Astrodia duospina, Xie & Lu & Pang & Zhang, 2022

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

publication ID	https://dx.doi.org/10.3897/zookeys.1123.87397
publication LSID	lsid:zoobank.org:pub:DF436107-268C-4011-9D57-02B8C83C35ED
persistent identifier	https://treatment.plazi.org/id/FC14B3BB-E9BB-4E61-A959-266A0CA733C8
taxon LSID	lsid:zoobank.org:act:FC14B3BB-E9BB-4E61-A959-266A0CA733C8
treatment provided by	ZooKeys by Pensoft
scientific name	Astrodia duospina
status	sp. nov.

Treatment

Astrodia duospina sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Material examined.

Holotype: China • 1 specimen; Northwest Pacific , Nazimov Guyot; 15°11.34'N, 162°49.26'E; depth 2713 m; 16 September 2020; collected by ROV HAILONG III; preserved in alcohol; RSIO61068 GoogleMaps . Paratypes: China • 1 specimen; Northwest Pacific , Nazimov Guyot; 15°11.34'N, 162°49.26'E; depth 2713 m; 16 September 2020; collected by ROV HAILONG III; preserved in alcohol; RSIO61069 GoogleMaps • 1 specimen; Northwest Pacific , Caiwei Guyot; 15°40.61'N, 154°53.77'E; depth 2744 m; 7 September 2013; collected by HOV JIAOLONG; preserved in alcohol; RSIO31004 GoogleMaps • 1 specimen; the Philippine Sea , Kyushu-Palau Ridge, Roischesar Peak; 13°20.85'N, 134°32.81'E; depth 1900-2000 m; 2 August 2020; collected by ROV HAILONG IV; preserved in alcohol; RSIO59012 GoogleMaps .

Diagnosis.

Disc raised high above the arm. Aboral disc with plate-shaped external ossicles in the center and on the periphery. Radial shield narrow, longer than wide. Teeth triangular, oral papillae indistinct or underdeveloped. Genital slits short, approximately one-fourth of the height of the disc. Lateral arm plates crescent and not projecting on arms. Arm spines no more than two.

Description of holotype.

Disc pentagonal, notched interradial edges, 14 mm in diameter, 4.7 mm in height. Aboral surface almost flat, slightly depressed in the center, entirely covered by thickened skin with plate-shaped external ossicles in the center, about 220 μm long (Fig. 3A View Figure 3 ). Peripheral disc covered with a few plate-shaped external ossicles, similar to those in the center but larger, approximately twice in length. Radial shields narrow, tumid, bar-like, without granules or spines, and almost reach center of disc (Fig. 3A, B View Figure 3 ). Approximately 7.2 mm long and 550 μm wide in the center and 1.1 mm wide at periphery.

Oral surface flat, covered by thickened skin. Oral shield small to invisible, one madreporite. Adoral shield obscured by skin (Fig. 3C View Figure 3 ). Oral interradial surface covered with several plate-shaped external ossicles (Fig. 3C View Figure 3 ). Six teeth, triangular, forming vertical row on dental plate, each jaw covered by a pair of conical oral tentacles (Fig. 3C View Figure 3 ). Oral papillae invisible or underdeveloped. Two genital slits, small, about 1/4 as long of disc height (1.3 mm long and 260 μm wide), present on oral side of each interradius (Fig. 3D View Figure 3 ). Gonads visible on each interradius (Fig. 3C, D View Figure 3 ).

Five arms, long and slender, about eight to nine times as long as disc diameter, no abrupt change in width basally (Fig. 3E View Figure 3 ). Proximal segments 2.5 mm wide and 1.7 mm high, with arched aboral surface and flattened oral surface (Fig. 3E View Figure 3 ), gradually tapering toward tip. Arm spines only present on ventral side. First to fourth tentacle pores with one arm spine and following tentacle pores with two arm spines. Outer arm spines slightly shorter than inner ones at proximal segments, but only three-fifths as long as inner spines on middle and distal segments (Fig. 3F View Figure 3 ).

Color. Pink in situ, white in alcohol (Fig. 2 View Figure 2 ).

Ossicle morphology of holotype. Vertebrae articulation streptospondylous, wider than long in proximal segments (Fig. 4A, B View Figure 4 ), longer than wide in distal segments (Fig. 5A, B View Figure 5 ). Oral side of each vertebra with longitudinal groove along midline, deeply depressed, and no oral bridge (Figs 4C View Figure 4 , 5C View Figure 5 ). Pair of podial basins on oral side moderate in size (Figs 4C View Figure 4 , 5C View Figure 5 ). Aboral side of each arm vertebra with longitudinal aboral groove, moderately depressed (Figs 4D View Figure 4 , 5D View Figure 5 ). Lateral furrow of vertebrae declining obliquely from aboral to oral side (Figs 4E-F View Figure 4 , 5E-F View Figure 5 ). Lateral arm plates crescent-shaped, each associated with one or two arm spines and spine articulations with nerve and muscle opening separated. Spine articulation bulges outward (Fig. 6A, C View Figure 6 ). A ridge on inner side of lateral arm plate, parallel to proximal edge (Fig. 6B, D View Figure 6 ). Arm spines cylindrical, never hooked, bearing fine thorns at tip throughout arms (Figs 3F View Figure 3 , 6E-F View Figure 6 ).

Description of paratypes.

Two paratypes (RSIO31004, RSIO61069) share the same morphological characteristics as the holotype, disc diameter 10.17 and 13.94 mm, about 1/10 and 1/9 as wide as the length of the arms, respectively. However, the radial shields of RSIO31004 are shorter than the radial shields of the holotype and of

RSIO61069 (Fig. 7F View Figure 7 ). Three arm spines exceptionally occurred only once in both paratypes (RSIO31004 and RSIO61069), the innermost arm spine of RSIO61069 is the longest and the stoutest, while the middle arm spine of RSIO31004 is the stoutest. (Fig. 7A, B View Figure 7 ). The other paratype (RSIO59012) is smaller, only 6 mm in disc diameter, about 1/3 as wide as the length of the arms and may be a juvenile of this species. The radial shields and the genital silts are much shorter than in the other three specimens (Fig. 7C, D View Figure 7 ). Likewise, the arm spines are shorter than one segment (Fig. 7E View Figure 7 )

Etymology.

The species name duo is derived from the Latin numeral word, meaning two, and Latin feminine noun, spina, meaning spine, referring to the presence of no more than two arm spines throughout the arm.

Remarks.

This new species falls within the genus Astrodia by only possessing cylindrical unhooked arm spines. The new species resembles Astrodia abyssicola mostly by having plate-shaped external ossicles on the aboral disc and crescent-shaped lateral arm plates. However, the oral papillae are indistinct or underdeveloped in Astrodia duospina , which can be used to distinguish the two species from each other (Fig. 3D View Figure 3 ). Moreover, the genital slits are very short in Astrodia abyssicola , which are only one-fifth of the height of the disc, while Astrodia duospina has larger genital slits, being longer than one-fourth the height of the disc (Fig. 3C View Figure 3 ). Astrodia duospina can easily be distinguished from A. plana and A. excavata by external ossicles and lateral arm plates. External ossicles are plate-shaped on the aboral surface of the disc in Astrodia duospina (Fig. 3A, B View Figure 3 ), but are absent in A. plana . Lateral arm plates are not projecting in the new species (Fig. 3E View Figure 3 ), but are distinctly projecting from the oral surface of the arm in A. excavata . Additionally, the new species differs from A. tenuispina by having distinctly smaller genital slits (Figs 3C View Figure 3 , 7C View Figure 7 ).

Astrodia tenuispina is a widely distributed species and was characterized by having slender unhooked arm spines, small and short oral papillae, separated genital slits ( Verrill 1884). Baker (1980) compared specimens from south of Australia and the northwest Atlantic, described this species with 2 or 3 arm spines, and imbricating punctate scales on the disc surface. Okanishi and Fujita (2014) redescribed this species as with plate-shaped external ossicles on the periphery of the aboral disc, granule-shaped on the central disc, genital slits half of the height of the disc, lateral arm plates not projecting. According to these descriptions, A. duospina sp. nov. can be differentiated from A. tenuispina by having smaller genital slits and indistinct oral papillae. Furthermore, in two of the three large specimens of the new species, three arm spines were observed exceptionally at one arm segment (Fig. 7A, B View Figure 7 ), while the other three species possess three arm spines at several successive segments in the middle part of the arms. Since only a small number of specimens were examined, this characteristic was not used to distinguish the new species from its congeners, and more specimens should be examined before a robust result can be achieved.