Mikro oviceps, Ortega & Gofas, 2019

Ortega, José Rafael & Gofas, Serge, 2019, The unknown bathyal of the Canaries: new species and new records of deep-sea Mollusca, Zoosystema 41 (26), pp. 513-551 : 520

Mikro oviceps n. sp. ( Fig. 4 A-H)

urn:lsid:zoobank.org:act:D9DA7056-2000-417A-92C5-AEE1AF757354

TYPE MATERIAL. — Holotype. sh., MNHN-IM- 2000-34255 . Paratypes. 24 sh., MNHN-IM-2000-34256, all from SEAMOUNT 2, DW 130 .

TYPE LOCALITY. — Off NW Gran Canaria, 28°08.95’N, 15°53.11’W / 28°09.06’N, 15°52.92’W, 655- 660 m.

ETYMOLOGY. — From the Latin meaning “egghead”, referring to the shape of the protoconch.

DESCRIPTION

Shell minute, globular in shape, with a moderately high, somewhat cyrtoconoid spire and a distinct umbilicus. Protoconch proportionally very large, egg shaped with no sign of coiling, with a maximum diameter of 270 µm, separated from the teleoconch by a distinct scar; protoconch surface with a microscopically pitted texture seen only at high magnification under the SEM. Teleoconch of about 1 3/4 whorl. Spire whorls with a weak spiral cordlet running along the suture, a very distinct adapical shoulder delimited by a sharp keel, channelled between the suture and the keel and slightly convex below it. Surface mostly smooth except for growth lines, a cluster of 4-6 spiral cordlets below the periphery of the last whorl, and another cluster of three stronger spiral cords surrounding the umbilicus. Aperture with a somewhat rhomboidal shape, with the adapical part definitely angled. Outer lip rather thick but simple, orthocline; parietal area without any callosity, columellar edge of the aperture increasing in thickness abapically. Umbilicus open, deep and relatively broad, inside with axial growth lines of a very rough texture, and with an additional spiral cord situated deep inside and abutting into the abapical part of the columella.

Colour opaque white, with a somewhat pearly aspect, the protoconch slightly yellowish. Maximum diameter up to 0.8 mm (holotype 0.84 mm height × 0.80 mm diameter).

REMARKS

The generic assignment of this species is tentative; shared characters with the type species Mikro globulus Warén, 1996 are the minute size, the protoconch with a rough but not distinctly sculptured surface, the presence of a distinct adapical keel at a short distance from the suture, and of a distinct spiral ridge inside the umbilicus. Lopheliella Hoffmann, van Heugten & Lavaleye, 2008 is similar in shape but has a distinct honeycomb sculpture on the protoconch which is not seen here; Lopheliella also either lacks an internal ridge inside the umbilicus or has it very close to its edge, not far inside as in Mikro globulus . Lopheliella species are also considerably larger, with an adult size of 2 to 3 mm.

Mikro oviceps n. sp. is unique in having a protoconch which shows no sign of coiling, contrary to M. globulus and M. hattonensis Hoffman, van Heugten & Lavaleye, 2010 which were also collected in the same dredge haul.

Mikro globulus ( Fig. 4 I-L) is similar in size but has a higher spire, not cyrtoconoid. It lacks the clusters of spirals on the periphery and the abapical part of the last whorl; the subsutural shoulder disappears on the later whorls, and the umbilicus is narrower with only one periumbilical ridge, and no spirals inside. Mikro hattonensis ( Fig. 4 M-P) is more similar to M. oviceps n. sp. in outline, but also lacks the spirals on the last whorl and is more broadly umbilicate. Both M. globulus and M. hattonensis have a protoconch as usual in Vetigastropoda i.e. coiled with hardly more than half a whorl ( Fig. 4L, P ). Both also have been found in the same sample as M. oviceps n. sp. and are new records for Spanish waters (see below).

Figures

FIG. 4. — A-H, Mikro oviceps n. sp.: A, B, holotype (sh.) from DW130 (diameter 0.8 mm); C, paratype (sh.), same locality (diameter 0.70 mm); D, paratype (sh.), same locality (diameter 0.76 mm); E, detail of the umbilicus, same specimen; F, protoconch, same specimen; G, paratype, (sh.) in apical view, same locality (diameter 0.67 mm); H, protoconch, same specimen; I-L, Mikro globulus Warén, 1996: I, shell from DW130 (height 1.50 mm); J, apical view of another shell, same locality (diameter 0,84 mm); K-L, protoconch and early teleoconch whorls of another shell, same locality; M-P, Mikro hattonensis Hoffman, van Heugten & Lavaleye, 2010, M, shell from DW130 (diameter 0.78 mm); N, detail of the umbilicus, same specimen; O, apical view of another shell, same locality (diameter 0.65 mm); P, detail of protoconch and first teleoconch whorl, same specimen. Scale bars: 100 µm.