Cnidom variation through distinct developmental stages in the sea anemone Aulactinia marplatensis (Zamponi, 1977) (Cnidaria: Actiniaria)

Abstract

The cnidae are the exclusive diagnostic structures of phylum Cnidaria. The inventory of all cnidae types of a particular species is called the cnidom. The study of cnidae has been widely addressed in all classes of cnidarians. Particularly in the order Actiniaria (sea anemones), the study of the composition, size and distribution of cnidae is essential to the identification and description of species. In the present study, we examine the cnidom of the sea anemone Aulactinia marplatensis in three different stages of development throughout its life cycle. We found that the composition and abundance patterns are very similar between the adult and juvenile stages, although significant differences in the size capsules were found between both stages and in all cnidae types observed, being bigger those from the adult forms. The planula larvae stage presents a less diverse cnidom in comparison to the juvenile and adult stages; however, it presents an exclusive cnidae type (the mesobasic p-mastigophore) which is the biggest in size of all the cnidae types observed in the species. These results highlight the importance of considering the stage of development when cnidae is used as a diagnostic character, and the particular relevance of the study of the cnidom in larval stages.

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

“…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.…”

“…Although not unheard of (Garese et al, 2016, 2019), actiniarian mesenterial filaments are believed to rarely contain spirocysts (Van‐Praët, 1985). Although it is possible that the spirocysts reported here in the mesenterial filaments may be an artifact of exogenous contamination between samples, Fautin (1988) has cautioned that the presence of unexpected cnida may indeed signify a rare variety within the tissue.…”