Planobranchia elongata, Ferratges & Domínguez & Ossó & Zamora, 2023

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

Planobranchia elongata n. sp.

Figures 5 A-B and 6

zoobank.org/ 8FE98FE3-0E49-4C45-A30A-73324B9512B3

Type material. One partial specimen, partially decorticated: MPZ 2023 /4.

Diagnosis. Carapace pyriform, longer than wide, maximum width in mesobranchial region; front singular, sulcate longitudinally, pseudorostral spines short, fused; orbits small, laterally situated, with strong and subtriangular orbital spines; dorsal regions swollen, distinct, bounded by grooves; mesogastric region inflated and smooth, narrow and elongated anteriorly, bounded by two elongated ridges; metagastric region narrow, Ushaped; branchial regions differentiated; mesobranchial region arched; posterior margin broad, rimmed.

Description. Carapace pyriform in outline, longer than wide; dorsal surface covered by small pits, convex in both directions; maximum width in mesobranchial region; front produced, straight, directed forwards, with two fused spines, with longitudinal ridges; orbits anterolaterally directed, supraorbital margin with strong spines: antorbital spine is the largest, triangular in shape and slightly forward; intercalated spine shortest, conical, separated by supraorbital sutures; postorbital spine triangular, medium sized, facing out. Lateral margins smooth, arched; hepatic region slightly inflated, defined by shallow groves; notable subtriangular spine in the postorbital lobe; mesogastric region inflated, ushaped, apparently smooth and anterior portion ridged; protogastric region weakly defined; urogastric region bounded by shallow grooves; branchial regions delimited from axial regions by grooves; cardiac region triangular; epibranchial region inflated, oblique, arched posteriorly; mesobranchial region broadly inflated; metabranchial region depressed; intestinal region not preserved; posterior margin not preserved, appears broad.

Etymology. The specific name refers to its elongated morphology.

Remarks. The type species, Planobranchia laevis , from the Lutetian of Egypt, shows clear affinity with P. elongata n. sp., but has some differences: 1) distinct hepatic region, with smaller hepatic spine than the new species; 2) gastric regions less pronounced and more elongated and dorsal surface ornated with very small granules, instead of the smooth surface with setal pits that the new species has. Planobranchia palmuelleri from the Lutetian of Catalonia is clearly different from P. elongata n. sp. in some aspects like: 1) its carapace outline, being much wider and shorter than the new species; and 2) by its shorter rostrum. Planobranchia simplex from the Lutetian of Senegal, shows certain similarities with the new species, such as an arched margin, defined by a thin rim that does not appear to be separated by strong depressions on the branchial regions, however; P. simplex clearly differs from the new species in: 1) the outline of the carapace, much wider than the new species and 2) the deeper axial grooves. The new taxon differs from? P. egyptensis from the Lutetian of Egypt, in having a slimmer outline and more inflated dorsal regions.

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.