Haloclava hercules, Izumi, 2021

Izumi, Takato, 2021, The Largest Cnidae Among the Sea Anemones; Description of a New Haloclavid Species from Japan, Haloclava hercules (Cnidaria: Actiniaria: Enthemonae: Haloclavidae), Species Diversity 26, pp. 241-247 : 244-246

Haloclava hercules sp. nov.

[New Japanese name: herakuresu-no-konbou] ( Figs 2 , 3 ; Table 2)

Material examined. NSMT-Co 1754 (the holotype): dissected specimen, embedded tissues in paraffin, histological sections, prepared nematocysts; 9 May 2017, off Jogashima, Misaki, Kanagawa Pref., 35°06.838′N, 139°34.063′E (St. 1), at 272–370 m depth, collected by Hiroshi Namikawa using a 50 cm biological dredge, kept in a tank of Misaki Marine Biological Station , and fixed and preserved by Takato Izumi; CMNH-ZG 09758 (a paratype): dissected specimen, embedded tissues in paraffin, histological sections, prepared nematocysts; 9 November 2017, south off Shima, Shima Peninsula, Mie Pref, 34°10.109′N, 136°44.644′E (St. 7), at 130–132 m depth, collected by Itaru Kobayashi using a 50 cm biological dredge.

Description of the holotype (NSMT-Co 1754) and a paratype (CMNH-ZG 09758). External feature: Column barrel or corn-like, not differentiated into parts, with high degree of expansibility, length ca. 15–20 mm, diameter ca. 7–12 mm in live specimens, and length ca. 15 mm, diameter ca. 7–10 mm in preserved specimens. Body pale brownish orange ( Fig. 2A, B ), with transversal wrinkles ( Fig. 2A ), and mesenterial insertions. Small papillae lows on the column surface, but no apertures ( Fig. 2A ). Aboral end physa-like, rounded, with a tiny pore in the center, same in color as column, and slightly sticky and adheres to substrate. Oral disc with 20 tentacles in two indistinct cycles of 10 each ( Fig. 2B ). Outer tentacles protruding outside or hanging along the column, and inner ones protruding upwards. Morphological differences between the inner and outer tentacles followings: outer ones more robust and longer (ca. 9–12 mm in length) than inner ones (ca. 5–7 mm in length) when fully expanded; outer ones apparently capitate with large robust acrosphere-like knobs though inner ones with indistinct small acrospheres on the tips ( Fig. 2B ). Both inner and outer tentacles uniform sizes and shapes in its middle part. Tentacles pale orange, translucent, smooth ( Fig. 2A, B ). Acrospheres patchy pattern with dark red and white, surface rough. Oral disc diameter ca. 12 mm, uniformly orange, in live specimens. Mouth at the center of oral disc, not swollen; conchula absent ( Fig. 2B ).

Internal anatomy: Twenty mesenteries, all macrocnemes. Ten pairs; 6 pairs of them in the first cycle and 4 pairs in the second cycle ( Fig. 2E ). All macrocnemes perfect, fertile, and continuing along the whole-body length. Microcnemes absent. All tentacles arise from each endocoel and exocoel. Tentacular longitudinal muscles ectodermal ( Fig. 2C ); tentacular circular muscles endodermal ( Fig. 2D ). Acrosphere on tentacle tips with densely arranged large basitrichs ( Fig. 2D ; Table 2). Retractor muscles restricted, limited at the center of each macrocneme ( Fig. 2E ), with approximately 25–40 multiple-branched muscular processes ( Fig. 2F ); parietal muscles of macrocnemes distinct, in peculiar shape: muscle with 10 slightly branched processes on each side bared from thin mesenteries by body wall, and additional muscle with simple 10–20 processes bared from thick mesoglea between the body wall and the retractor muscle ( Fig. 2F ). Moreover, several small slightly-branched muscular processes on opposite side of retractor muscle on macrocnemes. Mesoglea in the body wall far thicker than the ectoderm and remarkably thicker than the endoderm of body wall, actinopharynx and siphonoglyph ( Fig. 2E ). Actinopharynx smooth, grooved, approximately 2/3–3/4 the column length. Single distinct siphonoglyph on the ventral side of actinopharynx, always connected to it, and sustained by the ventral pair of directive mesenteries ( Fig. 2E ). Sphincter muscle absent. Filaments limited near the aboral end. All specimens dioecious; mature ovary contains several oocytes in the mesoglea of each mesentery ( Fig. 2G ).

Cnidom: Basitrichs, microbasic b -mastigophores. See Table 2 for size and distribution.

Etymology. The new specific epithet “ hercules ” is a noun referring to blunt outer tentacles with apparent acrosphere-like cudgels containing gigantic strong basitrichs of this new species, which remains me of the thorns on the cudgel of Hercules, the famous hero of Greek Mythology.

Derivation of Japanese name. The genus Haloclava had been named “konbo-isoginchaku-zoku” in H. Uchida and Soyama (2001); “konbo” means the cudgel because anemones in this group have blunt tentacles with acrospheres. Thus, I omit the phrase and added Hercules at the beginning of the name, following the pattern in Antennapeachia jambio Izumi, Fujita, and Yanagi, 2017 (“misaki-no-antenna”).

Remarks. Haloclava hercules sp. nov. is the first unquestionable specimen-based record of the genus Haloclava from Japanese waters [H. Uchida and Soyama (2001) recorded H. aff. producta from Japanese waters, but the identification in this field guide is uncertain since its description is too short and lacking diagnostic characters of Haloclava below-mentioned]. This new species falls within the genus Haloclava by virtue of having following two features: the simple siphonoglyph without a conchula ( Fig. 2B ; strong acrospheres exist only in the genera Haloclava and Anemonactis Andres, 1881 , and are thus distinguished from the other genera, e.g., Antennapeachia Izumi and Yanagi, 2016 , Harenactis Torrey, 1902 , Metapeachia Carlgren, 1943 , Peachia Gosse, 1855 , Stephanthus Rodríguez and López-González, 2003 , Synpeachia Yap, Fautin, Ramos, and Tan, 2014 , and Tenactis Barragán, Sánchez, and Rodríguez, 2019 ) and the surface of the body without any apertures ( Fig. 2A ; distinguished from the genus Anemonactis ).

Haloclava hercules sp. nov. has a peculiar retractor muscle shape, not only for the genus, but also for the family ( Fig. 2F ). Moreover, the difference in shape between the inner and outer tentacles is considerably apparent in this species ( Fig. 2B ). Previously, no Haloclava species with such differentiated tentacles have been described ( Stimpson 1856; Verrill 1868; Carlgren 1931).

The other minor differences of this new species from other congeners are as follows: Haloclava capensis ( Verrill, 1865) has six inner tentacles ( Verrill 1865), in contrast to the 10 of H. hercules ; H. stimpsonii ( Verrill, 1868) has not developed acrospheres whereas H. hercules has an outer cycle with distinct acrospheres and an inner cycle with indistinct acrospheres ( Verrill 1868); H. brevicornis ( Stimpson, 1856) has 20 uniform blunt tentacles, not resembling the tentacles of H. hercules in shape; H. producta Stimpson, 1856 has 20 lines of sticky papillae on its column ( Pei 1998), while the surface of H. hercules is smooth, and the body length of H. producta reaches 70 mm, larger than that of H. Hercules (15–20 mm); H. chinensis Carlgren, 1931 most strongly resembles H. hercules , but the shapes of retractors of H. chinensis are more circumscribed and strongly restrict-ed ( Carlgren 1931; see also Table 3).

The basitrichs of the acrosphere of H. hercules , reaching 273 µm, are extremely large for Actiniaria , for which it is rare that basitrichs reach over 200 µm (e.g., Edwardsia alternobomen ). This is the maximum length record of basitrich among sea anemone.

Figures

Fig. 2. Haloclava hercules sp. nov., holotype, NSMT-Co 1754, external morphology in living state (A, B) and internal morphology of the preserved specimen (C–H, histological section stained by hematoxylin and eosin). A, Lateral view of the whole body; B, oral view; C, transverse section of a tentacle; D, longitudinal section of a tentacle; E, transverse section of the column; F, enlarged view of the transverse section of the column; G, enlarged view of the transverse section of an oocyte; H, longitudinal section of the aboral end. Abbreviations: a, actinopharynx; ac, acrosphere; D, dorsal directive; fi, filament; ma, macrocneme; oo, oocyte; pa, parietal muscle; rm, retractor muscle; s, siphonoglyph; scs, scapus; tcm, tentacular circular muscle; te, tentacles; tlm, tentacular longitudinal muscle; V, ventral directive; 1, first cycle mesentery; 2, second cycle mesentery. Scale bars: 10mm in A and B, 1mm in E, F, H, 500µm in D, G, and 100µm in C.

Fig. 3. Cnidom of Haloclava hercules sp. nov., holotype, NSMT-Co 1754. A, Basitrich of an acrosphere; B, small basitrich in a tentacle; C, large basitrichs in a tentacle; D, small basitrich in the actinopharynx; E, large basitrich in the actinopharynx; F, small basitrich in the column; G, large basitrich in the column; H, small basitrich in a filament; I, large basitrich in a filament; J, microbasic b-mastigophore in a filament. Scale bars: 100µm for A, and 50µm for all other sub-figures.