Asteromorpha koehleri ( Döderlein, 1898 )

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 : 472-476

Asteromorpha koehleri ( Döderlein, 1898)

( Figs. 10–12 )

Astroschema koehleri Döderlein, 1898: 131–132 , pl. 5, 5a

Asteroschema koehleri Döderlein, 1911: 111

Astroschema rousseaui Koehler, 1905: 123 . Non Asteromorpha rousseaui ( Michelin, 1862)

Ophiogelas perplexum Koehler, 1930: 43–45 , pls. 2, 6; pls. 4, 9–12

Asteromorpha perplexum Mortensen, 1933: 60–62 , 73, figs. 45, 46

Materials examined. — One ethanol preserved syntype of Astroschema koehleri, ZSM 424/1, off Ambon, eastern Indonesia: dry holotype of Ophiogelas perplexum, MCZ E 5864, off Ambon, eastern Indonesia, 125 m; 16 ethanol preserved specimens, MV F111585, collected by R / V SOUTHERN SURVEYOR, SS10/2005 18, off D’Entrecasteaux National Park, 34°53'10.S, 115°30'25.E–34°53'02.S, 115°29'56.E, 95–100 m, 21 Nov.2005.

Diagnosis. — Two types of external ossicles on aboral surface of body, white, domed and round plate-shaped ossicles and brown, flat and polygonal plate-shaped ossicles. Brown ossicles regularly arranged on radial shields. External ossicles on aboral and lateral surface of arms forming alternative transverse rows of brown and white ossicles on each arm segment. Two rows of brown ossicles on each arm segment in basal portion of arms. No tubercles on radial shields. Usually six arms, fissiparous.

Description of MCZ E5864. — Disc diameter 2.3 mm, arm length at least 12 mm (arms convoluted).

Disc six-lobed in shape with no fission plane. Aboral surface tumid in radial regions, covered by white, domed and round plate-shaped external ossicles as well as brown, flat and round plate-shaped external ossicles ( Fig. 10 A–C). Aboral surface of disc covered by white external ossicles with brown external ossicles scattered at regular intervals ( Fig. 10B, C ). White external ossicles and brown external ossicles ca. 70–110 μm long and 30–40 μm long, respectively ( Fig. 10B, C ). Radial shields oval, completely covered by external ossicles, ca. 1.1 mm long and 0.4 mm wide ( Fig. 10A, C ).

Oral surface of the disc entirely covered by only white, flat and polygonal plate-shaped external ossicles, ca. 80 μm long ( Fig. 10D ). Three to four teeth forming a vertical row on dental plate, except on two jaws that have two parallel teeth are in oral-most position ( Fig. 10D ). Four to five domed oral papillae lying on each side of the jaw ( Fig. 10D ).

Lateral interradial surface of disc nearly vertical, covered by white, flat and polygonal plate-shaped external ossicles similar to those on oral surface ( Fig. 10E ). Two narrow genital slits in each interradius, 50 μm long and 7.5 μm wide. No distinct ossicles suggesting existence of madreporites ( Fig. 10E ).

Arms simple, six. Two arms thickened (0.9 mm and 0.7 mm width, respectively) on basal third to fourth segments with flattened aboral and oral surfaces. Remaining segments, 0.3 mm in width, with arched aboral surface and flattened oral surface. Arms tapering gradually towards tip of arm from middle. Remaining four arms flattened on both aboral and oral surfaces, square in cross-section and tapering gradually towards arm tip.

In basal portion of arms, aboral and lateral surface completely covered by white, domed and round plate-shaped external ossicles, ca. 90–105 μm long, and brown, flat and round plate-shaped external ossicles, ca. 45–60 μm long ( Fig. 10C ), similar to those on aboral disc. Each arm segment entirely covered by two pairs of brown and white external ossicles forming alternately arranged transverse rows ( Fig. 10C ). Oral surface covered by white, flat and polygonal plate-shaped external ossicles ca. 45–60 μm long ( Fig. 10F ), similar to those on oral surface. In middle portion of arms, the aboral and lateral surface also covered by white and brown external ossicles similarly arranged to those on basal portion of arms, both ca. 60 μm long ( Fig. 11A ). Oral surface covered by white, flat and polygonal external ossicles, similar to those on basal portion of the arms, ca. 45 μm long. The distal aboral and lateral surfaces covered only with white granule-shaped external ossicles, ca. 45 μm long ( Fig. 11B ). No external ossicles on oral surface of distal portion of arms.

First to third tentacle pores lacking arm spines; from fourth pores, two arm spines present ( Fig. 10F ). In first third of arms, arm spines ovoid ( Fig. 10F ) with inner and outer arm spines almost same length, approximately half the length of corresponding arm segment ( Fig. 10F ). In second third of arms, inner arm spines half length of corresponding arm segment with outer arm spines four-fifths length of inner one ( Fig. 11A ) and from first third to midpoint of that, arm spines cylindrical ( Fig. 11A ) and from that midpoint to second third of the arm, arm spines hook-shaped ( Fig. 11A ). In distal third of arms, all arm spines hook-shaped, inner arm spines half length of corresponding arm segment and outer arm spines almost same length as inner ones ( Fig. 11B ).

Colour: Aboral surface of disc white with brown spots scattered between white ones at regular intervals ( Fig 10A ). Arms banded from basal to middle portion of arms on aboral and lateral surfaces, ( Figs. 10C , 11A ). Distal portion of aboral arms ( Fig. 11B ) and whole oral surface uniformly white.

Ossicle morphology of MV F111585. — Disc diameter 3.2 mm, arm length ca. 20 mm.

White and domed plate-shaped external ossicles on aboral surface of middle portion of arms, ca. 80 μm long and 40 μm thick ( Fig. 12A, B ) and white granule-shaped external ossicles on aboral surface of distal portion of arms, ca. 50 μm long and 20 μm thick ( Fig. 12C, D ). Lateral arm plates in middle portion of arms with one or two pairs of a muscle and a nerve opening, and each of them associated with arm spine articulation ( Fig. 12E ).

Vertebrae with oral bridge in distal portion of arm ( Fig. 12F, G ). Arm spines for first third of arms ovoid and minute ( Fig. 12H ) with remaining arm spines hook-shaped with inner teeth and smooth lamina on distal side gradually decreasing in size ( Fig. 12I, J ).

Variation. — This specimen and a syntype of Astroschema koehleri ( Döderlein, 1898) show irregular brown bands on aboral and lateral surface of basal to middle portion of the arms, but 16 specimens from south-western Australia show thicker brown bands every three to five arm segments. This specimen shows an abrupt gap on basal portion of the arms in thickness, but this is not evident in any of the other specimens examined .

Distribution. — INDONESIA: off Ambon Island and off Kei Island, eastern Indonesia, 90–125 m ( Döderlein, 1898; Koehler, 1930); AUSTRALIA: off D’Entrecasteaux National Park, south-western Australia, 95–100 m (present study).

Remarks. — Asteromorpha koehleri was originally described by Döderlein (1898) as a species of the genus Asteroschema . Koehler (1930) described Ophiogelas perplexum as a monotypic genus. Mortensen (1933) transferred O. perplexum to Asteromorpha , synonymising it with A. koehleri in a postscript. Baker (1980) also included A. koehleri in Asteromorpha .

Our comparison of a syntype of Astroschema koehleri with a syntype of Ophiogelas perplexum showed that these species both have alternating transverse rows of white, domed external ossicles and brown, flat external ossicles, both with two pairs of rows in basal portion of the arms. Based on this diagnostic character, we certainly conclude that the latter species ( O. perplexum ) is a junior subjective synonym of A. koehleri as Mortensen (1933) suggested.

Asteromorpha koehleri ( Döderlein, 1898) can be distinguished from the other species of Asteromorpha by the following morphological characters: two types of external ossicles on the aboral body, first, white, domed and round plate-shaped ossicles, and second, brown, flat and polygonal plate-shaped ossicles; the radial shields covered in regularly arranged brown ossicles; on the aboral and lateral surface of the arms transverse rows of white ossicles and brown ossicles alternating; in the basal portion of the arms, two rows of brown ossicles on each arm segment; no tubercles on radial shields; usually six arms and fissiparous ( Table 1).

Both A. rousseaui and A. koehleri have two types of external ossicles on their aboral body. In the basal portion of the arm of aboral and lateral surface, A. koehleri has two transverse rows of brown ossicles while A. rousseaui has three (see also Remarks of A. rousseaui above). Asteromorpha capensis and A. tenax possess only one type of external ossicles on their aboral body.

Of 18 examined specimens of A. koehleri , 17 have six arms and only one has five arms. Twelve of the 17 six-armed specimens show conspicuous fission planes in their discs which suggests that A. koehleri is fissiparous. Asteromorpha tenax is also fissiparous (see also Remarks of A. tenax ), while A. capensis and A. rousseaui are non-fissiparous.

A. koehleri can be distinguished from the A. tenax by having no tubercles on their radial shields (see also Remarks of A. tenax ).

Figures

Fig. 10. Asteromorpha koehleri (MCZ E5864:holotype of Ohphiogelas perplexum): A, aboral disc and basal portion of arms; B, aboral central part of disc; C, aboral periphery part of disc and basal portion of arms; D, oral disc, two parallel oral-most teeth are indicated by arrows; E, lateral interradial part of disc; F, basal portion of oral arm. Abbreviations: AS, arm spine; GS, genital slit; T, teeth; OP, oral papillae.

Fig. 11. Asteromorpha koehleri (MCZ E5864: holotype of Ohphiogelas perplexum): A, lateral middle portion of the arm; B, aboral distal portion of the arm, tiny and scattered external ossicles are indicated by arrows. Abbreviation: AS, arm spine; BrTR, brown transverse row; WTR, white transverse row.

Fig. 12. Asteromorpha koehleri (MCZ E5864: holotype of Ohphiogelas perplexum), SEM photographs of internal ossicles: A, B, plateshaped external ossicles at aboral basal portion of the arm, external (A) and lateral (B) views; C, D, granule-shaped external ossicles at distal portion of the arm, external (C) and lateral (D) views; E, lateral arm plate at middle portion of the arm, external view, muscle openings are indicted by arrows; F, G, vertebrae at distal portion of the arm, oral view (F) and basal view (G); H–J, arm spines from basal portion of the arm (H), middle portion of the arm (I) and distal portion of the arm (J). Arrows indicate orientations (B, D, F): bas, basal side; dis, distal side; ext, external side; int, internal side. Abbreviations: L, lamina; NO, nerve opening; OB, oral bridge.