Acimetopus

Acimetopus; Temporal range: Botomian (Olenellus-zone) PreꞒ Ꞓ O S D C P T J K Pg N
	Acimetopus bilobatus
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Trilobita
Order:	Agnostida
Family:	Weymouthiidae
Genus:	Acimetopus; Rasetti, 1966
Type species
	Acimetopus bilobatus; Rasetti, 1966 [1]

Acimetopus is a genus of trilobites that lived during the Botomian stage.[1]

Distribution

Acimetopus is known from the Lower Cambrian of the United States (unnamed formation, East Chatham Quad, Columbia County, New York State 42°24′N 73°30′W),[2] and England.[3]

Description

Like in all Agnostida, the body of Acimetopus is diminutive, the headshield (or cephalon) and tailshield (or pygidium) are approximately the same size (or isopygious). The thorax is unknown but all weymouthiids where it is known have 3 thoracic segments. Acimetopus has no eyes. Its cephalic border is strongly convex, with a pair of lateral marginal spines. The entire exoskeleton of Acimetopus is covered in granules. The central raised area of the cephalon, called the glabella, is strongly divided by two deep furrows that merge when crossing the midline. The large and inflated anterior lobe is isolated from border furrow. Behind it is a pair of small, separated, subtriangular lobes. The posterior part of the glabella is large and carries an inflated spine that is directed upwards and backwards. Genal spines are present. The axis of the pygidium (or rhachis) has nine rings that are strongly inflated, with the second ring carrying a vertical spine. The border surrounding the pygidium is defined by a deep furrow, is narrow, and lacks spines.[3]

Ecology

Acimetopus bilobatus occurs in association with other Weymouthiidae (Acidiscus, Analox, Bathydiscus, Bolboparia, Leptochilodiscus, Serrodiscus), Calodiscus, several species of Olenellus and Bonnia (Dorypygidae).[2]

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References

Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Trilobita entry)". Bulletins of American Paleontology. 364: 560. Archived from the original on 5 September 2006. Retrieved 12 January 2008.
Paleobiology Database. "East Chatham Quad, unnamed fm., NY (Cambrian of the United States) (trilobite)". Retrieved 19 December 2012.
Whittington, H. B. (1997). Treatise on Invertebrate Paleontology. Part O, Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.

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[Sepkoski-1] Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Trilobita entry)". Bulletins of American Paleontology. 364: 560. Archived from the original on 5 September 2006. Retrieved 12 January 2008.

[PBDB-2] Paleobiology Database. "East Chatham Quad, unnamed fm., NY (Cambrian of the United States) (trilobite)". Retrieved 19 December 2012.

[Treatise-3] Whittington, H. B. (1997). Treatise on Invertebrate Paleontology. Part O, Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.