Capnea japonica ( Carlgren, 1940 )

Yanagi, Kensuke & Izumi, Takato, 2021, Redescription of the Sea Anemone Capnea japonica (Cnidaria: Anthozoa: Actiniaria), Species Diversity 26 (2), pp. 153-163 : 155-160

Capnea japonica ( Carlgren, 1940)

[New Japanese name: Yosai Isoginchaku]

( Figs 2–7 ; Table 1 )

Aureliana japonica Carlgren, 1940: 7 , 33, 35, 60, fig. IX9–12; Carlgren 1949: 71 (misspelled).

Material examined. UUZM 101 (collection of the Zoology Section of the Museum of Evolution, Uppsala University): two syntypes, collected on 6 June 1914, off the coast of Misaki, Sagami Bay , 210 m depth, collected by Dr. Sixten Bock. CMNH-ZG 06547 : one specimen, collected on 19 February 2014, off the coast SW of Jogashima, Misaki, Sagami Bay (from 35°06.086′N – 139°34.232′E and 35°05.862′N–139°34.089′E) at a depth of 238– 309m, collected by R/V Rinkai-Maru using a dredge, during a marine faunal research survey conducted by the Japanese Association for Marine Biology ( JAMBIO).

Description. External anatomy ( Figs 2 , 3 ). In freshly collected, living specimen (CMNH-ZG 06547), column orange in color, gradually paler towards the proximal end ( Fig. 2A, B ); tentacles pale orange with scattered dark orange spots ( Fig. 2A ). Expanded body, column height ca. 15 mm; oral disc diameter ca. 8 mm, pedal disc diameter ca. 12 mm; pedal disc adherent (adhered to a pebble when collected), circular in outline. In 2 syntypes (UUZM 101), column height 13 mm (small specimen) and 18 mm (large specimen); oral disc diameter 7 mm and 10 mm; pedal disc diameter 11 mm and 15 mm, respectively. In all specimens: scapus smooth, shallow fosse at the distal end ( Figs 2B , 3C ). Mouth oval, with indistinct lip ( Figs 2B , 3C ). Tentacles very short, knob like, smaller towards the center from margin ( Figs 2B , 3B, C ). Outer tentacles largest. Tentacles at least 42 in number (impossible to count all the tentacles in CMNHZG 06547 because of the condition of the specimen), 72 in smaller specimen of UUZM 101 ( Fig. 3C ), and nocountable in larger specimen of UUZM 101. Two tentacles in each exocoel and endocoel. The siphonoglyph less distinct from external and also internal view ( Figs 2B , 3C ).

Mesenteries ( Figs 3D , 4A, B ). 20 perfect mesenteries in CMNH 06546 and 18 in larger specimen of UUZM 101. Mesenteries not equally developed within the same pair ( Fig. 4A , see the pair numbered 19). Mesenteries at the base more numerous than at the margin. At least 7 pairs of imperfect small mesenteries in CMNH 06545 ( Fig. 4A, B ). Fertile mesentery not detected in examined specimens.

Musculature ( Figs 4 , 5 ). Retractors strong circumscript, distinctly restricted ( Fig. 4A ). Parietobasilar muscles distinct in perfect mesenteries without pennon ( Fig. 4A ). Columnar circular muscle well-developed ( Fig. 4C ). Sphincter muscle endodermal, strong pinnate circumscript, elongated, with thick mesogleal main lamella, which strongly fluoresced ( Fig. 5A, B ).

Cnidae ( Figs 6 , 7 ; Table 1 ). Spirocysts, basitrichs, microbasic p -mastigophores. See Table 1 and Fig. 7 for size and distribution.

Distribution. Known to occur in Misaki, Sagami Bay, Japan. Bathymetric range 210– 309 m.

Phylogenetic analyses. We performed phylogenetic analyses using the concatenated sequences of five regions, resulting in a total of 4159 bp. The resulting trees of the concatenated 12S, 16S, 18S, 28S and COX III DNA are shown in Fig. 8A (maximum likelihood: ML) and Fig. 8B (Bayesian inference: Bayes). Both trees showed Capnea japonica and C. georgiana in the same clade as the suborder Enthemonae (ML=100%, Bayes=1), and it is likely that Capnea is included in the superfamily Actinostoloidea (ML=54%, Bayes=0.994; Fig. 8A, B ).

Remarks. The newly collected specimen (CMNH-ZG 06547) from the type locality of Capnea japonica possesses very characteristic knob like tentacles, a smooth column, and strong endodermal sphincters. It also has two tentacles within the exocoels and endocoels. These features could support the identification of CMNH-ZG 06547 as a species of Capnea . The only species known from the Pacific is C. japonica . Except for the syntypes, no additional specimens of C. japonica have been recorded. The morphological characters of the syntypes and those included in Carlgren’s original description ( Carlgren 1940: 35, 60) were almost the same as those observed in CMNH-ZG 06547. Based on the morphological comparison between the syntypes and CMNHZG 06547, we identified the latter as C. japonica . This is the third known specimen of C. japonica after the two syntypes, collected in 1914.

Carlgren (1940) described 18 pairs of perfect mesenteries in the syntypes; however, we found that the smaller specimen had not been dissected. CMNH-ZG 06547 has at least 20 pairs of perfect mesenteries, although it is not a normal arrangement in that the mesenteries within the same pair are unequally developed ( Fig. 4A ). In the larger specimen of the syntypes, it is difficult to identify the pairs of mesenteries because no histological sections were prepared for detailed observation, and, therefore, we could not examine them. Dunn (1983: 39) said “Up to four cycles of thin mesenteries; regularly arrayed but those of highest cycle may develop asynchronously…”, in the description of C. georgiana . This does not mean asynchronous development of the mesenteries within the same pairs; however, this is not the “regular arrangement.” The mesenterial arrangement of the other Capnea species has not been investigated in detail and therefore further investigation of the developing of mesenteries of Capnea species is needed.

Phylogeny of Capneidae . Rodríguez et al. (2014) considered Capneidae to be included in Actinioidea. This might be because Capnea has no characters in common with the other two superfamilies; it has neither mesenteries arranged according to the Actinostola rule, the characteristic feature of the part of Actinostoloidea ; nor acontia, a characteristic feature of Metridioidea. Their phylogenetic analyses, however, indicated different results: C. georgiana was nested in the clade of Actinostoloidea , despite the reliability being low. By including C. japonica , our phylogenetic analyses reinforced the hypothesis of Capneidae belonging within Actinostoloidea . In the present study, the mesenterial arrangement of C. japonica . japonica was not the regular arrangement seen in most Actiniidae species. The unequally developed mesenteries within the pair might be because of the ‘ Actinostola rule’ which Carlgren (1949: 77) stated as “In the younger cycles the mesenteries of each pair are usually unequally developed in such a way that the mesentery with turns its longitudinal muscle towards nearest mesentery of the preceding cycle is larger than its partner.” The possession of a strong endodermal sphincter, however, still needs to be evaluated in terms of its origin and homology between the different types of endomyarian sphincters. Also, the development of mesenteries of Capnea species should be examined in detail to discuss the phylogenetic relationships between Capneidae and the other family, Actinostolidae , in Actinostoloidea .

Figures

Fig. 2. Living Capnea japonica from the type locality of Misaki, Sagami Bay, Japan (CMNH-ZG 06547), oral view. A, Slightly expanded state; B, contracted state. Scale bars: 5mm.

Fig. 3. Syntypes of Capnea japonica (UUZM 101). A, Two syntypes with the labels of the specimen; B, oral view of two syntypes, the larger specimen (left and center ones) dissected horizontally at the level of pharynx; C, oral view of the smaller specimen; D, enlarged view of crosssectional surface of larger specimen. Abbreviations: d, pairs of directive mesenteries; f, fosse; p, pharynx; s, siphonoglyph. Scale bars: 10mm in B; 5mm in C and D.

Fig. 4. Histological aspects of Capnea japonica (CMNH-ZG 06547). A, Transverse section, the number indicating the order of each pair of mesenteries from one directives, numbers 23 to 29 indicate the pairs of the rudimental small mesenteries; B, enlarged A showing immature small pair of mesenteries (arrow heads); C, longitudinal section of the gastrodermis of the column. Abbreviations: ccm, columnar circular muscle; d, directive mesentery; g, gastrodermis; m, mesoglea; p, pharynx; pbm, parietobasilar muscles; r, retractor muscle. Scale bars: 1mm in A; 500µm in B; 100µm in C.

Fig. 5. Sphincter muscle of Capnea japonica (CMNH-ZG 06547). A, Longitudinal section through the upper part of the column; B, same as A but under fluorescent light. Abbreviations: c, column; m, mesoglea; sp, sphincter. Scale bars: 200µm.

Fig. 6. Cnidae from tentacle, pharynx, mesenterial filaments, column, and limbus of Capnea japonica (CMNH-ZG 06547). For letters a–i, refer to Table 1. Scale bar: 20µm.

Fig. 7. Size distribution of cnidae of Capnea japonica (CMNH-ZG 06547). X and y axes represent the length and width of cnidae in µm, respectively. “n” is the number of capsules measured.

Fig. 8. Concatenated phylogenetic trees based on 12S, 16S, 18S, 28S, and COX III sequences. A, Tree inferred by Maximum likelihood (ML) analysis; B, tree inferred by using Bayesian inference (BI) method. Numbers on nodes represent bootstrap values (in ML tree) or posterior probabilities (in BI tree).