Brachiopoda

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Brachiopoda (lampshells) A phylum of solitary, benthic, marine, bivalved, coelomate, invertebrate animals that have existed from the Lower Cambrian to the present day. Brachiopods are commonly attached posteriorly to the sea bed by a stalk (pedicle), but may be secondarily cemented, or free-living (e.g. the fossil form Productus which, like many productids, was spinose, thick-shelled, and lived partly buried in the mud of the sea bed). Usually they consist of two unequal valves: a larger pedicle (ventral) valve and a brachial (dorsal) valve, lined by reduplications (mantle lobes) of the body wall which enclose the large mantle cavity. They are bilaterally symmetrical about the posterior-anterior mid-line of the valves (i.e. through the valves, compare BIVALVIA). The characteristic feeding and respiratory organ, the lophophore, surrounds the mouth and is covered by ciliated tentacles. It may be a simple horseshoe but more often forms two ciliated arms or brachia that project through the gape (thus giving the phylum its name). The alimentary canal is divided into oesophagus, stomach, and intestine, with or without an anus. The nervous system consists of a circum-oesophogeal ring with a small aggregation of nerve cells on the ventral side. The excretory organs are one or two pairs of nephridia (excretory tubules) also acting as gonoducts (for the release of eggs and sperm). The circulatory system is open, with the contractile vesicle (heart) near the stomach. Considerably more than 3000 fossil species are known and about 100 are alive today; these are widely distributed and occur at all depths. Brachiopods are divided into three classes: Lingulata, Inarticulata, and Articulata.

Brachiopoda

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Brachiopoda (lamp shells) A phylum of solitary, marine, bivalved, coelomate invertebrates that live attached to the seabed by a muscular stalk (pedicle), or are secondarily cemented, or are free-living. Usually they consist of a larger, pedicle (ventral) valve and a brachial (dorsal) valve, lined by reduplications (mantle lobes) of the body wall which enclose the large mantle cavity. They are bilaterally symmetrical about the posterior-anterior mid-line of the valves. The lophophore surrounds the mouth and is covered by ciliated tentacles. Brachiopods first appeared in the Lower Cambrian and since then have undergone numerous adaptive radiations, the first involving the inarticulate brachiopods. The articulate groups became more important after the Cambrian. Many of the larger articulate groups are now extinct.

Brachiopoda

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Brachiopoda (lampshells) Phylum of c.260 species of small, bottom-dwelling, marine invertebrates. They are similar in outward appearance to bivalve molluscs, having a shell composed of two valves; however, unlike bivalves, there is a line of symmetry running through the valves. They live attached to rocks by a pedicle (stalk), or buried in mud or sand. There are 75 genera including Lingula, the oldest known animal genus. Most modern brachiopods are less than 5cm (2in) across. More than 30,000 fossil species have been found and described.

Brachiopoda

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Brachiopoda A phylum of marine invertebrates – the lamp shells. They live in shallow waters, attached to a firm substratum by means of a flexible stalk (peduncle), and are protected by a bivalved shell consisting of dorsal and ventral valves. A food-gathering lophophore protrudes from the shell. Brachiopods thrived in Palaeozoic times but are now much less numerous; living brachiopods include Terebratella, with an articulated shell; and Lingula, in which the shell valves are held together by muscles only.