THE GENUS XANTHILITES BELL, 1858 AND A NEW XANTHOID FAMILY (CRUSTACEA: DECAPODA: BRACHYURA: XANTHOIDEA): NEW HYPOTHESES ON THE ORIGIN OF THE XANTHOIDEA MACLEAY, 1838

摘要

The xanthoid genus Xanthilites Bell, 1858 is herein restricted to contain only the type species X. bowerbanki and possibly a second species. Xanthilites sensu stricto, Pulalius, Tumidocarcinus, Paratumidocarcinus, and Baricarcinus are placed within the Tumidocarcinidae new family within the Xanthoidea. It is hypothesized that the Carpiliidae, Platyxanthidae, Tumidocarcinidae new family, Zanthopsidae, and at least some subfamilies of the Eriphiidae form a natural group and may belong to a discrete superfamily, based upon paleontological and neontological evidence. The earliest documented occurrence in the fossil record for the xanthoid Platyxanthidae is in Eocene rocks, with the referral herein of a fossil species to the family. The two related families, Eriphiidae and Platyxanthidae, are difficult to distinguish from one another in fossil specimens; diagnoses which take into account preservable characters are provided. Moreover, based upon morphological features the Eriphiidae as currently defined may comprise at least two families. Revision of Xanthilites has resulted in two new genera, Jakobsenius and Rocacarcinus, erected for Xanthilites? cretacea and X. gerthi respectively, both placed within the extinct Palaeoxanthopsidae. The common ancestor of at least some families currently referred to the Xanthoidea may lie within the Palaeoxanthopsidae, which may have embraced "pre-adapted survivor" taxa, surviving the end-Cretaceous extinction event. Goniocypoda tessieri is confirmed as a member of the Hexapodidae, extending the range of that family into the Cretaceous; however, the family is not a likely candidate for embracing the ancestral xanthoids. The illustrated specimen of Menippe frescoensis retains a barnacle epibiont, very rare in the fossil record of decapods.