Phylum Brachiopod A

Marine animals with a lophophore (similar to the Bryozoa) protected by a bivalved shell. They are normally attached to the sea floor by a pedicle which emerges from the larger valve, but some brachiopods lose the pedicle and rest (on one valve) directly on the sea floor. Brachiopods use their lophophore to circulate water in the cavity between the valves, where they can extract organic matter in suspension or in solution. They have a free-swimming larval stage (of from one to twenty days) which allows them to disperse. Most brachiopods are confined to shelf seas, but a few live in very deep water.

class INARTICULATA (Cambrian to Present)

Brachiopods with no hinge teeth to hold the valves in place. The shell often chitinophosphatic, but can be calcareous. Most live on the sea floor attached by a pedicle, but some (e.g. Lingula) burrow, and others lose the pedicle and become cemented (e.g. Crania).

class ARTICULATA (Cambrian to Present)

The majority of brachiopods are in this class. They all have a calcite shell. Most articulates have two teeth in the pedicle valve which fit into sockets on the smaller (brachial) valve and hold valves in place; a few groups have lost their teeth.

order Orthida (Cambrian to Present)

The earliest articulate brachiopods; probably ancestral to the rest of the class. The calcite shells generally have radial ribs or striations and a broad hinge line. Most orthides have a large triangular pedicle opening, situated in a distinct interarea.

order Strophomenida (Ordovician to Jurassic)

Most strophomenides have no functional pedicle in the adult, most forms have large valves, one of which is convex; an adaptation for resting on the sea floor. Other adaptations for loss of pedicle are seen in cemented forms and in those (like Chonetes and Productus) which develop spines. This order is the largest in the Brachiopoda, with nearly 400 genera.

order Pentamerida (Cambrian to Devonian)

Biconvex shells, usually smooth, with a spondylium. The penta-merides possibly had functional pedicles, but the thickened shell near the umbones could have allowed some to be stable on the sea floor without the need for a pedicle.

order Rhynchonellida (Ordovician to Present)

Biconvex shells with a pointed umbo. Pedicle usually functional. Shell normally with strong radial ribs, and with a marked fold anteriorly.

order Spiriferida (Ordovician to Present)

Spiriferides usually with a functional pedicle and the lophophore supported by a spiral brachial skeleton.

order Terebratulida (Devonian to Present)

The lophophore is supported by a calcareous loop, and thpse with a long loop usually have dental plates. The umbo is truncated by a large pedicle opening. This is the most abundant brachiopod order still alive today. The Thecideidina (Triassic to Present) are a group of small, cemented brachiopods which may be related to the Tere-bratulida.

Was this article helpful?

0 0

Post a comment