Deltentosteus planus, Schwarzhans, 2023

Deltentosteus planus n. sp.

Figure 19f–j View Fig

Holotype SMF PO 101.227 ( Fig. 19f View Fig ), Dar bel Hamri, coquina at river level of Oued Beth, Zanclean.

Paratype 4 specimens SMF PO 101.228 , same data as holotype .

Further material 21 specimens, Zanclean , 20 specimens same data as holotype , 1 specimen Asilah .

Etymology From planus (Latin) = flat, referring to the relatively flat inner face.

Diagnosis OL:OH = 1.02–1.1. Dorsal rim regularly curved, smooth. Sulcus shape very asymmetrical with a wide ostium and a narrow, tapering and pointed cauda. Ostium inclined at 22–25°.

Description Small otoliths with rounded shape without prominent angles or projections but resembling a well-rounded rectangle. Size up to 2 mm in length (holotype 1.8 mm). OH:OT = 2.7–3.0. Ventral rim shallow, nearly straight; dorsal rim slightly elevated with well-rounded pre- and postdorsal angles at about same level. Anterior and posterior rims nearly vertical. All rims smooth.

Inner face relatively flat, only slightly convex, and rather smooth. Sulcus positioned slightly eccentrically towards anterior and very asymmetrical with a wide ostium and a narrow cauda. Ostium dorsally and ventrally widened, steeply inclined at 22–25°, with angular or rounded anterior tip. Ostial-caudal joint marked by angle on ventral sulcus margin. Cauda narrow and short, with tapering, pointed tip, inclined at 7–12°. OL:SuL = 1.85– 2.1; OsL:CaL = 1.85–2.2; OsH:CaH = 2.5–2.8. Subcaudal iugum very feeble and small. Dorsal depression small, cup like, high above sulcus and dorsally open; ventral furrow weak, close to ventral rim of otolith, fading upwards anteriorly and posteriorly. Outer face evenly but relatively faintly convex, smooth.

Discussion Deltentosteus planus was apparently a relatively small species with otoliths not exceeding 2 mm in length. Te otoliths are nevertheless easily recognized by the nearly flat inner face, the smooth, rounded rectangular outline, and the specific asymmetric sulcus. Of the two extant species, it most resembles D. collonianus (Risso, 1820) ( Fig. 18e View Fig ) in the relatively flat inner face and the low OL:OH ratio known from the Mediterranean and adjacent part of the Atlantic. Deltentosteus planus differs from D. collonianus in the smooth, rounded rectangular outline (vs. bulged dorsal rim and distinct crenulation and undulations), the distinct shape of the sulcus, and the rather steep inclination of the ostium (22–25° vs. 15°). Furthermore, otoliths of D. planus do not reach the size of its extant congener.