Spinirostrimaia echinata, 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 : 17

Spinirostrimaia echinata n. sp.

Figures 7-9

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Type material. The holotype is a female specimen, near-complete carapace, partially decorticated, with one cheliped and thoracic sternum ( MPZ 2023 /6) ( Figure 7 ). There are four paratypes ( MPZ 2023 /7-2023/10) ( Figure 8 ) .

Additional material. Thirteen additional specimens composed by near-complete carapaces ( MPZ 2023/11-2023/23).

Diagnosis. Carapace pyriform, longer than wide, convex; regions separated by shallow grooves; dorsal surface covered by small spines. Frontal margin narrow, sulcate, with two long, subparallel pseudorostral spines with spiny outer margin proximally situated; dorsal surface covered by spines (pearl-shaped tubercles if partially decorticated); orbits with prominent supraorbital eaves, without orbital spines; anterolateral margins elongated, interrupted with hepatic and branchial grooves; hepatic lobe with three lateral spines; mesobranchial margin strongly convex, with numerous spines (10-13); posterior margin with small spines.

Description. Carapace pyriform, twice as long as wide, (not counting the pseudorostrum), ovate; pseudorostrum long, bifid, composed of two spines which have three tiny spines on outer margin; frontal region with two longitudinal crests, tuberculate. Almost complete orbits, with prominent supraorbital eave, without antorbital spine, but marked preorbital lobe; intercalated spine triangular; postorbital spine elongated, slightly curved forward; hepatic lobe with three pointed spines, slightly curved forward. Lateral margins convex, notched by the cervical groove. Dorsal regions ornamented with sharp spines, with pearl-shaped tubercles appearance if partially decorticated; carapace regions well defined by relatively shallow grooves; axial regions elevate above other regions. Proto- and mesogastric regions inflated; meta- and urogastric regions narrower than mesogastric and cardiac regions; hepatic region inflated; branchial regions wide; epi- and mesobranchial regions inflated, poorly differentiated by a shallow groove; metabranchial region slightly depressed; cardiac region inflated, with two lateral subtriangular extensions defined by shallow grooves; intestinal region small, slightly depressed; posterior margin broad, rimmed, with small spines. Branchiocardiac grooves deep.

Epistome wide, smooth, and rimmed. Female thoracic sternum strongly concave, with interrupted sutures (only preserved 1/2 to 5/6, see Figure 7B ). Female chelipeds elongated and thin; merus elongated, with longitudinal depression on the ventral surface, surrounded by well-separated blunt spines; carpus slightly elongated, ornamented with small spines; palm slightly compressed, oval in cross section; fingers acute, relatively short, square in section, with longitudinal striae. Basal antennal article moderately wide, broader at the base than at its distal extremity.

Etymology. The specific epithet make reference to its spinose carapace.

Remarks. The new species shows similarities with the type species Spinirostrimaia margaritata in the general shape of the carapace, piriform and elongated, and long pseudorostral spines. However, the new species differs in some aspects: 1) subparallel pseudorostral spines, not convergent as in S. margaritata ; 2) slightly smaller postorbital spine, without ornamentation; 3) the dorsal ornamentation, more spinose in the new species (instead of pearl-shaped tubercles of S. margaritata ); 4) prominent spine in the margin of the hepatic region, that is absent in S. margaritata ; 5) small, sharp spines covering the dorsal surface, lacking pearl-shaped tubercles as in S. margaritata ; 6) wider posterior margin than S. margaritata , and less convex and rimmed; and 7) more spiny margins in the carapace of the new species than S. margaritata (see Beschin et al., 2012, figures 41, 80; t. 6, figures 3, 6a, b, 7a, b).

The fossil species Cromimaia meneguzzoi (Beschin, Busulini, De Angeli, and Tessier, 1985) bears some resemblance to the new species. However, S. echinata n. sp. differs in some aspects: 1) the urogastric region is narrower in the new species, with three tubercles forming a triangle, and not aligned as in C. meneguzzoi ; 2) narrower cardiac region, better delimited by branchiocardiac grooves in the new species; 3) the pseudorostral spines are exceedingly shorter in C. meneguzzoi , in contrast to the long spines of the new species (see Beschin et al., 2012, figure 40; t. 6, figures 4ac). The new species also shows similarities with Micromaia tuberculata Bittner, 1875 , but has differences in the branchiocardiac groove and both the urogastric region and the beginning of the cardiac region are narrower; the intestinal region is slightly more swollen; and chiefly in having two long and parallel pseudorostral spines, whereas in M. tuberculata they are much shorter and flattened subtriangular (see Beschin et al., 2012, figure 38; t. 6, figure 2).

Figures

FIGURE 7. Female specimen of Spinirostrimaia echinata n. sp. (Holotype MPZ 2023/6) from the Pamplona Marls Formation (upper Eocene, southern Pyrenees) in A: dorsal; B: ventral; C: frontal, and D: lateral views.

FIGURE 8. Paratypes of Spinirostrimaia echinata n. sp. from the Pamplona Marls Formation (upper Eocene, southern Pyrenees). A: Large specimen MPZ 2023/7. B-C: Specimen MPZ 2023/8 in dorsal (B) and frontal (C) view; D: specimen MPZ 2023/9 in dorsal view; E: specimen MPZ 2023/10 in dorsal view. Abbreviations: hl: hepatic lobe; hs: hepatic spine; is: intercalated spine; pl: preorbital lobe; ps: postorbital spine; r1-3: spines of pseudorostral spines; se: supraorbital eave.