Marine Phyla Pages -- Coastal Carolina University 

BRACHIOPODA

Lophophorata

   Bryozoa

   Brachiopoda

   Phoronida

____________________

Main

Defining Characteristics ¹

Brachiopods are marine animals that, upon first glance, look like clams. They are actually quite different from clams in their anatomy, and they are not closely related to the molluscs. 

Systematics ^{1   2}

All brachiopods have two shells. This makes brachiopods look superficially like bivalved molluscs (clams, oysters, etc.) However, a closer inspection shows some striking differences.  Each shell valve is symmetrical about the midline, but the two shell valves are often unequal in size. This is unlike most clams, which have two equal valves, each of which is slightly torted and thus asymmetrical across the midline.

The interior of the shell is lined with a mantle, a membranous duplication of the body wall, through which respiration may occur and which secretes the shells.  The shell is closed and opened by  adductor and diductor muscles respectively.  The scars of these muscles may be seen on the inside of the valves.  The body of the animal occupies only about one-third of the interior of the shell.  The rest is taken up by the lophophore, which is supported by a two-limbed, calcareous structure, the brachidium.  The brachidium is variable in shape consisting in its simplest form of the loop of two short or moderately long, curved structures, and in its more complex form of two thin, spirally coiled ribbons or spires.  The shape of the brachidium is very important in determining the classification of brachiopod types.  The brachidium supports the brachia, the fleshy arm-like part of the lophophore which bear the tentacles or cirri that sweep food particles into the mouth.

Feeding & Habitat ^{1   2}

Unlike their cousins the bryozoans, brachiopods are solitary, and never form colonies.  They are limited to marine environments, although some inarticulate brachiopods like Lingula tolerate brackish water.

Brachiopods are sessile (attached to a substrate), benthic (bottom-living) suspension-feeders, feeding on micro-organisms or organic particles dissolved in the water.  Most brachiopods were or are epifaunal, living on the surface of the sea-bottom, but a few, like the very primitive and ancient inarticulate genus Lingula is infaunal, burrowing in the sediment. 

They often make their homes in very cold water, either in polar regions or at great depths in the ocean. 

Other Information ¹

Although they seem rare in today's seas, brachiopods are actually fairly common.  There are about 300 living species of brachiopods.

Traditionally, the brachiopods have been split into two major groups, the Inarticulata and the Articulata. The Inarticulata got their name from the fact that they possess two valves that do not have an articulating hinge. The groups above that fit this description are the Lingulata and Obolellida; all others have articulating hinges. Recently it has been argued that hinge articulation is not a good character on which to make brachiopod groups.

Brachiopoda Links

1.  http://www.ucmp.berkeley.edu/brachiopoda/brachiopoda.html

2.  http://www.palaeos.com/Invertebrates/Brachiopods/brachiopoda.htm