Astrodia abyssicola (Lyman, 1879)

Xie, Xiaojun, Lu, Bo, Pang, Jie & Zhang, Dongsheng, 2022, Description of two species of the genus Astrodia Verrill, 1899 (Ophiuroidea, Euryalida, Asteronychidae), including a new species from seamounts in the West Pacific, ZooKeys 1123, pp. 99-122 : 99

Astrodia abyssicola (Lyman, 1879)

Figs 8 , 9 , 10 , 11 , 12

Ophiocreas abyssicola Lyman, 1879: 64-65, plate 17, figs 470-473.

Astrodia abyssicola : Okanishi and Fujita 2014: 188-192, figs 2-4.

Material examined.

China • 1 specimen; Philippine Sea , Kyushu-Palau Ridge, Mugiboshi Seamount; 16.57.14'N, 134.52.7'E; depth 3225 m; 11 August 2021; collected by an HOV JIAOLONG; preserved in alcohol; RSIO68002 .

Description.

Disc pentagonal and almost flat, 10 mm in diameter, 3.2 mm in height, skin wrinkled under dry conditions (Fig. 9A, B ). Aboral surface of disc lacks external ossicles (Fig. 9A, B ). Radial shields narrow, slightly tumid, bar-like, without granules or spines, and almost reaching center of disc. (Fig. 9A ). Approximately 3.8 mm long and 0.6 mm wide in center and 0.8 mm wide on periphery (Fig. 9A ).

Oral surface flat, covered by thin skin, and lacking external ossicles (Fig. 9C ). Oral shield triangular, one madreporite (Fig. 9D ). Adoral shield big and thick, quadrangular, and longer than wide (Fig. 9D ). Teeth spearhead-shaped, vertically on dental plate; each jaw bears a pair of short, conical oral tentacles (Fig. 9C ). Oral papillae indistinct or underdeveloped (Fig. 9C ). Two genital slits very short, 560 μm long and 110 μm wide, present on oral side of each interradius. Gonads visible in each interradius (Fig. 9D ).

Five arms, long and slender, about nine to ten times as long as disc diameter, no abrupt change in width basally (Fig. 9E ). Proximal portion of arm 1.8 mm wide and 420 μm high, with arched aboral surface and flattened oral surface. Arms tapering gradually toward tip. Arm spines only present in ventral part of arm. First to third tentacle pores without arm spines, fourth tentacle pores with one arm spine and following tentacle pores with two arm spines. Inner arm spines longer than outer arm spines. On middle and distal part of arm, outer arm spines three-fourths as long as inner spines (Fig. 9F ). Three arm spines occurred once in two of the five arms. Lateral arm plates not projecting on arms.

Color. Bright pink in situ, entirely white in alcohol (Fig. 8B, C ).

Ossicle morphology . Vertebrae articulation streptospondylous, wider than long in proximal segments (Fig. 10A, B ), longer than wide in distal segments (Fig. 11A, B ). Oral side of each vertebra with longitudinal groove along midline, deeply depressed, and no oral bridge (Figs 10C , 11C ). Pair of podial basins on oral side moderate in size (Figs 10C , 11C ). Aboral side of each arm vertebra with longitudinal aboral groove,moderately depressed (Figs 10D , 11D ). Lateral furrow of vertebrae declining obliquely from aboral to oral side (Figs 10E, F , 11E, F ). Lateral arm plates crescent-shaped, each associated with one or two arm spines. Spine articulations with separated nerve and muscle openings, bulging outwards (Fig. 12A, C ). A ridge on inner side of lateral arm plate (Fig. 12D ). Arm spines cylindrical, never hooked, bearing fine thorns at apex throughout arms (Fig. 12E, F ).

Remarks.

Ophiocreas abyssicola was first described by Lyman (1879). Okanishi and Fujita (2014) transferred O. Ophiocreas abyssicola to the genus Astrodia and redescribed it. This specimen (RSIO68002) was identical to Astrodia abyssicola by having 0~2 arm spines, rather short genital slits and crescent-shaped lateral arm plates. However, this specimen lacks external ossicles on the disc and arms, which is different from previous descriptions of Astrodia abyssicola by Okanishi and Fujita (2014) as having plate-shaped external ossicles on the periphery. Nevertheless, the genetic distance of COI and 16S (2.9% and 1.9%) between the new collected specimen and A. abyssicola are too small to justify two different species. Therefore, this specimen was identified as A. abyssicola , thus the external ossicles on the aboral surface of the disc could be plate-shaped or absent in this species.

Figures

Figure 8. In situ and on-board photos of Astrodia abyssicola A photo in situ (RSIO 68002, attached to an unidentified sea pen species) B, C photos on board (RSIO 68002), aboral side (B), oral side (C). Scale bars: 10 mm (B, C).

Figure 9. Morphological characters of Astrodia abyssicola (RSIO 68002) A aboral view of the disc B center of the aboral disc C oral view of the disc D genital silts E aboral view of the arms F arms spines. Abbreviations: RS radial shield; M madreporite; T teeth; ADS adoral shield; OT oral tentacle; GS genital slit; G gonad; LAP lateral arm plate; AS arm spine. Scale bars: 2 mm (A, C, E); 1 mm (B, D, F).

Figure 10. Vertebrae in basal arm of Astrodia abyssicola (RSIO 68002) A proximal view B distal view C oral view D aboral view E, F lateral view. Abbreviations: PB podial basin; LF lateral furrow. Scale bars: 150 μm (A-F).

Figure 11. Vertebrae in distal arm of Astrodia abyssicola holotype: RSIO 68002) A proximal view B distal view C oral view D aboral view E, F lateral view. Abbreviations: PB podial basin; LF lateral furrow. Scale bars: 150 μm (C, D, E); 90 μm (A, B, F).

Figure 12. Lateral arm plates and arm spines of Astrodia abyssicola (RSIO 68002) A, B lateral arm plates from the proximal arm, outer view (A), and inner view (B) C, D lateral arm plates from the distal arm, outer view (C), and inner view (D) E, F arm spines from proximal (E) and distal (F). Abbreviations: MO muscle opening; NO nerve opening; R ridge. Scale bars: 90 μm (A, B, F); 60 μm (C, D, E).