Postembryonic growth and morphological variability in Turbanella mustela (Gastrotricha, Macrodasyida)

The macrodasyid gastrotrich Turbanella mustela was studied by light microscopy and analyzed for postembryonic growth and variation. Growth was characterized by a positive relationship between the length of the body and the lengths of the pharynx and intestine, widths of the head and body, and diameter of the buccal capsule. Evidence of early growth in many of these structures is indicated by strong positive correlations between their dimensions and body length in the smallest size class. It is hypothesized that early and rapid growth of the buccal capsule and pharynx may be of particular importance in the trophic ecology of the species. An analysis of the relative proportions of the alimentary structures to one another throughout ontogeny is thought to be of limited taxonomic importance, but may be of significance in understanding the evolution of the phylum. Ontogenetic variation in metric and meristic features does not affect species identification and juveniles appear as miniature forms of the adult. Juveniles have fewer adhesive tubules than adults and ontogeny contributes to a significant increase in the number of lateral, caudal and dorsal adhesive tubules. Early meristic development may represent an adaptation to rigorous beach conditions, and increase anchorage and adhesion in species common to high-energy beaches. Further, ontogenetic variation in the number of adhesive tubules may contribute to intraspecific differences in the distribution of Turbanella mustela and affect the species' susceptibility to passive dispersal by wave action. J. Morphol. 237:117-126, 1998. (C) 1998 Wiley-Liss, Inc.