Halityle regularis Fisher 1913

Mah, Christopher L., 2023, A new species of Astrosarkus from Western Australia including new Mesophotic occurrences of Indian Ocean Oreasteridae (Valvatida, Asteroidea), Memoirs of Museum Victoria 82, pp. 143-165 : 152-156

Halityle regularis Fisher 1913

Figure 7a–g , Figure 8a–f

Halityle regularis Fisher 1913: 211 ; James 1973: 557; Baker and Marsh 1976: 107; Rowe and Gates 1995: 102; Branch et al. 2010: 224; Marsh and Fromont 2020: 422

Culcitaster anamesus H.L. Clark 1914: 145

Diagnosis. Specimens massive, bodies pentagonal to weakly stellate, thickened (R/r=1.18–1.66) with distinct lateral surfaces, abactinal surface with distinctive reticulate pattern. Body surface covered by continuous fine granular cover. Up to 22 superomarginals and 40–50 inferomarginals in each interradius. Actinal surface with distinct rhombic plates with strikingly darkcoloured regions around mouth.Adambulacral plates with furrow spines, 8–11, closely adpressed, flat.Two to three subambulacrals, domed, tips wrinkled. Modified from Baker and Marsh (1976).

Colour ranges from orange to red, maroon or purple with white, yellow to orange papular areas. Actinal surface apricot to pink with adjacent actinal plates orange or violet outlined with orange granules (modified from Marsh and Fromont, 2020). Exceptionally with white to yellow coloration extending over arm tips from actinal surface. Smaller individuals with more mottled variable colouration, with darker irregular plates around the periphery of the abactinal surface.

Comments. Although readily recognisable, relatively little is known about the biology and ecology of H. regularis . Numerous taxa are associated with this species, including parasitic cyclopodid copepods from Madagascar ( Humes, 1971), the symbioticshrimpandpolychaete( Periclimenes and Hololepidella , respectively)in Vietnam (Antokhina and Kritayaev, 2012), pontoniine shrimp in Australia and New Caledonia ( Bruce, 1980, 1983), and parasitic eulimid snails ( Gosliner et al., 1996).

Size changes in Halityle regularis . Several if not all members of the Oreasteridae possess a dramatic shift in body morphology and colour as the individual develops from a relatively small to larger body size. This smaller size is similar to body forms observed in the Goniasteridae , with a more pentagonal to weakly stellate shape (R/r= approximately 1.0), as well as a more flattened abactinal surface with more weakly developed features, such as spines, granules, relative to the strongly arched larger forms. This change has been observed most notably in Culcita species (Döderlein, 1917; Kano et al., 1991) whose adult form is relatively large and strongly arched (approximately 20–30 cm in diameter, 10-20 cm in height) relative to the smaller form (at approximately 0.5–4.0 cm), which is pentagonal in outline with a flattened abactinal surface, displaying few if any of the tubercles, spines or other characters observed in the larger forms. The differences were so pronounced that this smaller form was identified as a separate genus until intermediate sizes were recognised. Other oreasterids with documented changes of this kind include the tropical Atlantic O. reticulatus , which undergoes both a morphological but also colour change ( Hendler et al., 1995) as it approaches a larger size. Although this morphological change is thought to be present throughout the Oreasteridae , size-related data across all genera remains incomplete, especially for those genera with more unusual, large-sized forms, such as Halityle .

USNM 1688944 is one of the smallest of reported Halityle specimens, and was compared with descriptions in Baker and Marsh (1976) as well as with other specimens at R=5.9, 9.1 and 13.0 cm. This specimen was recognised as Halityle based on its distinctive actinal plate pattern as well as the distinctive scalar granules covering the plate surface. It shares other recognisable features such as a consistent number of furrow spines, as well as the enlarged and identical number of subambulacral spines, the intercalated 22opular pores with the superomarginal plates, as well as the marginal plate shape. Nearly all the superomarginal plates, as well as numerous enlarged, strongly convex abactinal plates present on the distal surface of the arm, display pronounced tubercles or short, pointed spines. Inferomarginals also display 1–4 enlarged round tubercles or spines centrally on the plate surface.

Numerous differences between USNM 168894 and the other, larger specimens are apparent. Note, however, that individuals from different areas may also show variation in morphological character development as they increase in size. Perhaps the most distinct difference is the presence of tubercles with spiny tips on distalmost abactinal and superomarginal plates. Tubercles/spines seem to be, at first, distinctly at odds with the morphology of adult specimens, because nearly every detailed description of H. regularis notes the complete absence of spines or similar accessories on the abactinal and marginal plate surfaces. However, careful examination of the sequentially larger specimens, USNM E45474 with R=9.1 and USNM E13719, R=5.9, 6.4, shows very small, low, mound-like tubercles present in the distal and lateral regions on the disk and arms, sitting on the plates between the papular areas. These tubercles appear lower and broader as the animal becomes larger among the Somalian specimens studied herein. Among the larger specimens available (USNM 40867, no data) and the holotype (USNM 32634, which have R>13.0 cm, there appear to be minute, weakly expressed rugosities in these areas. This implies that these more acutely pointed tubercles are covered over by the granular cover or the plates are expanded as the animal grows. Prior accounts, such as Fisher (1919), have not mentioned these rugose projections, likely owing to their small size and relatively nondescript appearance consistent with the granular surface. The spine-like tubercles on the superomarginal plates appear to be displaced to a location above the contact between superomarginal plates in each interradius. Curiously, although abactinal and superomarginal tubercle/spines appear to be compensated for on larger specimens, these structures do not show relictual presence on the inferomarginal plates.

Pedicellariae were not observed in USNM 1688944 but are present in specimens with R>5.9 on the adambulacral plates, with descriptions mentioning further pedicellariae in large specimens, suggesting they emerge in larger individuals. Papular regions show an increase in the number of papular pores between the specimen showing R=4.5 and r=5.9. These areas become more triangular and better developed in larger individuals. The substantial changes to body shape occur between R=4.5 and R=5.9: the disk begins developing the strong arched convex shape, arms become more lateral facing, and the reticulate pattern in the adult forms takes on its more distinct appearance.

USNM 1688944 is otherwise consistent with prior descriptions of this species (Baker and Marsh, 1976). This includes a similar granular covering, rhombic actinal plates, a consistent number of furrow spines (8–11), domed subambulacral spines (two to three), and identical pedicellariae.

Occurrence. Widely distributed throughout the Indo-Pacific. Southern Japan, Enewetak Atoll , New Caledonia, the Philippines, Lembeh Strait , Indonesia, Vietnam, the Lakshadweep Archipelago , southern India, east Africa , Madagascar; Ningaloo Reef , Exmouth Gulf , North West Shelf , Western Australia ; Keppel Bay and Heron Island, Queensland. 3–275 m.

Material examined. USNM E13719 SW of Gas Jinnah, Somalia, Indian Ocean. 9.68° N, 51.05° E, 60– 70 m. Coll . R / V Anton Bruun , 16 Dec 1964. 2 dry specs . R=5.9, r=3.7; R=6.4 r=3.9.

USNM E45470 Off NE coast, Somalia, Indian Ocean. 10.3843° N, 51.2517° E, 26– 37 m. Coll . R / V Anton Bruun, 8 Jan 1987.1 dry spec . R=13.0 r=8.0.

USNM E45474 Off NE coast, Somalia, Indian Ocean. 10.3843° N, 51.2517° E, 40– 49 m. Coll . R / V Anton Bruun, 8 Feb 1987. 1 dry spec . R=9.1, r=5.5.

USNM 168894 Balut Island , Philippines, North Pacific Ocean. 50–150 m. 1 dry spec . R=4.5, r=2.5.

Figures

Figure 7. Halityle regularis USNM 1688944, Philippines, small individual. a, Abactinal view. Scale bar=0.5 cm; b, Close-up on armtips showing enlarged distal and superomarginal plates. Scale bar=0.2 cm; c, Close-up on abactinal-superomarginal contact showing spiny tubercles on superomarginals. Scale bar=0.2 cm; d, Lateral view showing spiny tubercles and large spines on superomarginal, inferomarginal plates. Scale bar=0.2 cm; e, Inferomarginal and superomarginal plates. Scale bar=0.2 cm; f, Actinal view. Scale bar=0.5 cm; g, Closeup oral region, adambulacral furrow. Scale bar=0.2 cm.

Figure 8. Halityle regularis USNM E45474, Somalia, larger individual. a, Abactinal view. Scale bar=1.5 cm. b, Closeup of armtip showing low tubercles on distal surface. Scale bar=0.8 cm; c, Lateral view showing superomarginal plates and low tubercles. Scale bar=0.5cm; d, Lateral view of armtip showing marginal plates, inferomarginal, superomarginal surface. Scale bar=0.5 cm; e, Actinal view. Scale bar=1.5 cm; f, Closeup of oral and adambulacral furrow. Scale bar=0.5 cm.