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 : 166

Palaeocorystoidea versus Homoloidea De Haan, 1839

Extant Homoloidea are discussed and listed by e.g. Gordon (1950), Serène & Lohavanijaya (1973), Guinot & Richer de Forges (1981, 1995), Wicksten (1985), Guinot & Bouchard (1998), Castro et al. (2003), Guinot & Quenette (2005), Richer de Forges & Ng (2007, 2008), Garassino (2009), Ahyong et al. (2009), Naruse & Richer de Forges (2010) and Guinot et al. (in press).

Carapace.

‒ Carapace varying from elongated to subcircular or subhexagonal in Palaeocorystoidea (invariably elongated or pyriform in Homoloidea).

‒ Orbits well protected in Palaeocorystoidea (cornea often external: ‘false orbit’ sensu Wright & Collins 1972: 44; ‘plage orbitaire’ sensu Guinot & Richer de Forges 1995: 303, in Homoloidea).

Pterygostome, endostome and mxp3.

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

‒ Mxp3 oxystomian condition in Palaeocorystoidea (mxp3 pediform to almost operculiform, never oxystomian in Homoloidea).

Appendages.

‒ Chelae in Palaeocorystoidea with spiny lower margin (adaptation to burying) (margins smooth, granular, or with small spines on the whole surface but never with row of long spines in Homoloidea).

Thoracic sternum.

‒ Sternite 2 concealed in Palaeocorystoidea (sternites 1‒3 forming a triangle, well visible between mxp 3 in Homoloidea).

‒ Suture 6/7 only lateral in Palaeocorystoidea (complete in Homoloidea).

‒ Sterno-abdominal depression regularly excavated in Palaeocorystoidea (floor of sterno-abdominal depression with distinctive flat surface in Homoloidea).

Abdomen.

‒ Male abdomen not longitudinally filling sterno-abdominal depression; telson partially covering sternite 4, leaving anterior portion of sternites 3 and 4 exposed in Palaeocorystoidea (male abdomen entirely covering sternoabdominal depression, so thoracic sternum not exposed in Homoloidea, except for sternites 1‒3 visible between mxp3).

‒ Telson in Palaeocorystoidea not reaching mxp3 (reaching mxp 3 in Homoloidea).

Abdominal holding.

‒ Paired tooth (double peg) on episternite 5 in Palaeocorystoidea for holding the abdomen (coxal holding by mxp3, P1‒P 3 in Homoloidea (except in Latreilliidae ); presence of ‘homoloid press-button’ on sternite 4 acting with a socket on abdominal somite 6).

‒ Mxp3 never involved in abdominal holding in Palaeocorystoidea (base of mxp3 may be used in Homoloidea).