It’s not what it looks like: molecular data fails to substantiate morphological differences in two sea hares (Mollusca, Heterobranchia, Aplysiidae) from southern Brazil

Luiza De Oliveira Saad,Ángel Valdés,Carlo Magenta Cunha,Karine Delevati Colpo

doi:10.1007/s10152-014-0408-1

Abstract

Species of sea hares have been recognized traditionally based on morphological traits, mainly the radula, external coloration, and reproductive anatomy. However, recent studies have shown substantial color variation in some sea slug species. Molecular data have been successfully used to differentiate morphologically similar species of “opisthobranchs” and resolve questions on the taxonomic value of color. The objective of this paper is to use molecular data in an attempt to elucidate whether specimens of Aplysia brasiliana with distinct colorations and morphologies are actually the same species. To this end, DNA from 14 specimens of A. brasiliana was extracted, including five specimens identified as a distinct morphotype from typical A. brasiliana. Although the two morphotypes have consistent differences in their external morphology and radula, the molecular data confirmed that there are no significant genetic differences between them. This is another example of the need to re-evaluate taxonomic decisions based on morphology in light of molecular evidence.

Highlights

Species of sea hares have been recognized traditionally based on morphological traits, mainly the radula, external coloration, and reproductive anatomy (Eales 1960)
We study two different morphotypes of Aplysia brasiliana (Rang, 1828) collected from Southern Brazil
To assess whether the three genes have significantly conflicting signals, the incongruence length difference (ILD) test (Mickevich and Farris 1981; Farris et al 1994), implemented in PAUP*4.0 as the partition homogeneity test (Swofford 2002), was calculated for all genes combined with 2,000 replicates

Summary

Introduction

Species of sea hares have been recognized traditionally based on morphological traits, mainly the radula, external coloration, and reproductive anatomy (Eales 1960). The original descriptions of most species of Aplysia were based solely on external morphological characteristics, body and shell shape and color pattern (see Eales 1960). Marcus and Marcus (1958) and Eales (1960) were the first authors to described species of Aplysia including illustrations of the radula and the reproductive anatomy, but always stressing color differences between species for taxonomic decisions. New species names for Aplysia and other ‘‘opisthobranch’’ molluscs have been introduced based on color differences with closely related species.

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