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Order Paxillosida Perrier 1884
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Family Astropectinidae Gray 1840
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?Genus Pentasteria Valette 1929
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Type species: Pentasteria boisteli Valette 1929, by monotypy.
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Pentasteria? splendida n. sp. (Fig. 1)
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*Pentasteria sp. Neumann(2010), p. 35, Figs. 1–3.
Material
GPIMH 3100 (leg./don. Norbert Nordmeyer), the holotype and sole specimen known to date, in the collections of the Geologisch-Paläontologisches Institut und Museum der Universität Hamburg.
Locality and stratigraphy
Former clay pit Engelbostel, about 5 km north of Hannover, northern Germany; earliest Hauterivian (lower Endemoceras Beds; Endemoceras amblygonium ammonite Zone; see Mutterlose (1998), pp. 73, 74, Fig. 34; Mutterlose et al. (1998, Fig. 4).
Derivation of name
Named after Norbert Nordmeyer, the name ‘Norbert’ in Germanic language meaning ‘the splendid one from the north’.
Diagnosis
Medium-sized astropectinid, with narrow, long arms; superomarginals with close-set granule pits only, lacking large spine pits; inferomarginals with distal row of three equal-sized spines, plus two oblique lateral rows of larger horseshoe-shaped spine bases to which are attached spines of variable length; adambulacrals lacking large spine pits, oral intermediate ossicles close to disc margin apparently with large spine base.
Description
Fragmentary proximal arm (eight supero- and eight inferomarginals); greatest length (as preserved) 18.2 mm, distal width 7.8 mm, proximal width 10.8 mm; pyritised and compressed laterally, making measurements of arm width approximate; comparison with well-preserved astropectinids such as a specimen of Pentasteria
longispina Hess 1968 (see Hess 1975, p. 1), suggests a medium-sized individual, with a major radius (R) of c. 80 mm and a minor one (r) of c. 20 mm. Superomarginals near disc margin (Fig. 1a, right-hand side) rather tall (ossicular angle c. 48 degrees), progressively becoming longer more distally and more quadrangular in outline; length between 2.0 and 2.2 mm proximally to 2.4–2.5 (and more) distally (Fig. 1a, b); only with closely spaced, small granule pits; in places, diminutive, roundish and flat granules preserved (Fig. 1a, b) where ossicles abut; aboral surface of superomarginals bulging, ridge-like but merging smoothly into remainder of ossicle (Fig. 1a, b), flatter more distally and corrugated to some extent (Fig. 1a, left-hand side), but lacking large spine pits. In lateral view (Fig. 1b), supero- and inferomarginals alternate in the proximal and median arm portion, but are opposed more distally; proximal facets of infero- and superomarginals with rather shallow intermarginal fascioles. Proximal inferomarginals more cuneate (Fig. 1c), becoming more quadrangular distally (Fig. 1c) and there with at least three equal-sized, close-set, striate spines (length c. 50% of marginal length) on oral surface, near distal margin (Fig. 1c) and up to six (in two oblique rows) on lateral surface, three stouter, the others of variable length, all finely striate; the longest spine at least corresponds to the length of an inferomarginal ossicle; spine bases horseshoe shaped, one row of four, near-equal sized spine bases distal margin oblique towards proximal–intermarginal corner, second row of two slightly smaller, horseshoe-shaped spine bases distal to first row (Fig. 1c–e). Ambulacrals not visible; aboral ossicles quadrangular, blocky (Fig. 1a), near-flat to slightly bulbous, with smooth surface; paxilliform adoral ossicles close set, at least 9–11 rows abreast, pillar like, c. 0.5 mm in length, with only slightly widened and rounded base (Fig. 1a). Adambulacrals blocky, with uneven outer surface, smooth, alternating in opposite rows, with close cover of similar-sized spines, straight to lightly curved (Fig. 1c, d), striate and up to 2 mm in length, and up to 5–6 per ossicle. No larger spines, but a row of oral intermediate ossicles proximally with 3–4 smaller spines, and even more proximal ones, at disc margin (Fig. 1c, lower right-hand side), apparently with a single, large spine base.
On some marginal ossicles (Fig. 1b, arrowed) tooth marks are visible [compare Neumann (2000); Zatoń et al. (2007)], which would indicate a predator attack and might also explain the fragmentary preservation of this individual, which otherwise retains many skeletal appendages.