The NSS Bulletin - ISSN 1090-6924
Volume 47 Number 2: 118-121 - December 1985
A publication of the National Speleological Society

Regressive Evolution in Stenasellids (Crustacea Isopoda Asellota of Underground Waters)
Guy J. Magniez

Abstract

The morphological features of the family Stenasellidae are strongly conservative. Only a few characters show an evolutionary species in natural phyletic lines. This evolution appears to be bound to the ecological re-adaptation undergone by strains now living in underground waters of temperate regions. These characters are body size and shape, the amount of respiratory blood pigments, the shape of the exopodites of 4th and 5th pleopods and the number of spines in the sternal row of pereopods 2-7 dactylopodites. This evolutionary trend behaves as a progressive drift of the characteristics of these organs and never as sudden modifications in the morphology. So, it seems difficult to assume that classical mutations at structural loci would be responsible for these gradual regressive phenomena.

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