Halicarcinus popeius Gašparič & Hyžný & Hitij & Šoster 2024, sp. nov.
Creators: name: Gašparič, Rok
name: Hyžný, Matúš
name: Hitij, Tomaž
name: Šoster, Aleš
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Hymenosomatidae
Halicarcinus
Halicarcinus popeius

description: Halicarcinus popeius sp. nov.
Figures 3, 4 A-D, 5A-C
zoobank.org/ BC3F122F-89A8-4BDB-A174-664B834FA1D1
2023 Majoidea gen. et sp. indet. – Kovalchuk et al., p. 5, figs. 2E, F.
Etymology. The species name originates from a Latinised name of the cartoon character Popeye, the sailor man. A fictional character who, despite the diminutive stature, possesses strong, bulging forearms, reminiscent of the chelipeds of the new species.
Diagnosis. Carapace oval, wider than long, surrounded by a wide rim. Trilobate to trapezoid rostrum; length not extending as far as eyes. Eyes on short, stout eyestalks; extending beyond rostrum. Anterolateral corners forming a rounded postocular projection; either as rounded lobe or a pair of forward pointing teeth. Lateral side of carapace rounded; almost vertical posteriorly; with a concavity at posterolateral margin. Dorsal carapace with continuous gastro-cardiac groove, forming a hexagonal cardiac region. Chelipeds massive in males, sub-equal, homomorph, with swollen barrel-like propodus; more slender in females. Both fingers long, occluding with a gape; no dentation of the occlusal margin. Pereopods very long and slender. Dactylus broad, distinctively curved, tip composed of two developed, sub-equal, teeth; ventral edge armed by a row of blunt tubercles.
Type material. Holotype is RGA / SMNH 6377-6378 (part and counterpart) (Figure 4A), paratypes are RGA / SMNH 6373-6374 (part and counterpart) (Figure 4B, 6C), RGA / SMNH 6371-6372 (part and counterpart), RGA / SMNH 6369-6370 (part and counterpart), RGA / SMNH 6385-6386 (part and counterpart) (Figures 4C, 5A) and RGA / SMNH 2041 (Figures 4D, 5B). Other specimens are RGA / SMNH 2039-2040 (part and counterpart), RGA / SMNH 6375-6376 (part and counterpart), RGA / SMNH 6381-6382 (part and counterpart) and RGA / SMNH 6389-6390 (part and counterpart). Measurements are given in Figure 7, Table 1 and Table 2.
Type locality. Trbovlje, Slovenia.
Description. Carapace oval, wider than long (CL/ CW = 0.82–0.93) (Table 1), surrounded by a wide hymenosomian rim. Trilobate to trapezoid rostrum; wide and short; width approx. 0.1–0.2 times carapace width; length not extending as far as eyes (Figure 5A). Lobes close together; sub equal in length; median lobe slightly bigger than the other two, sometimes not differentiated and forming a single trapezoidal rostrum (Figure 4B). Eyes on short, stout eyestalks; extending beyond rostrum (Figure 5A). Anterolateral corners rounded, forming a rounded postocular projection; either as rounded lobe or a pair of forward pointing teeth. Lateral side of carapace rounded; almost vertical posteriorly; with a concavity at posterolateral corner (Figure 4 A-D).
Dorsal carapace with continuous gastro-cardiac groove, extending concavely from one side of hymenosomian rim to the other; forming a hexagonal cardiac region (Figure 4A, D). Frontal region trapezoidal; not differentiated from gastric region posteriorly. Hepatic and prebranchial regions small; triangular. Postbranchial region square; separated from cardiac region by the thoracic groove. Cardiac region ornamented by three longitudinally oval areas of brighter colour (Figure 4A); smaller oval coloration of dorsal carapace also in gastric region, anteriorly of gastro-cardiac groove; crescentshaped coloration of carapace at posterior border.
Chelipeds massive, with swollen barrel-like propodus (Figure 4A, C); length approx. 1.1-1.7 times of carapace length; slighter in females. Ischium short; merus slightly longer than wide; carpus longer than merus, swollen with rounded margins, almost as broad as long; manus greatly inflated, margins rounded and convex. Both fingers long, occluding with a gape; no dentation of the occlusal margin observable. Pereopods very long and slender (Figure 4B, Table 2), almost same length, approx. 2.0-3.5 times of carapace length. Ischium very short; merus longest; carpus about one-thirds as long as merus; propodus almost as long as merus. Dactylus shorter than the propodus, broad, distinctively curved, tip composed of two developed, sub-equal, teeth; ventral edge armed by a row of blunt tubercles (Figure 5C).
Remarks. Halicarcinus popeius sp.nov. is the first fossil representative of the genus. Thus, by the general habitus it would be most similar to Halicarcinus quoyi (H. Milne Edwards, 1853), with which it shares a wider than long carapace with broad rim, a trilobed rostrum, shape of pereopodal dactyli and strongly swollen, bulbous propodi of male chelipeds. The new fossil species differs from H. quoyi in possessing postorbital projections at anterolateral corners of carapace and in development of dorsal carapace regions, especially wide hexagonal cardiac region. Additionally, we recognize heterogeneity in development of rostra within the fossil material, which can be explained as intraspecific variations or possible sexual dimorphism. Lucas (1981) previously recognized that the shape and relative length of the rostrum within Halicarcinus are sometimes sexually dimorphic, although such variations were not reported in Halicarcinus quoyi.
Range. Late Oligocene (Chattian).
Occurrence. To date, known only from the type locality.
description: Published as part of 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, pp. 1-16 in Palaeontologia Electronica (a 4) (a 4) 27 (1) on pages 4-8, DOI: 10.26879/1312, http://zenodo.org/record/10962373