Liocarcinus kuehni ( Bachmayer, 1953 )

Ossó, Àlex, Gagnaison, Cyril & Gain, Olivier, 2022, A re-appraisal of the middle-late Miocene fossil decapod crustaceans of the ‘ Faluns’ (Anjou-Touraine, France), Geodiversitas 44 (6), pp. 207-228 : 220

Liocarcinus kuehni ( Bachmayer, 1953)

( Fig. 5N-Q )

Portunites kühni Bachmayer, 1953a: 249-251, pl. 2, fig. 2. — Karasawa 1990: 17.

Liocarcinus kuehni – Müller 1984: 84, pl. 71, figs 2, 3. — Hyžný et al. 2015: 226. — Hyžný & Dulai 2021: 208, fig. 80.14.

MATERIAL EXAMINED AND MEASUREMENTS (in mm). — Two dorsal carapaces, ULB-IV-A (10): L = 15, W = 17, F = 7, FOW = 12. — ULB-IV-A (13): L = 6, W = 6.5, F = 3, FOW = 5,5.

LOCALITY AND HORIZON. — ‘Blandinerie’ quarry, Breil (Maine-et-Loire). ‘Savignean facies’, Langhian (middle Miocene).

DESCRIPTION

Small sized carapace, subhexagonal, slightly wider than long; carapace surface covered by transverse rows of minuscule granules forwardly directed, forming terraces of different sizes. Regions weakly defined. Front gently trilobate, edge finely serrate, medial tooth slightly more advanced than the lateral teeth. Orbits relatively large; supraorbital margin arched, finely serrate, with two closed fissures, first at mid length second near outer orbital tooth; inner orbital tooth blunt; outer orbital tooth broad subtriangular, forwardly directed; infraorbital margin not preserved.Anterolateral margin slightly arcuate, with four subtriangular teeth (excluding the outer orbital tooth), the latest (epibranchial tooth) the sharper. Posterolateral margin slightly concave; anterior half sharp edged, with serrate keel; posterior half blunt edged; reentrant of fifth pereiopod well marked, gently concave. Posterior margin slightly convex, finely rimmed. Frontal region flattened.Gastric process poorly defined. Epigastric lobes slightly marked. Protogastric lobes slightly swollen. Mesogastric region weakly marked, very narrow anteriorly, subrhomboidal posteriorly, slightly elevated above the rest of regions. Metagastric region faintly defined. Urogastric region slightly depressed. Cardiac region broad, swollen anteriorly. Intestinal region depressed. Hepatic region depressed. Epibranchial region sigmoidal, interrupted medially, defined by long terraces, and a sharp ridge distally that ends in the epibranchial tooth. Mesobranchial region slightly swollen internally. Metabranchial region depressed. Cervical groove faintly marked.Branchiocardiac groove weakly marked. Ventral parts and appendages not preserved.

REMARKS

The dorsal morphology of the two samples of decapods described herein correspond exactly with the holotype of Liocarcinus kuehni from the upper Miocene of Austria, described and depicted as Portunites kühni by Bachmayer (1953a: 249-251, pl. 2, fig. 2) (see also Müller 1984: 84, pl. 71, figs 3, 4). The carapace outline, same number and shape of anterolateral teeth, shape of the orbits, similar size, and in particular the squamous carapace surface formed by transverse terraces of different sizes, in despite that the holotype and paratypes does not preserve the front, allows to consider the ‘Faluns’ specimens conspecific of Liocarcinus kuehni with confidence.

Strikingly, the dorsal carapace, the only part preserved of our specimens and of Bachmayer’s types, seems identical to that of the extant Liocarcinus corrugatus ( Pennant, 1777) . However, they apparently differ in having a much smaller size than the extant species. In this respect, it is interesting to know that molecular analyses byPlagge et al. (2016), concluded that the European and the Asian populations of Liocarcinus corrugatus , only separated morphologically by subtle dorsal and penial differences, are in fact two genetically separated species, as the results of their analyses demonstrated, thus recognizing the Asian population as L. strigilis Stimpson, 1858 . In view of that, and given the scarce number of specimens of the fossil form, the two samples herein studied, and the three Bachmayer’s samples seen by Müller, is not sufficient to infer that Liocarcinus kuehni is the same species that L. corrugatus . In addition, Plagge et al. (2016: 386) suggested that both extant species are relict of a former range of the eastern Tethys Ocean”, Liocarcinus kuehni would confirm it.

Ossó & Gagnaison (2019: 374-376, fig.5A-B) reported and described a specimen from the ‘Faluns’ as Liocarcinus sp. , and compared it with all the known fossil forms of Liocarcinus . However, it was left in open nomenclature due to its poor preservation and the sole available specimen. Now, compared with the two new specimens of Liocarcinus kuehni , it still appears to be different. Its smooth carapace surface could be due to the reworking, but the specimen of Liocarcinus kuehni ULB-IV-A (13) ( Fig. 5P, Q ) although it is also strongly worn, it retains still the terraces in the carapace, absent in Liocarcinus sp. In addition, the three characteristic tubercles, longitudinally aligned three tubercles at both sides of carapace that Liocarcinus sp. exhibits, are not present, or at least not interpreted as such, in the specimens of L. kuehni described herein. Consequently, we retain the former in open nomenclature.

Figures

FIG. 5. — Decapods from the ‘Savignean facies’ (Langhian) of the ‘Blandinerie’ quarry,Breil (Maine-et-Loire):A, indeterminate majoid,ULB-IV-A (26): dorsal view;B-E, Derilambrus cf.szaboi (Müller,1974):B, ULB-IV-A (33),right propodus,outer margin;C, inner margin;D, ULB-IV-A (35),right propodus,outer margin;E, right propodus, inner margin;F-K, Pilumnus mediterraneus (Lőrenthey, 1897):F, ULB-IV-A (14),dorsal view;G, frontal view;H, ULB-IV-A (18),dorsal view;I, frontal view;J, ULB-IV-A (20), left chela,outer margin;K, inner margin;L-M, undeterminated Carcinidae:L, ULB-IV-A (52),right chela;M, ULB-IV-A (50) left chela;N-Q, Liocarcinus kuehni (Bachmayer, 1953a):N, ULB-IV-A (10),dorsal view;O, frontal view;P, ULB-IV-A (13), dorsal view;Q, frontal view.Scale bars:A-I, N-Q, 5 mm;J-M, 10 mm. Photographs by À. Ossó.