conispiral
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Torsion (gastropod) — Torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle and shell 180˚ with respect to the head and foot of the gastropod. This brings the mantle cavity… … Wikipedia
anterior — adj. [L. ante, before] 1. Before or toward the front. 2. Pertaining to the direction in which the head tends to point when an animal is active. 3. (MOLLUSCA: Gastropoda) In a crawling gastropod, pertaining to the head being closest to that part… … Dictionary of invertebrate zoology
umbilicus — n.; pl. lici [L. umbilicus, navel] 1. A navel, or navel like depression. 2. (MOLLUSCA: Gastropoda) A cavity formed around the shell axis between the faces of the adaxial wall of the whorls where these do not coalesce to form a solid columella. a … Dictionary of invertebrate zoology