Palaeocorystoidea

Van Bakel, Barry W. M., Guinot, Danièle, Artal, Pedro, Fraaije, René H. B. & Jagt, John W. M., 2012, A revision of the Palaeocorystoidea and the phylogeny of raninoidian crabs (Crustacea, Decapoda, Brachyura, Podotremata) 3215, Zootaxa 3215 (1), pp. 1-216 : 164-165

Palaeocorystoidea versus Homolodromioidea Alcock, 1900

Extant Homolodromioidea are discussed and listed by e.g. Baéz & Martin (1989), Martin (1990, 1992, 1994), Guinot (1995), Guinot & Bouchard (1998), Ho & Ng (1999), Martin et al. (2001), Dawson (2002), Tavares & Young (2004), Guinot & Quenette (2005), Ng & Naruse (2007), Ahyong et al. (2009) and Guinot et al. (in press). The fossil record of Homolodromioidea (sensu Schweitzer & Feldmann 2009; Schweitzer et al. 2010) comprises four families: Bucculentidae Schweitzer & Feldmann, 2009 , Goniodromitidae Beurlen, 1932 , Prosopidae von Meyer, 1860 , and Tanidromitidae Schweitzer & Feldmann, 2009 . So far, all four are known solely from carapaces, which demonstrate a highly diverse pattern of carapace bauplan; their suprafamilial assignment remains doubtful. Discovery of ventral morphology may change the taxonomic composition of the extinct portion of this superfamily.

Carapace.

‒ Carapace varying from elongated ( Palaeocorystidae ) to subcircular or subhexagonal ( Camarocarcinidae , Cenomanocarcinidae , Necrocarcinidae and Orithopsidae ), always narrowing posteriorly in Palaeocorystoidea (always longer than wide, and generally constant in width or wider posteriorly in Homolodromioidea).

‒ Front subtriangular to subtrapezoidal in Palaeocorystoidea (two strong triangular teeth in Homolodromioidea).

‒ Branchial groove not notching the carapace margins in Palaeocorystoidea (notching margins in Homolodromioidea).

Pterygostome, endostome and mxp3.

‒ Endostome elongated (‘oxystomian mouth’) in Palaeocorystoidea (normal condition in Homolodromioidea).

‒ Mxp3 with oxystomian condition in Palaeocorystoidea (pediform, never oxystomian in Homolodromioidea).

Appendages.

‒ Only P5 dorsal and reduced in Palaeocorystoidea (P4 and P5 reduced in Homolodromioidea).

‒ P2‒P4 with flattened articles in Palaeocorystoidea (cylindrical articles in Homolodromioidea).

‒ Chelae with spiny lower margin in Palaeocorystoidea , an adaptation to burying (smooth in Homolodromioidea).

Thoracic sternum.

‒ Sterno-abdominal depression wide, weak in Palaeocorystoidea ( Cenomanocarcinidae , Orithopsidae and Palaeocorystidae ) or strongly excavated ( Camarocarcinidae and Necrocarcinidae ) (long, wide and well excavated in Homolodromioidea).

‒ Spermathecal apertures large, oval in Palaeocorystoidea (small, circular in Homolodromioidea).

‒ Thoracic sternum with crescent-shaped (horizontal outer part, and deep, vertical inner part) sutures 4/5 and 5/ 6 in Palaeocorystoidea (anterior sutures hidden in sterno-coxal depressions in Homolodromioidea).

‒ Sterno-coxal depressions absent in Palaeocorystoidea (present in Homolodromioidea).

Abdomen.

‒ Male abdomen not longitudinally filling sterno-abdominal depression with telson partially covering sternite 4, leaving anterior portion of sternites 3 and 4 exposed in Palaeocorystoidea (entirely filling sterno-abdominal depression, with long telson reaching mxp 3 in Homolodromioidea, so thoracic sternum not exposed at all).

‒ Male abdomen without distinct pleura in Palaeocorystoidea (distinct pleura in Homolodromioidea).

‒ Abdominal somite 6 long in both sexes of Palaeocorystoidea (normal in length in Homolodromioidea).

‒ Telson rounded in Palaeocorystoidea (elongated, distinctly triangular in Homolodromioidea).

Abdominal holding.

‒ Paired tooth on episternite 5 to hold the abdomen in Palaeocorystoidea (only coxal locking structures in Homolodromioidea).

‒ Male abdomen in contact with coxae, but no locking by appendages in Palaeocorystoidea (structures on P1 and P2 to hold the abdomen in Homolodromioidea).