Cyamidia nummulitica nummulitica ( Duncan & Sladen, 1884 )

Mooi, Rich, Kroh, Andreas & Srivastava, Dinesh K., 2014, Phylogenetic re-evaluation of fossil and extant micro-echinoids with revision of Tridium, Cyamidia, and Lenicyamidia (Echinoidea: Clypeasteroida), Zootaxa 3857 (4), pp. 501-526 : 511-513

Cyamidia nummulitica nummulitica ( Duncan & Sladen, 1884)

Figures 4 , 6 .

1884 Echinocyamus nummuliticus Duncan & Sladen : 132–134, pl. 25: figs 14–20.

1914 C. [ Cyamidia ] nummulitica Duncan et Sladen (Echinocyamus) —Lambert & Thiéry: 288.

Type material. Syntypes in the collection of the Geological Survey of India, Kolkata [not seen].

Material studied. NHM E692, from Sind, Pakistan.

Type locality. Several localities were listed by Duncan & Sladen (1884), but because none of the known specimens were selected as the name-bearing type, a type locality is likewise unknown.

Type stratum. Kirthar Formation, Middle to Late Eocene (Jafa & Rai 1994; Rai 2007).

ZooBank LSID. urn:lsid:zoobank.org:act:6A8F5B2A-5FE2-400B-AD93-D7785BBD18E5

Description. Size and shape —Corona small, approximately 6 mm in TL; shape ovoid when viewed aborally; slightly flattened in profile, maximum height less than 50% of TL.

Internal buttressing —Absent.

Apical system —Situated centrally, at the apex of the corona; monobasal, with four gonopores and a single central hydropore, not situated in a pit or groove; ocular pores are small and indistinct, lying well outside the area enclosed by the gonopores, almost directly between most proximal pores in each petal.

Ambulacra —Ambulacral plating simple; ambulacra expanding distal to peristome to form fan-shaped array at least twice the width of interambulacra at ambitus; petals short, with 10 to 17 faintly conjugate respiratory pore pairs in each ambulacrum; pore pairs lying strongly oblique, crossing the ambulacral plates; distal pore pairs becoming even more strongly oblique with distance between pores in each pair slightly decreasing; width of interporiferous zones remaining largely constant along each paired petal, but increasing slightly at the distal end of the anterior, unpaired petal; petaloid region large, extending about 70% of TL; food grooves absent; buccal pores large, facing obliquely towards the peristome; accessory pores situated in oblique patches in centres of plates, axis of patches angled towards perradial suture proceeding distally, apparently not along sutures; ambitus initiating at approximately seventh pair of ambulacral postbasicoronal plates.

Interambulacra —Adapically, two unpaired plates lie in tandem adjacent to apical system; four or five postbasicoronal interambulacrals in each column visible in oral view; posterior unpaired interambulacrum expanding slightly in region accommodating periproct; a few scattered accessory pores visible near centres of some interambulacrals, particularly on the ambitus and oral surface.

Tuberculation —Primary tubercles crenulate, perforate; approximately same diameter on oral and aboral surfaces, evenly distributed in ambulacra and interambulacra without differentiation into locomotory regions; miliary tubercles distributed among primaries.

Peristome —Larger than periproct, about 13% TL; infundibulum extremely shallow; peristomial opening facing directly downwards almost at midpoint of oral surface; framed by basicoronal circlet in which ambulacral plates are approximately same length as adjacent interambulacrals, although basicoronals are slightly longer around posterior half of peristome; 4 to 6 enlarged primary tubercles, areoles abutting, in each interambulacral area adjacent to peristome; in each ambulacrum, slightly elevated ridge or bar of stereom just distal to buccal pores, each bar extending slightly laterally from perradial bulge containing sphaeridium.

Periproct —Small, approximately 10% TL; facing downwards approximately halfway between posterior edge of peristome and posterior edge of the corona in oral view; distinctly elongated along anterior-posterior axis; bounded by first (5.a.2, 5.b.2) and second (5.a.3, 5.b.3) pairs of post-basicoronal plates.

Perignathic girdle —Consisting of five small processes (auricles), one on internal surface of each interambulacral basicoronal.

Sphaeridia —One per ambulacrum; fully enclosed; situated beneath distinct transverse bar just distal to buccal pores.

Spines, pedicellariae, lantern —Unknown.

Remarks. Duncan & Sladen (1884) distinguished three varieties (to be treated as subspecific taxa according to The Code) of Echinocyamus (= Cyamidia ) nummulitica in addition to the form n. nummultica upon which we are basing our descriptions: C. n. obesa, C. n. oviformis and C. n. plana. These differ mainly in overall shape of the corona, particularly in terms of test height and degree of petaloid development. They might well represent valid species or subspecies, but this can only be clarified by re-examination of types, and analysis of intraspecific variation based on a large number of specimens.

A fourth form described by Duncan & Sladen (1884), Echinocyamus rotundus , later placed in Cyamidia by Lambert & Thiéry (1914), may or may not represent a second species in the genus. It is based on a unique, worn specimen that, judging from the poor figures, does not show the typical peribuccal stereom bars observed in Cyamidia nummulitica . It does, however, appear to have the elongate periproct that seems to separate this genus from most other fibulariids.

Figures

FIGURE 4. Morphology of the peristomial region in six species of fibulariids, including Cyamidia, Tridium (= Fibularia), Lenicyamidia, and Leniechinus. On the left for each species is the oral view depicting tuberculation, sculpturing, and positions of buccal pores and sphaeridial chambers, with accompanying scale bar. On the right for each species is a sagittal section through the test (hatched) around the peristome, anterior to the left, with accompanying scale bar. In all cases, scale bar is 1.0 mm long.

FIGURE 6. Partial plate architecture of Cyamidia nummulitica nummulitica, NHM E692. In aboral view, pores of each respiratory tube foot linked by finely dotted lines. In oral view, peristome and periproct in solid black, buccal pores indicated by small dots adjacent to peristome. Interambulacra shaded. For side view, upward arrow indicates peristome, downward arrow indicates periproct. The hole at the ambitus seen in lateral view is a likely predatory borehole (ichnogenus Oichnus sp.).