Squamophis albozosteres, Okanishi, Masanori, O'Hara, Timothy D. & Fujita, Toshihiko, 2011

Okanishi, Masanori, O'Hara, Timothy D. & Fujita, Toshihiko, 2011, A new genus Squamophis of Asteroschematidae (Echinodermata, Ophiuroidea, Euryalida) from Australia, ZooKeys 129, pp. 1-15 : 5-9

Squamophis albozosteres sp. n. Figs 1B37

Type materials.

MV F 162657, holotype, stn SS05/2007 116, off Broome, northwestern Australia, 16°45.09'S, 121°02.48'E - 16°44.36'S, 121°02.12'E, 100-108 m, rocky bottom, 23.3 °C, 30 Jun 2007, epibenthic sled. MV F162658, two paratypes, stn SS05/2007 188, off Ashmore Reef, northwestern Australia, 12°26.42'S, 123°36.03'E - 12°26.58'S, 123°36.35'E, 95-96 m, rocky bottom, 24,8 °C, 7 Jul 2007, benthic dredge (Fig. 2).

Diagnosis.

Epidermal ossicles conspicuous white, slightly domed and round plate-shaped, irregularly placed on aboral side of disc and forming two transverse bands on aboral and lateral sides of each arm segment. Rest of the aboral surface uniformly brown except light purple near the tips of arms and finally without color at the tip.

Description of holotype.

MV F162657: disc diameter 3.4 mm, arm length approximately 50 mm (Fig. 3).

Disc. Disc five-lobed with slightly notched interradial edges: lacking evidence of fission (Figs 3, 4A). Aboral surface almost flat, but radial shields and their surrounds slightly tumid, covered by white, slightly domed and round plate-shaped epidermal ossicles and brown, flat and polygonal plate-shaped epidermal ossicles (Fig. 4 A–C). Epidermal ossicles covered by a thin skin. White epidermal ossicles forming transverse rows at the aboral disc (Fig. 4A), almost uniform in size on aboral disc, 70-120 µm long, approximately 100 µm thick. Brown epidermal ossicles obscured by skin and cannot observed externally (Fig. 4 A–C); relatively large near the periphery, 150-250 µm long, approximately 50 µm thick, and relatively small at the disc center, 100-150 µm long, approximately 50 µm thick. Radial shields completely covered by epidermal ossicles, oblong, approximately 1.2 mm long and 0.6 mm wide, not reaching the center of the disc.

Oral surface of disc entirely covered by only white, flat and polygonal plate-shaped epidermal ossicles, 50-100 µm long and approximately 50 µm thick (Fig. 4 D–G). Four to five triangular teeth forming a vertical row on dental plate. Domed granule-shaped oral papillae lying on either side of jaw (Fig. 4F).

Lateral interradial surface of disc nearly vertical, covered by epidermal ossicles similar to those on oral surface (Fig. 4H). Two genital slits (0.6 mm long and 0.3 mm wide) present in each interradius. No distinct ossicles suggesting existence of madreporites or oral plates observed on any oral interradius, and only epidermal ossicles covered these surfaces (Fig. 4H).

Arms. Arms simple, five in number, no abrupt change in width near the arm base (Fig. 3). The basal portion of the arm 1.4 mm wide and 1.5 mm high, with an arched aboral surface and flattened oral surface. Arms tapering gradually toward the arm tip (Figs 3, 5A, D, G).

The aboral and lateral surface of the base of arms completely covered by white epidermal ossicles, 150-300 µm long, approximately 60 µm thick, and brown epidermal ossicles, 100-300 µm long, approximately 50 µm thick (Fig. 5A, B), similar to those on aboral periphery of disc. Epidermal ossicles on basal portion of arms covered by thin skin. Brown epidermal ossicles obscured by skin, similar to those on aboral surface of disc. Oral surface of the base of arm covered by white epidermal ossicles, 50-100 µm long, approximately 50 µm thick, similar to those on oral surface of disc (Fig. 5C). From basal to middle portion of the arms, the size of plate-shaped epidermal ossicles decreasing on both the aboral and lateral surfaces (Fig. 5D, F), the white domed ones to 100-200 µm and the brown polygonal ones to 100-150 µm. Brown polygonal ones on oral surface decreasing to 50 µm (Fig. 5E). The distal sections of arms covered by scattered granule-shaped epidermal ossicles of 30 µm, finally disappearing near arm tip (Fig. 5G, H).

First to third tentacle pores lacking arm spines; 4th and more distal pores with one arm spine. Arm spines on basal one-third of arm ovoid, minute, approximately one-third to one-half the length of corresponding arm segment (Fig. 5C). Arm spines in middle one-third of arm the same length as corresponding arm segment, bearing fine thorns at their apex (Fig. 5E, F). Arm spines on distal one-third of arm hook-shaped with conspicuous lateral secondary teeth along inner edge (Fig. 5G, H). Length of hook-shaped arm spines gradually decreasing to two-thirds of the corresponding arm segment on distal third of arm, and number of secondary teeth decreasing from two to one. All tentacles pores lacking a sheath around the cylindrical, narrow tube feet (Figs 4E, 5G).

Lateral and ventral arm plates completely concealed by epidermal ossicles over basal to middle portion of arms, but lateral arm plates visible in distal portion of arms (Fig. 5G).

Color.Aboral surface of disc brown, with white spots highlighting the domed epidermal ossicles. Pigmentation on aboral distal portion of arms lighter and appearing purple, finally disappearing at the tip (Fig. 5H). Oral side entirely white (Fig. 3).

Ossicle morphology of one paratype.

MVF162658: Disc diameter 5.3 mm, arm length at least 200 mm.

Flat and polygonal plate-shaped epidermal ossicles at aboral periphery of disc, approximately 236 µm long and 43 µm thick (Fig. 6A, B), the white, round and domed plate-shaped epidermal ossicles approximately 136 µm long and 40 µm thick (Fig. 6C, D). On aboral surface at base of arm, domed ossicles slightly oblong, approximately 226 µm long and 34 µm thick (Fig. 6E, F), whereas the other ossicles flat and round, granule-shaped, 64 µm long and 20 µm thick (Fig. 6G, H).

The radial shields flat and oblong, single-layered, approximately 1.15 mm in length and 0.57 mm in width (Fig. 1B).

Arm spines on basal one-third of arm ovoid (Fig. 6I), in middle cylindrical, bearing fine thorns at tip (Fig. 6J), and distally, they hook shaped with conspicuous secondary teeth along inner edge (Fig. 6K). Number of secondary teeth decreasing gradually to one along distal quarter of arm.

Each lateral arm plate associated with one arm spine and has separate muscle and nerve openings ( Martynov 2010) (Fig. 7A). Oral side of each arm vertebra with a longitudinal groove along midline, no oral bridge ( Okanishi et al. in press) formed to surround the radial water vessel and nerve (Fig. 7B, C).

Variation.

Although only three specimens have been collected, some morphological variation was observed. The smaller holotype (3.4 mm in disc diameter) has no abrupt reduction in arm thickness, but the basal portion of the arm on the two larger paratypes (5.3 mm and 5.6 mm in disc diameter) are slightly widened. The difference between the three specimens may be due to a difference in their sexual maturity or reproductive state similar to the congener, Squamophis amamiensis ( Okanishi and Fujita 2009).

Distribution.

North-western Australia; 95-108 m. Type locality: off Broome, 100-108 m (Fig. 2).

Etymology.

The specific name is a masculine noun in apposition formed as a compound of Latin words, albus (adjective, meaning “whitish”) and a plural form of zoster (masculine noun, meaning “ring”), referring to the rings of white plate-shaped dermal ossicles of arms.

Remarks.

Squamophis albozosteres sp. n. and its congener, Squamophis amamiensis , are similar to each other, however, they can be distinguished by the morphology of the epidermal ossicles on the aboral body and by pigmentation. Squamophis albozosteres has conspicuously white, domed and plate-shaped epidermal ossicles on the aboral side of the disc and basal to middle portion of the arms, forming two transverse rows on the lateral and aboral surfaces of each arm segments (Fig. 5F). Whereas Squamophis amamiensis has only uniform coloured, flattened and plate-shaped epidermal ossicles on the corresponding surfaces. The aboral body surface of Squamophis albozosteres is basically brown with white spots and the tips of the arms are light purple, finally with no color, but that of Squamophis amamiensis is uniformly orange or pinkish brown ( Okanishi and Fujita 2009).