Vitrumanthus oligomyarius (Wassilieff, 1908)

Kise, Hiroki, Montenegro, Javier, Santos, Maria E. A., Hoeksema, Bert W., Ekins, Merrick, Ise, Yuji, Higashiji, Takuo, Fernandez-Silva, Iria & Reimer, James D., 2022, Evolution and phylogeny of glass-sponge-associated zoantharians, with a description of two new genera and three new species, Zoological Journal of the Linnean Society 194, pp. 323-347 : 341

VITRUMANTHUS OLIGOMYARIUS ( WASSILIEFF, 1908) COMB. NOV.

( FIG. 8A–G )

Basionym: Gemmaria oligomyaria Wassilieff, 1908: 47 , fig. 29; taf. I, fig. 29.

Material examined: CMNH ZG-4785, off Katsuura, Chiba, Japan, 34°50′N –35°00′N, 140°20′W –140°30′W, 390, vertical long line fishing, coll. A. Tamura on vessel Kiyo-maru, 19 Jan 2006, divided into two pieces, one portion fixed in 5–10% saltwater formalin and other in 99.5% ethanol.

Description: External morphology. Circa> 300 cylindrical polyps. Solitary polyps arise from Tretochone duplicata ( Topsent, 1928) in preserved specimen. Preserved polyps dark-yellow in coloration and trapezoid when opened. Polyps located all over the three-dimensional structured hexactinellid sponge body. Surface of column smooth, and ectoderm continuous. Ectoderm of polyps partially encrusted with small sized sand and silica particles (c. <0.1 mm). The transparent capitulum contracted and rounded. Contracted preserved polyps 0.5–3.1 mm in height, 1.2– 3.4 mm in diameter. Capitulary ridges indiscernible when contracted. Tentacles 32–36 in number.

Internal morphology: Zooxanthellae absent. Cyclically transitional marginal musculature from endoderm to mesogleal, and lacunae confined toward endoderm proximally. Encircling sinus or mesogleal canal usually imperceptible and basal canals of mesenteries absent. Mesenteries thin, 32–36 in number, in brachycnemic arrangement. Mesoglea thickness 0.7–1.0 mm. Mesoglea thicker than endoderm but thinner than ectoderm in the body wall. Siphonoglyph distinct and U-shaped. Mesenterial filaments present.

Cnidae: Basitrichs and microbasic b-mastigophores, microbasic p-mastigophores, holotrichs and spirocysts ( Fig. 5D ; Table 2 ).

Distribution and habitats: Pacific coast of Japan: Suruga Bay, Shizuoka and off Katsuura, Chiba at depths of <390 m.

Associated host: Tretochone duplicata ( Topsent, 1928) .

Remarks: The morphological characteristics of Vitrumanthus oligomyarius collected in this study are identical to those of the original description by Wassilieff (1908). The musculature of the sphincter of the examined specimen is in a cyclically transitional arrangement containing several mesogleal lacunae; identical musculature was also mentioned by Wassilieff (1908), Moreover, the examined specimen by Wassilieff (1908) and this study both have brachycnemic mesenterial arrangements, with incomplete mesenteries in the fifth mesenterial pair from the dorsal directive, a diagnostic characteristic of the suborder Brachycnemina . This finding is unusual as V. oligomyarius is clearly phylogenetically placed in the suborder Macrocnemina , which have complete fifth mesentery pairs from the dorsal directive. On the other hand, the other morphological characteristics of V. oligomyarius are similar to those of other macrocnemic species. It should be noted a similar case has been reported in the past. Parazoanthus douglasi Haddon & Shackleton, 1891b , which likely belongs to the genus Hydrozoanthus Sinniger et al., 2010 ( Reimer & Sinniger, 2021), also has a brachycnemic mesenterial arrangement, while its other characteristics, such as being epizoic on hydroids and its marginal musculature, are similar to other macrocnemic species. Vitrumanthus oligomyarius can be easily distinguished from other Vitrumanthus species by the numbers of tentacles and its unique mesenterial arrangement. This study reports on the existence of this species for the first time since its original description. The Japanese name is 'Subesube-ruri-sunaginchaku'.

Figures

Figure 5. Cnidae in the tentacles, column, actinopharynx and mesenterial filaments of holotypes of new species in this study. A, cnidae of Churabana kuroshioae; B, cnidae of Vitrumanthus schrieri; C, cnidae of Vitrumanthus vanderlandi; D, cnidae of Vitrumanthus oligomyarius. Abbreviations: Hl, holotrichs large; Hm, holotrichs medium; Hs, holotrich small; O, basitrichs and microbasic b-mastigophores; Pm, microbasic p-mastigophores; S, spirocysts.

Figure 8. Images of external and internal morphology of Vitrumanthus oligomyarius (CMNH ZG-4785). A, preserved polyps on Tretochone duplicata; B, C, cross-section of polyp; D, longitudinal section of polyp; E, F, close-up images of cyclically transitional marginal musculature; G, close-up image of tentacle musculature. Abbreviations: A, actinopharynx; Dd, dorsal directives; Ctmm, cyclically transitional marginal musculature; Ec, ectoderm; M, mesoglea; Mm, marginal musculature; S, siphonoglyph; O, oral disk; 5th, fifth mesentery from dorsal directives. Scale bars: 5 mm (A), 1.5 mm (B, C), 0.5 mm (D, E), 0.1 mm (F), 0.25 mm (G).