Lucascinus trifailensis, Gašparič & Hyžný & Hitij & Šoster, 2024

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 : 8-11

Lucascinus trifailensis sp. nov.

Figures 4 E-F, 5D, 6

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Etymology. The species name refers to old name for coal mining town of Trbovlje (Trifail). Trbovlje is Slovenia’s tenth-largest town and closest to the type locality of new species.

Diagnosis. Carapace trapezoid, longer than wide, fully surrounded by a rim. Rostrum formed as a long triangular plate. Postocular anterior margin sinuous; defined by a postocular tubercle and a more pronounced tooth at anterolateral corner of the carapace. Lateral side of carapace almost straight; diverging posteriorly; with a single projection near base of cheliped. Posterior border of carapace sinuously rounded. Dorsal carapace with visible gastro-cardiac groove and posteriorly developed thoracic grooves. Frontal region trapezoidal; not differentiated from gastric posteriorly. Cardiac region simple and posteriorly not bordered. Male pleon triangular; pleonal somites 1-5 free; somite 1 widest. Chelipeds long; propodus elongated and slightly swollen. Fingers short. Pereopods very long and slender; almost same length. Dactylus short, curved, teeth not observed.

Type material. Holotype is RGA / SMNH 6384-6383 (part and counterpart) ( Figure 4E ) ; paratypes are RGA / SMNH 6391 ( Figure 4F ), RGA / SMNH 6387- 6388 (part and counterpart) ( Figure 5D ), RGA / SMNH 6379-6380 (part and counterpart) and RGA / SMNH 6392 . Measurements are given in Figure 7 , Table 1 and Table 2.

Type locality. Trbovlje , Slovenia .

Description. Carapace trapezoidal, longer than wide (CL/CW = 1.13–1.30) ( Table 1), fully surrounded by a hymenosomian rim ( Figure 4E - F ). Rostrum formed as a long triangular plate; twice as long as wide; width approx. 0.1–0.15 times carapace width ( Figure 5D ). Postocular anterior margin sinuous; defined by a postocular tubercle and a more pronounced tooth at anterolateral corner of the carapace. Lateral side of carapace slightly convex; almost straight; diverging posteriorly; with a single projection near base of cheliped. Posterior border of carapace sinuously rounded ( Figure 4F ).

Dorsal carapace with visible gastro-cardiac groove and posteriorly developed thoracic grooves. Frontal region trapezoid; not differentiated from gastric posteriorly. Cardiac region simple and posteriorly not bordered ( Figure 4E ). Male pleon triangular; pleonal somites free; somite 1 widest, with rounded convex lateral sides; rest of the somites with straight and anteriorly converging lateral margins; pleotelson much longer than wide, triangular, with rounded apex ( Figure 5D ).

Chelipeds long; length approx. 0.85-1.0 times of carapace length. Ischium short; merus and carpus longer than wide; propodus elongated and lightly swollen. Fingers shorter than manus. Pereopods very long and slender ( Figure 4F , Table 2); length approx. 1.9-2.3 times of carapace length, P3 and P4 longest. Ischium short; merus almost as long as propodus, carpus less than one third of merus; propodus longest, but narrower than the merus. Dactylus short, curved, teeth not observed.

Remarks. Lucascinus trifailensis sp. nov. is the first fossil representative of the genus and among extant species most closely resembles Lucascinus bedfordi ( Montgomery, 1931) . The shared similarities between the fossil and extant species are in ornamentation of dorsal carapace and the shape of a triangular rostrum. However, Lucascinus trifailensis sp. nov. has a narrower carapace, with distinct sinuous shape of the anterior margin, defined by a small postocular tubercle, and a more pronounced tooth at the anterolateral corner of the carapace. Additional spinose projection is located at lateral margin, near the base of cheliped, which is typical for Lucascinus ( Poore et al., 2016) , but much less pronounced in Lucascinus trifailensis sp. nov. Such combination of characters has not been observed in any of the extant species. However, we prefer to use the most parsimonious way and include the fossil species in the closest extant genus.

Range. Late Oligocene (Chattian).

Occurrence. To date, known only from the type locality.

Figures

FIGURE 4. Halicarcinus popeius sp. nov. (A–D) and Lucascinus trifailensis sp. nov. (E, F): A. RGA/SMNH 6377, dorsal, (holotype), visible hymenosomian rim (hr) and coloration patterns; B. RGA/SMNH 6373, dorsal, (paratype), male with well-preserved chelipeds and pereopods (P2-P5); C. RGA/SMNH 6385, dorsal, (paratype), male with bulbous chelipeds; D. RGA/SMNH 2041, ventral, (paratype), female with missing sternum; E. RGA/SMNH 6384, dorsal, (holotype), indicated rostrum and hymenosomian rim (hr); F. RGA/SMNH 6391, dorsal, (paratype), elongated chelipeds and well preserved pereopods (P2-P5). All scale bars equal 5 mm.

FIGURE 5. Scanning electron photomicrographs of Halicarcinus popeius sp. nov. (A–C) and Lucascinus trifailensis sp. nov. (D): A. RGA/SMNH 6385, details of anterior and left lateral border in dorsal view, pereopods (P2-P5), (composite of several photomicrographs); B. RGA/SMNH 2041, ventral side with missing sternum, details of anterior margin and buccal cavity, coxa of pereopods (cx2-cx5), pereopods (P2-P5), (composite of several photomicrographs); C. RGA/ SMNH 6373, detailed view of pereopodal (P3) dactylus; D. RGA/SMNH 6387, ventral side with male pleon, pereopods (P2-P5), abdominal somites (s1-s5), pleotelson (pt), sternites (st4-st8), sternal shield (s), third maxilliped (mxp3). Scale bars indicated on the photomicrographs.

FIGURE 7. Carapace length vs. maximum carapace width of hymenosomatid specimens from the “Neža” locality. Halicarcinus popeius sp. nov. are marked in blue triangles (circles when trapezoid rostrum), Lucascinus trifailensis sp. nov. specimens are marked with orange squares. All measurements in mm.