda) are solitary marine lophophorate animals. Their shells are divided into two parts

(a) Lophopus crystallinus

(a) Lophopus crystallinus

Ectoprocts

32.19 Ectoprocts (a) Branching colonies of ectoprocts may appear plantlike. (b) Ectoprocts have greater control over the movement of their lophophores than members of other lophophorate phyla.

Mollusk Anatomy Physiology

Lophophore spreads

Lophophore oscillates Lophophore and rotates retracts

Lophophore spreads

Lophophore oscillates Lophophore and rotates retracts

32.20 Brachiopods The lophophore of this North Pacific brachio-pod can be seen between the valves of its shell.

Ectoprocts

Laqueus sp.

Lophophore

Laqueus sp.

Lophophore

32.20 Brachiopods The lophophore of this North Pacific brachio-pod can be seen between the valves of its shell.

that are connected by a ligament (Figure 32.20). The two halves can be pulled shut to protect the soft body. Bra-chiopods superficially resemble bivalve mollusks, but the brachiopod shell differs from that of mollusks in that the two halves are dorsal and ventral rather than lateral. The two-armed lophophore of a brachiopod is located within the shell. The beating of cilia on the lophophore draws water into the slightly opened shell. Food is trapped in the lophophore and directed to a ridge, along which it is transferred to the mouth. Most brachiopods are between 4 and 6 cm long, but some are as long as 9 cm.

Brachiopods live attached to a solid substratum or embedded in soft sediments. Most species are attached by means of a short, flexible stalk that holds the animal above the substratum. Gases are exchanged across body surfaces, especially the tentacles of the lophophore. Most brachiopods release their gametes into the water, where they are fertilized. The larvae remain among the plankton for only a few days before they settle and develop into adults.

Brachiopods reached their peak abundance and diversity in Paleozoic and Mesozoic times. More than 26,000 fossil species have been described. Only about 335 species survive, but they are common in some marine environments.

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