Arenorbis Hess, 1970

Genus Arenorbis Hess, 1970 View in CoL

Type species: Aspidura squamosa Picard, 1858 , by original designation.

Emended diagnosis: Ophiodermatin genus with disc densely covered by tiny granules except for rounded triangular to pear-shaped radial shields; small, short adoral shields and large, arrow-shaped oral shields, both with proximal tips covered by granules; two tooth papillae per jaw apex, bordered on both sides by a single larger infradental papilla, two to three lateral oral papillae and two adoral shield spines; arms slender; lateral arm plates relatively stout, not constricted, with relatively large spine articulations integrated in outer surface stereom and separated from distal edge by a thin ledge; arm spines conical, pointed, as long as one arm segment or shorter; tentacle pores covered by two large tentacle scales and several much smaller scales.

Arenorbis santameraensis sp. nov.

Holotype: MUJA-1215.

Paratypes: MUJA-0511, MUJA-0811 (specimen exposing ventral side), MUJA-3785 (complete specimen exposing dorsal side, 5 mm disc diameter); MUJA-3785 (specimen exposing dorsal side, 4.2 mm disc diameter).

Type locality and stratum: Punta La Llastra W section along sea cliffs at Santa Mera in the municipality of Villaviciosa (Asturias, Spain); Buerres Member, Rodiles Formation, upper Sinemurian, Obtusum ammonite Zone and Subzone, Lower Jurassic.

Etymology: Species name refers to the village of Santa Mera (near Villaviciosa), closest to the Punta La Llastra W section cliffs.

Diagnosis: Species of Arenorbis with adoral shields meeting proximally, arm spines as long as one arm segment, and small spine articulations.

Description of holotype: MUJA-1215 ( Fig. 3 View Fig ) is an articulated skeleton exposing the ventral side. Disc rounded pentagonal ( Fig. 3a, b View Fig ), 5.4 mm in diameter, interradii covered by small, rounded, imbricating scales bearing a dense cover of tiny, spherical granules ( Fig. 3d View Fig ); oral shield as long as wide, accounting for a quarter of the disc radius ( Fig. 3b View Fig ), proximal tip covered by granules, arrow shaped, with a right proximal angle composed of straight latero-proximal edges, incised latero-distal edges and a narrower, rounded distal tip; adoral shields ( Fig. 3c View Fig ) relatively wide and short, narrowly meeting proximally but not extending around the lateral corner of the oral shield, proximal tips covered by granules; oral plates relatively slender and short; buccal skeleton ( Fig. 3c View Fig ) composed of an assumed triangular Lyman’s ossicle at the edge between first ventral arm plate and adoral shield, two relatively large, oval adoral shield spines on the edge of the adoral shield, followed by two to three smaller, leaf-shaped lateral oral papillae, a single slightly larger infradental papilla and a slightly larger, conical tooth papilla; ventralmost tooth slightly larger than tooth papillae, conical; genital slits covered by matrix; five arms preserved ( Fig. 3a View Fig ), relatively slender, longest arm 14.3 mm in length; three first arm segments incorporated into disc; first ventral arm plate ( Fig. 3c View Fig ) 1.5 times wider than long, drop shaped; following ventral arm plates in contact in proximalmost arm segments ( Fig. 3d View Fig ), approximately as long as wide, with a convex distal edge, incised lateral edges and a pointed proximal tip; tentacle pores large ( Fig. 3e View Fig ), encompassed by ventral and lateral arm plates, covered by two large, operculiform main scales and two to three much smaller additional scales; lateral arm plates ( Fig. 3e View Fig ) relatively thin, with large, ventral to ventro-distalwards pointing tentacle notch, ventro-proximalwards projecting ventral portion, outer surface smooth; at least two conical, pointed arm spines ( Fig. 3e View Fig ) on distal edge of lateral arm plates, half as long as an arm segment; lateral arm plates meeting ventrally and separating ventral arm plates into median to distal arm segments ( Fig. 3f View Fig ).

Paratype supplements and variation: MUJA-0511

( Fig. 4 View Fig ) is an articulated skeleton exposing the dorsal side, disc 5.4 mm in diameter, rounded pentagonal outline ( Fig. 4a View Fig ) as in holotype, covered by numerous small, rounded, imbricating scales, covered by tiny granules

( Fig. 4b View Fig ) originally forming a dense cover; central primary plate ( Fig. 4a View Fig ) slightly larger than surrounding scales; radial primary plates not discernible with certainty; radial shields ( Fig. 4b View Fig ) rounded triangular to pear-shaped, exposing most of their surface, not covered by granules, fully separated over entire length, accounting for one-third of disc radius; proximal dorsal arm plates

( Fig. 4c View Fig ) slightly longer than wide, fan shaped with convex distal edge and straight lateral edges, in contact; proximal lateral arm plates carrying up to four arm spines similar to those in holotype, adpressed or at a low angle to the arm, second dorsal spine longest, as long as one arm segment; dorsal arm plates in median arm segments ( Fig. 4d View Fig ) in contact, clearly longer than wide.

MUJA-0811 is a slab with two specimens; the paratype specimen designated herein is an articulated skeleton exposing the ventral side ( Fig. 5a, b View Fig ), disc diameter of 5 mm; buccal skeleton ( Fig. 5a View Fig ) as in holotype; ventral interradii better preserved, showing relatively long genital slit ( Fig. 5a View Fig ) extending to the edge of the disc; arms as in holotype, longest arm 22 mm in length; details of ventral arm skeleton ( Fig. 5b View Fig ) better preserved, showing shallow groove lining tentacle notch in lateral arm plates.

MUJA-3785 is a slab with four specimens; one of the paratypes designated herein being a complete specimen exposing the dorsal side, with a disc diameter of 5 mm; one arm partly disintegrated, with arm plates scattered; proximal lateral arm plate exposing external side ( Fig. 5c View Fig ), with straight dorsal edge, ventro-proximalwards protruding ventral portion, rounded convex distal edge, and concave proximal edge with at least three small, poorly defined spurs; outer surface smooth; three moderately large spine articulations at the same level as outer surface stereom, separated from distal edge by a thin ledge; large but relatively shallow tentacle notch.

Te second paratype on slab MUJA-3785 is a specimen exposing the dorsal side, with a disc diameter of 4.2 mm; disarticulated arm plates include a median lateral arm plate showing the internal side ( Fig. 5d View Fig ), with a single, large, well-defined, arched vertebral articular ridge devoid of conspicuous kinks, extensions of thickened parts; tentacle notch well defined and distally bordered by a slightly thickened ventro-distal tip of the lateral arm plate.