Eucorystes navarrensis, 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 : 27

Eucorystes navarrensis n. sp.

( Fig. 6B, D )

Diagnosis. Small-sized carapace, subhexagonally elongated, maximum width at level of epibranchial spine. Dorsal surface with numerous strap-like lobes, grooves, separating dorsal regions into numerous portions. Front narrow, bifid, with 2 long, divergent spines. Narrow, rounded, salient axial carina along entire carapace axis. Dorsal regions defined by narrow, clearly flat-topped lobes; hepatic region with 2 small protuberances; mesogastric region rhombic; urogastric region V-shaped; epibranchial region subdivided. Posterior half of carapace lacking welldefined regions.

Derivation of name. From Navarra (northern Spain), the type location .

Material examined. Holotype, a dorsal carapace ( MGSB75291 ); paratype, a dorsal carapace preserved upside down ( MGSB75292 a); a cast with well-preserved front ( MGSB75292 b), all from approximately 1.5 km northwest of the village of Alloz (Navarra), from limestones considered to be of Albian age ( Instituto Geológico de España 1978).

Description. Carapace small, subhexagonally elongated in outline, maximum width at base of epibranchial region, dorsal surface weakly convex in both directions. Orbitofrontal margin wide, only partially preserved. Front narrow, bifid, with long, divergent spines. Lateral margins broadly arched, lateral spines incompletely preserved. Posterior margin strongly concave, notably shorter than orbitofrontal margin. Mesogastric region small, markedly rhombohedric in shape, well defined by furrows, anterior process narrow, ridged, not reaching base of front. Protogastric region clearly subdivided into 3 isolated, flat-topped lobes. Epigastric regions elongated, joining central protogastric ridge. Urogastric region V-shaped, with lateral portions extending obliquely forwards. Hepatic region with 2 notable small protuberances; anterior one conical, below orbital margin, posterior one larger, slightly elongated. Cervical groove well-defined, deeper at axial portion, interrupted by axial carina. Epibranchial region divided into 3 strap-like lobes; anterior portion subtriangular, median portion near straight, directed obliquely towards lateral margins, fairly well separated from urogastric lobe, posterior portion arched. Cardiac region relatively narrow, elongated, anterior portion laterally bounded by deep branchiocardiac grooves. Continuous axial carina along carapace fairly salient, rounded. Posterior half of carapace, strap-like lobes covered by fungiform granules, markedly enlarged on axial carina; grooves, furrows in anterior half of carapace densely covered by minute setal pits.

Remarks. The new species is differentiated from all congeners in having an uninterrupted axial carina over the complete dorsal surface. In E. ligulatus , the only other species that shows a distinct axial carina on the posterior carapace ( Wright & Collins 1972: pl. 16, fig. 4), the carina is interrupted at both sides of the urogastric region. In addition, E. ligulatus bears additional branchial strap-like lobes, which are absent in E. navarrensis n. sp. Apart from the nature of the axial carina, the new species can be distinguished from E. carteri and E. iserbyti n. sp. by the different nature and organisation of dorsal grooves and strap-like ridges. In E. navarrensis n. sp. the grooves are broader and more numerous, which lead to narrower, more acute lobes; in E. iserbyti n. sp. the lobes are rounded, rather than flat-topped. Eucorystes eichhorni , a much younger (late Campanian) species from Montana ( U.S.A.), also has profuse dorsal regional ornament, presents distinct, long grooves bounding the anterior mesogastric process, as well as a different distribution of strap-like lobes. Eucorystes exiguus , from the lower Cenomanian of Bathurst Island ( Australia), and E. oxtedensis exhibit less clearly subdivided anterior regions and deeper branchiocardiac grooves. Eucorystes intermedius shows a much weaker dorsal ornament, whereas E. mangyshlakensis exhibits deeper branchiocardiac grooves and merged, rather than isolated protogastric strap-like lobes, which have a more forwardly directed course.

Figures

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.