Helobdella melananus Lai and Chang

Lai, Yi-Te, Chang, Chih-Han & Chen, Jiun-Hong, 2009, Two new species of Helobdella Blanchard 1896 (Hirudinida: Rhynchobdellida: Glossiphoniidae) from Taiwan, with a checklist of hirudinea fauna of the island, Zootaxa 2068, pp. 27-46 : 34-37

Helobdella melananus Lai and Chang , n. sp.

( Fig. 3 & Fig. 4 )

Holotype: L00081, deposited in the Invertebrate Zoology and Cell Biology Lab, Department of Life Science in National Taiwan University, Taipei. Underneath stone in Guandu Plain, Taipei, Taiwan (25° 07' 59' 69''' N, 121° 28' 74'' 07''' E), collected by Yi-Te Lai, 12 October 2007.

Paratypes: L00082&L00083, deposited in the Invertebrate Zoology and Cell Biology Lab, Department of Life Science in National Taiwan University, Taipei. Underneath stone in Guandu Plain, Taipei, Taiwan (25° 07' 59' 69''' N, 121° 28' 74'' 07''' E), collected by Yi-Te Lai, 12 October 2007. Mounted specimen SLD0002R, SLD0003L, SLD0004L&R, SLD0006R, SLD0007L, SLD0008L&R, and SLD0009L&R, deposited in the Invertebrate Zoology and Cell Biology Lab, Department of Life Science in National Taiwan University, Taipei. Underneath stone in Guandu Plain, Taipei, Taiwan, collected by Yi-Te Lai, 01 October 2006.

Etymology: The specific name is alluding to the conspicuous black pigmentation around the anus and the gradual increase of black pigmentation on the annuli and papillae of the posterior body.

Diagnosis: The body length is less than 10 mm. No scute. On the pale dorsum, the papillae are more and more apparent and pigmented on the posterior annuli. The anus is significantly pigmented. Hence this species can be easily distinguished by the obviously pigmented anus as well as the increasing pigmentation and protrusion of dorsal papillae. Internally, five pairs of crop caeca and four pairs of testisacs are significant characters to be recognized.

Form: Body length 4.0–5.5 mm, maximum body width 2.0–2.3 mm, anterior sucker diameter 0.3–0.4 mm, posterior sucker diameter 0.9–1.0 mm. Ovate-lanceolate in relaxed specimens; uniformly flattened dorsalventrally; dorsum slightly convex; venter flat. Cephalic sucker cupuliform with thickened rim; proboscis pore small, in centre of cavity. Posterior sucker circular, diameter almost equal to half to one third of maximum body width, with thick margin and flat venter, broadly attached, directed ventrally or slightly caudalventrally. No nuchal scute present.

Color and pattern: When alive, body translucent, color of gray, green, pink, or unpigmented. Dorsum with tiny black or olive dots arranged transversely in every annulus but indistinct in those of one third of anterior body. Pale brown or green chromatophores arranged through the body surface, accumulated more in more posterior annuli. Venter without any chromatophores, with tiny black dots arranged transversely and marginally. Dorsum of posterior sucker with irregularly distributed black spots. Venter without any dots or spots.

Eyes: One pair, punctiform to triangular in median field in III (3rd annulus).

Annulation: 67 annuli in holotype specimen. I, II and III uniannulate, indistinctly separated from each other. IV biannulate with (ala2)>a 3. V biannulate, with (ala2)>a3, and in some cases an indistinct furrow in a1/a 2. VI –XXIII midbody somite and triannulate. XXIV and XXV biannulate. XXVI and XXVII uniannulate. Anus in the furrow of XXVI/XXVII (66th/67th annulus).

Papillation: Anterior half dorsum smooth; posterior half dorsum with three rows of papillae, one large median row and one mild row on each side submarginally. The middle row of papillae distinguishable and black-tipped from XVII–XXVII; while the submarginal rows of papillae from XXIII–XXVI. Dorsum of posterior sucker with no distinct papillae. Venter smooth.

Gonopores: Separated by one annulus; male at XII a1/a2 (26th/27th annulus); female at XII a2/a3 (27th/28th annulus); both strictly within furrows.

Digestive system: Proboscis cylindrical and robust; in flattened specimens, no more in length than 10 annuli. Salivary glands diffuse; gland cells loosely distributed beside the pharynx in XI–XIV. Crop in XV–XIX; 5 pairs of caeca; first 4 pairs in XV–XVIII simple, unlobed and unbranched, directed laterally and confined to their respective segments as the first pair often indistinct and vague when empty; fifth pair in XIX elongate, deflected posteriorly and lateral to intestine, extended to about XXIII obliquely. Four pairs of unlobed intestinal caeca in XX–XXIII. Hind gut saccate, rectum narrow and oblique, tapering towards anus.

Male reproduction system: Four pairs of testisacs, intersegmentally arranged at XV/XVI–XVIII/XIX. Vas deferens enters sperm duct in XII/XIII, expands into seminal vesicle with S-shaped loop. Ejaculatory duct straight, uniformly broad and proceeds sometimes obliquely inward and forward up to XI. Terminal end of ejaculatory duct turning smoothly inwards towards atrial cornu at XI/XII, narrows at junction with cornu at XI/XII. Cornua muscular, strongly divergent, ovate in dorsal view. Atrium short and indistinct.

Female reproduction system: Ovisacs directed caudally; oviducts joined into short and indistinct atrium in XII.

Habitat: Attached on the surface of submerged or semisubmerged stones, woodblocks, artificial trash, and the shell surface of apple snail P. canaliculata and the viviparid snail Sinotaia quadrata Benson in flowing water. Rarely in irrigation ditches, drainage ditches and open sewers in Taipei.

Prey or host: Unknown. Tubificid worms and other aquatic oligochaetes may be the host or prey because the leeches exhibit foraging behavior while they are put into the same aquatic tank in lab. Viviparid snails may also be a prey item as H. melananus are usually attached on the shell surface.

Remarks: Compared with other Helobdella species, H. melananus is small and thin. The unique arrangement of pigmented papillae and the significantly pigmented anus make this species different from most other known Helobdella species. According to our review, H. conifera from Yeman (Al-Safadi & El- Shimy 1993) is the only described Helobdella species with similar external morphology as H. melananus . The pattern of papillae distribution in these two species looks alike. However, the mature body size of H. conifera (8–15 mm in length, 2–3 mm in width) is much larger than H. melananus (4–5.5 mm in length, 2–2.3 mm in width). The papillae of H. conifera are not pigmented, while the papillae of H. melananus are obviously pigmented. In addition, the black-pigmented anus, which is the significant character on H. melananus , was not noted on H. conifera .

Anatomically, H. melananus is different from most other Helobdella species by possessing five pairs of crop caeca and four pairs of testisacs, which is fewer than the number of testisacs in most of other Helobdella species. In addition, although the numbers of crop caeca and testisacs of H. melananus are the same as H. conifera from Yeman, these numbers do not match the original description of H. conifera (Al-Safadi & El- Shimy 1993). Hence, with the external and internal differences, H. melananus should be a new species rather than a described species.

Since it has been demonstrated that Helobdella leeches have origins in the Central and South America and dispersed passively from those regions, H. melananus is possibly an invasive species in Taiwan with an unknown origin in the Central and South America.

Figures

FIGURE 3. External morphology of Helobdella melananus n. sp. The scale indicates 1 mm.

FIGURE 4. Internal morphology of Helobdella melananus n. sp.. Roman numerals of X and XX indicate the orders of the ganglia. an. Anus; atr. Atrium; br. Brain; cr. Crop and crop caeca; ejc. Ejaculatory duct; g. Ganglion; int. Intestine and intestine caeca; mth. Mouth; ov. Ovary; prb. Proboscis; rt. Rectum; salg. Salivary gland; te. Testisacs.