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: 102

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Genus Zoanthus  Lamarck, 1801

Type species. Zoanthus sociatus (Ellis, 1767)  , by monotypy ( Lamarck 1801).

Diagnosis. Colonial Zoanthidae  free-living and lacking a scleroprotein skeleton. Known from tropical habitats around the world at 0– 40 m. Zooxanthellate. Polyps with highly variable coloration of the oral disk. Marginal musculature mesogleal and divided into distinct distal and proximal sections, 1000–5000 Μm in length, composed of 50–250 attachment points. Superficial encrustations may be present; canal system throughout the mesoglea does not form encircling sinus (diagnosis of Duerden 1898, expanded using data presented here and Swain 2010).

Remarks. Species of Zoanthus  have highly variable oral disk coloration, size of polyps, and numbers of tentacles and mesenteries, which make species identification and circumscription challenging. Earlier authors recognized the utility of the apparently species-specific morphology of the marginal musculature of Zoanthus  and usually included meticulous representations of its form in species descriptions (e.g., Duerden 1898), sometimes with no other drawings or images. That the form of the marginal musculature is a diagnostic character for Zoanthus  species circumscription should be evaluated using modern molecular phylogenetics; in addition to assessing whether it is reflective of molecular evolution, this would provide broadly applicable morphological characters for new evolutionary hypotheses.