Eosymethis aragonensis, 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 : 104

Eosymethis aragonensis n. sp.

( Fig. 32A–C )

Diagnosis. As for genus.

Derivation of name. From the region of Aragón, northern Spain.

Material examined. Holotype, and only specimen so far known, a near-complete carapace with remains of the pereiopods, preserved as a natural mould, from the marls of the ‘ upper Ilerdian’ (lowermost Ypresian, Eocene ) Roda Formation ( Cuevas-Gozalo et al. 1985), approximately 7 km northwest of the village of Isabena ( Huesca , Aragón) ( MGSB75293 ; ex José Enrique Ortega Collection).

Description. Carapace small, subovally elongated in outline, longer than wide; maximum width at confluence of lateral margins, posterior of mid-length. Dorsal surface slightly concave in both directions. Orbitofrontal margin narrow, markedly advanced; orbits small, directed anteriorly; front strongly projected with triangular tip. Anterolateral margins long, with notable angular hepatic node after concave first portion; posterior portion nearly straight, diverging posteriorly. Posterolateral margins shorter, from straight to slightly concave, rimmed, convergent to the rear. Posterior margin fairly concave, much broader than orbitofrontal margin. Dorsal regions poorly defined; postfrontal depression present; gastric regions weakly defined; branchial regions with notable oblique branchial scars, lateratelly disposed; cardiac region large, elongated, bounded by marked branchiocardiac grooves, with angular node at lateral upper portion; anterior portion separated from gastric regions by subtle groove. Dorsal surface covered by large, dense pits, uniformly distributed over entire carapace; some granules in posterior portion of posterolateral margins. Pereiopods partially preserved, showing short, flattened articles with falciform dactylus.

Remarks. The species exhibits features that permit placement in Symethinae : the carapace has a narrow, projected anterior portion of the carapace and a post-frontal depression; the dorsal surface shows an isolated, lateral, acute groove; the anterolateral margin has only a diminutive node; and falciform dactyli of the pereiopods. Symethinae so far consists of a single genus, Symethis , with only three extant species ( Ng et al. 2008: 43). Eosymethis n. gen. can be distinguished from Symethis on the basis of a smoother, less ‘eroded’ anterior carapace and in having the cuticle microstructure consisting of large perforations or setal pits rather than fungiform nodes ( Waugh et al. 2009). Eosymethis aragonensis n. sp. originates from what appears to have been a fairly muddy-bottom habitat.

Figures

FIGURE 32. A–C. Eosymethis aragonensis n. gen., n. sp. (Raninidae, Symethinae), lower Eocene (Ypresian), Isabena (Huesca, northern Spain), MGSB75293 (holotype; ex José Enrique Ortega Collection; indeterminate sex); overview of specimen, detail showing carapace, and detail showing falciform dactylus of right P2/P3. Scale bars: 5mm.