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 : 169

Palaeocorystoidea versus Dakoticancroidea Rathbun, 1917

The extinct Dakoticancroidea are discussed and listed by e.g. Weller (1905), Rathbun (1917, 1923), Kesling & Reimann (1957), Roberts (1962), Bishop (1981, 1988), Vega & Feldmann (1991), Guinot (1993b), Bishop et al. (1998) and Artal et al. (2008).

Carapace.

‒ Carapace varying from elongated to subcircular or subhexagonal in Palaeocorystoidea (subquadrate to subrectangular in Dakoticancroidea).

Pterygostome, endostome and mxp3.

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

‒ Mxp3 oxystomian in condition: distinctly elongated in Palaeocorystoidea (operculiform in Dakoticancroidea).

Appendages.

‒ Only P5 reduced in Palaeocorystoidea , as in Dakoticancridae (P4 and P5 reduced in Ibericancridae ).

‒ Articles of P2‒P4 modified (propodus, dactylus flattened) in Palaeocorystoidea ( Cenomanocarcinidae , Palaeocorystidae , unknown condition in others) (pereiopods stronger developed, distal articles not modified in Dakoticancroidea).

Thoracic sternum.

‒ Thoracic sternum narrow in Palaeocorystoidea (wide in Dakoticancroidea, in which sutures are much longer).

‒ Thoracic sternum entirely covered in width by abdomen in both sexes in Palaeocorystoidea (laterally exposed in male and even in female Dakoticancroidea).

‒ Sterno-abdominal depression in Palaeocorystoidea (distinct, rather deep sterno-abdominal cavity in male Dakoticancridae ; sterno-abdominal depression towards a cavity in male Ibericancridae ).

‒ Spermathecal apertures elongated, oval in Palaeocorystoidea (circular in Dakoticancroidea).

Abdomen.

‒ Sexual dimorphism indistinct in Palaeocorystoidea (well-defined, i.e., abdomen much wider in female Dakoticancroidea).

‒ First abdominal somites in prolongation with the carapace, thus visible in dorsal view, in Palaeocorystoidea (completely folded in Dakoticancroidea).

‒ Telson as wide as abdominal somite 6 in both sexes of Palaeocorystoidea (telson narrower than abdominal somite 6 in females, but as wide as abdominal somite 6 in males in Dakoticancroidea).

Abdominal holding.

‒ Sternal paired teeth on episternite 5 near outer lateral margin of thoracic sternum in Palaeocorystoidea (one or more tubercles in the medial part of thoracic sternum, thus at the margin of the sterno-abdominal cavity in Dakoticancroidea).