Terrazoanthus Reimer & Fujii, 2010

Swain, Timothy D. & Swain, Laura M., 2014, Molecular parataxonomy as taxon description: examples from recently named Zoanthidea (Cnidaria: Anthozoa) with revision based on serial histology of microanatomy, Zootaxa 3796 (1), pp. 81-107 : 93-94

Genus Terrazoanthus Reimer & Fujii, 2010

Type species. Terrazoanthus onoi Reimer & Fujii, 2010 , by original designation.

Diagnosis. Hydrozoanthidae not obligately associated with Hydrozoa and lacking scleroprotein skeleton. Known from subtropical and tropical regions, azooxanthellate, and may be brightly colored (diagnosis of Reimer & Fujii 2010). Found at 1– 35 m. Polyps white, yellow, red or brown, expand to 12 mm wide and 20 mm long, with 15–20 capitular ridges. Marginal musculature transitional with approximately half its length mesogleal (distal) and half endodermal (proximal), 550–1536 Μm in length, composed of 17–110 attachment points. Encrustations of the column to endodermal surface of mesoglea; sparse mesogleal canals form an indistinct encircling sinus (diagnosis expanded using data presented here and Swain 2010).

Remarks. Species of Terrazoanthus are extraordinarily similar (in both morphology and genetics) to Epizoanthus californicus , Epizoanthus patagonichus , and Epizoanthus minutus . Nucleotide sequences of highly conserved genes (mitochondrial 16S ribosomal RNA & cytochrome oxidase I) are identical, and hypervariable genes (complete internal transcribed spacer of nuclear ribosomal RNA) contain few mutations and may not consistently differentiate species for which we have multiple sequences ( Table 1 ). With the available morphologic and genetic evidence, species assigned to Terrazoanthus could have reasonably been assigned to Epizoanthus and many of the taxa listed in Table 1 could be considered conspecific. Of particular similarity are species pairs E. patagonichus and T. onoi and E. californicus and T. sinnigeri ; with the small data sets currently available, it is not yet possible to determine if they are congeneric species or if the observed differences (the Terrazoanthus paratypes appear to be slightly smaller and have fewer mesenteries then the Epizoanthus species) reflect variation among conspecifics.

The genetic similarity of Terrazoanthus to E. californicus , E. patagonichus , and E. minutus suggests that revision of the genera involved will be necessary for the taxonomy of this clade to reflect molecular evolution (see Swain 2010). The type species of Epizoanthus is Epizoanthus papillosus (Johnston, 1842) , and as a symbiont of hermit crabs of family Paguridae , it is not expected to be closely related to these species (inferred from the distribution of symbioses across the phylogeny of Swain 2010). Therefore, upon future reexamination of morphology (particularly the marginal musculature), we suggest that reassigning E. californicus , E. patagonichus , and E. minutus to Terrazoanthus may be the most effective means of making taxonomy consistent with phylogeny. This reassignment would require further expansion of the definition of Terrazoanthus to include species that are facultative symbionts of Hydrozoa ( E. patagonichus associates with hydroids: McMurrich 1904).

Identification of the facultative hydrozoan-symbiont E. patagonichus as a close relative and potential congener to Terrazoanthus species introduces the possibility that others in this clade are unobserved symbionts of Hydrozoa as well; this would be consistent with the patterns of symbiosis of most non-Brachycnemic Zoanthidea ( Swain 2010) . Reciprocal monophyly between Hydrozoanthus and potential Terrazoanthus species reported by Swain (2010) provides support for the utility of the taxonomic concept of Terrazoanthus , even if it is eventually revealed to be a misnomer or that the type species is a junior synonym (if T. onoi was confirmed to be conspecific to E. patagonichus ), and suggests that marginal musculature may be a key character in distinguishing between the two sister genera (endodermal in Hydrozoanthus and transitional in Terrazoanthus ).