Eodromites polyphemi (Gemmellaro, 1869)

Klompmaker, Adiël A., Starzyk, Natalia, Fraaije, René H. B. & Schweigert, Günter, 2020, Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura), Palaeontologia Electronica (a 32) 23 (2), pp. 1-54 : 10

Eodromites polyphemi (Gemmellaro, 1869)

Figure 2 L-O

1869 Prosopon polyphemi Gemmellaro , p. 169, pl.

7.59.

Diagnosis. Carapace widest at epibranchial regions; moderately convex longitudinally and transversely; anterolateral margin curving inward; lateral margins rimmed from orbital angle to intersection with branchiocardiac groove, strongest anteriorly; cervical and branchiocardiac groove prominent; cervical groove weakly sinuous.

Material studied. Holotype: MGUP-020.18.

Description. Carapace large for genus, subcircular in dorsal view as preserved, widest at epibranchial regions, moderately convex longitudinally and transversely. Fronto-orbital width ~80% of maximum width. Orbital structure incompletely preserved, containing vertical ridge with augenrest lateral to it. Rostrum downturned, incomplete. Epigastric regions subcircular and swollen, marking base of rostrum. Protogastric, hepatic, and mesogastric regions not differentiated. Base of mesogastric region with posterior gastric muscle scars. Cardiac and meta-urogastric regions not preserved. Epibranchial regions rectangular as preserved. Meso-metabranchial regions confluent, incomplete. Cervical groove prominent, widely Vshaped, somewhat sinuous; where preserved, prominent branchiocardiac groove parallels cervical groove; both grooves curve forward on flank. Obliquely oriented, lateralmost parts of post-cervical groove present. Lateral margins mostly rimmed, very strongly so anterolaterally, less so at epibranchial regions, and not rimmed at meso-metabranchial regions. Posterior margin not preserved. Flanks inclined inward as preserved. Ornamentation poorly preserved; cuticle appears pitted where present (new description based on photographs only; see also Gemmellaro (1869: p. 169- 170)).

Occurrence. Late Jurassic (Tithonian) of northern Sicily, Italy (precise coordinates unknown).

Dimensions. (In mm) MGUP-020.18: max. length excl. rostrum=-, max. width=33.

Remarks. This species has been only known from a drawing since the erection of the species (Gemmellaro, 1869, plate 7.59). Some authors have suspected that this species represents a junior synonym of Eodromites grandis while maintaining them as separate species (Van Straelen, 1925; Schweitzer and Feldmann, 2008a; Klompmaker et al., 2012), whereas Wehner (1988) synonymized the two taxa. The holotype of Eodromites polyphemi has never been studied since Gemmellaro, and several researchers called for a study of the holotype (Schweitzer and Feldmann, 2008a; Klompmaker et al., 2012). Without having seen the specimen ourselves, we here provide the first photographs of the holotype. The holotype of E. polyphemi represents a large specimen (33 mm in maximum width), but the posterior part is mostly lacking. In this case, the drawing in Gemmellaro represents the actual specimen fairly well. Possible differences between the two taxa were discussed previously (Gemmellaro, 1869; Schweitzer and Feldmann, 2008a; Klompmaker et al., 2012). However, the best possible comparison between E. grandis and E. polyphemi can only be made using similar-sized specimens so that any differences due to allometric growth can be ruled out. Although an equally-sized specimen of E. grandis has been reported (33 mm in width, see Moericke, 1889, p. 67), this specimen has never been figured. The largest figured specimens of E. grandis known to us are ~ 22 mm wide (see Schweitzer and Feldmann, 2008a, plate 4E; Schweitzer and Feldmann, 2010b, figure 5.3). Any other specimens of E. polyphemi are unknown. We also note that E. polyphemi possesses an anterior dorsal region reminiscent of E. dobrogea , but the lack of the posterior part of E. polyphemi precludes a full comparison as well as the lack of similarly large specimens of E. dobrogea . Therefore, we cannot fully evaluate differences between E. polyphemi and E. grandis / E. dobrogea , so we questionably maintain E. polyphemi as a separate species for now.

Figures

FIGURE 2. Specimens of the crab Eodromites spp. from the Late Jurassic of Europe. A, F, G, Eodromites grandis (von Meyer, 1857) from the Upper Jurassic (upper Kimmeridgian) coral limestones of Saal an der Donau in southern Germany in dorsal, frontal, and left-lateral views, resp. (SNSB-BSPG 2016 XXI 404). B-E, Holotype of Eodromites bernchrisdomiorum sp. nov. from the Upper Jurassic (lower-middle Oxfordian) deposits of Ogrodzieniec in southern Poland in dorsal, frontal, right-lateral, and orbital views, resp. (I-F/MP/6259/1588/11). E, an oblique view of right orbital structure, primarily the lateral margin with a wide fissure. H-K, Late Jurassic (Oxfordian) Eodromites bernchrisdomiorum sp. nov. from southern Poland in dorsal view (H, I-F/MP/4874/1534/08, Niegowonice, middle-late Oxfordian; I, I-F/ MP/6255/1588/11, paratype, Niegowonice, middle-late Oxfordian; J, I-F/MP/6258/1588/11, Ogrodzieniec, early-middle Oxfordian, paratype; K, I-F/MP/1369/1508/08, Bzów, middle Oxfordian). L-O, Holotype of Eodromites polyphemi (Gemmellaro, 1869) from the Late Jurassic (Tithonian) of Sicily, Italy, in dorsal, frontal, right-lateral, and left-lateral views, resp. (MGUP-020.18). Scale bar width is 5.0 mm, except for E (1.0 mm).