Scolanthus ena, Izumi, Takato & Fujita, Toshihiko, 2018

Izumi, Takato & Fujita, Toshihiko, 2018, Description of three new species of Scolanthus (Cnidaria, Anthozoa, Actiniaria, Edwardsiidae): first records of the genus from Japan, ZooKeys 794, pp. 1-21 : 1

Scolanthus ena sp. n. Figs 3, 6B, 7 F–I

Material examined.

Holotype. NSMT-Co 1610. One specimen cut into several parts, histological sections (23 slides) and prepared nematocysts (5 slides), 17 May, 2014, Ena Bay (Fig. 1 B– 1), Kanagawa, Japan, mud in the intertidal zone, collected by wading with a shovel, by Masanori Taru.

Description.

External anatomy. Column rough, rugged and uneven, ca. 80 mm in whole length in holotype, and 10-15 mm in width, pipe-like in form both in living (Fig. 3A) and fixed specimen. The most upper part narrower to some extent. The most proximal part of column capitulum, dark brownish semitransparent, and the remaining part to aboral end scapus. The periderm of column orange, with no pattern in color, but thinner on the mesenteries so that the mesenterial line visible through the body wall. Scapus with scattered nemathybomes but no papillae. Aboral end rounded, not differentiated from scapus, with nemathybome (Fig. 3A, H). No pedal disk, but no physa or physa-like structure. Tentacles slender, no acrosphere, brownish, semi-transparent with white patch on each surface (Fig. 3A). Tentacles 20 in number, in two cycles; ten in inner and ten in outer cycle (Fig. 6B), 7.0-10.0 mm in length, longer than oral disk diameter and the inner tentacles shorter than outer ones. Oral disk ca. 5.0 mm in diameter. The mouth swelled and dome-like.

Internal anatomy. Eight perfect mesenteries, all macrocnemes. Four dorsal and ventral directives, and four lateral mesenteries not-paired with other macrocnemes (Figs 3E, 6B). All macrocnemes present along whole length of the body, from oral to aboral end and bearing distinct retractor and parietal muscles. The retractor muscle of lateral mesenteries all ventrally facing (Fig. 6B). Twelve tiny microcnemes, without muscles, confirmed only in 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 (Fig. 6B), an unusual arrangement for Edwardsiidae . Each tentacle between either exo- or endocoelic (Fig. 6B). Each retractor muscle pennon-like, restricted throughout the whole body (Fig. 3E, F), comparatively smaller next to actinopharynx but largely developed in lower part, limited in the part next to actinopharynx or filaments of each macrocneme (Fig. 3E, F). Muscle pennons consisting of approximately 30-60 muscular processes, some of which are well-branched into 10 or more branches (Fig. 3F). Parietal muscles with approximately 15 branched muscular processes (Fig. 3F). Actinopharynx short, no distinct siphonoglyph (Fig. 3E). Tentacular circular muscle endodermal (Fig. 3D) and longitudinal muscle ectodermal (Fig. 3C), both distinct. Mesoglea thickest in the aboral end, thick in body wall, approximately 70-120µm thick (Fig. 3B, F, H). However, mesoglea far thinner in actinopharynx and thinnest in mesenteries (Fig. 3E, F). Nemathybomes, around 200 µm in diameter, half buried into mesoglea on the column including the aboral end (Fig. 3G). Marginal sphincter muscle and basilar muscle absent (Fig. 3B, H). Gonads next the retractor muscle, comparatively long (Fig. 3F). Testes in gonads of holotype, between filament and retractor muscle.

Cnidome. Spirocysts (in tentacles), basitrichs (in every tissue), microbasic b-mastigophores (in filament) and microbasic p-mastigophores (in actinopharynx, and filament) (Table 2, Figs 7 F–I). Basitrichs in actinopharynx and nemathybome are distinguished into two types by their size. No nematocysts in body wall.

Distribution.

Ena Bay, Kanagawa. Known only from the type locality.

Etymology.

The species epithet is named after the type locality, Ena Bay. The word " ena " is a noun in apposition. Origin of Japanese name: new Japanese name: taru-ashinashi-mushimodoki. “Taru” is the name of the collector of this new species.

Remarks.

Scolanthus ena sp. n. has 20 tentacles, as do Scolanthus ignotus (Carlgren, 1920) and S. isei sp. n.: other edwardsiid species have 16 tentacles ( England 1987, Daly and Ljubenkov 2008, and this study). Small and large types of basitrichs in nemathybomes of S. ena are far smaller and far larger, respectively, than basitrichs in nemathybomes of S. ignotus ( Carlgren 1920, England 1987). Moreover, S. ena sp. n. is 80 mm in body length, approximately three to four times longer than the 20-30 mm of S. ignotus . Scolanthus ena sp. n. is different from S. isei sp. n. in its tentacular arrangement (Fig. 6B, C), structure of column surface (periderm of S. ena sp. n. does not have trichome-like structures [Fig. 4A] unlike S. isei sp. n.; the nemathybomes of S. ena sp. n. are far more sparse than those of S. isei sp. n.), body size ( S. ena sp. nov. is far bigger than S. isei sp. n.), and cnidome (only S. ena sp. n. has microbasic b-mastigophores in their filaments) (see Table 2). In addition, S. isei sp. n. lives in cavities of bare rocks, a different habitat compared to that of S. ena sp. n. (see Remarks of S. isei ).

This species is one of the biggest species in the genus Scolanthus : all previously reported species of nominal Scolanthus have bodies less than 80 mm in length ( Gosse 1853, McMurrich 1893, Carlgren 1920, Carlgren 1921, Pax 1924, Carlgren 1931, Carlgren 1942, Daly and Ljubenkov 2008).

Despite several sample collection surveys at Ena Bay, S. ena sp. n. was collected only once, and no specimens have been collected from any other locality. It is said by local people that the environment of Ena Bay has changed from several decades ago; the bottom of bay was previously rocky, and a muddy flat has formed in recent years by inflow of sediment. Considering some Scolanthus live in rocky habitats compared to other edwardsiids (e.g. S. isei sp. n.), the primary habitat of S. ena sp. n. might be rocky, and perhaps the numbers of individuals have decreased in Ena Bay by recent rapid changes in the environment. It is difficult, however, to examine this hypothesis because Edwardsiidae sea anemones living in or between rocks often cannot be collected easily even if there are many individuals present.

Even though there is only one specimen of S. ena , the character differences from other Scolanthus species make it obvious that this specimen is not a formerly described Scolanthus species. Examination of additional specimens in the future may help better delineate this species.