Eyeballs and pitfalls: Estimating the degree of heterostrophy in the heterobranch shell (Gastropoda : Heterobranchia)

R. Cipriani et R. Bieler, Eyeballs and pitfalls: Estimating the degree of heterostrophy in the heterobranch shell (Gastropoda : Heterobranchia), MALACOLOGIA, 43(1-2), 2001, pp. 327-336
Citations number
Categorie Soggetti
Animal Sciences
Journal title
ISSN journal
0076-2997 → ACNP
Year of publication
327 - 336
SICI code
Heterostrophic gastropod shells, in which the coiling axes of proto- and te leoconchs diverge, pose interesting ontogenetic questions and complex morph ological characters for systematic analyses. The inclination angle of the p rotoconch in relation to the axis of coiling of the teleoconch has been use d to distinguish between otherwise similar heterostrophic species. The prec ision of this metric, however, is very sensitive to measurement biases. Thi s paper introduces a new technique, the box method, which provides a more p recise estimate of the angle of inclination of the protoconch. A rectangula r box is drawn around an image of the protoconch; the box diagonal then is used as an estimator of the angle of inclination. The accuracy of the techn ique is investigated with a simulation model that calculates two-dimensiona l projections of realistic three-dimensional coiling morphologies. The resu lts of the model suggest that the studied metric is dependent on the morpho logy of the protoconch and on its degree of immersion in the first teleocon ch whorl. Caution is in order when basing taxonomic decisions on difference s in the inclination of the protoconch without considering the underlying m orphologies and without knowing the error associated with these differences . Given that the accuracy of this metric cannot be achieved or known, the p recision of this angular measure should be maximized and its limits demonst rated. Authors are encouraged to include in their reports a description of the technique used to estimate the protoconch inclination and to give a mea sure of the error of the angular measurement made for each particular taxon or sample.(3)