Intraspecific variations in species of Ophiuroidea (Echinodermata) from the Tropical Southwest Atlantic, Northeast Brazil.

Class Ophiuroidea groups the most diverse and abundant organisms of the phylum Echinodermata, having approximately 2100 described species. They have a simple body plan, consisting of a central disk, where their main internal organs are located, and to which the arms are attached. Species are identified based mostly on external morphological characters. However, many species present similar diagnostic characters in several families, which makes their phylogenetic reconstruction quite complex. Furthermore, many of these characters undergo changes during post-larval development and growth. Therefore, ontogenetic studies become relevant. Progress is still slow in this field, however, mainly due to difficulties in identifying some species in these stages. Despite significant advances in the number of species described for the Northeast region of Brazil, studies on the growth series of species of Ophiuroidea reported for this region are still scarce. The present work describes the intraspecific variations of Ophionereis reticulata (Say, 1825), Ophionereis squamulosa Koehler, 1914, and Amphipholis squamata (Delle Chiaje, 1828), considering young and adult specimens. The morphometry of individuals and aspects of microstructure are included. The description of morphological characters in growth series allowed us to identify typical characteristics of certain stages. Some structures remained almost unchanged, while others underwent most of the changes, being used to characterize different growth stages. Such stages are helpful for the correct identification of these species. In addition, the study of morphological variations between young and adult specimens contributes to our understanding on evolutionary relationships within Ophiuroidea. [ABSTRACT FROM AUTHOR]