Anchistrocheles seguenzai, Sciuto & Pugliese, 2013

Sciuto, Francesco & Pugliese, Nevio, 2013, Description of two new species of ostracods from the Strait of Messina (central Mediterranean), Zoosystema 35 (1), pp. 35-44 : 37-38

Anchistrocheles seguenzai n. sp. ( Fig. 2 )

TYPE MATERIAL. — Holotype: Strait of Messina , central Mediterranean, R / V Universitatis, cruise MERC, sampling station MERC 10 (38°07’14’’N, 15°32’55”E; 545 m depth), terrigenous mud, 12.XII.2005, right valve (L 0.530 mm, H 0.280 mm), MNHN PMC. O7 H. 1.10.2012 ( Fig. 2A ).

Paratypes: same data as holotype, the left valve MNHN PMC.O 25P. 1.10.2012 ( Fig. 2C ), station MERC 148, 327 m depth, terrigenous mud, 18.VI. 2006, and two valves not figured MNHN PMC.O 26P. 1.10.2012 ; MNHN PMC.O 27P. 1.10.2012 .

OTHER MATERIAL EXAMINED. — One fossil complete carapace found in the Pleistocene (Calabrian) sedimentary succession cropping out at Scoppo (ME) ( Fig. 1 ) along the sicilian side of the Strait of Messina ( Fig. 2B ).

STRATIGRAPHIC RANGE.— Early Pleistocene (Calabrian) to Recent.

ETYMOLOGY. — This species is dedicated to Giuseppe Seguenza (Messina, 1833-1889) one of the most important Sicilian naturalists and palaeontologists of the 19th century.

DIAGNOSIS. — Anchistrocheles seguenzai n. sp. is characterised by valves reniform-subquadrangular laterally compressed with anterior and postero-ventral marginal area narrow and flattened.

DESCRIPTION

Carapace medium-sized, reniform-subquadrangular in lateral view, elongate and compressed in dorsal view with the posterior end more acute than the anterior one ( Fig. 2 A-C).

Valves almost symmetric with RV slight overlapping LV in dorsal area. Anterior margin regularly rounded with a wide bending radius, dorsal margin convex and sub-polygonal in RV, somewhat flatter in LV, posterior margin straight passing to the postero-ventral margin through an obtuse angle. Ventral margin concave and sinuous with a marked oral curvature. Anterior and postero-ventral marginal area narrow and flattened: larger anteriorly and narrower postero-ventrally ( Fig. 2C ).

Outer surface smooth. Normal pore-canals little, simple, numerous and evenly distributed on the external surface ( Fig. 2A, B ).

Inner lamella anteriorly and postero-ventrally wide. Anterior and postero-ventral vestibula narrow ( Fig. 2D, H ). Marginal pore-canals ( Fig. 2D, H ) straight and simple; a few ones close set.

Eye tubercles absent.

Hinge adont ( Fig. 2C, F ). A thin dorsal groove in the left valve that corresponds with a complementary thin dorsal edge in the right valve.

Four large and clear adductors muscle scars, one frontal scar and two mandibular scars ( Fig. 2G ).

REMARKS

The generic attribution of Anchistrocheles seguenzai n. sp. is difficult as its carapace is characterised by morphological features that are shared by Bythocypris Brady, 1880 . Until now the differences between the two genera can be defined only in the presence of soft parts ( Van Morkoven 1963; Maddocks 1969). Nevertheless, the present species has been confidently assigned to Anchistrocheles following Aiello et al. (1996) using the characters listed below: the anterior margin more obliquely subtruncated, the more subrectangular outline of the valves, the almost symmetrical right and left valves and the sharppointed dorsal margin exhibited by Anchistrocheles in comparison to that of Bythocypris .

Anchistrocheles has a Recent and fossil worldwide distribution. The genus is known from the Early Pliocene and Pleistocene of Italy ( Colalongo 1965; Greco et al. 1974; Colalongo & Pasini 1980, 1988; Barra et al. 1998; Aiello & Barra 2001; Sciuto 2005; Sciuto & Rosso 2008), the Pleistocene of Rhodes ( Mostafawi 1989), the Pleistocene of the Atsumi Peninsula, central Japan ( Yajima 1987) and the Neogene of the Hawaii Island ( Brady 1890). The genus seems to have been found also in the Late Tortonian-Messinian of Morocco ( Aiello et al. 1996).

Recent species (13 species) are known from the North Sea, the Irish Sea and the English Channel ( Brady & Norman 1889), from Madagascar ( Brady 1890; Maddocks 1969; Scott 1905), from Bermuda ( Maddocks 1976) and from Mozambique ( Maddocks 1969), from bathyal thanatocoenoses off Santa Maria di Leuca (Ionian Sea) ( Rosso et al. 2010) and from the Gulf of Aqaba ( Bonaduce et al. 1980).

To date the genus Anchistrocheles is known from the Recent Mediterranean only with A. tenera ( Breman, 1975) , a species reported from the western Mediterranean ( Bonaduce et al. 1983), including the Gulf of Naples ( Aiello et al. 1996), and from the Adriatic Sea ( Breman 1975) and documented also from bathyal environments of the Atlantic Ocean.

Anchistrocheles seguenzai n. sp. is distinguishable from all other species of the genus because of the more reniform-subquadrangular outline of its carapace and the different H/L values.

Anchistrocheles seguenzai n. sp. resembles: 1) Anchistrocheles sp. described by Bonaduce et al. (1980) from Recent shallow-water (30 m deep) sediments from the Gulf of Aqaba; 2) A. barnharti Maddocks, 1976 , from Recent lagoonal sands on the Bermuda platform; and 3) A. acerosa (Brady, 1868) , reported by Brady & Norman (1889) from the North Sea, the Irish Sea and the English Channel. Nevertheless, specimens of these species show lateral outlines of their carapace less subquadrangular and more rounded than A. seguenzai n. sp.

Figures

FIG. 2. — Anchistrocheles seguenzai n. sp.: A, holotype (MNHN PMC.O7H.1.10.2012); B, specimen from Scoppo; C, D, F-I, paratype (MNHN PMC.O25P.1.10.2012); A, right valve,external lateral view; B, left valve,external lateral view;C, left valve, internal lateral view; D, left valve, internal lateral view, detailed of the anterior marginal area with marginal pore-canals; E, right valve, dorsal view, drawing of outline; F, left valve, detail of the hinge; G, left valve, internal lateral view, muscle scars; H, left valve, internal lateral view, detail of the posteroventral marginal area with marginal pore-canals;I, left valve,internal lateral view, detail of the anterior marginal area.Scale bars: A-C, E, 200 µm; D, I, 50 µm; F-H, 100 µm.

FIG. 1. — Geographical location of sampling stations in the Strait of Messina.