Isozoanthus Carlgren, in Chun, 1903

Low, Martyn E. Y., Sinniger, Frederic & Reimer, James Davis, 2016, The order Zoantharia Rafinesque, 1815 (Cnidaria, Anthozoa: Hexacorallia): supraspecific classification and nomenclature, ZooKeys 641, pp. 1-80: 15-16

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Isozoanthus Carlgren, in Chun, 1903


Isozoanthus Carlgren, in Chun, 1903 

Polythoa (Taeniothoa)  Andres, 1883a: 521, 532 [nomen oblitum].

Isozoanthus  Carlgren, in Chun, 1903: 520 [nomen protectum].

Type species.

Isozoanthus giganteus  Carlgren, in Chun, 1903, by monotypy (Articles 68.3, 68.3.1, ICZN, 1999: 71).




Macrocnemic zoanthids with a marginal endodermal sphincter muscle (=cteniform endodermal [ Swain et al. 2015]) and inconspicouous mesogleal ring-sinus.


The genus Isozoanthus  was first made available in Carlgren (in Chun 1903: 520). The type species by monotypy is Isozoanthus giganteus  (first very briefly diagnosed and figured by Carlgren (in Chun 1903: 520, unnumbered fig.). Carlgren’s (in Nordgaard 1905: 159) use of " Isozoanthus (Epizoanthus) arborescens  " and subsequent designation (i.e. Carlgren 1913: 39) of Epizoanthus arborescens  (Danielssen, 1890) as type species are thus invalid (Article 67.2, ICZN 1999: 66, 67) (see also Williams 2000: 195).

The status of this genus is currently very confused. With the utility of the characters of the sphincter muscle in zoantharians in question (see Swain 2010, Sinniger et al. 2010a), it is clear that more research is needed to clarify the diagnosis and taxonomic position of Isozoanthus  . The taxonomy is further complicated by the recently described species (the hydroid-associated Hydrozoanthus antumbrosus  (Swain, 2009) originally described within Isozoanthus  ), and the octocoral-associated Isozoanthus primonodius  Carreiro-Silva, Braga-Henriques, Sampaio, de Matos, Porteiro & Ocaña, 2010) clearly belong to other genera based on ecology and morphology. Furthermore, only limited molecular data is available for the type species Isozoanthus giganteus  . Data in Swain (2010) indicate that Isozoanthus giganteus  is highly divergent from both the well-researched species of Isozoanthus  - Isozoanthus sulcatus  (Gosse, 1859)-and all known zoantharians. Recent work by Fujii and Reimer (2013) shows that Isozoanthus sulcatus  is likely within the Nanazoanthidae  Fujii & Reimer, 2013. However, as additional information on Isozoanthus giganteus  is lacking, the diagnosis is retained with the caveat that any assignment of species to this genus should include: 1) phylogenetic confirmation of a close relationship with Isozoanthus giganteus  ; and 2) the elimination of any possibility that the species in question does not belong to another parazoanthid genera based on morphology, ecological associations, and/or habitat.