Chlinocephalus demissifrons Ristori, 1886

Charbonnier, Sylvain, Garassino, Alessandro, Pasini, Giovanni & Chény, Cédric, 2024, Review of brachyuran crabs from the late Miocene (Messinian) of Oran, Algeria, Geodiversitas 46 (2), pp. 13-29 : 23-25

Chlinocephalus demissifrons Ristori, 1886 ( Figs 5 ; 6 ; 7 A-C)

Chlinocephalus demissifrons Ristori, 1886: 101-103 , pl. 2, figs. 5, 6. — Glaessner 1929: 113. — Delle Cave 1981: 46. — Karasawa & Kato 2003: tab. 5. — Garassino et al. 2004: 275-278, figs. 15, 16. — De Angeli & Garassino 2006: 64. — Pasini & Garassino 2013: 321, fig. 2. — Baldanza et al. 2018: 27, fig.7. — Pasini et al. 2020: 54, fig. 3c-d.

Geryon latifrons Van Straelen, 1937: 477 , 478, pl. 33, fig. 4, n. syn. — Vía 1948: 145, fig. 4. — Imaizumi 1961: 165. — Saint Martin & Müller 1988: 251. — Moissette & Müller 1990: 758. — Karasawa & Schweitzer 2006: 60. — Hyžný & Dulai 2021: 228, fig. 89.5.

Geryon cf. latifrons – Müller 1984: 96, pl. 93, fig.1. — Hyžný 2016: 477.

TYPE MATERIAL. — Ristori (1886: 103) reported “ specimens collected in the Pliocene marls ”, but he figured just one sole specimen (pl. 2, figs. 5, 6), considered as the unique survived syntype . Indeed, Delle Cave (1981) reported this syntype with the catalogue number IGF 628E. The other syntypes were not found in the palaeontological collection of IGF (S. Dominici, pers. comm. 2023). Therefore, the specimen IGF 628E is herein designated as the lectotype (see Fig. 5 ).

TYPE LOCALITY. —? Fornaci (Savona, Liguria, north-west Italy). Ristori (1886) recorded Fornaci as the type locality of the type material. Fornaci is a hamlet of municipality of Savona so named because of the presence of several kilns (= fornaci in Italian language) now dismantled. Mainly bricks were produced in these kilns, using clays excavated at different localities in Savona province and maybe from the southern Piedmont, but there is no historical evidences of outcropping Pliocene clays at this locality. We could suppose that the type material could be collected during some digging works close to Fornaci hamlet. In conclusion, the locality that yielded the only available specimen of the type material remains unknown.

TYPE AGE. — Pliocene.

STRATIGRAPHIC RANGE. — Late Miocene (late Messinian )-early Pleistocene.

ADDITIONAL MATERIAL. — Algeria. Type material (Arambourg coll.) of Geryon latifrons Van Straelen, 1937 from Les Planteurs quarry , holotype MNHN.F.R03977 (figured by Van Straelen 1937: pl. 33, fig. 4) and three paratypes MNHN.F.R65071 , R66625 , R67112 . — 10 historical specimens MNHN.F.A51751 , A51752, A51753, A51754, A51755, A51756, A51757, A51758, A51759, A51760 (Arambourg coll.) from Les Planteurs quarry . — Three new specimens MNHN.F.A57345 , A87800, A87801 (Geslin coll.) from Ravin Blanc quarry .

Italy. MUSNAF /GEO/7179 a, b, figured by Pasini et al. (2020: fig. 3c, d), Miocene of Valmarecchia, Emilia-Romagna. — PU 41187 figured by Garassino et al. (2004: fig. 16), Pliocene of Cossato, Piedmont. — MSNM i22756 figured by Pasini & Garassino (2013: fig. 2), Pliocene of Castellarano, Emilia-Romagna. — MUAL 2 , 10, 11-12 figured by Baldanza et al. (2018: fig. 7.2, 7.3), early Pleistocene of Bargiano, Umbria .

DESCRIPTION

Carapace

Suboval carapace convex longitudinally and transversally, longer than wide; wide front extended beyond orbits; straight frontal margin with small, short median fissure (as preserved); rimmed frontal margin; wide orbits oblique to frontal margin marked by narrow incision at inner orbital angle; concave supraorbital margin with one fissure and one short outer-orbital tooth; divergent anterolateral margins with two sharp spines, one at level of hepatic margin and the second, longer than the first one, at level of epibranchial angle; convex, smooth posterolateral margins; wide, straight, and rimmed posterior margin; first transverse, curved, and raised carina crossing whole carapace width at level of epibranchial region; second transverse, curved, and raised carina crossing whole carapace width at level of metabranchial regions; indistinct dorsal carapace regions; urogastric and cardiac regions marked by weak branchiocardiac grooves; short, wide urogastric region; suboval cardiac region; depressed intestinal region; smooth dorsal surface of carapace.

Thoracic appendages

Well-developed P 1; subcylindrical P 1 propodus, longer than wide, narrowing posteriorly; P 1 merus and carpus poorly preserved; elongate fingers; poorly preserved straight fixed finger with several teeth on occlusal margin; curved, pointed dactylus, with almost four strong teeth on occlusal margin; P 2- P 5 poorly preserved.

Thoracic sternum

Thoracic sternum wide; thoracic suture 2/3 complete, straight, close to anterior margin of sternum; suture 3/4 deep, short, interrupted; sutures 4/5, 5/6, 6/7, 7/8 apparently interrupted. Sterno-pleonal cavity of male deep, long, nearly reaching anterior margin of sternite 4.

Pleon (male)

Male pleon typically narrow, slender (T-shaped), lateral margins of s4-s6 abruptly narrowing from s3 to narrow telson; telson slender, slightly longer than wide; s5 as long as wide; s6 much longer than wide.

DISCUSSION

After Van Straelen (1937), only two doubtful records of Geryon cf. latifrons were reported from the Miocene of Spain ( Vía 1948) and Hungary ( Müller 1984), whereas Saint Martin & Müller (1988) and Moissette & Müller (1990) simply listed the species without a critical systematic discussion.

According to Karasawa & Schweitzer (2006: 60), G. latifrons cannot be considered as a Geryonidae Colosi, 1923 and they proposed to move it in Chlinocephalus Ristori, 1886 though it apparently lacks the arcuate carinae on the dorsal carapace evident on Chlinocephalus (Garassino et al. 2004: fig. 16).

Ristori (1886) described Chlinocephalus demissifrons based on one complete carapace ( Fig. 5 ). Later Garassino et al. (2004: 276, figs 15, 16) updated the morphological description and proposed a careful reconstruction of the carapace based on a very well-preserved specimen from the Pliocene of Piedmont (NW Italy).

After direct observation of the type material of G. latifrons and additional specimens, we observed the presence of two transverse arcuate carinae on the dorsal carapace, concurring with the generic placement in Chlinocephalus .

The specimens from Oran do not preserve or have poorly preserved carapace dorsal cuticle. They result as inner molds partially washed and eroded, not allowing a detailed evaluation of some dorsal characters. Indeed, the studied specimens seem not to have apparently the distinct weak median incision of the frontal margin due to the poorly preserved compressed carapace frontal margins. Anyway, the apparently lacking of these characters do not justify the description of a new species for the Algerian specimens, since the main dorsal and pleonal characters fit well those of Chlinocephalus demissifrons . Moreover, the variability of the shape of the carapace outline is a character discussed by Baldanza et al. (2018: 11) and considered related to the different stages of growth and/ or to intraspecific sexual difference. The studied specimens seem to confirm the high variability of the carapace shape in this species.

In conclusion, we consider G. latifrons as a junior synonym of C. demissifrons sharing the main morphological characters of the type species, such as the straight, rimmed front with a small median incision, the supraorbital margin with one fissure, the anterolateral margin with two spines, and the two transverse, arcuate carinae.

Chlinocephalus demissifrons had a stratigraphic range from the Miocene ( Italy and probably Spain and Hungary) to the early Pleistocene ( Italy). Its report in North Africa enlarges its palaeobiogeographic range around the Proto-Mediterranean Basin.

Figures

FIG. 5. — Chlinocephalus demissifrons Ristori, 1886 from the Pliocene of?Fornaci (Savona, Liguria, north-west Italy). Lectotype herein designated IGF 628E: A, dorsal view; B, frontal view; C, posterior view; D, left lateral view; E, ventral view; F, right lateral view. Scale bars: 1 cm. Photographs: Stefano Dominici.

FIG. 6. — Chlinocephalus demissifrons Ristori, 1886 from the late Messinian of Oran (Les Planteurs quarry,Arambourg coll.): type material of Geryon latifrons Van Straelen,1937 and one additional specimen:A, holotype MNHN.F.R03977, dorsal view;B, paratype MNHN.F.R67112, dorsal view;C, D, paratype MNHN.F.R65071, dorsal and ventral views; E, paratype MNHN.F.R66625, dorsal view; F, MNHN.F.A51759, dorsal view. Abbreviations: a3-a6, pleonal somites 3-6; c1-4, coxae 1-4; ep, epistome; st1-7, thoracic sternites 1-7; t, telson. Scale bars: 1 cm. Photographs: Lilian Cazes.

FIG. 7. — A-C, Chlinocephalus demissifrons Ristori, 1886 from the late Messinian of Oran (Ravin Blanc quarry, Geslin coll.): A, B, MNHN.F.A87800, dorsal and frontal views; C, MNHN.F.A57345, dorsal view; D-F, Goneplax gulderi Bachmayer, 1953 from the late Messinian of Oran (Ravin Blanc quarry, Geslin coll.); D, E, MNHN.F.A.57347, dorsal and frontal views; F, MNHN.F.A.57344, dorsal view. Scale bars: 1 cm. Photographs: Lilian Cazes.