Scolanthus kopepe, 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 kopepe sp. n. Figs 5, 6A, 7 N–R

Material examined.

Holotype. NSMT-Co 1613, histological sections (5 slides), and tissue for DNA analysis, 26 June 2014, Kopepe Seashore (Fig. 1 A– 3), Chichijima Island, Ogasawara Islands, Tokyo, Japan (27°3'52"N, 142°11'33"E), coral sand at 1 m depth, collected by snorkeling with a shovel and a sieve by Takato Izumi. Paratypes. NSMT-Co 1614, dissected tissues, and prepared nematocysts (5 slides), at same date, place, by same method, and collector as NSMT-Co 1613.; NSMT-Co 1615, prepared nematocysts (5 slides), at same date, place, by same method, and collector as NSMT-Co 1613.; NSMT-Co 1616, histological sections (2 slides), and dissected tissues, at same date, place, by same method, and collector as NSMT-Co 1613; NSMT-Co 1617, whole specimen, at same date, place, by same method, and collector as NSMT-Co 1613; NSMT-Co 1618, histological sections (5 slides) 21 June 2014, Miyanohama coast (Fig. 1 A– 1), Chichijima Island, Ogasawara Islands, Tokyo, Japan (27°6'18"N, 142°11'39"E), coral sand at 7 m depth, collected by scuba diving with a shovel and a sieve by Takato Izumi.

Description.

External anatomy. Column comparatively smooth, ca. 15-25 mm in whole length (25.0 mm in holotype), and 1-2 mm in width (1.8 mm in holotype), naked and extremely long and narrow pipe-like form both in living (Fig. 5A) or fixed specimens. The upper part as narrow as lower part. The most proximal part capitulum, transparent and thin. The remaining part to aboral end of body scapus, with white to pale yellow periderm, and with scattered nemathybome but no papillae. Aboral end a little rounded or tapered, not differentiated from scapus, with nemathybomes (Fig. 5A, I). Tentacles slender, capitated on the tentacle tip, transparent with white patch on each tentacle tip, 1.5-2.0 mm in length, longer than oral disk diameter, but well expanded and contacted. Tentacles 16 in number, in two cycles; eight in inner and eight in outer cycle, same as Edwardsia 's arrangement (Fig. 6A), the inner tentacles shorter than outer ones. Oral disk ca. 1 mm in diameter, white with a brownish red stripe from ventral side to dorsal side. The mouth not swollen.

Internal anatomy. Eight perfect mesenteries, all macrocnemes. Four dorsal and ventral directives, and four lateral mesenteries not-paired with other macrocnemes, arranged in normal Edwardsia pattern (Figs 5E, 6A). All macrocnemes present along whole length of the body, from oral to aboral end, and bearing retractor and parietal muscles. The retractor muscle of lateral mesenteries all ventrally facing (Fig. 6A). Eight tiny microcnemes, without muscles, only in distal most part. Four microcnemes between dorsal directives and dorso-lateral mesenteries, two between dorso- and ventro-lateral mesenteries, and two between ventro-lateral mesenteries and ventral directives, common arrangement in Edwardsiidae . Each tentacle between either exo- or endocoelic. (Fig. 6A). Each retractor muscles pennon-like, diffused, small and weak next to actinopharynx (Fig. 5E) but restricted, comparatively well developed, and limited besides gonads and integrated into them in lower part (Fig. 5F, G). Muscle pennons consisting of approximately 2-5 simple muscular processes (Fig. 4G). Parietal muscles of macrocnemes not very distinct (Fig. 5G). Actinopharynx very short, no distinct siphonoglyph (Fig. 5E). Tentacular circular muscle indistinct (Fig. 5C) and longitudinal muscle ectodermal and distinct (Fig. 5D). Marginal sphincter muscle and basilar muscle absent. Mesoglea generally thin in the whole body, a few micrometers even in body wall (Fig. 5 E–G, I). Nemathybomes, approximately 100 µm in diameter, protrude from the body wall as their diameter far larger than the thickness of mesoglea. Gonads next the retractor muscle, but no mature gametes in specimens we observed (Fig. 5G).

Cnidome. Spirocysts (in tentacles), basitrichs (in all tissues), microbasic b-mastigophores (in actinopharynx, column and filament) (Table 2, Fig. 7N-R; holotype). Basitrichs in tentacle, column and nemathybomes are distinguished into two types by their size.

Distribution.

Chichijima Island, Ogasawara. Known only from the type locality.

Etymology.

Most of the specimens were collected from Kopepe Coast. “Kopepe” is the name of the native people that used to live in the Ogasawara Islands, who had emigrated from the Gilbert Islands, now the Republic of Kiribati. The word " kopepe " is a noun in apposition. Origin of Japanese name: New Japanese name: kopepe -ashinashi-mushimodoki. “Kopepe” is originated from same coast.

Remarks.

This species resembles not only Scolanthus armatus but also S. scamiti Daly & Ljubenkov, 2008, S. triangulus Daly & Ljubenkov, 2008, S. curacaoensis (Pax, 1924), S. nidarosiensis (Carlgren, 1942) and S. callimorphus Gosse, 1853 in terms of having 16 tentacles ( Gosse 1853, Manuel 1981, England 1987, Daly and Ljubenkov 2008). Scolanthus kopepe sp. n. is similar to S. armatus , and both are found around the same island. Scolanthus kopepe sp. n., however, is morphologically distinguishable by several points as below: S. kopepe sp. n. is smaller than S. armatus , one-third to a half in length and one-fifth to one-third in width (the specimen of S. armatus is even far bigger than living S. kopepe sp. n.); S. kopepe sp. n. has brownish red stripe from ventral side to dorsal side on oral disk and white patch on capitated tentacle tip, both features are not present on S. armatus ; the number of muscular processes of both retractor muscles and parietal muscles of S. kopepe sp. n. are far fewer than those of S. armatus (Figs 2G, H, 5E, G; England 1987); moreover, the S. kopepe sp. n. holotype has two types of basitrichs in the tentacles, actinopharynx and nemathybomes while S. armatus has only one type (Table 2). The body of S. kopepe sp. n. is slender and uniform in width (both in living and preserved specimens) while that of S. scamiti is stout and increasing in width toward to the aboral end ( Daly and Ljubenkov 2008). Besides, the basitrichs in the nemathybomes of S. kopepe sp. n. are two types while those of S. scamiti are only one type (Table 2). Scolanthus kopepe sp. n. is 15-25 mm in body length while S. triangulus has a maximum body length of 11 mm ( Daly and Ljubenkov 2008), smaller than S. kopepe sp. n. Furthermore, basitrichs of S. triangulus are over 63 µm ( Daly and Ljubenkov 2008; table 3), larger than both types of basitrichs of S. kopepe sp. n. Basitrichs in the nemathybomes of S. callimorphus are of only one type and are over 60 µm in length ( Manuel 1981, p 265), while S. kopepe sp. n. has two types of basitrichs in the nemathybomes and both of them are less than 60 µm in length. Scolanthus curacaoensis has far larger body, 45 mm in length ( Pax 1924), and has a well-developed, circumscribed retractor muscle and rounded distinct parietal muscle ( Pax 1924; Figs 4, 5) while S. kopepe sp. n. has diffused and undeveloped retractor and indistinct parietal muscle. Scolanthus nidarosiensis lives in the deep sea of a cold region (125-150 m depth of Norway; Carlgren 1942) in contrast to S. kopepe sp. n., which lives in shallow waters in the subtropical region. The retractor muscles of S. nidarosiensis are well developed and muscle processes were obviously branching ( Carlgren 1942; fig. 71) while those of S. kopepe sp. n. are far less developed with simple processes. Moreover, nemathybomes of S. nidarosiensis contain longer basitrichs than the large basitrichs of S. kopepe sp. n., and S. nidarosiensis has only one type of basitrich ( Carlgren 1942) while S. kopepe sp. n. has two types of basitrichs.

Scolanthus kopepe sp. n. usually lives in coral sand, and prefers dark environments under large rocks.