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Trochotomidae is a small but distinctive extinct family of pleurotomarioidean gastropods characterized by trochiform shells with an elliptical trema. Two new species of trochotomids are described from Pliensbachian deposits in the Neuquén Basin, Argentina. The new genus-group name Placotoma is proposed to replace the pre-occupied name Discotoma Haber non Mulsant. The record of Trochotoma (Trochotoma) protonotialis new species and Trochotoma (Placotoma) neuquensis new species in the early Jurassic of Argentina extends the paleobiogeographical distribution of the genus (and the family) to the Southern Hemisphere. The new taxa reported here represent a component of the pleurotomarioidean adaptive radiation that took place in the Tethyan region during the earliest Jurassic. They are related to local patch coral reefs of shallow, open-marine paleoenvironments, agreeing with the known habitat of most species of this family. The group was well represented in the Tethyan region during the Mesozoic, especially during the Jurassic, and the new species represent its southernmost occurrence. [ABSTRACT FROM PUBLISHER]

Myzostome galls on arms of the Early Jurassic (Pliensbachian) Balanocrinus gracilis provide the first unequivocal evidence of such parasitic infestation in a post-Paleozoic crinoid. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]