Description
(Described in Latin as Pachystoma) Head and sensory organs:
The head is proboscis-shaped, free, large, and transversely wrinkled. Its cheeks expand into two tentacle-like lobes. The aperture is anterior, with folded lips. The mandibles are cartilaginous and appear swollen with strong muscles. The tongue is covered by elongated skin, and features numerous transverse ossicles in the middle, with anteriorly winged sides. The eyes are pedunculated (stalked), located at the external base of the tentacles. Two true tentacles are present, which are very long, bristly, and somewhat contractile.
Foot and operculum:
The foot is flattened and broad, with a subtriangular sole that is anteriorly margined and truncated. The operculum is horny, located on the dorsal side of the foot; it displays subtly concentric folds and a lateral-median nucleus.
Mantle and respiration:
The mantle is large and free; under the neck, it transforms into an elongated, flattened, retractor white muscle. The respiratory opening is large, situated under the mantle above the left siphon. The gills are comb-shaped, right-sided, and located under the mantle. An elongated fringe runs parallel to the rectum and oviduct. The respiratory organ (or respiratory antrum) is very large, dorsal, and sac-like, perforated above the very long siphon. The neck is equipped on both sides with broad, flattened wings, which are almost convoluted into two siphons. The left siphon, situated before the respiratory opening, inhales air, while the right, located under the anus, exhales and expels feces.
Anus and reproductive organ:
The anus is contractile, with an elongated rectum. The penis is exserted, very large, and fleshy, situated under the mantle margin on the right side near the anus (in males). Its apex is attenuated, and its base is appendiculated and gland-bearing; the appendix is perforated.
Shell characteristics:
The shell is right-handed, covered, delicate, longitudinally plicate, globose, and very ventricose (swollen). The spire is depressed or short; the body whorl is very large, and the base is broadly umbilicated. The peristome is simple, always thin, and rarely somewhat reflexed. The aperture is entire, oblong, very large, and expanded.
Movement and habits: Its movement is sluggish. When it needs to breathe, it seeks the surface and convolutes the left wing of the neck into a rigid tube. While it inhales, it flexes its tentacles and slowly retracts its head, receiving air at the tip of the siphon. It is tenacious of life. [4]
