Helobdella papilloprocta, Torres-Carrera & Duarte-De Lima & Oceguera-Figueroa, 2025

Torres-Carrera, Gerardo, Duarte-De Lima, Lucas & Oceguera-Figueroa, Alejandro, 2025, Description of two new species of freshwater leeches of the genus Helobdella (Hirudinea, Glossiphoniidae) from Mexico, with a redescription of Helobdella socimulcensis (Caballero, 1931), ZooKeys 1261, pp. 141-164 : 141-164

Helobdella papilloprocta sp. nov.

Figs 5 , 6 , 7

Type material.

Holotype. Mexico • adult; Rosendo Salazar , Municipio de Cintalapa, Chiapas; 16°28'14.696"N, 93°59'58.426"W, collected by GT-C and AO-F on April 2017; CNHE 12295 . Paratypes. Mexico • 28 adult paratypes; same data as for Holotype; CNHE 11132 .

Diagnosis.

Small leech, 5–9 length and 2.5–3.8 maximum width at somite XIX ( n = 14). Dorsal surface with ~ 40 longitudinal brown stripes. Brown coloration present or fade in larger specimens. Midline paired stripes not joining. Three longitudinal rows of black-tipped papillae, one median and two lateral rows, with additional incomplete marginal rows in all specimens. Papillae larger than the width of annuli. A pair of dorsal papillae located beside the anus. Eyespots oval, well separated. Whole body with a total of 67 annuli. Esophagus short. Crop with five pairs of caeca, the last pair forming post-caeca. Testisacs in five intersegmental pairs.

Description.

Based on adult specimen ( holotype), CNHE 12295 (stained), 7 length and 3.7 maximum width at somite XIX a 3. Twenty-eight paratypes, CNHE 11132, include 15 adult alcohol-preserved specimens, 10 flattened and stained specimens, and 3 specimens prepared for SEM.

External morphology. Body lanceolate to ovoid, 5–9 length and 2.5–3.8 maximum width at XIX. Ground color pale yellow or cream; dorsal preocular zone unpigmented. Dorsal surface with ~ 40 longitudinal stripes (visible in stained organisms). Patterns of metameric brown pigmentation and pigmented papillae, features otherwise characteristic of species in the “ triserialis ” series, are visible in some specimens. However, this pigmentation tends to fade in larger specimens (Fig. 5 A, B ). Paired midline stripes extend from annulus 5 (Va 1) to the anus at XXVII and remain not joined. Additional brown stripes extend from annulus 6 or 7 (Va 2 or Va 3) to the anus.

Dorsal surface with three longitudinal rows of pigmented papillae, one median and two lateral rows; an additional pair of incomplete paramedial rows present in all specimens. Median row of papillae from XII to XXVI, smaller additional paired papillae may be present in somite XXI and continue posteriorly (Fig. 5 D ). Lateral rows from XIV and continue posteriorly. Papillae generally wider than the width of individual annuli. A pair of prominent papillae located adjacent the anus (Fig. 5 D ). White dorsal spots faint, circular and larger than the length of an annuli, arranged in two pairs of rows per side, located at each a 2 adjacent to the papillae. White spots beside median papillae beginning at X and reaching XXVII, lateral white spots at XIV and reaching XIV. Eyespots cup-like at IVa 2, well separated. Ventral surface white (Fig. 5 C ). Mouth pore located at the anterior margin of the anterior sucker. Gonopores separated by a single annulus (XII a 2). Whole body with 67 annuli. Anus on XVII. Annulation: I – II fused; III uni-annulate; IV and V bi-annulate; VI to XXIV tri-annulate; XXV biannulate; XXVI and XXVII uni-annulate (Fig. 5 D ).

Internal morphology. Proboscis straight, not recurved, 1.8 length, extending from IX to XIV, or reaching XV when retracted. Salivary glands diffuse into parenchyma from XI to XVII; ductules not forming bundle, insert independently into base of proboscis. Esophagus short, located at XV a 1. Crop with five pairs of digitiform caeca; the first four pairs laterally directed, fifth pair with a posterior sinuous path or post-caeca, from XIX to XXIII (Fig. 6 A ). Intestine with four pairs of digitiform caeca, the first three slightly oriented anteriorly, and last pair directed posteriorly. Five pairs of testisacs, first pair between XIV / XV (Fig. 6 B ), last pair between XVIII / XIX. Ejaculatory ducts with a short posterior loop reaching XIV and then with an anterior trajectory to XIII. Ovisacs simple, elongated, extending posteriorly to XVII or XVIII (Fig. 6 C ).

Reproductive and ecological information. Specimens were found attached to the shells of the invasive Asian clam Corbicula fluminea (Müller, 1774) . Eight of 21 collected leeches with eggs or young leeches attached to the ventral surface, carrying between 21 to 36 eggs or 51 young leeches (Figs 5 C , 7 A ). Brooding area spans ~ 15 annuli, from XVIII a 3 to XXIII (Fig. 7 A ). Egg diameter 238–428 μm (322, n = 7). Spermatophores observed in three of 21 leeches, attached to the body wall, between annuli 24–27 (Fig. 7 B, C ). Each spermatophore ~ 350 μm length and 40 μm width. Spermatophores with a broad proximal portion attached on body wall of the recipient specimen, a narrow middle region or neck and distal portion with two horn-like tubes. Almost all leech specimens with epibionts (ciliates) attached to the body wall (Fig. 7 B ).

Etymology.

The specific epithet refers to the presence of a distinctive pair of papillae located adjacent to the anus.

Remarks.

The morphological characteristics of H. papilloprocta sp. nov. are consistent with those diagnostic of the genus ( Sawyer 1986; Siddall and Borda 2003); including the dorsoventrally flattened body, gonopores separated by a single annulus, one pair of cephalic eyespots, and the absence of esophageal organs (bacteriomes). The presence of multiple, longitudinal dorsal stripes and metamerically arranged papilla, particularly prominent in smaller leeches, clearly support its inclusion in the “ triserialis ” series sensu Sawyer (1986).

Species of the “ triserialis ” series can be differentiated from H. papilloprocta sp. nov. by distinct patterns of dorsal pigmentation and papillae distribution. Helobdella papillata has three rows of papillae restricted to the posterior third of dorsum (XIX or XX), while in H. papilloprocta sp. nov., dorsal rows of papillae begin at XII. Additionally, H. papillata lacks dorsal pigmentation. In H. lineata , dorsal papillae are irregularly scattered, while in H. papilloprocta sp. nov. dorsal papillae are regularly arranged. Helobdella transversa lacks both longitudinal pigmented stripes and papillae ( Sawyer 1972; Light and Siddall 1999), clearly contrasting with H. papilloprocta sp. nov. Helobdella lineata exhibits 12–14 longitudinal stripes on the dorsal surface, whereas H. papilloprocta sp. nov. display ~ 40. Helobdella fusca and H. virginiae are characterized by irregularly arranged dorsal spots, clearly contrasting with the pattern observed in H. papilloprocta sp. nov. (Table 2 ).

Helobdella papilloprocta sp. nov. is morphologically and phylogenetically (see below) closely related to H. socimulcensis , H. gulloae sp. nov., H. farmeri Kutschera, 2023 , H. europaea , and H. triserialis . Differentiation based on the morphological basis may be complex. However, the presence of two prominent papillae adjacent to the anus characteristic of H. papilloprocta sp. nov. appears to be a consistent and reliable character not present in other species of the genus.

Figures

Figure 5. Helobdella papilloprocta sp. nov. from Ejido Rosendo Salazar, Cintalapa, Chiapas, Mexico. A. Dorsal view of a small specimen with conspicuous pigmentation; B. Dorsal view of a specimen with faded pigmentation; C. Ventral view of faded-pigmentation specimen with young leeches attached; D. SEM microphotograph showing somite numbering. Abbreviations: an = anus; pa = papillae. Scale bar: 2 mm

Figure 6. Internal morphology of a stained paratype specimen of Helobdella papilloprocta sp. nov. A. Digestive tract details; B. Male reproductive system; C. Female reproductive system. Abbreviations: pr = proboscis; sg = salivary glands; cc = crop caeca; pc = post-caeca; int = intestine.

Figure 7. Helobdella papilloprocta sp. nov. A. Eggs attached to the ventral surface; B. Spermatophore attached to the body wall and epibionts are indicated with white arrows; C. SEM microphotograph of a spermatophore. Scale bars: 1 mm (A); 200 μm (B); 100 μm (C).