Stipilepas molerensis Carriol, 2016

Carriol, René-Pierre, Bonde, Niels, Jakobsen, Sten L. & Høeg, Jens T., 2016, New stalked and sessile cirripedes from the Eocene Mo Clay, northwest Jutland (Denmark), Geodiversitas 38 (1), pp. 21-32 : 23-28

Stipilepas molerensis Carriol , n. sp.

( Figs 1 B-D, 2, 3; Table 1)

DIAGNOSIS. — As for genus.

ETYMOLOGY. — After the Mo Clay Formation, ‘moler’ in Danish.

TYPE LOCALITY AND HORIZON. — Mors , northwest Jutland, Denmark ; Mo Clay Formation.

ENVIRONMENTAL SETTING. — Recent species of the Neolepadinae are restricted to hydrothermal vents and seeps in the Pacific and Indian oceans, occurring bathyal and upper abyssal waters. In contrast, Stipilepas molerensis Carriol n. gen., n. sp. occurred in an ‘ordinary’ North Sea habitat, on logs.

TYPE MATERIAL. — The holotype is MGUH 30522 ( Fig. 2C ) ; paratypes are MGUH 30523 ( Fig. 2D ), MGUH 30524 ( Fig. 2A ), MGUH 30525 ( Fig. 2B ), MGUH 30526 ( Figs 1B [26], 3A), MGUH 30527 ( Figs 1B [27], 3B), MGUH 30528 ( Figs 1B [28], 3E), MGUH 30529 ( Figs 1D [29], 3D), MGUH 30530 ( Figs 1C [30], 3F), MGUH 30531 ( Fig. 1C [31]), MGUH 30532 ( Fig. 1C [32]) and MGUH 30533 ( Fig. 3C ) .

DESCRIPTION

Tergum ( Fig.3F ) wide, subquadrangular.Apico-basal ridge thin, very low, situated less than half the valve width from the carinal margin.Occludent margin straight.Scutal margin sinuous. Upper carinal margin longer than the others, straight.Lower carinal margin convex to straight.Valve rounded and protuberant along occludent margin, this rounded margin is followed by a depression extending from the apex to about the middle of the scutal margin, a faint secondary ridge, extending from tergal apex to scutal margin,marking the limit of the depression.Outer surface ornamented with major and minor, thin transverse growth ridges and thin longitudinal ridges radiating from the apex.

Median latus ( Figs 2C , 3A ) short, an isosceles triangle, wider than high, with convex scutal and tergal margins, overlapping scutum and tergum. Outer surface ornamented with major and minor, thin transverse growth ridges.

Scutum ( Figs 1C ; 3A, D ) subrhomboidal in outline and, similar to tergum, ornamented with major and minor, thin transverse growth ridges and some thin longitudinal ridges radiating from the apex. The scutum is bent along a line extending from the apex to the baso-lateral angle and, less strongly, along a second line extending from the apex to a point of the basal margin distant, from the rostral angle, of two-thirds the length of this margin. In the part included between these two lines the growth ridges are curved downwards. There is no distinct ridge associated with the change in direction of the growth ridges along the apico-basal axis. Occludent, tergal and lateral margins convex to straight, basal margin sinuous.

Carina ( Fig. 3E ) and rostrum have the same shape and are difficult to tell apart when found isolated. Carina (or rostrum) strongly convex transversely, widening from the apex to the basal margin, not carinate, ornamented externally with major and minor growth lines.

Peduncle with scales ( Figs 2B, C , 3C ), wider than high, externally marked by thin growth lines, with apex rounded. These scales are difficult to count; nevertheless, it is possible to consider their number of tiers by whorl about six. Peduncle length equal to or shorter than that of capitulum.

REMARKS

Stipilepas molerensis Carriol n. gen., n. sp. is the first extinct taxon that is attributable to the Ashinkailepadini and, in addition to? Neolepas augurata Buckeridge & Grant-Mackie, 1985 from the Lower Jurassic of New Caledonia, the second known fossil taxon that is referable to the Neolepadinae .

Superorder SESSILIA Lamarck, 1818 Suborder BRACHYLEPADOMORPHA Withers, 1923 Family BRACHYLEPADIDAE Woodward, 1901

Figures

FIG. 1. — A, Sample with 18 fossils of Plesiobrachylepas jutlandica Carriol n. gen., n. sp.of which paratype MGUH 30513 [13] viewed from the right side, and paratypes MGUH 30514 [14], MGUH 30515 [15] and MGUH 30516 [16] viewed by below;B-D, Stipilepas molerensis Carriol n. gen.,n.sp.;B, sample with fragments of capitulum and isolated plates of which paratypes MGUH 30526 [26], MGUH 30527 [27] and MGUH 30528 [28]; C, sample with fragments of capitulum and isolated plates of which paratypes MGUH 30530,MGUH 30531 and MGUH 30532;D, sample with fragments of capitulum and isolated plates of which paratype MGUH 30529 [29]. Scale bars:5 mm.

FIG. 2. — Stipilepas molerensis Carriol n. gen., n. sp.: A, paratype MGUH 30524, right side; B, paratype MGUH 30525,right side; C, holotype MGUH 30522, right side; D, paratype MGUH 30523, left side. Abbreviations: C, carina; T, tergum; L, median latus; S, scutum; R, rostrum. Scale bars: 1 mm.

FIG. 3. — Paratypes of Stipilepas molerensis Carriol, n. gen., n. sp.: A, MGUH 30526 showing the right plates of its operculum, its rostrum and some scales of the peduncle; B, MGUH 30527 showing its carina and the right plates of its operculum; C, MGUH 30533 seen of the left side; D, MGUH 30529 showing its carina and the right plates of its operculum; E, MGUH 30528, carina; F, MGUH 30530, right tergum. Abbreviations: abr, apico-basal ridge; L, median latus; lcm, lower carinal margin; om, occludent margin; Ps, peduncle scale; R, rostrum; S, scutum; sm, scutal margin; T, tergum; ucm, upper carinal margin. Scale bars: 1 mm.