Edwardsia aff. tuberculata Duben and Koren, 1847

Izumi, Takato & Fujita, Toshihiko, 2019, Two species of Edwardsia having gigantic nematocysts, E. aff. tuberculata and E. alternobomen sp. nov. (Cnidaria; Anthozoa; Actiniaria; Edwardsiidae) from Japan, Zootaxa 4661 (3), pp. 533-544 : 535-536

Edwardsia aff. tuberculata Duben and Koren, 1847

(New Japanese name: oozutsu-mushimodoki-ginchaku)

Figs. 2 , 4 ; Table 1

Synonymy: see Fautin (2016)

Material examined. NSMT-Co 1654, dissected specimen, histological sections (7 slides), and prepared cnidae (5 slides), November 6, 2014, east of Ogishima Island, Kagawa Pref., Seto Inland Sea (34°24′54′′N, 134°05′30′′E; Fig. 1A ), 16 m depth, collected by Naoto Jimi. NSMT-Co 1655, histological sections of damaged individuals (3 slides), same date, locality, and collector as NSMT-Co 1654.

External anatomy. Column of contracted specimen 20–25 mm in whole length (25.0 mm in NSMT-Co 1654), and 6–7 mm in width (7 mm in NSMT-Co 1654), swelled by huge nemathybomes, cylinder-like in shape but slightly swollen proximally ( Fig. 2A ). Body divided into capitulum, scapus and physa; in our specimen, capitulum shrunken in column, invisible. About half of scapus occupied by nemathybomes, remaining half covered with brownishgrey periderm. Nemathybomes extremely large, like papillae, up to 1.5 mm in diameter ( Fig. 2B ), in eight rows in proximal part, gradually becoming smaller distally ( Fig. 2A ). Aboral physa differentiated from scapus, naked, not rounded but tapered, without nemathybomes ( Fig. 2A ). Tentacles 16 in number, in two cycles of eight, relative size of each cycle unclear because tentacles contracted into scapus.

Internal anatomy. Eight perfect mesenteries, macrocnemes, distributed along whole body from distal to proximal end. These eight are the paired dorsal and ventral directives plus four unpaired lateral mesenteries. Eight tiny microcnemes, without muscles, limited to distal-most part: four between dorsal directives and dorso-lateral mesenteries, two between dorso- and ventro-lateral mesenteries, and two between ventro-lateral mesenteries and ventral directives. All macrocnemic mesenteries bear retractor and parietal muscles. The retractor muscle of each lateral mesentery faces ventrally ( Fig. 2E, F ). Each retractor muscle distinctly developed; diffuse, with approximately 20 simple or slightly branched muscular processes next to actinopharynx ( Fig. 2D ); diffuse or restricted to parietal muscle side, developed like a pennon, with 10–25 simple or slightly branched muscular processes in lower part ( Fig. 2E, F ). Parietal muscles of macrocnemes distinct, semi-elliptic, with 10 slightly branched muscular processes in each side ( Fig. 2 D–F). Actinopharynx very short, grooved but without distinct siphonoglyph. One tentacle in each endo- or exo-coel. Tentacular longitudal muscle ectodermal and distinct. Marginal sphincter muscle and basilar muscle absent ( Fig. 2C, H ). Mesoglea generally thin in mesenteries, and comparatively thick in body wall (Fig, 2D, F). Nemathybomes far thicker than mesoglea, greatly protruding from body wall and containing very large basitrichs ( Fig. 2F, G ). Gonads on mesenteries between retractor muscle and filament; gametocytes immature.

Cnidome. Spirocysts, basitrichs, microbasic b -mastigophores, microbasic p -mastigophores, and microbasic amastigophores ( Table 1 , Fig. 4 A–D; NSMT-Co 1654). Two sizes of basitrichs in actinopharynx; three sizes of basitrichs in nemathybomes.

Deriviation of Japanese name. Japanese name “oozutu” means a cannon, because the huge nemathybomes of this species are suggestive of spherical projectiles of cannon, and the cylindrical shape of the body resembles to a cannon barrel. Nemathybome is called as “shihoudan” in Japanese, which is constructed by shihou (= cnidae) + dan (=projectile or bullet), so this Japanese name matches E. aff. tuberculata . “Mushimodoki-ginchaku” means Edwardsia .

Remarks. Edwardsia tuberculata was originally described in Duben and Koren (1847), and more detailed morphological features were described in Carlgren (1921). Morphology of the examined specimens agrees well with the description by Carlgren (1921): shrunken body size is 2 cm in length and 7 mm in width ( Fig. 2A ); a few outstandingly large nemathybomes look like papillae arranged in 8 rows ( Fig. 2B, F, G ); physa is developed but flattened or tapered ( Fig. 2A, H ); retractor muscle is diffused with slightly branched processes and parietal muscle is distinct with 20 processes ( Fig. 2 D–F). The cnidom also almost perfectly corresponds to the description of Carlgren (1921): this species is characterized by large nemathybomes that contain huge basitrichs. The larger type of basitrichs in nemathybomes of our specimen are 116–187 µm in length and 4.8–9.0 µm in width ( Table 1 ; Fig. 4C 2 ). This matches the nematocysts of E. tuberculata reported by Carlgren (1921), which he measured at 110–190 µm in length and 5–7 µm in width. In filaments, Carlgren (1921) mentioned that some of nematocysts are a little broader than the others. This observation would be convincing if one assumes that the wide nematocyst of Carlgren (1921) is what we identify as microbasic b -mastigophores in our specimen. There were some small differences between the description and our specimens. For example, the retractor muscle of our specimen is composed of 10–25 muscular processes while Carlgren (1921) mentioned more 30 processes, and we found some spirocyst in actinopharynx, although Carlgren (1921) did not mention these.

According to England (1987), in addition to E. tuberculata three other species of Edwardsia have basitrichs over 150 µm in length; E. californica McMurrich, 1913 , E. maroccana Carlgren, 1931 , and E. claparedi (Panceri. 1869) . However, they never exceed 170 µm even in maximum size ( Carlgren, 1931, 1936; England, 1987; Manuel, 1977). The huge basitrichs are, however, now also reported in Edwardsia alternobomen sp. nov., described below, which has basitrichs over 200 µm in length ( Table 1 , Fig. 2G2 ).

Edwardsia tuberculata is distinguished from the other species with large basitrichs in their nemathybomes by having larger basitrichs than those other species and by some anatomical features. Between mesenteries, E. tuberculata consistently has a single row of nemathybomes, whereas E. californica has two or three rows on the proximal part ( Carlgren, 1936). Edwardsia tuberculata has flattened physa but E. californica has very apparent, large, rounded physa. Edwardsia californica has a very characteristic restricted retractor muscle with approximately 40 muscular processes, whereas one of our specimens has diffuse retractor muscle composed of about 20 processes. According to Carlgren (1931), Edwardsia maroccana has more developed muscles with 30 processes, and it is apparently pinnate near the column, whereas those of E. tuberculata do not branch so much. In addition, Carlgren (1931) showed basitrichs of 30–40 µm in length and 6.5 µm in width bearing a shimmering thread in the capsule in the actinopharynx, these are likely a kind of mastigophore, a type of nematocyst not found in actinopharynx of the examined specimen of E. tuberculata . The body size of E. tuberculata (20–25 mm in length) is completely different from Edwardsia claparedi , which reach to 120 mm in length ( Manuel, 1981).

Edwardsia tuberculata can also be distinguished from the other species of Edwardsia that have two types of basitrichs in their nemathybomes (i.e., E. elegans Verrill, 1869 , Edwardsia handi Daly and Ljubenkov, 2008 , E. hantueusis England, 1987 , E. sulcata Verrill, 1864 ). However, the larger type of basitrichs in nemathybomes of those species barely exceed 100 μm and at most 117 µm for E. handi ( Daly and Ljubenkov, 2008) .

Although our specimens clearly align with the description of E. tuberculata , this species is distributed only in north western Europe and there is no record from the Pacific or from the eastern Arctic Ocean. Recognizing that expanding the range so much without intermediate populations or an explanation for the long-distance dispersal is problematic, and pending comprehensive analysis through genetics, we mark our specimens as having an affinity for E. tuberculata , rather than assigning that name to them definitively.

Figures

FIGURE 1. Sampling localities. A: Edwardsia aff. tuberculata; B: E. alternobomen sp. nov.

FIGURE 2. External view and histological section of Edwardsia aff. tuberculata Duben and Koren, 1847. A and B, External view of NSMT-Co 1654; A. Preserved specimen (dissected into two halves) B. Enlarged view of body wall and nemathybomes. C–H, histological section of NSMT-Co 1654; C. Longitudinal section of uppermost part. D. Transverse section of upper part. E. Enlarged view of a mesentery. F. Transverse section of lower part of body. G. Enlarged view of a nemathybome. Large basitrichs are indicated. H. longitudinal section of lowermost part. Abbreviations: dd, dorsal directive; dl, dorso-lateral mesentery; Me, mesoglea; Ne, nemathybome; Pa, parietal muscle; Ph, physa; Re, retractor muscle; Te, tentacle; vd, ventral directive; vl, ventro-lateral mesentery. Scale bars indicate 5 mm in A, 1 mm in B, 500 µm in C–H.

FIGURE 4. Cnidae of Edwardsia aff. tuberculata and Edwardsia alternobomen sp. nov. A–D: cnidae of Edwardsia aff. tuberculata (NSMT-Co 1654). A, tentacle; A1, spirocyst; A2, basitrich. B, actinopharynx; B1, spirocyst; B2, small basitrich; B3, large basitrich; B4, microbasic p-mastigophore. C, nemathybome; C1, small basitrich; C2, large basitrich. D, filament; D1, basitrich; D2, small microbasic b-mastigophore; D3, large microbasic b-mastigophore. E–H: cnidae of Edwardsia alternobomen sp. nov. (NSMT-Co 1656). E, tentacle; E1, spirocyst; E2, small basitrich; E3, large basitrich. F, actinopharynx; F1, basitrich; F2, microbasic p-mastigophore. G, nemathybome; G1, small basitrich; G2, large basitrich. H, filament; H1, spirocyst; H2, basitrich. All images are shown at the same scale.