Necronectes michelini (A. Milne-Edwards, 1861)

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 : 376-377

Necronectes michelini (A. Milne-Edwards, 1861) ( Fig. 5 D-F)

Scylla michelini A. Milne-Edwards, 1861: 137 , pl.3., figs 3-3A. — Couffon 1908: 3, 4, pl. 1, figs 6-10, pl. 2, figs 1, 2. — Schweitzer et al. 2006: 122; 2010: 110. — Karasawa et al. 2008: 106. — Emmerson 2017: 584.

Cancer macrochelus – Millet 1854: 152 (non Desmarest, 1817).

Scylla cf. michelini – Glaessner 1928: 184, 185.

Scylla ? michelini – Glaessner 1929: 374.

Scylla sp. ( cf. michelini ) – Lőrenthey & Beurlen 1929: 178, pl. 15, figs 5, 6.

Necronectes michelini – Glaessner 1933: 5-6. — De Angeli & Marangon 1992: 178, 179.

Scylla michelini ? – Betancort et al. 2014: 345, pl. 1, figs K1-K2 (non I1-I2)

MATERIAL EXAMINED AND MEASUREMENTS (in mm). — Two dactyli. Right dactylus, ULB-SO-9: L = 41.38, H = 25. — Left dactylus (tip broken off), ULB-SO-10: L = 32.53, H = 15.52.

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

DESCRIPTION

Right dactylus stout, gently curved forward; subrectangular in section with rounded upper angles; strong proximal knobstick molariform tooth followed by six serial rounded conical teeth of different sizes; rounded tip. Left dactylus stout, gently curved forward; subrectangular in section with rounded upper angles, proximal tooth and tip not preserved.

REMARKS

Scylla michelini was erected based on fragmentary chelipeds and was referred to Scylla De Haan, 1833 , because of its similarity to the strong chelipeds of the extant S. serrata ( Forskål, 1775) . Nevertheless, A. Milne-Edwards (1861: 136), pointed out the absence in S. michelini of the two typical distinct spines on the distal upper part of the palm, near the insertion of dactylus (see Couffon 1908: pl. 1, figs 6-10, t. 2, figs 1, 2; MNHN.F.B25950, which are present in Scylla species (e.g. Keenan et al. 1998; Trivedi & Vachhrajani 2013). Rathbun (1918: 168), when described Necronectes proavitus (as Gatunia proavita), pointed out as well, the absence of those spines as a differential trait with Scylla , and also noted the striking similarity between the cheliped of N. proavitus and that of S. michelini ( Rathbun 1918: 171) . Furthermore, A. Milne-Edwards (1861: 136) noted as well, that the upper margin of the palm of S. michelini is rounded, whereas it is usually more flattened and angled in Scylla species (see Keenan et al. 1998: fig. 8).

Subsequently, several authors assigned similar fragmentary remains of dactyli y to Scylla michelini (see synonym list). Glaessner (1933: 5), included S. michelini within Necronectes A. Milne-Edwards, 1881 , being followed by De Angeli & Marangon (1992: 178, 179). Nevertheless, this placement was questioned by Schweitzer et al. (2006: 121, 122), which retained S. michelini within Necronectes (see also Karasawa et al. 2008: 106).

The aforementioned differences in the palms, such as the absence of the outer and inner spines on distal margin, and the strong spine at carpal articulation of propodus, further, the absence of spines on the outer part of carpus, peculiar of the most species of Scylla possesses (e.g. Keenan et al. 1998: fig. 8; Trivedi & Vachhrajani 2013: fig. 5a-c), allow us to confirm the generic placement of S. michelini within Necronectes , as it was previously placed by Glaessner (1928, 1933).

Figures

FIG. 5. — A, B, Liocarcinus sp., MS2012 0 172b: A, dorsal view; B, frontal view; C, D, Necronectes michelini (A. Milne-Edwards, 1861): C, ULB-SO-9, right dactylus; D, ULB-SO-10, left dactylus; E, Paguristes gagnaisoni Gagnaison, 2012, MS2006 FS 134b, right chela; F-I, Xantho cf. moldavicus (Yanakevich, 1977): F, ULB-SO-11, left chela, inner lateral view; G, outer lateral view; H, ULB-SO-12, left chela, outer lateral view; I, frontolateral view; J-M, undetermined chelae: J, ULB-SO-13, lateral view of right chela; K, frontal view; L, ULB-SO-14, lateral view of left chela; M, close-up showing an encrusted colony of bryozoans. Scale bars: A, B, 5 mm; C-M, 10 mm. Photographs by À. Ossó.