Mesohalina margaritacea ( Brocchi, 1814 )

Thivaiou, Danae, Harzhauser, Mathias & Koskeridou, Efterpi, 2019, Early Miocene Gastropods from the Felli Section (Proto-Mediterranean Sea NW Greece), Geodiversitas 41 (8), pp. 323-366 : 334

Mesohalina margaritacea ( Brocchi, 1814) (Fig. 4 D)

Murex margaritaceus Brocchi, 1814: 447, pl. 9, fig. 24.

Cerithium (Tympanotomus) margaritaceum – Schaffer 1912: 154, pl. 52, figs 1, 2.

Tympanotonos margaritaceus – Cossmann & Peyrot 1921: 248, pl. 6, fig. 64. — Báldi 1973: 260, pl. 29, figs 1, 2.

Potamides margaritaceus – Cluzaud et al. 2014: 226, fig. 171I.

Mesohalina margaritacea – Harzhauser et al. 2016: 28, figs 11-13 (cum syn.).

MATERIAL EXAMINED. — Sample F1: AMPG ( IV) 2281-2283 (three specimens); sample F2: AMPG ( IV) 2284-2293 (ten specimens) ; sample F7: AMPG ( IV) 2294-2303 (ten specimens) .

DIMENSIONS. — Maximum height: 28.0 mm (incomplete).

DISTRIBUTION. — Oligocene. NE Atlantic: France ( Lozouet et al. 2001); Proto-Mediterranean Sea: Italy ( Esu & Girotti 2010), Greece ( Harzhauser 2004), Turkey ( İslamoğlu 2008); Paratethys ( Reid et al. 2008; Harzhauser et al. 2016).

Early Miocene. Aquitanian-mid-Burdigalian. NE Atlantic: France (Aquitaine Basin) ( Cossmann & Peyrot 1921; Lozouet et al. 2001); Proto-Mediterranean Sea: Greece ( Harzhauser & Kowalke 2001; Harzhauser 2004), Turkey ( Büyükmeriç 2017); Paratethys: Austria, Slovakia, Slovenia (Harzhauser et al. 2016).

REMARKS

A detailed description of the species is given in Harzhauser et al. (2016) and a long list of synonyms is provided by Esu & Girotti (2010). In addition to these descriptions, we observe a fine microstructure between the spiral cords that consists of very subtle fine threads.The specimens are not well enough preserved in order to count the threads, but there seem to be at least three. In Felli, the first (adapical) row of beads becomes more prominent and on some of the largest specimens it develops into a thick spinous keel on the last one or two whorls. The varices described in the largest specimens of the Oligocene (Rupelian) of the Thrace Basin (Harzhauser et al. 2016) are not present in the Felli material. Compared to the Oligocene samples from Greece ( Harzhauser 2004), the ornamentation is less prominent and the flaring outer lip is less developed. The morphology of the specimens from the Aquitanian stratotype ( Lozouet et al. 2001) is the most similar to the specimens from Felli.

The enormous shell variability seen in this species has led to the erection of a noumerous subspecific and varietal names (see Esu & Girotti 2010). Although M. margaritacea was placed in the Extant West African genus Tympanotonos Schumacher, 1817 by many authors, its separation from that genus and its placement in Mesohalina was clarified by Wittibschlager (1983), Kadolsky (1995) and Harzhauser et al. (2016) based on conchological features of the protoconch and early teleoconch. Reid et al. (2008) treat the genus Mesohalina as a synonym or subgenus of the genus Potamides Brongniart, 1810 . Nevertheless, we consider Mesohalina to be clearly separated from Potamides based on the much broader shell, the angular aperture and the different mode of formation of the sculpture of the early whorls (see Kadolsky 1995).

Figures

FIG. 4. — A1-A3, Bittium larrieyense Vignal, 1911: A1, AMPG(IV) 1891 (SEM image); A2, A3, AMPG(IV) 1646; B1-B3, Granulolabium plicatum (Bruguière, 1792): B1, AMPG(IV) 2089 (SEM image); B2, B3, AMPG(IV) 2167; C1-C3, Gibborissoia varicosa (de Basterot, 1825): C1, AMPG(IV) 2239 (SEM image); C2, C3, AMPG(IV) 2240; D, Mesohalina margaritacea (Brocchi, 1814), AMPG(IV) 2294 (SEM image); E1-E3, Terebralia lignitarum (Eichwald, 1830), AMPG(IV) 2304; F1-F3, Terebralia subcorrugata d’Orbigny, 1852, AMPG(IV) 2306; G1-G4, Finella perpusilla (Grateloup, 1827): G1, G2, AMPG(IV) 2308; G3, AMPG(IV) 2309 (SEM image); G4, AMPG(IV) 2309, protoconch (SEM image); H1-H4, Turritella turris de Basterot,1825:H1, H2, AMPG(IV) 2404;H3, AMPG(IV) 2405 (SEM image); H4, AMPG(IV) 2405, protoconch (SEM image). Scale bars: A1, C2, C3, G1, G2, H1-H3, 500 µm; A2, A3, D, 1 mm; B1, G3, C1, 400 µm; B2, B3, 5 mm; E1-E3, 10 mm; F1-F3, 2 mm; G4, H4, 200 µm.