Macrocheira sp.

Ferratges, Fernando A., Domínguez, Josep Lluis, Ossó, Àlex & Zamora, Samuel, 2023, Spider crabs (Decapoda: Brachyura: Majoidea) from the upper Eocene of south Pyrenees (Huesca, Spain), Palaeontologia Electronica (a 27) 26 (2), pp. 1-29 : 14-15

? Macrocheira sp.

Figure 5C

Material. One incomplete carapace with cuticle not well preserved: MPZ 2023/5.

Description. Carapace pyriform, moderately convex, slightly more swollen in gastric and epibranchial portions. Frontal, posterior, and anterolateral margins not preserved; lateral margins sinuous, with strong incision between hepatic and branchial margins; mesobranchial margin strongly rounded. Dorsal surface densely granulated. Branchiocardiac grooves very close to each other; hepatic region inflated; Protogastric region inflated, with two large tubercles; mesogastric region narrow, moderately inflated; urogastric region extremely narrow, not well defined. Mesobranchial region large, inflated and rounded, separated from gastric regions by the cervical groove, with two tubercles separated from each other. Cardiac, intestinal, and metabranchial regions not preserved.

Remarks. Species of Macrocheira are characterized by a pyriform outline of the carapace, hepatic spine, bifurcate rostrum (two spines), poorly developed supraorbital eave, small ant- and postorbital spines, and well-developed carapace regions (see Miers, 1886; Rathbun, 1926; Sakai, 1976; Schweitzer and Feldmann, 1999). Moreover, Macrocheira usually have inflated protogastric and mesogastric regions; depressed metagastric region; a urogastric region poorly developed; epi- and mesobranchial regions inflated, and depressed metabranchial region; cardiac region oblong and bounded by wide grooves with parallel crenulations positioned oblique to the axis of the grooves.

The different fossil species of the genus Macrocheira are differentiated by the degree of inflation and shape of carapace regions, ornamentation on dorsal regions, length of the rostrum and size of the orbital and hepatic spines (see Schweitzer and Feldmann, 1999). The genus is only represented by one modern species, Macrocheira kaempferi , from Japan, reported from mud or sand bottoms at 50-300 m depth ( Sakai, 1976).

Given the fragmentary condition of the specimen, the generic assignment is given tentatively and a proper specific assignation is not possible.

Figures

FIGURE 5. Planobranchia elongata n. sp. (A-B) and?Macrocheira sp. (C) from the Pamplona Marls Formation (upper Eocene, southern Pyrenees), A-B: Planobranchia elongata n. sp. Holotype MPZ 2023/4. A in dorsal view, B oblique frontal view. C:?Macrocheira sp. (MPZ 2023/5). Abbreviations: as: antorbital spine; is: intercalated spine; Ps: postorbital spine; Hs: hepatic spine.