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 : 165-166

Palaeocorystoidea versus Dromioidea De Haan, 1833

Extant Dromioidea are discussed and listed by e.g. Gordon (1950, 1963), Lewinsohn (1977, 1984), McLay & Crosnier (1991), Crosnier (1994), McLay (1991, 1993, 1999, 2001a–c, 2002, 2009), Guinot & Bouchard (1998), Ng et al. (2000), Chen & Sun (2002), Guinot & Tavares (2003), Tavares & Franco (2004), Guinot & Quenette (2005), McLay & Ng (2007), Ahyong et al. (2009), Ng & McLay (2010) and Guinot et al. (in press).

Carapace.

‒ Branchial grooves present as scars, or absent in Palaeocorystoidea (carapace mostly with well-defined branchial grooves in Dromioidea).

Pterygostome, endostome and mxp3.

‒ Mxp3 oxystomian: distinctly elongated in Palaeocorystoidea (normal/operculiform in Dromioidea).

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

Appendages.

‒ Only P5 (sub)dorsal and reduced in Palaeocorystoidea (dorsal P4 and P 5 in Dromiidae ; only P 5 in Dynomenidae ).

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

‒ Chelae always with spiny lower margin in Palaeocorystoidea , an adaptation to burying (non-spinose margins in dromioids).

Thoracic sternum.

‒ Sternite 3 visible in Palaeocorystoidea (sternite 3 either dorsally visible at the same level as preceding ones or sternites 1‒3 at a lower level in Dromiidae ; anterior sternites crown shaped, sternite 3 variable in Dynomenidae ).

‒ Female suture 7/8 rather long, but not forming a tube in Palaeocorystoidea (forming a spermathecal tube of variable length in Dromioidea, usually conspicuously long in Dromiinae, short in Sphaerodromiinae and Dynomenidae ).

‒ Thoracic sternum with crescent-shaped sutures 4/5 and 5/6 (sutures short, hidden in sterno-coxal depressions in Dromiidae and Dynomenidae ).

Abdomen.

‒ Dorsal uropods absent in Palaeocorystoidea (present as dorsal plates in most Dromiidae , in some as ventral lobes, and all Dynomenidae ).

Abdominal holding.

‒ Male abdomen in contact with coxae but no locking by appendages in Palaeocorystoidea (locking by appendages, acting often with uropods, in Dromioidea, except for Dynomeninae , which shows a sternal structure beside the uropod).

‒ Paired sternal tooth (double peg), on episternite 5 in Palaeocorystoidea (no sternal locking structures in Dromioidea, except in Dynomeninae , where the impaired sternal ‘button’ is not covered by abdomen, nor by uropod, thus no abdominal socket, the small sternal structure being located aside the abdomen and not facing any abdominal complementary part; e.g., Dynomene hispida (Latreille, in Milbert 1812)).