Edwardsianthus smaragdus sp. nov.

Japanese name: emerarudo-mushimodoki-emeginchaku Figs 7E-H, 8

Material examined.

Holotype. CMNH-ZG 09762: histological sections, tissues in paraffin, and prepared nematocysts, collected by SCUBA diving on 31 January 2016, off Shirahama seashore, Amami-Oshima Island, Kagoshima, Japan, 15 m depth, by Daisuke Uyeno.

Description.

External anatomy. Size: preserved specimen ca. 70 mm in whole length, and ca. 15 mm in width, and ca. 100 mm in living specimen. Column: cylinder-like in form, and the middle part swollen to some extent (Fig. 8A, B). The column consisting of capitulum, scapus and quite small physa. The distal-most part of the capitulum whitish transparent in living animals, short, without nemathybomes. Scapus with thick periderm, brownish black in color, and with protruding scattered tiny, dingy grey color nemathybomes in the living specimen (Fig. 8A). Aboral end differentiated small, tapered physa. Tentacles: 20 in number in two cycles: inner tentacles five and outer 15, brilliant green in color and pale purple at the tips, no pattern, comparatively slender, without acrospheres. Inner tentacles ca. 7 mm and outer ones ca. 10-15 mm in length in the living specimen. Mouth: at the center of oral disc, slightly swollen both in living and preserved specimen. Internal anatomy. Mesenterial arrangement: eight perfect mesenteries, all macrocnemes. Four dorsal and ventral directives, and four lateral mesenteries not paired with other macrocnemes, arranged in normal Edwardsia pattern (Fig. 8F). All macrocnemes are present along the whole body length from oral to aboral end and bear distinct retractor and parietal muscles. Twelve tiny microcnemes, without muscles, only confined to distal-most part. Four microcnemes between dorsal directives and dorso-lateral mesenteries, four between dorso-and ventro-lateral mesenteries, and four between ventro-lateral mesenteries and ventral directives. Each tentacle exo- or endocoelic. Retractor muscles: at the mid part of column, weakly developed but distinct, diffused (Fig. 8C), pennon-like, arranged with 50-60 muscular processes, simple or slightly branched. One process nearest to body wall well-branched (Fig. 8C). Parietal muscles indistinct, elongated in direction of mesenteries, consisted of short and slightly branched processes, sparsely, <ten on each side (Fig. 8C). Others: each with one tentacle from each endo- or exocoels. Existence of siphonoglyph unknown because of contracted state of specimen. Tentacular circular muscle endodermal, distinct, and longitudinal muscle ectodermal, both distinct. Mesoglea thickest in body wall and actinopharynx, maximum 400 µm in thickness (Fig. 8F), but far thinner in parietal muscle and tentacles (Fig. 8C-E), and thinnest, <10 µm, in mesenteries. Nemathybomes protruding from mesoglea (Fig. 8H). Marginal sphincter muscle and basilar muscle absent. Gametogenic tissue apart from retractor muscles, distinct (Fig. 8G), with matured oocytes. Cnidom. Basitrichs, spirocysts, microbasic p -mastigophores. See Fig. 7E-H and Table 5 for sizes and distribution.

Etymology.

This species epithet refers to an emerald, a gemstone, and is named so after the bright green coloration of its tentacles. Derivation of the Japanese name is the same as that of the Latin species name.

Remarks.

Edwardsianthus species usually have strongly developed and diffused retractor and parietal muscles (Figs 2F, 4F, 5E, 6E, 9E), but those of Edwardsianthus smaragdus form an exception by their less distinct development (Fig. 8F). This character is clear in addition to its brilliant light green tentacles. Concerning the cnidom, E. smaragdus can be distinguished from E. pudicus and E. gilbertensis by containing two types of basitrichs in its nemathybomes, and from the other three new species of Edwardsianthus by having microbasic p -mastigophores in its actinopharynx (Tables 4, 5).

In the phylogenetic tree (Fig. 10; Suppl. material 1 Fig. S1), E. smaragdus sp. nov. has a far longer branch than the other species, and therefore its phylogenetic position is not stable; the ML bootstrap value was 57, which is comparatively low, and not supported by BI posterior probability; Fig. 10). Nevertheless, it is most probable that E. smaragdus n. sp. belongs to this genus (ML bootstrap value was 79) despite the BI posterior probability not being well-supported. Considering that the morphology of this species corresponds completely with the diagnosis of Edwardsianthus, this species is classified as E. smaragdus .