Helobdella malvinensis

External morphology

Body small and stout, of normal shape, with the acetabulum situated in a ventral position. Individuals bearing ovisacs and juveniles measure between 8 and 10 mm. The ratio of total length to maximum width—measured in three typical, slightly contracted specimens—is 1.9, 2.1, and 2.4. The ratio of maximum body width to acetabulum diameter is 3.7, 4.3, and 3.5. The mouth is located within the concavity of the acetabulum, at the level of somite III. Two eyes are present on somite IV. The annuli are simple, lacking secondary transverse grooves, tubercles, or papillae. The gonopores are separated by annulus XIIa2; the male gonopore is situated at XIIa1/a2, and the female at XIIa2/a3. The anus is located at the junction of somites XXVI and XXVII. Somites I and II are fused into a single annulus; somites III and IV are uniannulate; somite V is biannulate; somites VI through XXIV are triannulate (i.e., complete); somites XXV and XXVI are biannulate; and somite XXVII is uniannulate. Color greenish-gray, light and uniform, without longitudinal lines, maculae, or bands.

Internal morphology

The pharynx is very long, extending as far as somite XIV, with its distal end curved into a small crook—that is, exhibiting a brief ascending or procurrent course. Two compact salivary glands discharge into its distal end via thick ducts. The esophagus, located in somite XIV, is short and not U-shaped. The crop extends from somite XV to XIX and features five pairs of small, simple lateral ceca; the pair of post-ceca in somite XIX descends toward the posterior end of the body. There are five pairs of testes, extending from the junction of somites XIV/XV to XVIII/XIX. The vasa deferentia do not follow a descending or recurrent course; at the end of somite XII, each continues into its respective sperm duct, which then ascends through somites XV/XVI, transitioning into an ejaculatory duct. Ovaries U-shaped with unequal branches, whose caudal extent barely reaches XIV/XV.

Habitat & range

Habitat

Freshwater

Region

South America

Recorded from

Chile, Argentina

Junior synonyms

Adaetobdella malvinensis