Carvalho de Lima T., Barreto Braga Mello V., de Castro Oliveira C.D.

Cardiomya Adams, 1864 is a genus of septibranch bivalves normally found in deep water. Morphological characters of Cardiomya include a rostrate shell and radial sculpture composed by radial ribs. Despite being strongly indicative for generic differentiation, for specific identification, these same characters are extremely plastic and uninformative. Added to this, the rarity of the specimens and the difficulties in collecting make this genus a group full of misidentification and underestimated diversity. Currently, approximately 50 species of the genus are known, of which six have registered occurrences in brazilian waters: Cardiomya cleryana d’Orbigny, 1842; Cardiomya ornatissima d’Orbigny, 1853; Cardiomya striata Jeffreys, 1876; Cardiomya perrostrata Dall, 1881; Cardiomya striolata Locard, 1897 e Cardiomya minerva de Lima, Oliveira & Absalão, 2020. In order to select and test the smallest and most efficient set of characters that are efficient in classifying these species, 29 variables of approximately 200 specimens were selected and measured. To test whether the variables were informative, a discriminant analysis was performed, the average accuracy was 88%. After that, we use the Bayes Information Criterion (BIC) to select the most informative variables within the initial set. Of the 29 initial variables, a set of five was selected as being the most efficient, and a new discriminant analysis was performed using only these five variables in order to test if they were really efficient in discriminating species. Discriminant analysis obtained an average accuracy of 90%, demonstrating the efficacy of these variables even when used alone. This dataset is entirely related to the contour of the shell, demonstrating that these characters should be given greater attention when examining specimens.