Alokistocaridae

Alokistocaridae is a family of ptychopariid trilobites that lived from the Botomian epoch of the Early Cambrian until the Late Cambrian. Alokistocarids were particle feeders and left small furrows with are occasionally preserved.[1] Their remains are found worldwide. Elrathia kingii, one of the most collected trilobites in the world, is a typical alokistocarid.

Alokistocaridae Temporal range: Botomian-Upper Cambrian PreꞒ Ꞓ O S D C P T J K Pg N
Elrathia kingii, an Alokistocarid
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Trilobita
Subclass:	Librostoma
Order:	Ptychopariida
Suborder:	Ptychopariina
Superfamily:	Ptychopariacea
Family:	Alokistocaridae Resser, 1939
genera
Alokistocare Lorenz, 1906 = Amecephalus, Strotocephalus Alokistocarella Resser, 1938 Amecephalina Poulsen, 1927 Annamitia Mansuy, 1916 Arellanella Lochman, 1948 Bythicheilus Resser, 1939 Chancia Walcott, 1924 Chelidonocephalus King, 1937 Dunderbergia Walcott, 1924 Ehmania Resser, 1935 Ehmaniella Resser, 1937 = Anomalocephalus, Clappaspis Elrathia Walcott, 1924 Elrathiella Poulsen, 1927 = Coelaspis, Glassocoryphus Elrathina Resser, 1937 Inglefieldia Poulsen, 1927 Ithyektyphus Shaw, 1956 Kistocare Lochman, 1948 Kochiella Poulsen, 1927 Kochina Resser, 1935 Kounamkites Poletaeva & Chernysheva, 1956 Kujandaspis Ivshin, 1956 Megadunderbergia Kobayashi, 1938 Mexicella Lochman, 1948 Orlovia Walcott & Resser, 1925 Pachyaspis Resser, 1939 Parehmania Deiss, 1939 = Mcnairia, Rowia, Thompsonaspis Perioura Resser, 1938 Proveedoria Lochman, 1948 Ptychoparopsis Hupé, 1953 Trachycheilus Resser, 1945

Description

Alokistocarids have an exoskeleton that is elongated ovate to inverted egg-shaped. The headshield (or cephalon) is semicircular and has a well-defined border. The central raised area of the cephalon (or glabella) is somewhat tapering forward, generally with 3 or 4 pairs of more or less distinct lateral furrows. The front of the glabella is rounded or truncate, and is separated from the border by a wide, moderately convex to flat (or rarely concave) so-called preglabellar field. Narrow ridges that connect the eyes with the glabella are well developed. The distance between the eye and the glabella (or palpebral lobe) is small. The fracture lines (or sutures) that in moulting separate the fixed from the free cheeks (fixigenae and librigenae) may converge or diverge in front of eyes. Behind the eyes they cut the posterior margin of the cephalon inside the inner bend of the genal spine (or opisthoparian sutures). The genal spines are short or moderately long. Alokistocarids have a relatively large articulating middle part of the body (or thorax), consisting of 12 to 19 segments. The thorax axis is moderately convex and sharply defined, while the areas lateral of the axis (or pleurae) are nearly flat with distinct grooves. The tailshield (or pygidium) is small, with few segments, and lacks a border. The surface is generally smooth.[2]

References

1. Coppold, Murray and Wayne Powell (2006). A Geoscience Guide to the Burgess Shale, p.54. The Burgess Shale Geoscience Foundation, Field, British Columbia. ISBN 0-9780132-0-4.
2. Moore, R.C. (1959). Arthropoda I - Arthropoda General Features, Proarthropoda, Euarthropoda General Features, Trilobitomorpha. Treatise on Invertebrate Paleontology. Part O. Boulder, Colorado/Lawrence, Kansas: Geological Society of America/University of Kansas Press. pp. O233, O238–O241. ISBN 0-8137-3015-5.