Persoonaster kianiae ( Thuy, 2005 )

Persoonaster kianiae ( Thuy, 2005)

Figs 2–3 View FIGURE 2 View FIGURE 3

Description of articulated skeleton: MNHNL OPH045( Fig. 2 View FIGURE 2 ) is a fully articulated skeleton exposing both dorsal and ventral sides and preserving proximal to median portions of fours arms, one of which broken after discovery; disc round, 1.6 mm in diameter, dorsal side with rounded-trapezoidal radial shields forming a closed circle accounting for half the disc radius and enclosing a poorly preserved set of rounded pentagonal primary plates; ventral side of disc with very large, conspicuous, bulging adoral shields meeting over their entire length; no oral shields discernible; only inconspicuous proximal tips of oral plates exposed; three to four relatively large, block-shaped oral papillae; single, short, rounded-triangular ventralmost tooth, slightly smaller than oral papillae; second oral tentacle pores entering mouth slit via shallow embayment between adoral shield and small, pentagonal first ventral arm plate.

Arms very short, rapidly tapering, longest preserved arm (broken after discovery) slightly shorter than disc diameter, composed of six segments; lateral arm plates thick, stout and strongly bulging, meeting dorsally and ventrally in all segments including those incorporated into the disc; proximal lateral arm plates higher than long, distal ones as high as long; at least three tiny, conical arm spines at the distal edge of the lateral arm plates, equalling one quarter of an arm segment in length; dorsal arm plates very small, fan-shaped; ventral arm plates small, mushroomshaped with a pointed proximal tip, concave lateral edges and an expanded distal portion showing a convex distal edge; tentacle pores relatively large, developed as between-plate openings in all observable segments, covered by a row of tiny scales attached to a low, slender ridge along the tentacle notch on the lateral arm plates, and two to three larger, block-shaped tentacle scales; vertebrae unknown.

Description of dissociated lateral arm plates (MNHNL OPH046–OPH049): lateral arm plates ( Fig. 3 View FIGURE 3 ) thick, stout, of characteristic rounded rectangular outline and with bulging edges; proximal lateral arm plates slightly higher than long, distal ones as high as long; dorsal, ventral and distal edges evenly convex, proximal edge evenly concave, lined by a very poorly defined band of slightly more coarsely meshed stereom, devoid of spurs; outer surface stereom moderately coarsely meshed but without tubercles or other elements of ornamentation, large but poorly defined depression in the centre of the outer surface at the proximal edge, resulting in bulging dorsal and ventral plate portions; distal edge with two (distal lateral arm plates) to four (proximal lateral arm plates) small, inconspicuous spine articulations inserted in the outer surface stereom and composed of a slit- to comma-shaped muscle opening bordered by very poorly defined, arched and rugose ridge proximally, and by a slender to moderately thick, well-defined, lip-shaped vertical ridge distally; spine articulations of equal size and equidistant. Inner side of lateral arm plates with conspicuously large dorsal and ventral contact surfaces with the opposite lateral arm plate; vertebral space small and with a small, poorly defined, rounded triangular vertebral articular ridge composed of slightly more finely meshed stereom, distally bordered by a large, ventrally pointing tentacle notch.