Belonometra kogoi, Obuchi, Masami & Omori, Akihito, 2015

Obuchi, Masami & Omori, Akihito, 2015, A new genus and new species of family Antedonidae (Echinodermata: Crinoidea) from southern Japan, Zootaxa 3972 (3), pp. 441-449 : 444-448

Belonometra kogoi n. sp.

[New Japanese Name: Matsuba-Umishida] ( Figs. 1–5 )

Types. Holotype: OMNH-Iv5432, R 185 mm, west coast of Otsuki, Shikoku Island, Japan, 40.6 m depth, 7 March 2013, SCUBA, coll. M. Obuchi.

Paratypes: OMNH-Iv5433, R 200 mm, same data as OMNH-Iv5432 (except depth, 30.4 m). OMNH-Iv5434, R 190 mm, same data as Cr 130307 (except depth, 30.4 m). OMNH-Iv5435, centrodorsal and radials, R estimated 180 mm, same data as OMNH-Iv5432 (except depth, 27.0 m). OMNH-Iv5436, R 115 mm, Horse Shoe Cliff, Onna, Okinawa Island, Ryukyu Islands, Japan, 18.0 m depth, 16 April 2013, SCUBA, coll. M. Obuchi. OMNH- Iv5437 (dissected), R estimated 80 mm, Horse Shoe Cliff, Onna, Okinawa Island, Ryukyu Islands, Japan, 20.4 m depth, 16 April 2013, SCUBA, coll. M. Obuchi.

Description of holotype. Centrodorsal low hemispherical, 7.8 mm across ( Fig. 1 B); polar area narrow, slightly concave, 18% of centrodorsal diameter, smooth without papillae; cirrus sockets closely crowded rather than forming regular rows ( Fig. 3 A).

Cirri numerous, XCVI (including XXV functional scars), slender, laterally compressed, easy to detach ( Fig. 1 B). Peripheral cirri much longer than apical ones, 27–30 mm long, composed of 21–22 segments (Fig. 2A); cirrals elongated except short proximal two, smooth without aboral keel or process except opposing spine; distal segments with flared distal end, especially on aboral side, overlapping base of next cirrals; c1 L/ W 0.5; c2 L/ W 1.0; c3 L/ W 1.4 –1.7; c4 L/ W 2.0 –2.3; c5–10 longest, L/ W 2.4 –3.0; following cirrals gradually decreasing in length, laterally compressed; antepenultimate L/ W 1.0; penultimate elongated again, L/ W 1.6 –1.8, with straight opposing spine on distal part; terminal claw curved, approximately as long as antepenultimate. Apical cirri approximately 15 mm long, composed of 16 segments; c5–7 longest, L/W up to 2.7 (Fig. 2B).

FIGURE 2. Belonometra kogoi n. gen, n. sp. (A–K, OMNH-Iv5432, holotype; K, OMNH-Iv5436). A, peripheral cirrus; B, apical cirrus; C, proximal brachials; D, P1; E, P2; F, P3; G, P4; H, P5; I, P m; J, P d; K, P1 of small specimen. Scale bars 5 mm.

Radials, also Ibr1, completely concealed by centrodorsal (Fig. 2C). Ibr2 (axillary) proximally concealed by centrodorsal, connected to Ibr1 by synarthry, 3.3 mm wide. Each ray well separated.

Ten arms almost equal in length, 175 mm long, 3.0 mm wide at first syzygy. Brachials without aboral projection and modified distal end (Fig. 2C); proximal four brachials oblong; br1 united interiorly, W/L 3.0; br2 completely separated from neighbor, with interior margin proximally notched, W/L 2.3; weak synarthrial tubercle present between br1 and br2; br3+4 oblong, W/L 2.7: following brachials until middle arms (about br60) wedgeshaped, gradually decreasing in length, each with aboral swellings on proximal edge of pinnule-bearing side and distal edge of side opposite pinnule, making proximal arms appear aborally rough; brachials on distal half of arms short, almost oblong, W/L 3.0–4.0, wider than long even at arm tips, with smooth surface ( Fig. 1 C).

First syzygy at br3+4; second at br9+10 (seven of ten) or br10+11 (three); following at intervals of three (occasionally four) muscular articulations.

Pinnules flagellate, greatly elongated except for short P1 and P2, lacking aboral carination, comb, side- and covering-plates, and terminal hook; comparative lengths P1=P2<P3≥P4>P5<P M≤P D; pinulars finely rough or spinous along lateral margin facing arm tip. P1 on br2, shortest, 14.5–16.5 mm long, composed of 30–34 short segments (Fig. 2D); proximal five to seven pinnulars rounded rhombic, broader than long, more or less projected aborally; following pinnulars to 18–20th L/ W 1.0, with proximal lateral margin towards arm base notched; distal pinnulars gradually elongated but not much longer than broad, L/W less than 1.5, with margin towards arm tips shorter and slightly convex. P2 similar to P 1 in length but with fewer longer segments, 14.5–16.0 mm long, composed of 27–28 segments (Fig. 2E); proximal pinnulars short; distal pinnulars elongated; distalmost L/ W 1.8. P3 usually longest pinnule in proximal arm, rarely shorter than those following, 22.0–27.0 mm long, composed of 32–40 segments, likely first genital pinnule but not swollen (Fig. 2F); middle and distal pinnulars elongated, cylindrical with slightly flared distal end, L/W up to 3.5. Succeeding pinnules similar to P 3 in shape, with fusiform gonad; P4 15.0–26.0 mm long, 32–39 segments, and longest L/ W 3.5 (Fig. 2G); P5 16.5–22.0 mm long, 27–40 segments, and longest L/ W 3.5 (Fig. 2H). Pinnules on inner side of arms similar to outer ones. Middle pinnules 31–33.5 mm long, 40 segments (Fig. 2I). Distal pinnules densely crowded due to short distal brachials, up to 35.0 mm long, composed of 42–48 elongated segments, and longest L/ W 4.5 (Fig. 2J). Pinnules on distal half of arms aligned in three-dimensional ( Fig. 1 C); the bases of successive pinnules on one side of arm oriented directly outward from arm, away from ambulacram (abambulacral direction), toward ambulacram (adambulacral), and then again directly outward from arm; pinnules on opposite sides of arm orient outward-adambulacral, abambulacral-outward, and adambulacralabambulacral, making six rows on each arm.

Disk large, globular, 20 mm in diameter, smooth without nodules, covering proximal rays until about br8 ( Fig. 1 D); mouth central; anal cone sub-central close to mouth, projecting upward, 25 mm high from adoral surface of centrodorsal.

Notes on paratypes. OMNH-Iv5434: almost same size specimen as holotype. Centrodorsal 7.6 mm in diameter; polar area 28% of centdrodorsal diameter. Cirri C; peripheral cirri 26 mm long, up to 19 segments; longest L/ W 3.0. Ten arms 180 mm long; brachials on distal half of arms short, W/L up to 4.0. Pinnules preceding P4 with proximal segments aborally projected, more distinctly than those on holotype; comparative pinnule lengths P1<P2<P3≥P4>P5<P M≤P D, but P3 sometimes shorter than P4. P1 13.0–14.0 mm long, 34–35 short segments; P2 14.0– 16.0 mm long, 27–33 segments; P3 21.5–30.0 mm long, 37–46 segments; P4 19.0–27.0 mm long, 40–41 segments; P5 15.0–17.0 mm long, 35–39 segments; P M 29.0 mm long, 48–54 segments; P D up to 36.0 mm long, 58 segments. Disk 24 mm in diameter.

OMNH-Iv5436: small but mature specimen with gonads. Centrodorsal 5.0 mm in diameter, with cirri in four to five crowded rows; polar area 30% of centrodorsal diameter. Cirri LXVII; peripheral ones 16–17 mm long, 13– 14 segments; longest L/ W 3.2 –4.0. Ten arms 110 mm long; distal brachials short but not remarkably so, W/L 2.0. Pinnules preceding P4 with distinct aboral projections on proximal segments, creating saw-like aboral profile (Fig. 2K); comparative pinnule lengths P1≤P2<P3>P4>P5<P M≤P D; P3 always longest of proximal pinnules; P1 5.0–6.0 mm long, 24–26 segments; P2 6.5–7.0 mm long, 18–21 segments; P3 14.3–16.0 mm long, 28–31 segments; P4 8.5–9.5 mm long, 23 segments; P5 11.5–12.0 mm long, 25–29 segments; P M up to 18.0 mm long, 33 segments; P D up to 20 mm long, 36 segments. Disk 17 mm in diameter.

Skeletal morphology. OMNH-Iv5435. Adoral surface of centrodorsal concave, rugged, with five interradial ridges and several radiating furrows ( Fig. 3 B); interradial ridge with median groove, low and indistinct adjacent to opening of centrodorsal cavity, gradually becoming higher, highest and thickest at outer margin. Diameter of adoral opening of centrodorsal cavity 17% of centrodorsal diameter; opening narrowed by overhanging rim at adoral edge; thus internal diameter of cavity probably larger than opening.

Basal rosette located above proximal surface of radial pentagon, perforated centrally, with five radial and five narrower, not spout-like interradial processes ( Fig. 4 A); basal rays rod-shaped, broad, each with distinct median groove, strongly curved upward and exposed as globular tubercles at each corner of radial pentagon ( Fig. 4 B, 5B); interior end of basal rays adjacent to thin circlet enclosing and slightly overhanging radial cavity. Radial cavity with sparse calcareous filling.

Radial pentagon much smaller than centrodorsal in diameter, but each corner reaching almost to margin of centrodorsal ( Fig. 5 A). Radial facets high trapezoidal with broadened bottom, H/ W 1.3, concaved ( Fig. 5 B); muscular fossae almost parallel to oral-aboral axis, interarticular ligament fossae steep, and aboral ligament fossa more gently sloping; pairs of muscular and interarticular ligament fossae laterally separated from adjacent ones. Muscular fossae, thin, flange-like, slightly higher than interarticular ligament fossae, H/ W 1.5, deeply concave near intermuscular septum; intermusclar notch distinct; intermuscular septum broad, running from just above central nerve canal to near intermuscular notch, with deep median furrow. Interarticular ligament fossae proximally broadened, H/ W 1.3, shallowly concave, separated from muscle fossae by narrow diagonal ridge; lateral edge shallowly notched. Aboral ligament fossa low semicircular, much lower than interarticular ligament fossae, H/ W 0.3. Central nerve canal rounded square; ligament pit slightly larger than central nerve canal. Radial clefts distinct ( Fig. 5 A).

Cr 130416 d: small but mature specimen. Opening of centrodorsal cavity larger, 25% of centrodorsal diameter; adoral edge of cavity thickened, forming distinct lip. Radial cavity without calcareous filling, completely empty. Radial facet with lateral margins not notched at interarticular ligament fossae.

Coloration in life. Ground body color chrome yellow to dark brown ( Fig. 1 A). Cirri khaki. Arms with two dark longitudinal lines gradually fading in distal arm, unclear in life but recognizable in preserved specimens ( Fig. 1 B, C). Pinnules faded distally, yellow to whitish at tip; each pinnular with dark pigmentation on side toward arm tip; fleshy part of genital pinnules containing bright orange gonad ( Fig. 1 D). Distal end of brachials and pinnulars sometimes whitish.

Habitat and ecology. The specimens were found usually deeper and rarely shallower than 25 m in rocky areas in Kochi, and in small crevices on drop-offs of coral reefs at Okinawa Island. Living animals were usually located behind overhanging rocks, but sometimes exposed on pinnacles where current flows, exhibiting multidirectional posture in which pinnules were aligned in six rows along each arm ( Fig. 1 A, C). When disturbed, the animals vigorously swam away from the substratum.

Etymology. Named for Ichizo Kogo in recognition of his contributions to understanding the Japanese crinoid fauna.

Remarks. Some characters are different between large and small specimens, suggesting difference with regards to individual growth. As mentioned above, in the small specimen, the size of centrodorsal cavity is smaller, and the overhanging lip on the adoral edge of the centrodorsal cavity is distinct. Distal arm brachials are short but not remarkably so in small specimens. Aboral processes on proximal segments of proximal to middle pinnules are more distinct in small specimens, although this feature varies between the same-sized specimens, e.g., OMNH- Iv5432 and OMNH-Iv5434.

Figures

FIGURE 1. Belonometra kogoi n. gen, n. sp. (A, C, D, OMNH-Iv 5432, holotype; B, OMNH-Iv 5433). A, feeding posture in life; B, centrodorsal, cirri and proximal ray, aboral view, in life; C, distal arm with base of pinnules, aboral view; D, disk, oral view, in life.

FIGURE 3. Belonometra kogoi n. gen, n. sp., OMNH-Iv 5435. A, centrodorsal, aboral view; B, centrodorsal, oral view. Scale bars 1 mm.

FIGURE 4. Belonometra kogoi n. gen, n. sp. OMNH-Iv 5437. A, basal rosette, lateral view; B, radial cavity, aboral view. Abbreviations: BR, basal ray; R, radial. Scale bars 0.5 mm.

FIGURE 5. Belonometra kogoi n. gen, n. sp., OMNH-Iv 5435. A, radials and centrodorsal, oral view; B, radial facet, lateral view. Abbreviations: ALF, aboral ligament fossa; BR, basal rays; C, centrodorsal; ILF, interarticular ligament fossa; MF, muscular fossa. Scale bars 1 mm.