Plesiobrachylepas 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 : 28-30

Genus Plesiobrachylepas Carriol , n. gen.

DIAGNOSIS. — Operculum including a pair of median latera, large relatively and not very high, as well as paired scuta and terga; wall consisting of rostrum and carina surrounded by whorls of imbricating plates, without basal interlocking device, arranged in a few tiers (three).

TYPE SPECIES. — Plesiobrachylepas jutlandica Carriol , n. sp.

ETYMOLOGY. — From Greek plesio, meaning near.

AFFINITIES. — In having imbricating plates without a basal interlocking peg, Plesiobrachylepas n. gen. differs from other brachylepadids, but it has this character in common with Neobrachylepas Newman & Yamaguchi, 1995 . It can be distinguished from the latter in having fewer tiers of imbricating plates and subrhomboidal scuta, terga without apico-basal ridge, and relatively large and triangular median latera.

Plesiobrachylepas jutlandica Carriol , n. sp. ( Figs 3A , 4 , 5 ; Table 2)

DIAGNOSIS. — As for genus.

ETYMOLOGY. — After Jutland (Jylland), Denmark.

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

ENVIRONMENTAL SETTING. — Plesiobrachylepas jutlandica Carriol , n. sp. attached to logs.

TYPE MATERIAL. — The holotype is MGUH 30517 ( Figs 4B [17], 5D) ; paratype are MGUH 30518 ( Figs 4B [18], 5B), MGUH 30513 ( Figs 1A [13], 5C), MGUH 30514 , MGUH 30515 , MGUH 30516 ( Fig. 1A [respectively 14, 15 and 16]), MGUH 30519 ( Figs 4A [19], 5A), MGUH 30520 ( Figs 4A [20], 5A) and MGUH 30521 ( Figs 4A [21], 5E) .

DESCRIPTION

Tergum ( Fig. 5C, D ) wide, subquadrangular. Apex hardly curved towards the scutum. No apico-basal ridge. Occludent margin concave. Scutal margin sinuous. Upper carinal margin convex, as long as the lower. Lower carinal margin sinuous. Valve rounded and protuberant along the occludent margin forming a scutal auricle (terminology according to Gale & SØrensen 2014). Outer surface ornamented with thin transverse growth ridges and thin longitudinal ridges radiating from the apex.

Median latus ( Fig. 5D ) relatively large, an isoceles triangle, taller than wide, scutal and tergal margins straight. Outer surface ornamented with thin transverse growth ridges and thin longitudinal ridges.

Scutum ( Fig. 5D ) subrhomboidal, ornamented with thin transverse growth ridges and thin longitudinal ridges radiating from the apex. Plate plicated longitudinally in the centre, but no apico-basal ridge; occludent margin as long as the tergal margin, occludent margin straight to convex, tergal margin straight, basal margin as long as the lateral margin, basal and lateral margins straight.

Carina and rostrum: the present state of preservation does not allow to determine whether or not the carina and rostrum abut at their lateral margins. Paratype MGUH 30513 ( Fig. 5C ) has a carina which is transversely convex, widening from the apex to the basal margin, and with an external ornament of growth lines and thin longitudinal ridges.

Imbricating plates ( Fig. 5 ), are wider than high and are marked externally by thin growth lines and thin longitudinal ridges; occasionally the plate shows a longitudinal median prominence which widens from the apex to the basal margin, apex rounded. Imbricating plates, without basal interlocking device, are arranged in 12-14 tiers of 3 plates each.

Figures

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.

FIG. 4. — Plesiobrachylepas jutlandica Carriol n. gen., n. sp.: A, internal mould of wood log with 36 fossils of which paratypes MGUH 30519 [19], MGUH 30520 [20] and MGUH 30521 [21]; B, wood log with 13 fossils of which holotype MGUH 30517 [17] and paratype MGUH 30518 [18]. Scale bars: 1 cm.

FIG. 5. — Plesiobrachylepas jutlandica Carriol n. gen., n. sp.: A, paratypes MGUH 30519 [19] and MGUH 30520 [20], viewed by above; B, paratype MGUH 30518 viewed by above; C, paratype MGUH 30513 viewed by the right side; D, holotype MGUH 30517 viewed by above; E, paratype MGUH 30521 viewed by above. Abbreviations: C, carina; Ip, imbricating plates; L, median latus; R, rostrum; S, scutum; T, tergum. Scale bars: 1 mm.

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.