Nudator elegantulus, Legiot, 2019

Legiot, Nicolas, 2019, Silurian myodocope ostracods from Poland, Acta Palaeontologica Polonica 64 (2), pp. 379-397 : 387-388

Nudator elegantulus sp. nov.

Figs. 5–7 .

ZooBank LSID: urn:lsid:zoobank.org:act:01C7B8C0-33F5-4067-939B-1568F17AB8C9

Etymology: From Latin elegantulus , fine, elegant.

Holotype: A laterally compressed left valve ( ZPAL O.63/15); Fig. 5C .

Type locality: Niestachów, Holy Cross Mountain, Poland.

Type horizon: Niewachlów Beds, Lower part of the Ludlow Series, based on graptolites, Cucullograptus (Lobograptus) scanicus Biozone.

Material.—Four valves from two localities (Widełki and Niestachów), Holy Cross Mountain, Poland, Ludlow Series, Silurian.

Measurements (in mm).—Size range: L = 2.35, H = 1.6 (ZPAL O.63/13, Fig. 5A ) to L = 2.75, H = 1.9 (holotype,

ZPAL O.63/15, Fig. 5C ). L/H ratio and adductor muscle position for four specimens from two localities ( Fig. 4 ) .

Diagnosis.— Nudator with ornament consisting of very delicate reticulation to backward oriented “chevrons”, excluding the triangular smooth area in front of carapace.

Description.—Valve large, bean-shaped in lateral outline. Greatest length at mid height; greatest height at the level of the adductorial sulcus. Valve outline in lateral view is straight dorsally, gently curved ventrally and rounded posteriorly and anteriorly. Valve surfaces gently inflated overall, lacking distinct or discrete lobes. Adductorial sulcus narrow, occurs just in front of mid-length, originates in the first third of the dorsal margin to just below mid-height ending with the adductor muscle spot. A simple elliptical adductor muscle scar occurs at the slightly widened ventral extremity of the sulcus. The triangular smooth area in front of the carapace has a slightly negative relief and covers an area representing 1/4 of the maximum length and 1/3 of the maximum height. The valve surface is ornamented apart from the anterior triangular smooth area. This ornament consists mainly of small backward oriented “chevrons” that are possibly the remains of a delicate reticulation ( Fig. 6 ). There are about 200–250 chevrons per mm 2, each about 20–50 μm across. During ontogeny, valve lateral outline changes from rounded to more ovoid.

Remarks.— Nudator elegantulus differs from N. angiportatus by its more distinct triangular smooth anterior area and by its ornament.

Stratigraphic and geographic range.—Known only from the type locality.

Figures

Fig. 5. Myodocope ostracod Nudator elegantulus sp. nov., Holy Cross Mountains, Poland; Ludlow Series, Silurian. A. ZPAL O.63/13, left valve. B. ZPAL O.63/14, right valve. C. Holotype ZPAL O.63/15, left valve. Light stereo-pair photographs in lateral view (of silicone casts of external moulds).

Fig. 6. Myodocope ostracod Nudator elegantulus sp. nov., details of the ornament, Holy Cross Mountains, Poland; Ludlow Series, Silurian. A. Holotype ZPAL O.63/15. Left valve (A1): detail of the ornament anterodorsally (A3, A6); detail of the ornament anteroventrally (A2, A5). B. ZPAL O.63/13. Left valve (B1): detail of the ornament anteriorly (B3, B6); detail of the ornament posterior to the adductorial sulcus (B2, B5). A4, B4, light photographs; A5, A6, B5, B6, SEM photographs; A1–A3, B1–B3, explanatory drawings; all lateral views of silicone casts of external moulds.

Fig. 7. Idealized reconstructions and terminology of Nudator elegantulus sp. nov. (A) and Rhomboentomozoe rhomboidea (B) from the Holy Cross Mountains, Poland; Ludlow Series, Silurian. In left lateral (A1, B1) and dorsal (A2, B2) views.

Fig. 4. Valve length/height plot (A) and position of the adductor muscle scar (A/B, where A and B are the distance between the muscle scar and the posterior end of the valve and the ventral margin, respectively) against length/height (B) of complete specimens of entomozoid species from the Holy Cross Mountains, Poland; Ludlow Series, Silurian.