Edwardsiidae with body divisible into scapus and capitulum. Proximal part of body rounded, provided with nemathybomes and never forming physa. Nemathybomes scattered or forming longitudinal lines on scapus. At least eight microcnemes. Tentacle typically 16 to 20 in adults, arranged hexamerously, octomerously or decamerously. Tentacles on inner cycle shorter than those on outer cycle. Retractor muscles relatively large, well developed, and diffused, restricted or circumscribed. Parietal muscles distinct, symmetrical, well developed. Cnidome; spirocysts, basitrichs, microbasic b- and p-mastigophores (revised from Daly and Ljubenkov 2008).

Scolanthus callimorphus Gosse, 1853 by monotypy.

New Japanese name: Ashinashi-mushimodoki-ginchaku-zoku. This new Japanese name is constructed from “ashi-nashi” (which means no-foot) and “mushimodoki-ginchaku” (which means worm-like, the Japanese name for edwardsiids). “Ashi-nashi” is named after the most characteristic feature of this genus; no differentiated physa from scapus.

The genus Scolanthus currently contains seven valid species (Fautin 2013) not including new species in the current study, and there also are two more species once accommodated within Isoedwardsia, which was synonymized to Scolanthus in Manuel (1981). This genus is widely distributed, from tropical (S. armatus [Carlgren, 1931]) to subarctic regions (S. nidarosiensis [Carlgren, 1942]). No Scolanthus species, however, have previously been collected from Japan. In this study, Scolanthus armatus and three new species of Scolanthus are reported from Japan, representing the first records of this genus from Japan. Consequently, the number of Scolanthus species is now 12.

NSMT-Co 1609, histological sections (7 slides), dissected tissues, tissues embedded in paraffin, and prepared nematocysts (6 slides), 27 June 2014, Seihyo Coast (Fig. 1A–2), Chichijima Island, Ogasawara Islands, Tokyo, Japan (27°09'47"N, 142°20'26"E), coral sand, 3 m depth, collected by scuba diving with a shovel and a sieve, by Takato Izumi.

External anatomy. Column rough, ca. 40 mm in whole length, and ca. 5 mm in width, worm-like form, and the proximal part narrower to some extent. The column consists of capitulum, scapulus and scapus. The most proximal part of column capitulum, distinct, extremely short, whitish and semitransparent, but scapulus and scapus indistinct. The periderm-like cuticle, brownish orange with no pattern in color, covering the whole column except capitulum and tentacle but easily stripped off from epidermis (Fig. 2A). The scapus beneath periderm semitransparent, with scattered small prominent nemathybomes but no papillae (Fig. 2A). Aboral end of the column tapered or flattened, not differentiated from scapus, with scattered nemathybomes (Fig. 2, A and 2I). No pedal disk, and no physa or physa-like structure. Tentacles in two cycles, 16 in number, eight in inner and eight in outer cycle (Fig. 6A). All tentacles long and slender, 1.5–2.0 mm in length, the inner tentacles as long as outer ones, transparent or semi-transparent, and capitated on their tip (Fig. 2B). Oral disk ca. 1.5 mm in diameter.

Figure 2. 

External and internal views of Scolanthus armatus (NSMT-Co 1609). External views (A, B) and internal histological sections (C–I). A Whole living specimen of S. armatus. The periderm of aboral end was stripped off while the sampling B enlarged view of most distal part C longitudinal section of oral end D longitudinal section of a tentacle E transverse section of a tentacle F transverse section of actinopharynx of the longitudinal half of body G transverse section of mesentery H transverse section of filaments I longitudinal section of aboral end. Nemathybomes distributed up to the tip of aboral end. Abbreviations: a, actinopharynx; Ne, nemathybome; pm, parietal muscle; rm, retractor muscle; Te, tentacle; tlm, tentacular longitudinal muscle; Ts, testis. Scale bars: 5 mm (A); 1 mm (B); 500 µm (C, F, H, I); 100 µm (D, E, G).

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 (Fig. 6A). 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. 6A). Eight tiny microcnemes, without muscles, confined 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. Each tentacle between either exo- or endocoelic. (Fig. 6A). Retractor muscles strongly developed and diffused (Fig. 2F-H), pennon-like, configured with 15–30 muscular processes, each slightly branched (Fig. 2F). Parietal muscles with approximately 10 muscular processes (Fig. 2F). Actinopharynx short, ca. 2.5 mm in length, no distinct siphonoglyph (Fig. 2C). Tentacular circular muscle indistinct (Fig. 2D) and longitudinal muscle ectodermal and distinct (Fig. 2E). Mesoglea thin in the whole body, less than 100 µm even at the thickest part of body wall (Fig. 2C–I). Nemathybomes, ca. 100 µm in diameter, protrude from mesoglea on the column including the aboral end (Fig. 2I). Marginal sphincter muscle and basilar muscle absent (Fig. 2C, H). Gonads adjacent to the retractor muscle, relatively long (Fig. 2H). Testes between filament and retractor muscle, but no mature gametes in this specimen.

Cnidome. Basitrichs (in all tissues), spirocysts (in tentacles), microbasic b-mastigophores (in filaments) (Table 2, Fig. 7A–E). Basitrichs in filaments are distinguished into two types by their size.

Fiji (Carlgren 1931: type locality), Australia, Singapore (England 1987), and Japan (this study).

New Japanese name: Ogasawara-ashinashi-mushimodoki. “Ogasawara” is the locality name. In Japanese waters, this species has been collected only in the Ogasawara Islands. “Ashinashi-mushimodoki” is short for the Japanese name of this genus (see the etymology of genus).

Scolanthus armatus was originally described by Carlgren (1931) as Edwardsia armata when the genus Scolanthus was a junior synonym of Edwardsia. After Scolanthus was revived by Manuel (1981), this species was transferred to Scolanthus by England (1987). This species had no physa-like structure but many nemathybomes in the aboral end. This is the most characteristic feature of Scolanthus, and this feature is not found in Edwardsia. The specimen from the Ogasawara (Bonin) Islands almost completely agrees with the description of Scolanthus armatus in England (1987); e.g. 16 tentacles which are capitated on the tip; rounded or flattened aboral end; scattered nemathybomes extending to the proximal end; strong and diffused retractor muscle (slightly branched muscular processes also correspond to England, 1987; fig. 13). The proportion and size of body is also similar to England’s description. There are, however, a few differences in the cnidome; England (1987) mentioned nothing about b-mastigophores in the description; stating that basitrichs and microbasic b-mastigophores could be distinguished by both the large diameter of the capsule and the broadened shaft shape (England 1991). However, both cnidomes are still easily confused and they are difficult to delineate. Thus, microbasic b-mastigophores with their broadened shape were judged by England (1987) to probably be basitrichs. This probability is reinforced by England (1987: table 6): two types of “basitrichs” in filament of S. armatus, but one type of basitrich with apparently broader capsules than the other type while the lengths are not different. In addition, there are very long basitrichs in our specimen, but they are few in number. If the numbers of these long basitrichs are very low, it is possible that England (1987) did not observe them. Moreover, the other cnidae size ranges resemble those of specimens of England (1987).

In conclusion, we identified this specimen as S. armatus because of its similarity in almost all morphological features to the original description of the species. The slight difference observed in the cnidome may be simply individual variation.

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. 1B–1), Kanagawa, Japan, mud in the intertidal zone, collected by wading with a shovel, by Masanori Taru.

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 7F–I). Basitrichs in actinopharynx and nemathybome are distinguished into two types by their size. No nematocysts in body wall.

Figure 3. 

External and internal views of Scolanthus ena sp. n. (NSMT-Co 1610). A External view Whole living specimen of S. ena B–H internal view B longitudinal section of distal end C transverse section of tentacle D longitudinal section of tentacle E transverse section of actinopharynx F enlarged view of mesentery G transverse section of nemathybome H longitudinal section of aboral end. Nemathybomes distributed up to aboral end. Abbreviations: a, actinopharynx; Ne, nemathybome; pm, parietal muscle; rm, retractor muscle; tcm, tentacular circular muscle; Te, tentacle; tlm, tentacular longitudinal muscle; Ts, testis. Scale bars: 5 mm (A); 1 mm (B); 500 µm (E, F, H); 100 µm (C, D, G).

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

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.

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.

Holotype.NSMT-Co 1611. One specimen cut into several parts, histological sections (5 slides) and prepared nematocysts (5 slides), on August 1, 2014, Sugashima Island (Fig. 1B–2), Mie, Japan (34°29'4"N, 136°52'31"E), cavity of a rock at a depth around 50 cm at low tide, collected by snorkeling by hand, by Yuji Ise. Paratype. NSMT-Co 1612. Histological sections (5 slides), damaged slightly when collected, on August 4, 2014, Sugashima, Mie, Japan (34°28'51"N, 136°52'46"E), cavity of a rock at a depth around 30 cm at low tide, collected by hand, by Yuji Ise.

External anatomy. Column rough, rugged and uneven, ca. 30 mm in whole length in fixed holotype, and 10–12 mm in width, truncated cone-like form both in living and fixed (Fig. 4A) specimen, comparatively tubby form for edwardsiids. Paratype a little small, ca. 18 mm in length and ca. 9 mm in width. Upper part narrower than lower part. No apparent capitulum, all parts of column uniformly scapus. Periderm brownish or whitish, no pattern in color, with trichome-like structure (Fig. 4A), and easily stripped. Column with highly densely scattered nemathybome but no papillae, and the surface on the mesenteries slightly sunken (Fig. 4A). Aboral end rounded, not differentiated from scapus, with nemathybome. No pedal disk, but no physa or physa-like structure (Fig. 4A, G). Tentacles slender, no acrosphere, completely transparent and white patches or stripes on each surface. Tentacles 20 in number, in two cycles; eight in inner and twelve in outer cycle (Figs 4B, 6C), 5.0–7.0 mm in length, longer than oral disk diameter and the inner tentacles shorter than outer ones. Oral disk ca. 4.0 mm in diameter. Mouth not swollen.

Internal anatomy. Eight perfect mesenteries, all macrocnemes. Four dorsal and ventral directives, and four lateral mesenteries not paired with other macrocnemes (Fig. 6C). 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. 6C). Twelve tiny microcnemes, without muscles, confined 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, in unusual arrangement for Edwardsiidae. One tentacle each between exocoels and endocoels (Fig. 6C). Retractor muscles pennon-like, diffused throughout the whole body, smaller next to the actinopharynx (Fig. 4F), but largely developed and almost integrated to gonads in lower part (Fig. 4G). Each muscle pennons consisting of approximately 20–30 single or slightly branched muscular processes (Fig. 4F, G). Parietal muscles with approximately 15–20 muscular processes (Fig. 4G). Actinopharynx short, no distinct siphonoglyphs (Fig. 4F). Both tentacular circular muscle and longitudinal muscle too weakly developed to observe (Fig. 4C, D). Mesoglea thickest in the body wall and aboral end, approximately 200–300 and in some parts over 500 µm thick. However, mesoglea far thinner in actinopharynx and mesenteries (Fig. 4E, F, G), and thinnest in tentacles (Fig. 4C, D). Nemathybomes, around 150 µm in diameter, protruded from body wall (Fig. 4I) in the column but a little buried into the mesoglea in the aboral end (Fig. 4G, J). Marginal sphincter muscle and basilar muscle absent (Fig. 4E, G). Gonads next to retractor muscle, short, and wide (Fig. 4G). Ovary between retractor muscle and filament, and oocytes in gonads of holotype.

Cnidome. Spirocysts (in tentacles), basitrichs (in all tissues), microbasic b-mastigophores (in actinopharynx) and microbasic p-mastigophores (in filament) (Table 2, Fig. 7J–M). Basitrichs in tentacles, nemathybomes and filaments are distinguished into two types by their size. No nematocysts in body wall.

Figure 4. 

External and internal views of Scolanthus isei sp. n. (NSMT-Co 1611). A, B External view A whole preserved specimen of S. isei B view of tentacular circle of living specimen C–J internal view (histological section) C longitudinal section of tentacle D transverse section of tentacle E longitudinal section of oral end F transverse section of actinopharynx (half of body) G enlarged view of mesentery H enlarged view of gonad. Several matured oocytes contained I densely distributed nemathybomes J enlarged view of transverse section of nemathybome. Abbreviations: a, actinopharynx; Ne, nemathybome; Oo, oocyte; Ov, ovary; pm, parietal muscle; rm, retractor muscle; Te, tentacle; TP, trichome-like structure on periderm. Scale bars: 5 mm (A, B); 500 µm (E, F, G, I); 100 µm(C, D, H, J).

Southwest coast of Sugashima Island, Mie. Known only from the type locality.

The species name was named after Yuji Ise, the collector of both holotype and paratype specimens. Origin of Japanese name: New Japanese name: sugashima-gareba-ashinashi-mushimodoki; “gareba” means rocky seashore, the habitat where this species inhabits.

In terms of having 20 tentacles, Scolanthus isei sp. n. resembles S. ignotus and S. ena sp. n., while all other edwardsiid species have 16 tentacles (England 1987, Daly and Ljubenkov 2008, and this study). This species is different from S. ignotus in having two types of basitrichs of different sizes in nemathybomes (Carlgren 1920), and the larger type is far bigger than the basitrichs of S. ignotus. The differences between S. isei sp. n. and S. ena sp. n. are principally regarding the tentacular arrangement and body size (see Remarks of S. ena sp. n.).

Exceptionally for edwardsiids, this species inhabits in the cavities of the underside of boulders, adhering by their aboral end, on rocky seashores. Edwardsiids usually inhabit in sand or mud, and only two species had been reported from other different environments: Edwardsiella andrillae Daly, 2013 living on ice (Daly et al. 2013), and Tempuractis rinkai Izumi, Ise & Yanagi, 2018 living in sponges (Izumi et al. 2018).

Holotype.NSMT-Co 1613, histological sections (5 slides), and tissue for DNA analysis, 26 June 2014, Kopepe Seashore (Fig. 1A–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. 1A–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.

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. 5E–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.

Figure 5. 

External and internal views of Scolanthus kopepe sp. n. A, B, F–INSMT-Co 1613 C–ENSMT-Co 1616 A, B external view A whole living specimen of S. kopepe B enlarged view of tentacular circle C–I internal view (histological section) C longitudinal section of tentacle D transverse section of tentacle E transverse section of actinopharynx F transverse section of filaments G enlarged view of mesentery H transverse section of nemathybome I longitudinal section of aboral end. Nemathybomes distributed up to the tip of aboral end. Abbreviations: a, actinopharynx; Ne, nemathybome; pm, parietal muscle; rm, retractor muscle; Te, tentacle; tlm, tentacular longitudinal muscle; Ts, testis. Scale bars: 5 mm (A); 1 mm (B); 500 µm (E, F, G, I); 100 µm (C, D, H, J).

Figure 6. 

Schematic representation of tentacular and mesenterial arrangements. A Scolanthus armatus and S. kopepe sp. n. B S. ena sp. n. C S. isei sp. n. Abbreviations: a, actinopharynx; bw: body wall; dd, dorsal directive; dlm, dorso-lateral mesentery; mi, microcneme; rm, retractor muscle; vd, ventral directive; vlm, ventro-lateral directive. White circles indicate the locus of tentacles.

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

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.

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.

Figure 7. 

Cnidae of Scolanthus species. A–E S. armatus (NSMT-Co 1609) A1 spirocyst in tentacle A2 basitrich in tentacle B1 basitrich in actinopharynx B2 microbasic b- mastigophore in actinopharynx C basitrich in nemathybome D basitrich in column E1 small basitrich in filament E2 large basitrich in filament E3 microbasic b- mastigophore in filament F–I S. ena sp. n. (NSMT-Co 1610) F1 spirocyst in tentacle F2 basitrich in tentacle G1 basitrich in actinopharynx G2 microbasic p- mastigophore in actinopharynx H1 small basitrich in nemathybome H2 large basitrich in nemathybome I1 basitrich in filament I2 microbasic b- mastigophore in filament I3 microbasic p- mastigophore in filament J–M S. isei sp. n. (NSMT-Co 1611) J1 spirocyst in tentacle J2 small basitrich in tentacle J3 large basitrich in tentacle K1 basitrich in actinopharynx K2 microbasic b- mastigophore in actinopharynx L1 small basitrich in nemathybome L2 large basitrich in regular tentacles M1 small basitrich in filament M2 large basitrich in filament M3 microbasic p- mastigophore in filament N–R S. kopepe sp. n. (NSMT-Co 1614) N1 spirocyst in tentacle N2 small basitrich in tentacle N3 large basitrich in tentacle O1 small basitrich in actinopharynx O2 large basitrich in actinopharynx P1 small basitrich in nemathybome P2 small basitrich in nemathybome Q basitrich in column R1 basitrich in filament R2 microbasic b- mastigophore in filament.