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 : 167-168

Palaeocorystoidea versus Cyclodorippoidea Ortmann, 1892

Extant Cyclodorippoidea are discussed and listed by e.g. Tavares (1991, 1992a, b, 1993a, b, 1994, 1996, 1997, 1998, 1999, 2006), Guinot & Bouchard (1998), Guinot & Quenette (2005), Ahyong et al. (2009) and Guinot et al. (in press).

Carapace.

‒ Carapace varying from elongated to subcircular or subhexagonal in Palaeocorystoidea (varying from longer than wide but never markedly elongated, to subcircular, wider than long, occasionally expanded posteriorly in Cyclodorippoidea).

Pterygostome, endostome and mxp3.

‒ Epistome normally visible in Palaeocorystoidea (covered by extended endostome in Cyclodorippoidea, having a complete oxystomian condition in most Cyclodorippidae , but epistome present in Phyllotymolinidae ).

‒ Endostome elongated in Palaeocorystoidea (long, extended and reaching the front, sometimes visible dorsally, except in Phyllotymolinidae , Cymonomidae and some Cyclodorippinae).

‒ No sternum/pterygostome junction and ‘normal’ Milne-Edwards openings in Palaeocorystoidea (a sternum/ pterygostome junction and absence of Milne-Edwards openings in Cyclodorippidae , which has a complete oxystomian condition, but no junction in Phyllotymolinidae and Cymonomidae ).

Appendages.

‒ Only P5 dorsal and reduced in Palaeocorystoidea (P4 and P5 reduced, usually subchelate, mobile, may be placed on dorsal carapace in Cyclodorippoidea; carrying behaviour described in some species, P4 and P5 are vestigial, reduced to an article in Elassopodus ).

Thoracic sternum.

‒ Thoracic sternum rather narrow, not exposed laterally in Palaeocorystoidea (thoracic sternum wide, largely exposed laterally in Cyclodorippoidea).

‒ No sternal extensions in Palaeocorystoidea (a sternum/branchiostegite junction in Cyclodorippoidea due to extension of episternites between P1 and P2, P2 and P3, variable between P3 and P4).

‒ Presence of a sterno-abdominal depression in Palaeocorystoidea (usually short, posterior sterno-abdominal cavity, occupying only sternites 5‒8 or 6‒8, in Cyclodorippoidea).

Abdomen.

‒ All (6 + telson) abdominal somites free in Palaeocorystoidea (a variable number of abdominal somites fused in Cyclodorippoidea, often with a pleotelson, i.e., somite 6 fused to telson).

‒ Abdomen with continuous margin in Palaeocorystoidea (various arrangements, often with elongated pleura, in Cyclodorippoidea).

Abdominal holding.

‒ Sternal paired tooth (double peg) on episternite 5 in Palaeocorystoidea (‘sliding system’ ( Cyclodorippidae ) or ‘block system’ ( Phyllotymolinidae ) to hold the abdomen; no system known in Cymonomidae ; absence of sockets in Cyclodorippoidea).