Bournelyreidus, Van Bakel & Guinot & Artal & Fraaije & Jagt, 2012

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 : 78-79

Genus Bournelyreidus n. gen.

Type species. Hemioon eysunesensis Collins & Wienberg Rasmussen, 1992 , by present designation.

Diagnosis. Carapace oval, elongated, widest at one-third of total carapace length from front, nearly flat in longitudinal, convex in transverse cross section. Posterolateral margin with divergent posterior portion, vertical anterior portion; anterolateral margin shorter, with 2 curved, spiniform teeth. Orbitofrontal margin straight, occupying more than half of maximum carapace width. Outer orbital corners prominent, supraorbital borders with 2 orbital notches. Rostrum trapezoidal, bifid or triangular, with single apex, excavated. Branchiocardiac grooves shallow, well-defined, cervical groove absent. Carapace surface with minute pits, granules (upright nodes). Pterygostome tumid, with a granular blunt ridge, posterior corner recessed for relatively large mxp3 coxa. Mxp3 strongly elongated, oxystomian condition; exopod narrow, slightly shorter than equal-sized endopod ischium, merus. Branchiostegite reduced, pleurites exposed. Sternite 3 crown shaped; sternite 4 long, wide anteriorly, forming junction with pterygostome, lateral sides strongly concave. Episternite 4 rather small. Sternite 5 large, broadly extended between P1, P2, reaching pleurites. No medial line, at least on sternites 1‒6. Holding mechanism present (see note under B. tridens n. comb.). Chelipeds flattened, fixed finger not downturned ( B. carlilensis n. comb.; Feldmann & Maxey 1980: 859, text-fig. 1E), closing, with sharp teeth; lower margin of chelipeds smooth to spinose. P2–P4 with paddle-shaped propodus, dactylus; P5 reduced, subdorsal. Abdomen flexed under carapace, abdominal somite 3 with medial elevation, somite 4 with prominent tubercle, somite 6 long ( Collins & Wienberg Rasmussen 1992: 21).

Derivation of name. In honour of the late G.C. Bourne, in recognition of his admirable contribution ( Bourne 1922b) to the knowledge of raninoid crabs.

Species included. Raninella carlilensis Feldmann & Maxey, 1980 , Hemioon eysunesensis Collins & Wienberg Rasmussen, 1992 , Palaeocorystes laevis Schlüter in von der Marck & Schlüter, 1868, Raninella manningi Bishop & Williams, 2000 ,? Raninella oaheensis Bishop, 1978 , B. teodorii n. sp., and Raninella tridens Roberts, 1962 . Also assigned here is Lyreidus sp. sensu Collins & Jakobsen (1995).

Remarks. Members of Bournelyreidus n. gen. were previously placed either in Raninella A. Milne Edwards, 1862 , or Hemioon A. Milne Edwards, 1862 , two genera considered here synonymous (see below).

Several characters distinguish Bournelyreidus n. gen. from Raninella . The carapace of the former has the posterolateral margin subdivided into a divergent and a vertical portion (entire posterolateral margin smoothly convex in Raninella ); moreover, the anterolateral teeth are spiniform in the new genus (flattened and strong in Raninella ) and all its members exhibit a straight, horizontal orbital margin (a concave orbital margin in Raninella ). In Bournelyreidus n. gen. (e.g., B. carlilensis ; Feldmann & Maxey 1980: 859, text-fig. 1E; B. eysunesensis ; Collins & Wienberg Rasmussen 1992: 20, fig. 10A), the cheliped merus lacks the subdistal granular crest (present in Raninella , see below), and the cuticle of the new genus comprises diminutive granules (upright nodes) and pits (larger, anteriorly directed granules (inclined nodes) in Raninella ) (see also Waugh et al. 2009: table 2). The most important difference between the two genera seems to be sternal, sternite 5 in Bournelyreidus n. gen. being devoid of a medial line, which is typically present in Raninella . An abdominal holding structure, i.e. projections on sternite 5, is also present in Bournelyreidus n. gen. (see remarks for B. tridens ), whereas in the species of Raninella no such structure has been observed.

Bournelyreidus n. gen. superficially resembles the monotypic genus, Heus . These genera can nevertheless be distinguished as follows: by Bournelyreidus n. gen. having a narrow carapace (wide in Heus ); anterolateral margins with two spines (one spine in Heus ); a wide, bifid front (narrow, strongly sulcate rostrum in Heus ); axial keel absent (axial keel extends onto the dorsal carapace in Heus ); closed orbital fissures (open orbital fissures in Heus ); and dorsal surface non-areolated (two epigastric and four protogastric swellings in Heus ).

Bournelyreidus n. gen. has exposed pleurites 5‒7, hence its placement in Raninoidea . Assignment to Lyreididae is based on the following features: carapace fusiform, with lateral margins vertical in the medial portion; cuticle smooth or pitted (see Waugh et al. 2009); no medial line on anterior sternites (excluding it from Ranininae , Raninoidinae , Symethinae , Notopodinae pro parte and Cyrtorhininae ); presence of projections for abdominal holding on sternite 5.

Bournelyreidus n. gen. comprises small crabs that have been recorded from the Upper Cretaceous of North America, Greenland and Germany. The youngest representative is known from the lower Paleocene (Danian) of Denmark ( Collins & Jakobsen 1995: 39, pl. 10, fig. 10).