Orchibdella pampeana

External morphology

Cyclobdellidae of relatively small size; mature individuals do not exceed 40 mm. Dimensions of the holotype: total length 30, length to the male gonopore 7.5, width at that level 4.0, maximum width 4.9, acetabulum diameter 2.9. Acetabulum with a thick anterior lip; The posterior lip is formed by V (a1 a2) or by V (a1 a2) and V a3 fused ventrally. Five pairs of eyes form a regular arc over annuli 2, 3, 4, 5, and 7—that is, on II, III, IV, V (a1 a2), and VI (a1 a2). The gonopores are separated by 1/2 + 4 + 1/2, by 5 + 1/2, or by 1/2 + 5 + 1/2 annuli, listed in order of decreasing frequency; the male gonopore is located on XII b1, on XI/XII, or on XI b6, while the female gonopore is always on XIII b1. Somites I–IV are uniannulate; V is biannulate, though its two components may be fused ventrally; VI is generally biannulate, or occasionally triannulate due to the separation of b5 and b6; VII is triannulate—with the final annulus (b5 + b6) either subdivided—or else quadriannulate; VIII is quadriannulate or quinquannulate; IX through XXV are quinquannulate (or complete); XXVI is triannulate, or consists of two subdivided annuli; XXVII is uniannulate or biannulate. The anus is located at XXV/XXVI. The sensillae are small and circular, with the dorso-paramedian and intermediate sensillae being relatively larger. The dorsal and ventral fields delimited by the sensillae exhibit the following relative proportions: The dorsomedian field is approximately equal in size to the paramedian field, twice the size of the intermediate field, and one-third larger than the supramarginal field. On the ventral side, the median field is nearly three times larger than the paramedian field, half the size of the intermediate field, and ten times larger than the submarginal field. There are 17 pairs of nephropores, with each pair situated on the caudal margin of the ...b2 annuli from V b3 to XXIV; each pore is situated in the intermediate field at a short distance from the sensilla of the same name. Clitellum formed by 15 annuli, from X b5 to XIII a2. The coloration of the dorsal surface features narrow gray or brownish bands superimposed upon a similar, though lighter, background hue. Two of these bands are paramedian, two are intermediate—characterized by sinuous margins—and two are supramarginal. In some individuals, the paramedian and intermediate bands on each side fuse to form a single continuous stripe.

Internal morphology

The oral chamber communicates freely with the buccal sinus, as there is neither a muscular velum nor jaws. Pharynx long and narrow, extending to XII: 187 the crop is simple, lacks caeca, and reaches as far as XIX/XX. Intestine broad; its proximal half—of larger diameter—possesses numerous horizontal folds on its inner wall; following this are two ovoid chambers with smooth inner walls, separated from one another—and from the first section—by respective sphincters. From XV to XXIV, two pairs of testes are found in each interganglionic space; however, the first pair in XV may be absent—or both this pair and the second pair in somite XXIV may be missing—such that the total number varies from 18 to 20 pairs. The vas deferens ascends to the level of ganglion XI, where it turns toward the median line and descends almost to ganglion XIII; that is to say, it follows a recurrent course or trajectory. Each vas deferens empties into the spermatic duct on its respective side, which consists of a tube folded into moderately tight coils. These ducts differ from one another, as one is more uncoiled than the other; the left duct occupies somite XIII, while the right duct occupies somites XIII and XIV. Emerging from the caudal extremity is a very short ejaculatory duct, featuring a fusiform distal bulb; there is an evident asymmetry, as one bulb (either the right or the left) opens into the posterior apex of the prostatic region of the atrium, while the other enters that same region laterally. The penial sac is a long, straight, cylindrical tube, the posterior portion of which is fusiform and somewhat globose—a section which... ...represents the prostatic region. The penis is housed within a narrow, cylindrical tube and is eversible. Its caudal extent reaches segment XIV/XV or the beginning of somite XV. The ovaries are located in the postgenital region, in segments XVI and XVII; each consists of a short, thick, semi-lobular tube, U-shaped—that is, possessing a procurrent limb. Additionally, each ovary features a lateral limb situated at its proximal end, from which the oviduct originates. After traversing a distance of three somites and following a path marked by several broad undulations, both oviducts converge within a minute female bursa embedded in the ventral body wall.

Habitat & range

Habitat

Freshwater

Region

South America

Recorded from

Argentina