Shell globose-ovate, fragile, with distinct growth lines. Fine regular spiral striations are visible with magnification and cover entire shell. Posterior end rounded, depressed, and imperforate, with aperture lip rising from the left side and rounding slightly above. Columella concave, continued on the parietal wall by a callus variable in breadth, but consistently thick. Callus widest on body whorl, then narrowing to encircle posterior end. Umbilicus not depressed. Animal elongated, too large to be fully retracted into the shell. Parapodial lobes reflected over anterior third of shell and not meeting dorsally. Cephalic shield deeply bifurcate posteriorly, and anteriorly extended into two small, lateral, flexible protrusions. Anterior part of the foot flared and flattened parallel to the eyes. Posterior pallial lobe partially reflected over the shell.
shell whitish with reddish tinge externally and internally. Callus usually white, but slightly creamy in some specimens. Soft parts from grey to light brown and slightly reddish in ground color. Many dark brown spots (of various sizes) distributed over entire animal, especially on the dorsal surface, and concentrated on the edges of cephalic and pallial lobes. Orange pigment is scattered over all, and distinct white spots are concentrated along the lobe margins.
common size :
shell up to 11 mm in length; entire animal up to 33 mm.
The reddish tinge of the shell (and several anatomical features) distinguishes H. callidegenita from all other Mediterranean species of this genus.
BIOLOGY / ECOLOGY
Herbivorous, grazes on seaweeds of the genera Chaetomorpha and Ulva, and on diatoms. Often its secretes a mucous tube when crawling, inducing trailing of other individuals along this tubes. Egg masses, sausage shaped, contain 300-700 yellow eggs. The development is lecithotrophic, and advanced veligers or crawling metamorphosed juveniles hatch from the egg capsules, indistinctly.
lives in shallow and sheltered areas and lagoons, mainly in muddy bottoms with seagrass and green seaweeds of Chaetomorpha and Ulva.