Anthomastus nanhaiensis, Li & Xu, 2023

Li, Yang & Xu, Kuidong, 2023, Anthomastus nanhaiensis, new species, and Bathyalcyon robustum Versluys, 1906, two mushroom soft corals (Octocorallia: Coralliidae) from Zhenbei Seamount in the South China Sea, Raffles Bulletin of Zoology 71, pp. 669-680 : 670-675

Anthomastus nanhaiensis , new species

( Figs. 2‒5 )

Material examined. Holotype: MBM286430 , station FXDive 310, Zhenbei Seamount , South China Sea (15°03.69′N, 116°33.03′E), 407 m, 22 July 2022.

Diagnosis. Anthomastus with capitate-shaped colony divided into a spherical capitulum and an inconspicuous stalk. Polyps dimorphic. Autozooids sterile, large, retractile, 92 in number. Siphonozooids fertile, minute, scattered among autozooids and forming a continuous layer. Sclerites including rods, platelets, highly tuberculated double spheroids, clubs and spindles. Anthocodial wall devoid of sclerites.

Description

Colony form and size. In life, animal attached to stone ( Fig. 2A ). Colony capitate, 50 mm long, stiff in ethanol preservation ( Fig. 2C, D ). Stalk short, about 20 mm high and 59 × 30 mm wide, emerging from a holdfast. Capitulum projecting from stalk, almost spherical, 46 × 34 mm in width and 30 mm high, occupying 60% of total colony length, and bearing 92 autozooids.

Polyps. Polyps dimorphic. Autozooids sterile, arranged evenly over capitulum, and mostly not retracted into capitulum, leaving tentacles and sometimes neck zone of anthocodia outside capitulum surface ( Fig. 2 ). Anthocodia outside capitulum up to 12 mm long and 3 mm wide, neck zone 2 mm wide, and anthostele flat and 3 mm wide. Tentacles up to 5 mm long with mostly 25–30 pairs of pinnules. Siphonozooids fertile (oocytes 0.25–0.45 mm in diameter), invisible to the naked eye, numerous, scattered among autozooids and forming a continuous layer, measuring about 0.2 mm wide ( Fig. 2E ). Adjacent siphonozooids interconnected beneath 0.6–0.7 mm of capitulum surface, indicated as white lines in longitudinal section ( Fig. 2E ).

Sclerites. Sclerites of tentacle mostly tuberculate rods usually with a twist, ranging 0.10–0.19 mm long; occasionally clubs and irregular crosses ( Fig. 3A ). Sclerites from uppermost of anthocodial wall same to that of tentacle, tuberculate rods mostly 0.12–0.19 mm long; these sclerites not arranged “en chevron”, and crown not developed ( Figs. 1B , 2B ). Sclerites absent from neck zone of anthocodial wall. Pharyngeal sclerites predominately platelets, mostly ranging around 0.05–0.08 mm long; fewer crosses derived from platelets, ranging 0.04–0.07 mm long ( Fig. 3C ). Sclerites of capitulum surface typically highly tuberculated double spheroids, ranging 0.10–0.15 mm long; highly tuberculated clubs, ranging 0.16–0.26 mm long; highly tuberculated spindles, ranging 0.20–0.46 mm long ( Fig. 4A ). Sclerites of capitulum interior mostly tuberculate spindles, ranging 0.21–0.52 mm long; fewer tuberculate rods, double stars and tuberculate clubs ( Fig. 4B ). Sclerites from stalk surface same as those from capitulum surface, tuberculate double spheroids ranging 0.10–0.18 mm long; tuberculate clubs ranging 0.18–0.26 mm long; tuberculate spindles ranging around 0.22–0.35 mm long ( Fig. 5A ). Sclerites from stalk interior mostly tuberculate spindles ranging around 0.32–0.44 mm long, fewer tuberculate double spheroids, and occasionally tuberculate clubs and crosses ( Fig. 5B ).

Colour. Stalk and capitulum pink both in situ and in ethanol. Expanded anthocodia pinkish to nearly transparent in situ; upper anthocodia and pharynx red, and neck white in ethanol. Sclerites pinkish or transparent under transmitted light.

Etymology. The specific name nanhaiensis refers in Chinese to the South China Sea, the type locality of the species.

Distribution and habitat. Known only from the type locality, where the water depth was 407 m and water temperature was 11.10°C. In the field, the species was attached to a small rock.

Remarks. Anthomastus nanhaiensis , new species, matches well with the definition of Anthomastus Verrill, 1878 by having a hemispherical colony with dome-shaped capitulum and inconspicuous stalk, platelets in pharynx, and predominately rods in tentacles. The new species is characterised by highly tuberculated double spheroids, clubs and spindles in the capitulum and stalk. These features make it resemble an unnamed species of the genus, Anthomastus (or Pseudoanthomastus ) n. sp. 1 described from New Caledonia by d’Hondt & d’Hondt (2018). However, the two species can be distinguished by the sclerites of tentacles and stalk surface: the sclerites from tentacles of A. nanhaiensis are slightly tuberculated and sometimes flat rods, while those from autozooids and tentacles of Anthomastus (or Pseudoanthomastus ) n. sp. 1 are mainly elongated and highly tuberculated double spheroids ( d’Hondt & d’Hondt, 2018: Fig. 62); the sclerites from stalk surface of A. nanhaiensis are more tuberculated than those of Anthomastus (or Pseudoanthomastus ) n. sp. 1 ( d’Hondt & d’Hondt, 2018: Fig. 57).

Anthomastus nanhaiensis is the first species of Anthomastus Verrill, 1878 recorded in the South China Sea, and the second one known from the northwestern Pacific after A. muscarioides Kükenthal, 1910 was reported from Japanese waters. Morphologically, A. nanhaiensis is distinct from A. muscarioides by platelets in pharynx (vs. rodlets), characteristic double spheroids in capitulum and stalk (vs. absence), and the absence of sclerites in anthocodial wall (vs. spindles) ( Kükenthal, 1910; d’Hondt & d’Hondt, 2020).

Figures

Fig. 2. Morphology of the holotype of Anthomastus nanhaiensis, new species. A, the animal in situ; B, an autozooid; C, the colony in top view; D, the colony in lateral view; E, the longitudinal section of the colony, showing large cavities of autozooids (au) and small cavities of siphonozooids (arrows). Scale bars = 1 mm (B), 10 mm (C‒E).

Fig. 3. Sclerites of Anthomastus nanhaiensis, new species. A, sclerites from autozooid tentacle tip; B, sclerites from tentacle base; C, sclerites from pharynx. Scale bars = 0.10 mm (A, B), and 0.05 mm (C).

Fig. 4. Sclerites of Anthomastus nanhaiensis, new species. A, sclerites from surface of capitulum; B, sclerites from interior of capitulum. Scale bars = 0.10 mm.

Fig. 5. Sclerites of Anthomastus nanhaiensis, new species. A, sclerites from surface of stalk; B, sclerites from interior of stalk. Scale bars = 0.10 mm.

Fig. 1. Distribution map of Anthomastus spp. and Bathyalcyon robustum.