Amphiura remota, O’Hara & Thuy, 2022

O’Hara, Timothy D. & Thuy, Ben, 2022, Biogeography and taxonomy of Ophiuroidea (Echinodermata) from the Îles Saint- Paul and Amsterdam in the southern Indian Ocean, Zootaxa 5124 (1), pp. 1-49 : 35-38

publication ID	https://doi.org/ 10.11646/zootaxa.5124.1.1
publication LSID	lsid:zoobank.org:pub:C015F8CB-799B-4A92-90AE-02B4C576089E
DOI	https://doi.org/10.5281/zenodo.6404743
persistent identifier	https://treatment.plazi.org/id/C72D87A1-537C-FFB5-FEA3-8290FCC1FA6F
treatment provided by	Plazi
scientific name	Amphiura remota
status	sp. nov.

Treatment

Amphiura remota View in CoL sp. nov.

Fig. 13E–J View FIGURE 13 , 14A–Q View FIGURE 14

http://zoobank.org/ urn:lsid:zoobank.org:act:2758B368-7570-4981-A052-D6A951012506

Type material. MD50 DC167, north of Île Saint-Paul , 38° 24.43´S, 77° 28.64´E, 1430–1600m, Charcot dredge, 24/7/1986 GoogleMaps , MNHN IE.2019.4748 (holotype) , MNHN IE.2009.1557 (16 paratypes) .

Other material examined. MD 50 DC34, MNHN IE.2009.1535 (2). MD 50 DC55, MNHN IE.2009.1537 (1). MD 50 DC137, MNHN IE.2009.1552 (1), MNHN IE.2009.1551 (3).

Holotype description. Disc is 4.4 mm dd, petaloid, indented interradially, covered in overlapping scales, 15–16 scales from disc centre to margin, some primary scales are evident (0.3 long, 0.4 mm wide), separate, scales in disc centre 0.18 to 0.3 mm wide, becoming abruptly smaller and denser near the disc margin and outside of the radial shields (0.125 –0.175 mm wide). A slender triangular scale (0.86 mm long) separates the radial shields ( Fig. 13F View FIGURE 13 ). Scales have microscopic glassy beads, marginal scales have finely denticulate margins ( Fig. 13H View FIGURE 13 ). Radial shields are long (0.3 mm wide and 1.1 mm long), contiguous distally but separated proximally by the long triangular and a few smaller rounded scales, rounded distally, tapered for the proximal 2/3 of their length and terminating in a sharp angle. Ventral disc surfaces ( Fig. 13G View FIGURE 13 ) have similar scales to dorsal margin, becoming less overlapped near oral shield. Genital slits are open along the first 3 arm segments, bordered by a prominent adradial genital scale that persists proximally until the 2nd set of arm spines, where it is followed along the slit by a series of stout plates until the distal projection of the oral plates to the rear of the oral shield.

Jaws are wider than long, slit open and teeth form a buccal funnel (sensu Hendler 2018). Oral shield spear-headshaped, as wide as long, with a small distal lobe. Madreporite is larger than other shields, longer than wide with a prominent wide distal lobe. Adoral shields are slightly separated interradially, with a concave proximal margin, rounded lateral angles and extending distally to border the genital slit; exposed surface of the oral plate rectangular, is separated distally. Four teeth are visible, upper ones rounded, lower ones truncate and longer, all bordered by imperforate stereom. Infradental papillae are pentagonal, square at their base and pointed proximally, a small conical buccal scale adjacent to each infradental papilla on the oral plate, tall flask-shaped to conical adoral shield spine, 2 times as long as wide, sitting proximoventral to the large exposed 2nd oral tentacle pore.

DAPs are fan-shaped then transversely ovoid, 1.3 times wider than long, with the glassy distal margin broadly convex and the proximal side produced into a very obtuse angle, separate. First VAPs are hourglass-shaped, with concave sides formed by the rounded edge of the adoral shields, a little longer than wide, with an obtuse proximal angle and truncate distal edge, contiguous with the 2nd VAP which is 1.25 times longer than wide with a straight proximal margin, divergent proximolateral sides, concave lateral margins around the large tentacle pores, and a rounded distal edge. Succeeding plates are similar but becoming progressively narrower and more tapered proximally, so that they are 2 times as long as wide by the 10th segment and only narrowly contiguous with neighbouring plates.

Two arm spines are on the first segments, thereafter 3 arise from the lateral side of the arm. Spines are long and rounded, gradually tapering to a fine rounded tip, composed of sculptured stereom and fine thorns, the 2 ventral ones are longest, to 0.55 mm, the dorsal one is more slender and 0.6 times shorter. One or two middle arm spines have a diminutive thorn at the tip. Two small tentacle scales occur at right angles to each other around each tentacle pore, one on the LAP and a slightly smaller one on the VAP, which do not completely cover the pore.

Colour (dry): white.

Paratype variations. Other specimens from stn DC167 measure 3.5 to 7.5 mm dd. One has two oral tentacle scales on one jaw. On some specimens, the adoral shield spine is very tall and slender after the swollen base, up to 4 times as tall as wide. On smaller specimens the primary plates are relatively large. All specimens have a white or pale-grey disc and white arms. A non-type specimen from stn DC55 is four-rayed ( Fig. 13I View FIGURE 13 ) and has notable distallydirected thorns on the tips of middle arm spines ( Fig. 13J View FIGURE 13 ).

Paratype ossicle description. Proximal ( Fig. 14A View FIGURE 14 ) and median ( Fig. 14B–C View FIGURE 14 ) LAPs are two times higher than long, strongly arched, relatively thin, with strongly protruding ventral portion; dorsal edge conspicuously angular; outer surface with moderately finely meshed stereom with trabecular intersections transformed into tiny tubercles; outer proximal edge with a central area of more finely meshed stereom. Spine articulations ( Fig. 14D View FIGURE 14 ) are freestanding in the centre of the distal edge, on the same level as the outer surface stereom, moderately large, composed of parallel and completely separated lobes, the dorsal one relatively slender and slightly arched and the ventral one shorter and thicker, encompassing a moderately large muscle opening and a slightly smaller nerve opening. Inner side of LAP has three round, moderately well-defined knobs, a large one close to the centre of the inner proximal edge, a second smaller knob in the dorso-proximal corner of the inner side of the LAP, and a third smaller knob between the large one and the distal edge of the LAP; single small perforation on the ventro-distal edge of the third small knob; tentacle notch large but very shallow and inconspicuous.

Vertebrae ( Fig. 14F–J View FIGURE 14 ) are small, delicate, with relatively small, rounded muscle fossae on the distal and proximal faces; articulations very small, typically zygospondylous, with a large zygosphene on the distal face; dorso-distal muscle fossae deeply carved into the lateral side of the vertebra, with converging dorso-distal tips strongly elongated and pointed, almost projecting beyond zygocondyles; very large, deep ventral furrow, with large, moderately well-defined podial basins.

Oral plates ( Fig. 14M View FIGURE 14 ) are nearly as high as long, with adradial muscle fossa transformed into a vertical spoonshaped depression lining the entire lateral edge of articulation area. Dental plates ( Fig. 14N View FIGURE 14 ) are undivided, rounded, with single row of large, tooth sockets surrounded by separate, strongly protruding knobs; dorsalmost tooth socket very large, perforating dental plate; second dorsalmost tooth socket smaller, penetrating dental plate but with a vertical septum. Abradial genital plates ( Fig. 14O View FIGURE 14 ) are slightly shorter than the adradial one ( Fig. 14P View FIGURE 14 ), very slender, bar-like, bent, without ridges or groves and with a small, concave adradio-distal tip. Radial shields ( Fig. 14Q View FIGURE 14 ) have an irregular, rounded triangular outline, slightly oblique, with a more finely-meshed stereom in the middle part of the outer surface. A proximal dorsal arm spine ( Fig. 14E View FIGURE 14 ), dorsal arm plate ( Fig. 14K View FIGURE 14 ), and ventral arm plate ( Fig. 14L View FIGURE 14 ) are also figured.

Distribution. SPA (1015–2200 m).

Remarks. This species shares many morphological features with the Amphiura joubini -group of species, that includes A. joubini Koehler, 1912 , A. joubini abyssalis Hertz, 1927a , Amphioplus acutus Mortensen, 1936 from the Southern Ocean; Amphiura lanceolata Lyman, 1879 , Amphioplus ctenacantha Baker, 1977 , Amphioplus (Unioplus) cipus Baker, 1977 from New Zealand; and Amphiura otteri Ljungman, 1872 from the North Atlantic. They all form a monophyletic clade on the phylogenies in O’Hara et al. (2017) and Christodoulou et al. (2019). They share discs with long divergent radial shields, fine disc scales, spear-head-shaped oral shields, one to two long spiniform adoral shield spines, long pointed arm spines often with a terminal thorn, and two small tentacle scales.

Here, all these species are reassigned to Amphiura pending a revision of this large genus. The fact that these species are spread over Amphiura , Amphioplus , Amphioplus (Unioplus) and (formerly) Amphiodia shows the artificiality of these genera ( O’Hara et al. 2017). Species in the joubini -group have been referred to Amphioplus or Amphiodia on the basis that some specimens can have two distal oral papillae. However, the presence of two distal oral papillae is homoplasic, and in the case of joubini-group can be interpreted as paired adoral shield spines rather than one being a superficial oral tentacle spine (sensu Clark 1970).

The new species differs from the other species in having only three arm spines, whereas all the other species have four to eight. Other differences include the bihamulate (two lateral terminal thorns) arm spines on A. ctenacantha , the notably denticulate disc scales on O. joubini , and the naked ventral side of the disc on A. lanceolata , A. ctenacantha and O. joubini abyssalis . O. joubini is partially scaled ventrally, with few scales next to the oral shields. Amphioplus acutus is a variant of O. joubini that has a third tiny oral papilla near the end of the jaw slit. The species limits of these species need to be determined. However, the morphology of the MD 50 specimens do not conform to any of these existing species.

Etymology. Named from “remota”, a female Latin adjective that means distant or far away, in reference to the presence of this species in the middle of the south Indian Ocean.