Parazoanthus Haddon & Shackleton, 1891

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: 91

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Parazoanthus Haddon & Shackleton, 1891


Genus Parazoanthus Haddon & Shackleton, 1891 

Type species. Parazoanthus axinellae (Schmidt, 1862)  , by original designation.

Diagnosis. Parazoanthidae  with encrusted column; mesoglea containing canals, cell-islets, and an encircling sinus; usually dioecious (diagnosis of Haddon & Shackleton 1891). Often associated with Demospongiae but not Hydrozoa; usually colonial; lacking scleroprotein skeleton (diagnosis expanded by Sinniger et al. 2008). Known from temperate and tropical regions at 1– 310 m. Some species zooxanthellate. Capitular ridges 10–22. Marginal musculature endodermal, 33–1251 Μm in length, composed of 7–63 attachment points. Encrustations of the column to endodermal surface of mesoglea (diagnosis expanded using data presented here and Swain 2010).

Remarks. The concept of Parazoanthus  has been refined by molecular phylogenetics with the loss of taxa to genus Hydrozoanthus Sinniger et al., 2010  . Although the morphological definition of Haddon & Shackleton (1891) continues to accurately describe the taxa included in Parazoanthus  (and Hydrozoanthus  ), morphological characters that circumscribe these taxa have not been identified and recent restrictions are based on ecological and nucleotide data; Parazoanthus  is now restricted to Demospongiae-symbiotic taxa and their free-living relatives ( Sinniger et al., 2010). Within Parazoanthus  , there are three distinct clades of taxa that are restricted to (and are diagnosable by) symbioses with sponges of specific pairs of Demospongiae orders: Halichondrida & Poecilosclerida, Hadromerida & Haplosclerida  , and Petrosina  & Agelasida (see Figure S 2 of Swain 2010). There are no current taxonomic distinctions between the three clades of zoanthid symbionts; however, it seems appropriate to create subgenera within Parazoanthus  that reflect molecular evolution and the specificity of these symbioses.