Polysertularella polyseriata, a new genus and species of hydroid (Hydrozoa; Leptothecata; Sertulariidae) from the Sea of Okhotsk Author Antsulevich, Alexander text Zootaxa 2011 3107 59 64 journal article 45927 10.5281/zenodo.202210 2a9a35ce-9307-47d2-8bbc-8c8676c88b55 1175-5326 202210 Genus Polysertularella gen. nov. Diagnosis. Sertulariidae with erect, branched colonies, with branches resembling hydrocaulus. Hydrothecae arranged in 5–8 longitudal rows along hydrocaulus and branches; hydrothecal rim with four very low cusps separated by shallow embayments; operculum of four equal triangular valves, flattened rather than pyramidal; hydranth with abcauline caecum. Gonothecae oval with strong transverse corrugations and rings, occurring in opposite pairs on lower part of stem. Type species. Polysertularella polyseriata , sp. n. , designated herein. Notes and differential diagnosis. In most genera of Sertulariidae , hydrothecae have an alternate to opposite biserial arrangement on branches, and especially on the stem. A few genera in the family, including Abietinaria Kirchenpauer, 1884 , Thuiaria Fleming, 1828 , Sertularia Linnaeus, 1758 , and Staurotheca Allman, 1888 include some species with multi-serial rows of hydrothecae on branches and very rarely on the stem as well. The nominal genus Selaginopsis Allman, 1876 , originally established for sertulariids having hydrothecae in more than two longitudinal rows, is no longer recognized as valid in some works because of its artificial composition and differences among included species in operculum structure (Peña-Cantero et al ., 1997). However, no species with a multiserial arrangement of hydrothecae and four-flapped operculum (resembling Sertularella ) has been known in the family until now. Polysertularella is phylogenetically close to the well-known and widely distributed sertulariid genus Sertularella Gray, 1848 . Their relationship is apparent from the similar four-flapped operculum, the four-cusped hydrothecal aperture, and the general structure of their gonothecae. The latter resemble those of many species of Sertularella , Symplectoscyphus Marktanner-Turneretscher, 1890 , and some other genera in the family. Distinctive characters of the new genus are as follows. Gonothecae arise from the apertures of tubular processes borne in opposite pairs on the stem that resemble and are probably homologous to hydrothecae. Insertion of gonothecae thus differs from that observed in Sertularella and Symplectoscyphus , in which gonothecae normally arise near the hydrothecal base. Gonothecal arrangement is superficially similar to that in Synthecium Allman, 1872 (family Syntheciidae ), a genus with hydrothecae in opposite pairs and with gonothecae arising from the hydrothecal orifices ( Millard 1975 ; Vervoort, Watson 2003 ). However, Polysertularella and Synthecium are not closely related because species of the latter lack an operculum ( Millard 1975 ; Vervoort & Watson 2003 ; Bouillon et al . 2006 ). Expanding the scope of Sertularella to accommodate the new species, with its multi-serial arrangement of hydrothecae, is inexpedient. Sertularella is already the largest genus in Hydrozoa, and all of some 300 nominal species of this genus have biseriate and alternately arranged hydrothecae, according to recent generic diagnoses ( Naumov 1960 ; Calder 1991 ; Vervoort 1993 ; Cornelius 1995 ; Hirohito 1995; Bouillon et al. 2006 ). Certain morphological characters observed on the type colony may be important, but were not included in the diagnosis of the new genus because of a shortage of material. These included the polysiphonic common stolon, and the origin of gonothecae from the apertures of hydrotheca-like processes. The generic name Polysertularella reflects both the multi-serial arrangement of hydrothecae and the relationship of the genus to Sertularella , as apparent from hydrothecal and gonothecal shape, and opercular structure. The gender of the name is feminine.