Eucorystes iserbyti, 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 : 23-26

Eucorystes iserbyti n. sp.

( Figs. 4A–E ; 5A–E )

Diagnosis. Carapace small, maximum width at level of epibranchial spine; front relatively broad, bifid, advanced, with 2 distal, 2 subdistal spines, posterior ones smaller, yet distinct; orbits large, with 2 supramarginal fissures, central portion broad, with oblique upper margin, outer orbital spine directed forwards, with robust base; anterolateral margins short, arched, with 2 spines deeply separated by cervical notch; 2 additional granular, small nodes present between extraorbital, hepatic lateral spines; regions with granular raised lobes; hepatic region with small tubercle; gastric, epibranchial lobes divided into several portions; cardiac region well-defined. Dorsal surface densely pitted, granular; raised lobes, lateral regions with inclined nodes. Sternite 3 with conspicuously narrow base; sternite 4 with axial granular tubercle; episternite 4 extended laterally, with large gynglyme; sternite 5 with medial surface flat, deep lateral depressions; episternite 5 with prominent double peg.

Derivation of name. In honour of Arne Iserbyt (Wilrijk, Belgium), who collected and donated the holotype .

Material examined. Holotype, MAB k. 2970, dorsal carapace, partial appendages, and abdomen (ex Arne Iserbyt Collection; male); paratype, MAB k. 2871, partial carapace with thoracic sternum (ex Arne Iserbyt Collection; indeterminate sex); paratype, MAB k. 2886, dorsal carapace, parts of appendages and abdomen (ex Yoeri Christiaens Collection; male); paratype, MAB k. 3006, dorsal carapace (ex Arne Iserbyt Collection; indeterminate sex); all from the middle Albian , Pargny , Haute-Marne , northern France. MNHN-B.146366, 2 partial carapaces, Albian , Fécamp, Haute-Marne, northern France.

Description. Carapace small, subhexagonally elongated in outline, weakly convex longitudinally, more so transversely. Maximum width at epibranchial spine. Front advanced, relatively broad, bifid with 2 distal, 2 subdistal spines, the latter smaller but well defined, differentiated. Orbits large, supraorbital margin divided by 2 fissures: outer ones twice the length of inner ones, supramarginal central portion with upper margin oblique. Anterior mesogastric process reaching base of rostrum. Anterolateral margins short, with hepatic spine, epibranchial spine (both with broadly triangular base), 2 granular nodes between extraorbital, hepatic spines at slightly lower level. Cervical notch deep, well defined. Posterolateral margins longer, rounded, anteriorly with small mesobranchial tooth. Posterior margin strongly concave, markedly shorter than orbitofrontal. Dorsal regions anteriorly well defined by lobes, grooves, posterior half with moderately marked, yet well-defined regions. Anterior mesogastric process narrow, long, reaching base of front. Mesogastric process broad, well defined posteriorly by a relatively deep cervical groove; gastric pits present. Protogastric region with 2 arched lobes. Epigastric lobes elongated, isolated. Hepatic region with small granular protuberance. Epibranchial region divided into 3 parts: anterior lobe with upper portion directed forwards, medial portion transverse, joining urogastric region, posterior portion obliquely directed, interrupted by cardiac groove. Urogastric region broadly arched, meeting the medial lobe of the epibranchial region. Cardiac region large, anteriorly bounded by deep branchiocardiac grooves. Intestinal region elongated, slightly inflated. Dorsal surface of carapace densely pitted, granulate, weakly inclined nodes on lobes, lateral regions. Pterygostome large, with blunt crests, buccal margin fairly concave, with broad buccal collar. Thoracic sternum elongated; sternite 3 crown shaped, conspicuously narrow at base; deep lateral incision, furrows separating sternite 3 from sternite 4; sternite 4 with axial granular tubercle; episternite 4 extended laterally, with large gynglyme; sternite 5 with deep lateral depressions, elevated granular ridge; episternite 5 elongated, somewhat raised, distally with double peg. Abdomen with all somites free, covering thoracic sternum in width in both sexes; somites 1‒6 with medial portion raised; somites 2‒5 with axial spines. P1 merus triangular in cross section, margins granular, upper margin spinose, distinct granular crest distally at outer surface; P2‒P4 with flattened merus, upper, lower margins granulate. P5 strongly reduced, subdorsal.

Remarks. All features of carapace outline and dorsal regions in Eucorystes iserbyti n. sp. are typical of Eucorystes . The new species has a unique set of characters: dorsal strap-like lobes are rounded; epigastric lobes isolated; transverse mesogastric lobe directed posteriorly; lower portion of epibranchial region inflated; cardiac region inflated; intestinal region surrounded by shallow depressions; cuticle granular, laterally granules inclined.

The new species can be easily distinguished from E. carteri ( Fig. 6A, C ) from the upper Albian of southern England and from E. navarrensis n. sp. from the Albian of northern Spain (see below) by the different organisation of grooves and division in the protogastric region, in having the posterior carapace half areolated and with tumid, rather than flat-topped, lobes and a granular cuticle microstructure (upright and inclined nodes) rather than fungiform nodes. Eucorystes mangyshlakensis , from the lower Albian of Kazakhstan, is relatively much longer on account of a longer posterior carapace, exhibits a narrow cardiac region and has fused protogastric and epigastric strap-like lobes.

Eucorystes iserbyti n. sp. appears closely related to E. oxtedensis , a poorly known species from the lower Albian of southern England (see above), as far as carapace ornament is concerned. The holotype of the latter is rather poorly preserved; however, it does reveal certain patches with fairly well-preserved cuticle. In E. oxtedensis the orbitofrontal width is smaller (wide in E. iserbyti n. sp.), the carapace is distinctly tumid in transverse direction (much flatter in E. iserbyti n. sp.), epibranchial lobes are weak (distinct in E. iserbyti n. sp.), the granules on the dorsal surface are small, not inclined laterally (larger, inclined near lateral margins in E. iserbyti n. sp.), and the posterolateral margin is sharp, rimmed (rounded, rim absent, in E. iserbyti n. sp.). Eucorystes oxtedensis shows more basal characters than does E. iserbyti n. sp.; the smaller orbitofrontal width and the rimmed posterolateral margin of the former resemble the disposition in Notopocorystes .

Thoracic sterna are known in E. carteri and E. iserbyti n. sp.; in the latter, the sternite 3 base is notably narrow (wider in E. carteri ); sternite 4 bears a granular tubercle on sternite 4 (absent in E. carteri ); episternite 4 is rather narrow (more laterally extended in E. carteri ); sternite 5 has deep, long lateral depressions (sternite 5 with short, arched lateral furrows in E. carteri ). A prominent double peg for abdominal holding is present in the holotype; it is raised from the sternum, consists of two conical structures, the distal structure being larger, with several granules a bit lower.

Eucorystes sp. figured by Waugh et al. (2009: fig. 10.5) represents E. iserbyti n. sp. Former records from France and Switzerland of E. carteri may in fact turn out to be E. iserbyti n. sp the presence of E. carteri outside England has yet to be verified.

Figures

FIGURE 4. Eucorystes iserbyti n. sp. (Palaeocorystidae), MAB k. 2970 (holotype, ex Arne Iserbyt Collection; male), middle Albian, Pargny (northern France); A, right lateral view; B, detail of abdomen; C, ventral view; D, dorsal view of carapace; E, detail of posterior margin of carapace, first abdominal somites and P5 coxae. a1, a2, a4, a5, a6, abdominal somites 1, 2, 3, 5, 6; cx5, P5 coxa. Scale bars: A, C, D: 5mm; B, E: 2mm.

FIGURE 5. Eucorystes iserbyti n. sp. (Palaeocorystidae), middle Albian, Pargny (northern France); A, D, MAB k. 2886 (paratype, ex Yoeri Christaens Collection; male) in dorsal and ventral views, latter showing thoracic sternum, abdomen and bases of appendages; B, MAB k. 3006 (paratype; indeterminate sex), dorsal view of carapace; C, E, MAB k. 2871 (paratype; indeterminate sex), ventral view (and detail) showing thoracic sternum. 3, 4, 5, thoracic sternites 3, 4, 5; e4, episternite 4; g2, gynglyme for P2 coxa; r,ridge. Scale bars: A-D: 5mm; E: 2mm.

FIGURE 6. A, C, Eucorystes carteri (McCoy, 1854) (Palaeocorystidae), IRScNB unregistered [Van Straelen Collection; female], upper Albian Cambridge Greensand, Cambridge (southern England), dorsal view of carapace, and ventral view showing thoracic sternum and appendages; B, Eucorystes navarrensis n. sp., MGSB75291 (holotype), Albian, Alloz (Navarra, northern Spain), dorsal view of carapace; D, Eucorystes navarrensis n. sp., MGSB75292a (paratype), silicone rubber cast of natural mould showing dorsal carapace, without cuticle. Scale bars: 5mm.