| Craniata | |
|---|---|
 | |
| Ordovician strophomenid brachiopod with encrusting craniid brachiopods (Philhedra, the round attached shells). | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Brachiopoda |
| Subphylum: | Craniiformea Popov, Basset, Holmer & Laurie, 1993 |
| Class: | Craniata Williams, Carlson, Brunton, Holmer & Popov, 1996 (nonLinnaeus 1758:preoccupied) |
| Orders | |
| Synonyms[citation needed] | |
(Class) Craniforma | |
Craniata is aclass ofbrachiopods originating in theCambrian period and still extant today.[1] It is the onlyclass within thesubphylumCraniiformea, one of three major subphyla of brachiopods alongsidelinguliforms andrhynchonelliforms. Craniata is divided into threeorders: the extinctCraniopsida andTrimerellida, and the livingCraniida, which provides most information on their biology. Living members of the class have shells which are composed ofcalcite, though some extinct forms my havearagonite shells. The shells areinarticulate (lack a hinge with distinct tooth-and-socket connections) and are usually rounded in outline. There is nopedicle; the rear edge of the body cavity is a smooth and flat wall perforated by theanus.[2]This class of brachiopods has an unsupportedlophophore with only a single row of tentacles. In the absence of a pedicle, the shell is usually attached directly to a hard substrate. Many craniiforms are encrusting animals which attach directly to the shell of another animal, usually another brachiopod. The plicae from the host brachiopod will then appear within the shell of the craniiform.[2]
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Living craniiforms have a distinctive muscle system, which can be reconstructed from muscle scars in extinct forms as well. There are two pairs of column-likeadductor muscles, which extend vertically and function to close the shell. There are also two pairs of oblique muscles, which lie at a shallow angle and help to slide and rotate the valves against each other. The internal oblique muscles are closely spaced, extending up and back from the middle of the ventral valve to the back of the dorsal valve. The lateral oblique muscles are widely spaced, extending forwards from the back of the ventral shell to the front of the soft body wall.[2]
Craniiforms share some similarities with both linguliforms and rhynchonelliforms, though they are distinct from either group. Like linguliforms, they have an anus, inarticulate shells, and a muscle system mainly based on adductor and oblique muscles. Like rhynchonelliforms, they have a calcareous shell and a modified lophophore.[2]
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