Enthemonae Rodríguez and Daly

Izumi, Takato, Yanagi, Kensuke & Fujita, Toshihiko, 2018, Re-description of Metedwardsia akkeshi (Cnidaria: Anthozoa: Actiniaria: Edwardsiidae), Discovered in Akkeshi, Hokkaido, Almost 80 Years after Original Description, with a Revision of the Diagnosis of Genus Metedwardsia, Species Diversity 23, pp. 135-142 : 138

Suborder Enthemonae Rodríguez and Daly in Rodríguez et al., 2014 Family Edwardsiidae Andress, 1881 Genus Metedwardsia Carlgren, 1947 [New Japanese name: Hoso-isoginchaku-zoku]

Diagnosis. Edwardsiidae , body more or less divisible into physa, scapus, and scapulus. Scapus and physa slightly differentiated from each other, the former with a thin epidermis without nemathybomes. No sphincter. Tentacles comparatively short, the inner shorter than the middle and outer ones. 8 perfect and fertile mesenteries arranged as the macrocnemes in Edwardsia . 16 microcnemes, elongated from distal to proximal end. The number distally is always equal or less than proximally. Retractors of macrocnemes reniform to circumscribed. Parietal muscles distinct but weak. No nematosomes in the coelenteron. Cnidae; basitrich, spirocyst, microbasic b -mastigophore, and microbasic amastigophore (Revised from Carlgren [1949]. Revised points are indicated in bold. The diagnosis of cnidom is newly added).

Type species. Milneedwardsia akkeshi Uchida, 1932 .

Remarks. Genus Metedwardsia was established in Edwardsiidae because of its worm-like shape and eight macrocnemes to accommodate Milneedwardsia akkeshi because some morphological characters of this species did not correspond to the diagnosis of Milneedwardsia ( Carlgren 1947) . Since then, the diagnosis of Metedwardsia has not been revised due to a lack of new specimens. Based on the current re-description of Metedwardsia akkeshi resulting from thorough examination of the characteristics of newly collected topotypic specimens, revision of this diagnosis is required. As the cnidom of M. akkeshi has never had been formally described, we have added a description of the cnidom to the diagnosis. The microcnemes extending from the oral to the aboral end are found only in this genus among the Edwardsiidae , suborder Anenthemonae . The 16 microcnemes are easily distinguishable from the eight macrocnemes by their smaller size, absence of retractor muscles, and the trilobated filament and gonad, and they are elongated from the distal to proximal end.

Although this genus has been included in Edwardsiidae for several decades, but there are some different opinions. Gusmão et al. (2016) recently suggested placing M. akkeshi in the Halcampidae , a family belonging to the different suborder, Enthemonae , because Metedwardsia does not have microcnemes but rather imperfect mesenteries extended along the entire body in which muscles develop, whereas the microcnemes in other Edwardsiidae genera are restricted to the distal-most column and have poorly developed musculature, which features rather resembles Halcampidae than Edwardsiidae . However, their taxonomic conclusion was based only on the reference citation of the morphological characteristics of M. akkeshi . Contrary, a molecular phylogenetic tree developed by Rodríguez and Daly (2010) assigned M. akkeshi to the Actiniidae subclade within the Endomyaria clade. Actiniid sea anemones belong to the farther clade from Halcampidae : this two families are different in superfamily level ( Rodríguez et al. 2014). Accordingly, based on this phylogenetic tree, Metedwardsia , which is strongly related to Actiniidae , should not be accommodated to Halcampidae . However, Rodríguez and Daly (2010) did not provide detailed information about the morphological features of M. akkeshi specimen on which their phylogenetic analysis was based. Therefore, it is still possible that the molecular data of M. akkeshi in Rodríguez and Daly (2010) might be based on a misidentified, or wrong specimen. As such, we concluded Metedwardsia should be remained within the Edwardsiidae for the time being (Izumi et al. 2018); molecular analysis of topotypic specimens is urgently needed in order to clarify the incontrovertible taxonomic and phylogenetic position of this genus.