Helobdella octatestisaca 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 : 30-34

Helobdella octatestisaca Lai and Chang , n. sp.

( Fig. 1 & Fig. 2 )

Holotype: L00077, 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' 55'' 71''' N, 121° 28' 79'' 33''' E), collected by Yi-Te Lai, 05 April 2008.

Paratypes: L00078, 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' 55'' 71''' N, 121° 28' 79'' 33''' E), collected by Yi-Te Lai, 05 April 2008. L00079 (four specimens), 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, 05 April 2008. Mounted specimen SLD0011R, SLD0015L&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. Mounted specimen SLD0020L, 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' 55'' 71''' N, 121° 28' 79'' 33''' E), collected by Yi-Te Lai, 05 April 2008.

Etymology: The specific name is “eight testisacs” in Latin, which describes the unordinarily low number of testisacs of the species.

Diagnosis: Morphologically, this species could be recognized with a pair of close eyes, scute of the middorsal nuchal region, smooth surface without papillae, transparent body, diffuse salivary tissues, six pairs of crop caeca, four pairs of intestine caeca, and four pairs of testisacs, which is the most important character that made the species be distinguished from other scutiferous Helobdella species.

Form: Body length 9–14 mm, maximum body width 2–5 mm, anterior sucker diameter 0.5–0.8 mm, posterior sucker diameter 0.8–1.5 mm. Ovate-acuminate, tapering towards anterior end, and ovate-lanceolate in relaxed specimens; moderately flattened; dorsum arched; venter flat or slightly indented. Cephalic sucker cupuliform with thickened rim; proboscis pore small, in centre of cavity. Posterior sucker circular, diameter almost equal to half of maximum body width, with thick margin and flat venter, broadly attached, directed ventrally or slightly caudalventrally. Nuchal scute round or backward pointed triangle, with color black, brown, or sometimes transparent gray.

Color and pattern: When alive, body translucent, color of dusky brown, pale, gray, or pink. Dorsum with tiny light brown dots arranged transversely in every annulus except the first ten. Dark green or olive chromatophores arranged irregularly under body surface. Venter without any chromatophores. Dorsum of posterior sucker with irregularly distributed brown spots. Venter of posterior sucker without any dots or spots.

Eyes: One pair, punctiform to triangular, close to each other, and sometimes separated only by a tiny space in median field in III (3rd annulus).

Annulation: 68 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 –XXIV midbody somite and triannulate. XXV biannulate with (ala2)>a3. XXVI and XXVII uniannulate. Nuchal scute in the middle VIII a1/a2 (14th/15th annulus). Anus in the furrow of XXV/XXVI (66th/ 67th annulus).

Papillation: Body smooth, papillae indistinct, a transverse row of tiny and vague papillae on each annulus dorsally. Sensory papillae not distinguishable from other papillae. Dorsum of posterior sucker with few scattered papillae. Venter smooth.

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

Digestive system: Proboscis cylindrical, slender, slightly tapered terminally; in flattened specimens about equal in length to total of 10 annuli. Salivary glands diffuse; gland cells loosely distributed beside the pharynx in XI–XIV. Crop in XIV–XIX; 6 pairs of caeca; first 5 pairs in XIV–XVIII simple, unlobed and unbranched, directed laterally and confined to their respective segments as the first two pairs often indistinct and vague when empty; sixth pair in XIX elongate, deflected posteriorly and lateral to intestine, extended to about XXII 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 XIII, expands into seminal vesicle with S-shaped loop. Ejaculatory duct almost straight, with the same wide and proceeds obliquely outward and forward up to XI. Terminal end of ejaculatory duct with vertical curve occasionally before turning smoothly inwards towards atrial cornu at XI/ XII, narrows at junction with cornu at XI/XII. Cornua muscular, strongly divergent, nearlyovate 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 under surface of submerged or semisubmerged stones, woodblocks, plastic bags, artificial trashes, stems of aquatic plants, and shell surface of apple snail Pomacea canaliculata Lamarck. Commonly in rice paddies, irrigation ditches, ponds, slow streams, drainage ditches and open sewers in Taipei, Taichung, Yunlin, Pingtung, Yilan, and Taitung.

Prey or host: Tubificid worms and other aquatic oligochaetes, and chironomids; occasionally found in group attaching on the body surface of predatory leech Whitmania laevis and sometimes on the surface of operculum and shell surface of the apple snail P. canaliculata .

Remarks: H. octatestisaca is similar to the widespread scutiferous species Helobdella stagnalis Linnaeus in both external and internal morphology. However, it can be distinguished from H. stagnalis and other scutiferous species of the genus by the first two pairs of crop caeca being unapparent, and by having only four pairs of testisacs; fewer than six pairs of testisacs in the Helobdella species is unusual.

Since H. octatestisaca has a conspicuous scute on the neck region of the middorsum, it is less likely that the species had been incorrectly identified as a nonscutiferous species by former researchers in Taiwan. In addition, the morphological similarity between H. octatestisaca and the well known widespread leech H. stagnalis , recorded for decades in China, India, and Japan, also reduced the possibility of misidentification ( Harding & Moore 1985; Uchida 1965; Yang 1996). In our survey, H. octatestisaca was found commonly in easily accessible habitats, such as rice paddies and irrigation ditches where they should have been discovered by past researchers. However, H. octatestisaca or any scutiferous leeches have never been discovered or mentioned in any hirudinea fauna survey in Taiwan ( Oka 1910, 1923, 1925, 1928 a– c, 1929 a – c, 1930, 1931, 1934; Takahashi 1931, 1933, 1934 a – b, 1935). Hence, it was inferred that H. octatestisaca is probably a recently invaded species in Taiwan.

Figures

FIGURE 1. External morphology of Helobdella octatestisaca n. sp. Notice the smooth dorsal surface and the scute located middorsally in the anterior region. The scale indicates 1 mm.

FIGURE 2. Internal morphology of Helobdella octatestisaca 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; scu. Scute; te. Testisacs.