Eucorystes Bell, 1863

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 : 21-23

Genus Eucorystes Bell, 1863

Eucorystes Bell, 1863: 17 .

Type species. Notopocorystes carteri McCoy, 1854: 118 , pl. 4, fig. 3, by monotypy.

Species included. Eucorystes carteri ( McCoy, 1854) [as Notopocorystes ], E. eichhorni ( Bishop, 1983a) [as Notopocorystes (Eucorystes) ], E. exiguus ( Glaessner, 1980) [as Notopocorystes (Cretacoranina) ], E. iserbyti n. sp., E. intermedius Nagao, 1931 , E. ligulatus Wright & Collins, 1972 [as Notopocorystes (Eucorystes) carteri ligulatus ], E. navarrensis n. sp., E. mangyshlakensis Ilyin & Pistshikova in Ilyin, 2005 [as Notopocorystes (Eucorystes) ], and E. oxtedensis Wright & Collins, 1972 [as Notopocorystes (Eucorystes) ].

Material examined. E. carteri: NHM In. 29645-1-7 and NHM In. 29903-1-5, 12 carapaces; SM B23091, well-preserved carapace, abdomen and sternum; IRScNB unregistered, Van Straelen Collection, drawer 218, approximately 100 specimens, some with remains of abdomen, thoracic sternum and pereiopods; all from Cambridge Greensand, upper Albian, Cambridge, southern England. E. iserbyti n. sp.: type series, see below. E. ligulatus : holotype, SM B23137, carapace, Cambridge Greensand, upper Albian, Cambridge, southern England. E. navarrensis n. sp.: type series, see below. E. oxtedensis : holotype, NHM In. 60983, poorly preserved carapace; paratype, NHM In. 60984, anterior portion of carapace; both lower Albian, Coney Hill Priory Sandpit, Oxted, southern England.

Diagnosis. Carapace small, subhexagonally elongated in outline, fairly convex in transverse cross section, weakly convex longitudinally; maximum width at epibranchial spine; orbits wide, with 2 deep supramarginal fissures; front narrow to relatively broad, bifid, with 2 distal, 2 subdistal spines, distal spines may be long; axial ridge partially discontinued by swellings, grooves, may be less evident in posterior half of carapace (e.g., Eucorystes carteri , E. iserbyti n. sp.) or clearly visible (e.g., E. ligulatus , E. navarrensis n. sp.); anterolateral margins short, arched, sharp, with 2 long spines with broadly triangular base, separated by deep cervical notch; small spine behind subtle branchial notch in nearly straight posterolateral margins converging backwards, first portion sharp, posterior portion rounded; posterior margin fairly concave, narrower than orbitofrontal margin; dorsal surface of carapace areolated in anterior half by numerous raised ‘straplike’ lobes, grooves; grooves relatively broad, shallow; cervical groove well defined; branchiocardiac groove relatively deep, short, arched; raised lobes flat-topped ( E. carteri , E. ligulatus , E. navarrensis n. sp.) or rounded ( E. iserbyti n. sp., E. oxtedensis ); some dorsal regions divided into separate portions; hepatic region with single small protuberance directed upwards, small additional protuberance may be present ( E. navarrensis n. sp.); gastric, epibranchial lobes divided into several portions. Dorsal regions may bear upright nodes, inclined nodes, fungiform nodes, pits; surface of grooves finely pitted. Pterygostome large, with blunt crests, buccal margin concave, with broad buccal collar; thoracic sternum narrow, never in contact with pterygostome, elongated, narrowing backwards; sternites 1, 2 narrow, situated at lower level; sternite 3 subpentagonal, apex pointed downwards; deep lateral incision separating sternite 3 from 4; sternite 4 subtrapezoidal, lateral margins concave; episternite 4 extending laterally; sternite 5 laterally with short, arched grooves ( E. carteri ) or deep, acute depressions ( E. iserbyti n. sp.); episternite 5 elongated, with a double peg for abdominal holding; sternite 6 narrow, episternites 6 elongated; sternites 7, 8 reduced in size, oblique; abdomen narrow, entirely covering the sternal space laterally, reaching sternite 4; all somites free, somites 1, 2 restricted for P5 coxae, somites 1‒6 with raised medial portion, somites 2‒5 with axial spines ( E. iserbyti n. sp.); mxp3 elongated, in oxystomian condition, coxae large, flabelliform, exopod slender, endopod lanceolated; P1 long, chelae homochelous, tuberculate, outer surface of merus with sharp distal crest. P2‒P4 with flattened propodus, dactylus; upper, lower margins granular. P5 strongly reduced, subdorsal.

Remarks. Bell (1863: 17) erected Eucorystes for Notopocorystes carteri , but there was little consensus about how this genus was to be defined. Eucorystes was treated, as was Cretacoranina , as a subgenus of Notopocorystes by Wright & Collins (1972) and Collins (1997), on account of the similar and gradational carapace morphology. These two subgenera were given generic rank by Tucker (1998: 331), a course of action that has received wide support (e.g., Haj & Feldmann 2002; Schweitzer & Feldmann 2002b; Collins 2003; Vega et al. 2007a; Guinot et al. 2008; Collins & Breton 2009; De Grave et al. 2009; Waugh et al. 2009; Schweitzer et al. 2010).

Eucorystes is distinguished from other palaeocorystids in that the anterior half of the carapace bears a set of raised, strap-like lobes. These lobes may be flat topped, or rounded, but are always clearly elevated from the dorsal surface. The epigastric region consists of an elongated, distinct lobe; the protogastric region bears two arched, admedial lobes, extended towards the front. The epibranchial region is subdivided into three raised lobes: the anterior portion subtriangular, the medial portion always as a raised oblique lobe directed to the marginal branchial notch, the posterior portion, also swollen, arched, bounding the cervical groove.

Although Schweitzer & Feldmann (2002b: 200) stated that strap-like ornament was ‘clearly observeable’ in their new species, Eucorystes platys , with which Schweitzer et al. (2003a: 24) concurred, Schweitzer et al. (2009b: 418, fig. 7) described new material that showed a ‘muted nature of the so-called strap-like ornamentation on the dorsal carapace’. This was explained by loss of exocuticular layers in their new specimens; however, strap-like lobes in Eucorystes are elevated and so distinct that loss of cuticular layers will not cause the strap-like ornament to efface. The entire cuticle of Eucorystes is undulated ( Waugh et al. 2009: fig. 10.3); thus, members of Eucorystes can be recognised whatever the degree of loss of cuticle may be ( Bishop 1983a: fig. 5). Eucorystes and Joeranina n. gen. are considered closely related; the well-defined groove system in the latter may give the dorsal surface an areolated appearance. Eucorystes platys is here transferred to Joeranina n. gen. (see below).

Noteworthy is the variety of cuticle microstructures within Eucorystes : the dorsal surface may bear upright, inclined or fungiform nodes and/or pits. In general, cuticle microstructures are remarkably constant in genera of Raninoidia (see also Waugh et al. 2009), only in Eucorystes being substantially variable.

Eucorystes , as considered herein, ranges from the lower Albian to the Campanian; the majority of species are Albian. Records are from England, France, Spain, Switzerland, Kazakhstan, U.S.A., Australia and Japan.

Eucorystes exiguus , from the Cenomanian of Australia, was originally assigned to the ‘subgenus’ Cretacoranina , a taxonomic position that was retained by Collins (1997: table 1) and, with Cretacoranina elevated to generic status, by Tucker (1995: 181, 1998: table 4). The anterior carapace is areolated and gently rounded lobes are visible; the carapace of the only specimen known lacks the deep frontal furrows that are present in Joeranina n. gen., but the presence of welldefined carapace grooves and lobes exclude it from Cretacoranina emend. Placement in Eucorystes is favoured pending the re-examination of the type specimen or additional material.

Eucorystes carteri ligulatus , a subspecies ( Wright & Collins 1972: 82) overlooked by Tucker (1998; see also Collins 2003: 84), is here considered valid and given full species rank. The examined holotype is slightly worn, but microstructures document that the ‘straps’, including the branchial ones, are by no means the result of taphonomic overprint, but rather are a characteristic of this species.

Eucorystes intermedius does not show clearly raised strap-like lobes, being ‘only marked by weak straps’ (Collins et al. 1993: 302), but presents a continuous anterior mesogastric extension with arched epigastric grooves. Specimens so far illustrated are decorticated or poorly preserved; the species seems to share characters of both Eucorystes and Joeranina n. gen., and better-preserved material is needed.