Necronectes cf. michelini A. Milne-Edwards, 1860

Gašparič, Rok, Hyžný, Matúš, Hitij, Tomaž & Šoster, Aleš, 2024, Late Oligocene decapod crustaceans from the Trbovlje Formation of Slovenia, with a description of two new species of hymenosomatid crabs, Palaeontologia Electronica (a 4) 27 (1), pp. 1-16 : 11

Necronectes cf. michelini A. Milne-Edwards, 1860

Figure 8 A-D

Material. A single “crusher” chela ( RGA / SMNH 5009-5010) preserved as an imprint. Measurements: length of propodus = 53.6 mm; maximum height of manus = 31.9 mm; length of dactylus = 31.0 mm.

Description. Chela robust. Manus trapezoidal to suboval in outline; upper and lower margin arched and converging proximally; surface appears smooth, without indication of spines on distal margin at dactylus articulation. Fingers long and stout; as long as manus. Fixed finger robust; occlusal margin with four large molariform teeth, followed by several smaller conical teeth distally; first and second proximal teeth joined; fingertip curved upwards. Dactylus stout, curved forward; with rounded upper margin; strong proximal knob-like flattened molariform tooth followed by six rounded conical teeth of different sizes; strongly curved fingertip.

Remarks. The original cuticle has been dissolved and the massive fingers are preserved as hollow imprints. Therefore, some details cannot be observed in the studied specimen. However, after preparing the latex cast, the preserved features of the chela are sufficient to assign the material to Necronectes A. Milne-Edwards, 1881 . Observed important taxonomic characters include lack of distal spines on manus at position of dactylus articulation and rounded upper margin of manus, which are the key characters for an assignment to Necronectes , and differentiate it from closely related Scylla De Haan, 1833 ( Ossó and Gagnaison, 2019). The herein presented specimen strongly resembles Necronectes michelini Milne-Edwards, 1860 , from the Miocene of France ( Figure 8 E-F), somewhat differing in well-developed proximal molariform teeth on fixed finger and dactylus. Given similarities in preserved specimen, the stratigraphic span and geographic distribution of N. michelini , it is also possible that the occurrence reported here, from the upper Oligocene of Slovenia, belongs to this species. Nevertheless, we refrain to assign it to N. michelini because of insufficient preservation of diagnostic features on the manus and absence preserved carapace remains. Due to the fragmentary preservation we leave the specimen in open nomenclature.

Range. Late Oligocene (Chattian).

Occurrence. Necronectes is a well-known genus known from a number of Oligocene and Miocene occurrences ( Schweitzer et al., 2006; Luque et al., 2017; Hyžný and Dulai, 2021). Necronectes michelini A. Milne-Edwards, 1860 , has so far been reported from the middle Miocene of France ( Ossó and Gagnaison, 2019) and the middle Miocene of Hungary ( Lőrenthey and Beurlen, 1929).

Figures

FIGURE 8. Necronectes cf. michelini Milne-Edwards, 1860 (A–D) and Necronectes michelini Milne-Edwards, 1860 (E, F): A. RGA/SMNH 5009, imprint of the outer side of chela; B. RGA/SMNH 5010, imprint of the inner side of chela; C. RGA/SMNH 5009, whitened latex cast; D. RGA/SMNH 5010, whitened latex cast; E. MNHN.F.R03775, (paralectotype), outer side of chela; F. MNHN.F.R03775, (paralectotype), inner side of chela. All scale bars equal 10 mm. Photos A and D: RECOLNAT (ANR-11-INBS-0004) - Jocelyn FALCONNET – 2017.