Edwardsianthus amethystus, Izumi & Fujii, 2021

Izumi, Takato & Fujii, Takuma, 2021, Gems of the southern Japanese seas - four new species of Edwardsianthus (Anthozoa, Actiniaria, Edwardsiidae) with redescriptions of two species, ZooKeys 1076, pp. 151-182 : 151

Edwardsianthus amethystus sp. nov.

Japanese name: amejisuto-mushimodoki-ginchaku Figs 7I-K , 9

Material examined.

Holotype. CMNH-ZG 09763: histological sections, tissues in paraffin, and prepared nematocysts, collected by SCUBA diving on 28 March 2013, in Oura Bay , Okinawa Island, Okinawa Pref., Japan, 15 m depth, by Takuma Fujii.

Description.

External anatomy. Size: preserved specimen ca. 200 mm in whole length, and 7 mm (narrower part)-20 mm (broader part) in width, and> 300 mm in living animal, one of the largest species in edwardsiids (Fig. 9B ). Column: worm-like in form, and the distal part swollen to some extent (maybe because of condition during preservation). The column consisting of capitulum, scapus and quite small physa. The distal-most part a short capitulum, without nemathybomes. Scapus with thin and easily stripped periderm, light brown in color, and surface completely smooth, with extremely small nemathybome-like spots (Fig. 9B ). Aboral end differentiated with small, rounded physa. Tentacles: 20 in number in two cycles: inner tentacles five and outer 15, slender, pale purple in color with several dark purple spots (Fig. 9A ; this color is lost in preserved specimen: Fig. 9B ). Inner tentacles ca. 10 mm and outer ones ca. 15-20 mm in length in the living specimen. Mouth: at the center of oral disc, apparently swollen in living animal. Internal anatomy. Mesenterial arrangement: eight perfect mesenteries, all macrocnemes. Four dorsal and ventral directives, and four lateral mesenteries not paired with other macrocnemes, arranged in the normal Edwardsia pattern. All macrocnemes are present along the whole body length from oral to aboral end and bear distinct retractor and parietal muscles. Twelve tiny microcnemes, without muscles, only confined to 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. Retractor muscles: at the mid part of column, strongly developed and diffused (Fig. 9E ), pennon-like, arranged with 100-150 muscular processes, simple to well branched. Processes near filament short and highly branched, and one process nearest to the body wall extremely well-branched, with ca. 80 secondary and thirdly branched processes (Fig. 9E ). Parietal muscles: distinct, rounded shape, consisting of 10-15 simple processes on each side (Fig. 9E ). Others: each with one tentacle from each endo- or exocoels. Existence of siphonoglyph unknown because of contracted state of specimen. Tentacular circular muscle indistinct (Fig. 9C ), and longitudinal muscle ectodermal, distinct (Fig. 9D ). Mesoglea thickest in body wall and actinopharynx, ca. 200 µm in thickness (Fig. 9E ), but far thinner in mesenteries, retractor muscles, and tentacles (Fig. 9C, D ). Nemathybome-like structures protruding from mesoglea, but without any nematocysts (Fig. 9G ). Marginal sphincter muscle and basilar muscle absent. Gametogenic tissue apart from retractor muscles, distinct (Fig. 9F ), with matured oocytes. Cnidom. Basitrichs, spirocysts, and microbasic p -mastigophores. There are no nematocysts in nemathybome-like structures. See Fig. 7I-K and Table 5 for sizes and distributions.

Etymology.

This species epithet refers to amethyst, a kind of gemstone, and is named after this species’ dark purple tentacle coloration. Derivation of the Japanese name is the same as that of the Latin species name.

Remarks.

The most characteristic feature of this species is the nemathybome-like features without nematocysts. Nemathybomes are pocket-like features on columns of some genera of Edwardsiidae , and they always contain large nematocysts (Carlgren, 1949; Brandão et al. 2019). Thus, the structures of Edwardsianthus amethystus cannot be called nemathybomes because they lack nematocysts. This is the first case of confirmation of this nemathybome-like feature in Edwardsianthus anemones, and by these E. amethystus can be easily distinguished from its congeners. We placed this sea anemone in the genus Edwardsianthus because of the characteristic arrangement of tentacles and mesenteries, but the generic diagnosis has now been modified to "sometimes without" nemathybomes (see the Remarks for the genus).

Phylogenetic analyses.

The concatenated phylogenetic tree of 12S, 16S, and 18S rDNA (total 2886 bp) is shown in Fig. 10 . All Edwardsianthus specimens formed a clade (indicated in red box) supported by a ML bootstrap value of 79%, but not well supported by BI posterior probability. In this clade, E. pudicus , E. carbunculus sp. nov., E. sapphirus sp. nov., and E. amethystus sp. nov. were closely related with high support (ML bootstrap value = 83%; BI posterior probability = 0.98), Edwardsianthus smaragdus sp. nov. was indicated as their sister group, but was only slightly supported by ML (bootstrap value = 57%) and not supported by the BI method. Edwardsianthus gilbertensis was nested with the other five species and positioned at the most basal node of this genus.

In addition, the most basal position of our phylogenetic tree of Edwardsiidae is taken by Tempuractis rinkai Izumi, Ise, & Yanagi, 2018. This edwardsiid is the only species of the genus Tempuractis Izumi, Ise, & Yanagi, 2018. It has a simple morphology compared to other edwardsiid species by showing a smooth body wall without particular structures, like nemathybomes, a simple aboral end without any apparent physa, and simple tentacles without any structures ( Izumi et al., 2018). This topology suggests that nemathybomes of Edwardsiidae were obtained within the family lineage (Fig. 10 ).

Figures

Figure 7. Cnidae of Edwardsianthus species A-D E. sapphirus sp. nov. (CMNH-ZG 09761) A 1 spirocyst in tentacle A 2 basitrich in tentacle B 1 small basitrich in actinopharynx B 2 large basitrich in actinopharynx C 1 small basitrich in nemathybome C 2 large basitrich in nemathybome D 1 small basitrich in filament D 2 large basitrich in filament D 3 microbasic p - mastigophore in filament E-H E. smaragdus sp. nov. (CMNH-ZG 09762) E 1 spirocyst in tentacle E 2 basitrich in tentacle F 1 small basitrich in actinopharynx F 2 large basitrich in actinopharynx F 3 microbasic p - mastigophore in actinopharynx G 1 small basitrich in nemathybome; G 2 large basitrich in nemathybome; H 1 spirocyst in filament; H 2 small basitrich in filament H 3 large basitrich in filament H 4 microbasic p - mastigophore in filament I-K E. amethystus sp. nov. (CMNH-ZG 09763) I 1 spirocyst in tentacle I 2 basitrich in tentacle J 1 small basitrich in actinopharynx J 2 large basitrich in actinopharynx K 1 spirocyst in filament K 2 small basitrich in filament K 3 large basitrich in filament K 4 microbasic p - mastigophore in filament.

Figure 9. External and internal morphology of Edwardsianthus amethystus sp. nov. (CMNH-ZG 09763) A oral view of living specimen in the habitat B outer view of preserved specimen C longitudinal section of tentacle D transverse section of tentacle E transverse section of retractor muscle F transverse section of testis G transverse section of trace of nemathybome. Abbreviations: fi, filament; me, mesoglea; ne, nemathybome-like structure; pa, parietal muscle; rm, retractor muscle; scs, scapus; te, tentacle; tlm, tentacle longitudinal muscle; ts, testis. Scale bars: 1 cm (A, B); 500 µm (E, F); 100 µm (C, D, G).

Figure 10. Maximum-likelihood tree of the order Actiniaria based on the combined dataset of mitochondrial 12 S and 16 S and nuclear 18 S rDNA (total 2866 bp). The clade of the genus Edwardsianthus is colored in a red box. Red bar at node indicates the position at which nemathybomes would be obtained. Numbers indicate ML bootstrap support values followed by BI posterior probabilities of the nodes (bootstrap values of ≥ 50 % and posterior probabilities ≥ 0.5 are shown).