Trimerellida is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

order of

craniate A craniate is a member of the Craniata (sometimes called the Craniota), a proposed clade of chordate animals with a skull of hard bone or cartilage. Living representatives are the Myxini (hagfishes), Hyperoartia (including lampreys), and the muc ...

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...

s, containing the

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

Trimerelloidea and the

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

Adensuidae, Trimerellidae, and Ussuniidae. Trimerellidae is a small but widespread family of warm-water brachiopods ranging from the mid

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

(Llandeilo) to late Silurian (

Ludlow Ludlow () is a market town in Shropshire, England. The town is significant in the history of the Welsh Marches and in relation to Wales. It is located south of Shrewsbury and north of Hereford, on the A49 road which bypasses the town. The t ...

). Adensuidae and Ussuniidae are monogeneric families restricted to the mid to late Ordovician (Llandeilo to lower Ashgill) of

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbeki ...

. Trimerellides were massive by the standards of early brachiopods. They had fairly smooth and unornamented shells which were probably

aragonitic Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

in composition. The shells were unequally biconvex (both

valves A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...

convex to different degrees), in some cases nearly spherical in shape. There is no opening for the pedicle; individuals were free-living or clustered into congregations similar to modern oyster reefs. Trimerellides have some similarities to

rhynchonelliform Rhynchonelliformea is a major subphylum and clade of brachiopods. It is equivalent to the former class Articulata, which was used previously in brachiopod taxonomy. Articulate brachiopods have many anatomical differences relative to "inarticulate" ...

(articulate) brachiopods, including mixoperipheral shell growth (where the rear of each valve converges towards each other) and the development a fixed hinge between a wide plate on the dorsal valve and a socket-like groove on the ventral valve. Like other craniate brachiopods, the

musculature Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

consisted of two pairs of large and vertically-oriented

adductor muscles The adductor muscles of the hip are a group of muscles mostly used for bringing the thighs together (called adduction). Structure The adductor group is made up of: *Adductor brevis *Adductor longus *Adductor magnus * Adductor minimus This is o ...

(which close the shell) alongside two pairs of horizontally-oriented oblique muscles (which slide each valve past each other). The inner (internal) pair of oblique muscles extend nearly straight back to the dorsal valve hinge plate, in contrast to craniids and craniopsids, where the oblique internals splay out and attach besides the posterior adductors. A shelf is usually present near the middle of each valve, in front of the anterior adductors

References

Bibliography

* Modzalevskaya, Tatyana Lvovna (2003). "Silurian and Devonian brachiopods from Severnaya Zemlya" (Russian Arctic). ''Geodiversitas'' 25 (1). pp. 73–107. Prehistoric brachiopods Prehistoric animal orders Brachiopod orders Craniata {{paleo-protostome-stub