Asteromorpha tenax Baker, 1980

Okanishi, Masanori, Olbers, Jennifer M. & Fujita, Toshihiko, 2013, A Taxonomic Review Of The Genus Asteromorpha Lütken (Echinodermata: Ophiuroidea: Euryalidae), Raffles Bulletin of Zoology 61 (2), pp. 461-480 : 476-479

publication ID	https://doi.org/ 10.5281/zenodo.4508609
persistent identifier	https://treatment.plazi.org/id/44116F51-FFA6-FF91-C5A9-4FA5FD53C03D
treatment provided by	Carolina
scientific name	Asteromorpha tenax Baker, 1980
status

Treatment

Asteromorpha tenax Baker, 1980 View in CoL

( Figs. 13–15 View Fig View Fig View Fig )

Asteromorpha tenax Baker, 1980: 70–72 View in CoL , figs. 26a, 32

Materials examined. — Twelve ethanol preserved specimens, MNHN IE-2013-4009 , collected by the R / V VAUBAN, station DW205, southeast of New Caledonia, 22°38.S, 167°07.E 140–160 m, 27 Sep.1989 : four ethanol preserved specimens, MNHN IE-2013- 4003 , collected by the R / V Le SUROIT, station PL18 , southeast of New Caledonia, 22°46.S, 167°20.E 70–301 m, 3 Sep.1989 .

Diagnosis. — External ossicles on aboral surface of body polygonal plate-shaped, densely tessellated. No regular transverse rows of external ossicles on aboral and lateral surface of arms. Body uniformly white. Large tubercles on radial shields. Usually six arms, fissiparous.

Description of MNHN IE-2013-4009. — Disc diameter 1.7 mm, arm length ca. 6.6 mm ( Fig. 13 View Fig )

Disc six-lobed with no fission plane ( Fig. 13A View Fig ). Radial shields and aboral interradial areas slightly tumid ( Fig. 13A View Fig ). Aboral surface of the disc covered by flat and polygonal plate-shaped external ossicles with three domed and round tubercles ( Fig. 13A, B View Fig ). On disc, external ossicles ca. 100 μm long and 50 μm thick on periphery and ca. 80 μm long and 40 μm thick in center ( Fig. 13B View Fig ). Tubercles ca. 4–6 mm in length, ca. 3–4 mm in height ( Fig. 13B View Fig ). Radial shields triangular, completely covered by external ossicles and tubercles, ca. 0.7 mm long and 0.2–0.4 mm wide ( Fig. 13A, B View Fig ).

Oral surface of disc entirely covered by domed and polygonal plate-shaped external ossicles, ca. 50 μm long and 50 μm thick ( Fig. 13C, D View Fig ). Three triangular teeth forming a vertical row on dental plate ( Fig. 13D View Fig ) with two or three domed oral papillae on either each side of jaw ( Fig. 13D View Fig ).

Lateral interradial surface of disc nearly vertical, covered by flat and polygonal plate-shaped external ossicles similar to those on oral surface ( Fig. 13E View Fig ). Two pore-like genital slits, 0.1 mm long and 0.06 mm wide in each interradius. No distinct ossicles suggesting existence of madreporites visible on oral interradius.

Arms simple, six, with no abrupt change in width of arms. Basal portion of arm 0.5 mm wide and 0.4 mm high, tapering gradually towards arm tip.

Basal portion of arms completely covered by flat and polygonal plate-shaped external ossicles, ca. 50–100 μm long and 50 μm thick on aboral and lateral surface ( Fig. 13F View Fig ), and ca. 50 μm long and 40 μm thick on oral surface ( Fig. 13G View Fig ). These ossicles densely tessellated ( Fig. 13F, G View Fig ). In middle portion of arms, aboral and lateral surface covered by flat and round granule-shaped external ossicles, ca. 50 μm long and 20 μm thick ( Fig. 14A View Fig ). Orally, external ossicles gradually decreasing in size disappearing from middle portion of arms. No external ossicles presenting on distal portion of arms ( Fig. 14B View Fig ).

First to third tentacle pores lacking arm spines; from fourth pores with two arm spines ( Fig. 13G View Fig ). In first third of arms, arm spines ovoid and minute, both inner and outer arm spines one-third of the length of corresponding arm segment ( Fig. 13G View Fig ). In second and distal thirds of arms, arm spines hook-shaped, their number decreasing to one ( Figs. 14B View Fig , 15A View Fig ) which is half the length of corresponding arm segment ( Fig. 14B View Fig ).

Lateral arm plates concealed by external ossicles ( Fig. 15B View Fig ). Vertebrae with an oral bridge in distal portion of arms ( Fig. 15C, D View Fig ).

Colour: Uniformly white ( Figs. 13 View Fig , 14 View Fig ).

Distribution. — AUSTRALIA: off Morton Bay, depth unknown ( Baker, 1980); NEW CALEDONIA: south-eastern New Caledonia, 70–301 m (present study, new locality).

Remarks. — Asteromorpha tenax is related to A. capensis in sharing polygonal plate-shaped external ossicles densely tessellated on aboral body while A. rousseaui and A. koehleri have two types of external ossicles on aboral body.

Asteromorpha tenax is also related to A. koehleri in sharing the same reproductive mode. Of the 16 examined specimens of A. tenax , 13 have six arms and the other three have three, four, and five arms. Eleven specimens with six arms and one specimen with four arms show conspicuous fission planes across their discs, suggesting fissiparous reproduction of this species. A. rousseaui and A. capensis are not fissiparous.

Asteromorpha tenax is distinguished from the other three species ( A. capensis , A. rousseaui , and A. koehleri ) in having large tubercles on the radial shields. One to four diagnostic large tubercles are present on the radial shields of 12 of the 16 examined specimens including specimens with/without fission planes. The other four specimens without the large tubercles have conspicuous fission planes and thus large tubercles may have been lost when their discs divided.

Asteromorpha tenax can also be distinguished from the other three species by having a uniformly white body colour (see Colour of A. capensis , A. rousseaui and A. koehleri ).