Homalopoma acaste, Thivaiou & Harzhauser & Koskeridou, 2019

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 : 327-328

Homalopoma acaste n. sp.

(Fig. 3 B1-B3)

urn:lsid:zoobank.org:act:59B2AFC6-2AF5-40BF-B619-5B3229CC64E8

TYPE MATERIAL. — Holotype: sample F11: AMPG ( IV) 1512. — Paratype: sample F11: AMPG ( IV) 1513.

OTHER MATERIAL EXAMINED. — Sample F10: AMPG ( IV) 1509- 1511 (three juveniles); sample F11: AMPG ( IV) 1516, 1517 (two juveniles).

DIMENSIONS. — Maximum height: 4.80 mm; maximum diameter: 6 mm.

ETYMOLOGY. — Named after the Oceanid Acaste of Greek mythology, one of the companions of Persephone when abducted by Hades (as noun in apposition).

TYPE LOCALITY. — Felli village section, 40°01’4.55”N, 21°33’34.37”E. Mesohellenic Basin, Grevena area, Greece.

TYPE LEVEL. — Pentalofos Formation, Aquitanian, lower Miocene. DIAGNOSIS. — A small Homalopoma species, with a granulated aspect of the spiral sculpture on top of whorls, prominent spiral sculpture and an umbilicus with strongly crenulated edge.

DISTRIBUTION. — Early Miocene. Proto-Mediterranean Sea: Greece (this paper).

DESCRIPTION

Shell small, solid, turbiniform. Teleoconch consisting of 3.5 slightly depressed convex whorls, suture impressed and linear. Spiral sculpture consists of four primary cords, adapical cord beaded to crenulated; four secondary spiral cords beneath the primary cords. Last whorl inflated, convex. Base with seven weakly granulose cords. Axial sculpture consists of very thin prosocline ribs. Aperture subcircular; umbilicus moderately wide, bordered by beaded edge.

REMARKS

In the present material the protoconch measures about 105 µm in all specimens. The colour patterns are still preserved as is often the case with other members of the genus in the Aquitaine Basin ( Cossmann & Peyrot 1917). The granulose appearance of the primary cords is irregular with weak beads of different sizes cords on the base of the shell having a more granulose aspect, whereas the cords adjacent to the umbilicus have larger but weaker beads. Two morphotypes were found in similar sandy sediments; they have the same spiral sculpture (number of primary and secondary cords) with one morphotype having more prominent, finer spiral cords, and more prominent axial sculpture.

The present Homalopoma differs from H. granulosa , a species from the Oligocene and Miocene of France ( Lozouet et al. 2001), in having a granulose aspect in its spiral sculpture, a wider umbilicus, as well as wider spirals. Another species from the early Miocene (Burdigalian) of the Aquitaine region of France is H. degrangei ( Cossmann & Peyrot, 1917) . It differs with the present species in having weak spiral sculpture and more convex whorls. Homalopoma laleensis Landau, Harzhauser, from the middle Miocene (Serravalian) of Turkey is smaller in size, has weak spiral sculpture and weaker umbilical crenulations.

Homalopoma includes hard-bottom dwellers and species that are adapted to cryptic environments ( Lozouet 2004), including the type species H. sanguineum , which is frequent in Mediterranean submarine caves ( Di Geronimo et al. 1997).

Figures

FIG. 3. — A1-A4, Paroxystele orientale (Cossmann & Peyrot, 1917), AMPG(IV) 1506; B1-B3, Homalopoma acaste n. sp., holotype, AMPG(IV) 1512; C1, C2, Vitta picta (Férussac,1823),AMPG(IV) 1517; C3, AMPG(IV) 1543 (SEM image);C4, AMPG(IV) 1544 protoconch (SEM image); D1-D4, Neritilia neritinoides (Cossmann & Peyrot, 1917); D1, AMPG(IV) 1517; D2, AMPG(IV) 1541 (SEM image); D3, D4, AMPG(IV) 1541 protoconch close-ups; E1, E2, Plesiotrochus fallax (juv.) (Grateloup, 1832), AMPG(IV) 1605; F1-F3, Melanopsis sp., AMPG(IV) 2276. Scale bars: A, C1, C2, E2, 1 mm; B, 2 mm; C3, D3, 100 µm; C4, D1, E1, F, 500 µm; D2, 200 µm; D4, 50 µm.