A Generic Character, Can It Be Lacking in Individuals or the Species in a Given Genus?

Abstract

The protean diversity of form in the family Ostreidae (Mollusca), displayed even within well-definable, geographically and genetically isolated, living oyster species, is not amenable to easy classification. As a consequence, many authors have expressed dismay at being unable to arrange the members of the family in a neat system of classification. The classical typological methods of systematics have been conspicuously unsuccessful in this task. If isolated specimens are compared with a solitary type specimen of a given species, the differences between them commonly appear to be so great and obvious that the classifier is often tempted to propose a new name as a means of extricating himself from a quandary. Small wonder that many species, including well-definable, geographically and genetically isolated, living oyster species, have received many formal species or variety names. The common living European oyster Ostrea edulis Linne, 1758, for instance, has received at least 26 formal names [saxatilis 1807, adriatica 1819, deformis 1819, fucorum 1819, hippopus 1819, ruscuriana 1819, cyrnusii 1826, depressa 1836, taurica 1837, obtusa 1848, corbuloides 1855, rostrata 1856, rutupina 1863, tincta 1863, crassa 1867, leonica 1870, tarentina 1882, tyrrhena 1882, venetiana 1882, cumana 1883, pinnalis 1895, punctodentata 1895, unifasciata 1895, payraudeaui 1900, dianae 1915, sublamellosa 1916]. These names are based on individual variants, ecomorphs, local races, and at best, possibly on geographic subspecies. The differences on which these names were based were recognized through typological comparison of features of the shell. The effort to name all these has been needless, and the superfluous names should be ignored as soon as the species is recognized as a biological entity and the scope of its variability becomes known. Past search for reliable morphological classification characters in the family Ostreidae reveals other examples of unsuccessful typological procedures. Generally, such a search seeks to find features that are the least variable and are shared by every individual of the taxonomic group studied, be that group a species or a supraspecific taxon.