Thalassina sp.

Hyžný, Matúš & Angeli, Antonio De, 2022, Mud lobster Thalassina Latreille, 1806 (Decapoda: Gebiidea: Thalassinidae), its Cenozoic occurrences in Italy and palaeobiogeography, Geodiversitas 44 (13), pp. 417-425 : 421-422

Thalassina sp.

( Figs 3 ; 4 )

MATERIAL. — Flattened near-complete individual ( MCZ.4516- I.G.367044 ; Fig. 3 ) ; articulated pereiopod 1 consisting of merus, carpus, propodus, and dactylus ( MSNM i13569 ; donated by Claudio Beschin in 1994; Fig. 4 ).

MEASUREMENTS. — MSNM i13569: propodus max length: 15.0 mm; propodus max height: 12.7 mm; carpus length: 7.8 mm; carpus height: 6.3 mm; merus length 13.5 mm; merus height 6.1 mm. MCZ.4516-I.G.367044: total length (preserved parts): 34.2 mm.

LOCALITY AND AGE. — Lower Oligocene (Rupelian) of Salcedo (Vicenza), NE Italy.

DESCRIPTION

Pereiopod1robust,similar,slightly unequal.Major cheliped merus ovoid in outline, approximately 2.5 times longer than high. Carpus short, triangular in outline. Manus slightly longer than high, distinctly higher than carpus; upper and lower margins parallel to each other; distal margin with a blunt tooth at articulation with dactylus; lateral surface poorly preserved, with faint carina running across the palm longitudinally in the upper half and two rows of indistinct tubercles on the lower half. Fixed finger short, triangular in outline, occlusal margin with small denticles. Dactylus much longer than fixed finger, elongated, slightly bent, ridged along lateral sides; occlusal margin with large blunt tooth positioned proximally. Minor chela slightly smaller than major chela.P2 merus elongated,carpus short and cup-shaped,propodus incomplete. Cuticular surfaces of all remains poorly preserved.

COMMENTS

The studied specimens are assigned to Thalassina based on the general morphology of pereiopod 1: a massive merus with an ovoid outline, a relatively small triangular carpus that is not as high as the propodus, and a subchela consisting of a propodus with a short fixed finger and a much longer and robust dactylus with a knobby tooth on its occlusal margin positioned proximally. Identification to the species is, unfortunately, not possible due to the insufficient preservation. Although one of the specimens (MCZ.4516-I.G.367044) shows virtually an entire animal, the individual is flattened and details are obliterated ( Fig. 3 ). General outline of chelipeds is visible, but their armament and ornamentation are not discernible. Another specimen (MSNM i13569) represents a major pereiopod 1 consisting of the last four elements, i.e., merus, carpus, propodus and dactylus ( Fig. 4 ). The cuticular surfaces are only partly preserved and carinae, important taxonomic characters (see above), are not recognizable. There are two faint rows of tubercles close to the lower margin and a faint carina extending across the palm in its upper half. The position of these characters suggests that the cheliped is slightly deformed, so the upper margin and characters positioned close to it are not discernible. Both studied specimens most probably represent the same species, although it cannot be stated for sure; the characters important for species identification (see above) are not preserved in a sufficient detail.

Figures

FIG. 3. — Thalassina sp. from the lower Oligocene of Salcedo,Italy,MCZ.4516-I.G.367044: A, flattened,almost complete specimen in natural light; B, interpretative drawing. Scale bar: 5 mm.

FIG. 4. — Thalassina sp. from the lower Oligocene of Salcedo, Italy, MSNM i 13569: A, articulated cheliped consisting of merus, carpus, propodus and dactylus; B, interpretive drawing of the cheliped; C, detailed view on the chela showing a faint carina (indicated with arrows); D, detailed view on the chela showing two rows of tubercles (indicated with arrows). Scale bars: 5 mm.