Soft Body-Related Features of the Carapace and the Lifestyle of Paleozoic Beyrichioidean Ostracodes

Abstract

The central muscle scar field of the beyrichioidean palaeocopid ostracodes includes an adductor muscle scar composed of many polygonal scars, a long mandibular scar composed of eight individual scars, and an oval frontal muscle scar. Probably, as in the extant ostracodes, the muscle scars served as attachment points for the closing muscles as well as for the muscles and chitinous supporting structures from the appendages. The fulcral depression, on which the dorsal apex of the mandible pivots in recent ostracodes, has also been recognized in the Early Carboniferous beyrichiids and paraparchitids.The pore systems of the beyrichioideans are more advanced than assumed so far, and they include, documented for the first time, the secretory (‘exocrine’) pores and ‘marginal’ pores in Paleozoic beyrichioideans. It seems likely that the development of these pores, was related to the transition of beyrichioideans from shallow marine into unstable, possibly brackish, water paleoenvironments.The partially calcified inner lamella and the ‘marginal’ pore canals are apomorphies of some Early Carboniferous beyrichioideans. Internal features of the paraparchitids confirm their beyrichioidean affinity. The adductor and mandibular scars are plesiomorphic in the Beyrichiidae and Paraparchitidae. The presence of mandibular scars and fulcral depressions may indicate that these ostracodes were actively feeding bottom crawlers.