Helobdella chaquensis

External morphology

A Glossiphoniidae of the Helobdella triserialis type , based on its exosomatic characters. Rings undivided, lacking a nuchal gland or dorsal plate. Three rows of dorsal tubercles on rings a2—one median and two lateral—which are acuminate but not darkly pigmented; it also presents three dorsal rows of sensillae situated atop protruding papillae—smaller than the tubercles—which we shall term "segmental papillae." Two paramedian rows, two intermediate rows, and two supramarginal rows are observed. Collectively, these elements delineate additional longitudinal rows of papillae. Two eyes in somite IV (rings a1–a2). Mouth situated at the base of the anterior lip, in somites II/III. Gonopores separated by a single ring: the male gonopore is located at the junction of XII a1/a2, and the female at XII a2/a3. Anus situated on the posterior furrow of somite XXVII. Somites I + II are fused into a single ring; somites III and IV are 2-ringed; VI through XXIV are 3-ringed; XXV and XXVI are 2-ringed; and XXVII is 1-ringed.

Internal morphology

The pharynx is long and straight—lacking a crook or ascending course—extending to the posterior third of somite XIII. Two thick collecting ducts from the salivary glands open into its base; these glands are located in somite XIII, forming a compact, oval mass on each side. A very short, undifferentiated esophagus is present. The crop is provided with six pairs of simple lateral cecae; the sixth pair—specifically the post-cecae—are very long and extend posteriorly to the very end of the body. The vasa deferentia exhibit no recurrent or descending course, as the pre-atrial loop of the spermiducts begins in segments XII/XIII via a thick spermatic duct. The pre-atrial loop of the male genitalia is very short, extending no further than segments XIII/XIV, and consists of a descending (recurrent) limb—the thick spermatic duct—and an ascending (or procurrent) limb—the ejaculatory duct. Both ejaculatory ducts empty into the thick atrial horn on their respective sides. The ovaries extend as far as somite XV and consist of two relatively slender tubes devoid of ova, as the dissected specimen (Paratype) bore 181 small-diameter eggs contained within several ovisacs on its ventral surface.

Habitat & range

Habitat

Freshwater

Region

South America

Recorded from

Argentina

Junior synonyms

Adaetobdella chaquensis