Comparison of cnidae sizes between the two morphotypes of the giant Caribbean sea anemone Condylactis gigantea (Actiniaria: Actiniidae)

Abstract

The sea anemone Condylactis gigantea is an ecologically important member of the benthic community in coral reefs of the tropical Atlantic, and displays two morphotypes with respect to the color in their tentacular tips: the green tip morphotype and the pink/purple tip morphotype. Although some molecular and ecological differences have been found between these morphotypes, no other morphological distinctions have been reported, and currently both are still considered a single taxonomic species. In the present study, we perform an exploration on the variability in the size of cnidae between these two morphotypes and performed statistical analyses to compare the 10 categories of cnidae from specimens hosted in the Cnidarian Collection of Gulf of Mexico and Mexican Caribbean, of the Universidad Nacional Autónoma de México, which were previously collected in several coral reefs localities of the Yucatán Peninsula. Results reveal no significant variation in cnidae size between the two morphotypes, but significant variations were found within each morphotype. In addition, we update the composition of the cnidom of C. gigantea, and the utility of the size of cnidae to distinguish between morphotypes or closely related species is discussed.

Variability of cnidae within a small clonal sea anemone (Isactiniasp.)

“…In Isactinia ‐MTQ, the cnidom of the actinopharynx was almost exclusively made up of large basitrichs, complimented by very low numbers of small basitrichs and p ‐mastigophores. This is consistent with other species in which basitrichs and sometimes mastigophores are found within the actinopharynx (Acuña et al, 2007; Chintiroglou et al, 1997; Garese et al, 2019; González‐Muñoz et al, 2018; Mitchell, 2010). Cnidae within the actinopharynx are believed to further assist in the immobilization and killing of prey (Van‐Praët, 1985) before it is passed further down the gastrovascular cavity towards the mesenterial filaments.…”

“…Once food has been captured, sea anemones use their tentacles to pass it towards the mouth, where it enters the actinopharynx (Lampitt & Paterson, 1987;Lindstedt, 1971;Nicol, 1959). In Isactinia- González-Muñoz et al, 2018;Mitchell, 2010).…”

Diversity, host specificity and biogeography in the Cladocorynidae (Hydrozoa, Capitata), with description of a new genus

“…The statistical treatment of cnidocyst size data was previously used to search for fine-scale variations in other hydrozoan species, revealing in some cases no differences (Wollschlager et al, 2013) or significant differences among genetic clades (Arrigoni et al, 2018;Manca et al, 2019;Maggioni et al, 2020c). Similar studies were performed also on sea anemones, in which only some cnidocysts, coming from particular structures, varied among morphs (Gonz alez-Muñoz et al, 2017), or did not vary at all (Gonz alez- Muñoz et al, 2018), showing a high intraspecific variability (Garese et al, 2016). The results obtained in this work are therefore in line with previous works showing limited, but in some cases still useful, power of discrimination of cnidocyst size among closely related species or populations.…”