Pilumnus mediterraneus ( Lőrenthey, 1897 )

Ossó, Àlex & Gagnaison, Cyril, 2019, An appraisal of the Middle-Late Miocene fossil decapod crustaceans of the ‘ Faluns’ (Anjou-Touraine, France), Geodiversitas 41 (9), pp. 367-383 : 373-374

Pilumnus mediterraneus ( Lőrenthey, 1897) ( Fig. 4 G-L)

Pilodius mediterraneus Lőrenthey, 1897: 160 , 167, 169; 1898a: 105, 113, 115; 1898b: 126-129, pl. 8, figs 5, 6; 1898c: 99-101, pl. 8, figs 5, 6. — Glaessner 1929: 315.

Pilumnus sp. – Glaessner 1928: 190.

Chlorodopsis mediterraneus – Lőrenthey in Lőrenthey & Beurlen 1929: 34, 225-227, pl. 12, figs 13-17, 19.

Chlorodopsis mediterranea – Bachmayer 1953a: 253 , pl. 3, fig. 5. — Bachmayer & Tollmann 1953: 314.

‘ Pilodius ’ mediterraneus – Müller 1974a: 122, pl. 3, fig. 3.

Pilumnus mediterraneus – Müller 1974b: 280; 1976a: 510; 1976b: 152; 1979: 274, pl. 21, fig. 3; 1984a: 93-94, pl. 87, figs 2-5, pl. 88, figs 1-5. — Radwański et al. 2006: 96, pl. 2, fig. 7. — Ossó & Stalennuy 2011: 37, fig. 9.3. — Górka et al. 2012: 171. — Górka in Wysocka et al. 2016: 379, fig. 14E.

Pilumnus sp. – Förster 1979: 260-261, pl. 3, fig. 6, pl. 5, fig. 1, 3, text-figs 8, 9.

Pince d’une patte de crabe – Gagnaison et al. 2009: 1, fig. 3.

Pilumnus cfr. P. mediterraneus – De Angeli et al. 2011: 112, fig. 4.

MATERIAL EXAMINED AND MEASUREMENTS (in mm). — Two complete dorsal carapaces with cuticle well preserved, ULB-SO-6: L = 19.5, W = 27, F = 8, FOW = 15.5; MS2012 0 170: L = 14, W = 20, F = 8, FOW = 13.5. — Two right chelae, ULB-SO-7: H = 8.72, W = 15.6; ULB-SO-8: H = 7.84; W = 12.8.

LOCALITY AND HORIZON. — ‘La Sonneterie’ quarry, Meigné-le- Vicomte (Maine-et-Loire). ‘Savignean facies’, Langhian-Serravallian (Middle Miocene).

DESCRIPTION

Carapace relatively small sized, subhexagonal, longitudinally vaulted anteriorly, regions faintly marked; surface smooth, weakly ornate with small acute granules and small clusters of acute granules of squamous aspect, spread mainly by anterior half of carapace; setal pits visible. Maximum width at level of fourth anterolateral tooth, at the anterior half of carapace. Front bilobed, medially notched, each half with inner lobes very wide, and the outer lobes smaller, and separated from the inner orbital angle by notches. Orbits small, subrectangular, complete, forward directed; supraorbital margin finely serrated, with two fissures, one median and a second close to outer orbital tooth. Anterolateral margin with four subtriangular teeth (excluding outer orbital tooth), the first one semifused with the outer orbital one, the second one broad, the third and fourth acute. Posterolateral margin slightly convex, smooth. Posterior margin clearly convex medially, rimmed. Frontal region with a short, longitudinal deep groove, lobes slightly swollen. Gastric process fairly defined. Epigastric lobes faintly swollen, ornate. Protogastric lobes rounded, swollen, faintly ornate. Mesogastric region subpentagonal elongated anteriorly, wider posteriorly. Metagastric region indistinct. Urogastric region slightly depressed and separated from meso- and metagastric lobes by two gastric pits. Cardiac region diamond shaped, weakly swollen. Intestinal region narrow, transversely elongate, faintly swollen laterally. Hepatic region with a short granulate ridge paralleling the anterolateral margin. Epibranchial region with a short, acute, half-moon ridge not reaching the fourth (epibranchial) anterolateral tooth. Meso- and metabranchial regions indistinct, swollen. Gastrohepatic groove well marked; cervical and branchiocardiac grooves slightly marked. Thoracic and abdominal features not preserved. Right chela stout, palm slightly wider than long, outer side smooth, spiny in the upper margin and the distal portion of palm, mainly in smaller individuals; articulation with the dactylus strong; dactyli stout, about one third of propodus length; dactylus curved with blunt teeth in occlusal margin; pollex strong, with three to four massive acute teeth in the occlusal margin; setal pits visible in both dactyli. Carpus stout, angle of upper and outer surface with scattered spiny tubercles; upper inner angle with prominent tooth.

REMARKS

The specific assignation of the French specimens to Pilumnus mediterraneus is unequivocal, in view of their stout, short palm with spiny upper margin and distal part, as well as their short dactyli (cf. Müller 1984a: 94, pl. 87, figs 2-5, pl. 88, figs 1-5; Radwański et al. 2006: fig. pl. 2, figs 7A, B; Ossó & Stalennuy 2011: fig. 9.3). Couffon (1908: 4, pl. 2, figs 5-7) reported a fragment and complete carapace and referred them to Titanocarcinus pulchellus (currently Haydnella pulchellus (A. Milne-Edwards, 1864)) and reproduced the diagnosis and the figures of the type of Milne-Edwards ( Couffon 1908: pl. 2, figs 5a-5b). The type specimen was found on the ‘Faluns’ of Maine-et-Loire, and is currently lost ( Couffon 1908: 1; Müller 1984a: 90). Strikingly, the diagnosis of H. pulchellus (see A. Milne-Edwards 1864: 33, 34), as well as its small size, fits well with that of P. mediterraneus . Given the abundance of chelae of P. mediterraneus in the ‘Faluns’ outcrops, it would be plausible that the small carapace described by A. Milne-Edwards as T. pulchellus was likely a specimen of P. mediterraneus . Since the transfer of this species from Titanocarcinus to Haydnella was made based on the drawings of A. Milne-Edwards (see Müller 1984a: 90; Schweitzer et al. 2007: 281, t. 1, fig. 1I), we suggest a revision of the systematic status of this taxon.

Pilumnus mediterraneus is by far the most abundant brachyuran of the ‘Faluns’ outcrops, in view of the great number of chelae remains found; although, complete carapaces, or even fragments of them, are very scarce. Müller (1984a: 94) pointed out already, referring to the Central Paratethys realm, that this species “is probably the most common crab in the Badenian [Langhian/Serravallian]. It occurs in all types of studied biotopes, even in reefs, but it is the most abundant in very shallow, almost eulittoral environments”, and stated: “ P. mediterraneus occurs in all substages of the Badenian”. It is present, furthermore, in the Proto-Mediterranean during the Late Miocene, in the Messinian reefal outcrops of Spain and Italy (e.g. De Angeli et al. 2011). As stated by Müller (1984a: 94), P. mediterraneus is very close morphologically to the extant P. hirtellus Linnaeus, 1761 that lives in the Eastern Atlantic and Mediterranean Sea. We concur.

Figures

FIG. 4. — A-F, Maja orbignyana Millet de la Turtaudière, 1865: A, ULB-SO-2, frontal view of left orbit; B, MS2012 0 172a, dorsal view of anterior part of carapace; C, ULB-SO-3, frontal view of left orbit; D, ULB-SO-3, frontal view of left orbit; E, ULB-SO-4, merus of ambulatory leg; F, ULB-SO-5, dactylus of ambulatory leg; G-L, Pilumnus mediterraneus (Lőrenthey, 1897): G, ULB-SO-6, dorsal view; H, frontal view; I, MS2012 0 170,frontal view; J, dorsal view; K, ULB-SO-7,left chela; L, ULB-SO-8, left chela. Scale bars: 10 mm. Photographs by À. Ossó.