Seasonal variation of morphological characters of Chondrilla aff. nucula (Porifera: Demospongiae) from the south-east coast of Brazil

Chondrilla nucula is a morphologically simple species defined by the presence of spherasters in its skeleton. For a long time C. nucula was considered a cosmopolitan species, however, in 1999, a molecular study demonstrated the existence of a species complex with at least four cryptic species, besides C. nucula. At that time, those four new species were not formally described because the morphological differences observed did not reflect species differences and were attributed to plasticity. Since then, researchers working on Chondrilla species suggested that the skeletal organization, the distribution of spherulous cells and the type of surface should be used to differentiate species. Individuals of Chondrilla aff. nucula from one population in Arraial do Cabo, Rio de Janeiro State, Brazil, were collected monthly and analysed in order to test the validity of those three characters to separate the species of Chondrilla. Moreover, to determine if the differences in spicule dimensions previously found were seasonal, we also quantified the diameter of the spherasters throughout the year. Our results demonstrate that all analysed characters are extremely variable and that spicule size can vary even at the same locality. The present study shows the importance of testing the variability of morphological characters before describing new species. Unfortunately, until valid taxonomic characters are found, the Atlantic Chondrilla species will have to remain undescribed.