Kingdom Animalia Class Trilobita Family Weymouthiidae | Phylum Arthropoda Order Agnostida Rank Genus | |
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Acidiscus is an extinct genus of eodiscinid agnostid trilobites. It lived during the Botomian stage of the Cambrian period.
Contents
Etymology
A. birdi is named for Dr. John M. Bird who collected the holotype. A. hexacanthus is derived from the Greek hexa "six" and acanthos "spine", for having two pairs of border spines in addition to one pair of genal spines.
Taxonomy
Acidiscus is most closely related to Bolboparia and slightly more distantly to Stigmadiscus.
Distribution
A. birdi 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), Canada (Newfoundland) and England (Purley Shales of Warwickshire).
Ecology
A. birdi occurs in association with other Weymouthiidae (Acimetopus, Analox, Bathydiscus, Bolboparia, Leptochilodiscus, Serrodiscus), Calodiscus, several species of Olenellus, and Bonnia (Dorypygidae).
Description
Like all Agnostida, Acidiscus is diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline. Like all Weymouthiidae, it lacks eyes and rupture lines (or sutures). The cephalic border carries one or two pairs of marginal spines. The central raised area of the cephalon (or glabella) does not touch the border furrow, and has two short, pitlike pairs of lateral furrows. Occipital and genal spines are present. Thorax is unknown, but all weymouthiids in which it is known have three segments. The pygidium is much like that in Serrodiscus. The pygidial axis has ten rings. The areas left and right of the axis, called pleura (or in plural pleurae) are without furrows. The edge of the exoskeleton on the ventral side (or doublure) may be extended into short spines.