Cenocorystes Collins & Breton, 2009

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 : 17-18

Genus Cenocorystes Collins & Breton, 2009

Cenocorystes Collins & Breton, 2009: 45 .

Type species. Cenocorystes fournieri Collins & Breton, 2009 , by original designation.

Species included. Cenocorystes bretoni n. sp., and C. fournieri Collins & Breton, 2009 .

Material examined. Cenocorystes bretoni n. sp.: type series, see below; C. fournieri: MAB k. 2881, cast of holotype NHN LM 2003-1-3813, lower Cenomanian , Sables & Grès de Lamnay Formation, Les Ormeaux quarry, Chambouquet (Saint-Maixent, Sarthe, France) .

Emended diagnosis. Carapace subhexagonal in outline; length, width nearly equal, widest one-third distant from front; surface fairly convex in both directions; orbitofrontal margin about three-quarters of total carapace width, orbits large, ovate, 2 long, relatively open fissures in upper orbital margins, elongated outer orbital spine; short, arched anterolateral margin with 3 well-spaced spines; 2 in front of, 1 behind cervical notch; posterolateral margin somewhat longer, slightly convex; posterior margin from straight to strongly concave; dorsal regions poorly defined, protogastric lobes may be with transverse row of 4 small tubercles ( C. fournieri ); cervical groove indistinct, incompletely defined, gastric muscle scars emphasised, gastric pits present; branchiocardiac grooves arched, short; branchial groove formed by muscle scars; dorsal surface of carapace finely granular. Pterygostome large, inflated, buccal margin concave with narrow buccal collar; mxp3 coxa large, flabelliform; endopod basis-ischium long, merus shorter, both grooved; thoracic sternum narrow, elongated, narrowing backwards, sternites 1, 2 narrowly triangular, at lower level; sternite 3 crown shaped, clearly separated from sternite 4 by oblique grooves; sternite 4 trapezoidal, episternite 4 suboval, robust, slightly extending laterally; suture 4/5 crescent shaped; sternite 5 without lateral depression; suture 5/6 crescent shaped. Arthrodial cavity of P4 tilted; P5 reduced, (sub)dorsal. Abdomen narrow, somite 1 tightly fitted between P5 coxae, somite 2 narrow.

Remarks. Collins & Breton (2009: 47) placed their new genus Cenocorystes in Palaeocorystidae , suggesting that it had, ‘characters in common to both Notopocorystes and Cretacoranina ’. Their opinion, however, was based on C. broderipii , which is here transferred to Joeranina n. gen. Characters that distinguish Cenocorystes from all other palaeocorystids are the relatively shorter carapace, large orbits, and the long and relatively open orbital fissures. Cenocorystes shares the above features with Orithopsidae . Cenocorystes , however, differs substantially from members of that family, which have a wider carapace with a pronounced, complete cervical groove, distinct axial and branchial carinae. In addition, the lateral spines are stronger and directed outwardly. Sternite 4 is deeply grooved medially in the orithopsids Orithopsis tricarinata and Silvacarcinus laurae ; this character is absent in Cenocorystes bretoni n. sp. (not preserved in C. fournieri ). It should be noted that the pterygostome of C. bretoni is weakly areolated for a palaeocorystoid, the branchiostegite being relatively high.

Cenocorystes is easily distinguished from Joeranina n. gen. by absence in the former of characteristic hepatic and protogastric protuberances, frontal furrows, deep and continuous cervical groove, and rimmed posterolateral margin; moreover, it has a relatively shorter carapace. Cenocorystes is easily distinguished from Ferroranina n. gen. by absence in the former of a post-frontal terrace and by having a shorter relative length and a gently rounded, rather than rimmed, posterolateral margin. Cenocorystes is also characterised by having a granular microstructure, instead of fungiform nodes in Ferroranina n. gen. This difference also separates Cenocorystes from Cretacoranina , in addition to the different carapace outline, definition of cervical groove and the architecture of the posterolateral margins. Cenocorystes is known exclusively from the Cenomanian of northern France and is typically found in coarse-grained sediments.