 |
| Helobdella viridoclypus K, Trivalairat, P. Trivalairat, Raquib & Purivirojkul, 2026 Emerald-charm leech | ปลิงสร้อยมรกต || RAFFLES BULLETIN OF ZOOLOGY. 74 |
Abstract
A new species of glossiphoniid leech, Helobdella viridoclypus, is described from the northern region of Thailand, representing the first record of the genus Helobdella from the country and Southeast Asia. Its characteristics are similar to those of the type species, H. stagnalis, but can be distinguished by its transparent rice-shaped and triannulated body, cephalisation, a single pair of dark eyes, a smooth dorsal surface without papillae, rich darkgreen pigmentation on the dorsum, six pairs of crop caeca with less developed first pair and unbranched second to sixth pairs (posterior caeca), male and female gonopore separated by a single annulus, and a triangular nuchal scute pointed backwards with yellowish-green colouring around the mid-dorsal region. The phylogenetic relationships of H. viridoclypus, new species, are clarified, showing that it is monophyletic within the stagnalis species-complex clade which includes H. adiastola, H. octatestisaca, H. modesta, and the type species H. stagnalis. The new species is a free-living leech that specifically preys on invertebrates and not on humans.
Key words. Annelida, Glossiphoniidae, Haementeriinae, jawless leech, freshwater, Huai Tueng Thao Reservoir
Order Rhynchobdellida Blanchard, 1894
Suborder Glossiphoniiformes Tessler & de Carle, 2018 in Tessler et al., 2018
Family Glossiphoniidae Vaillant, 1890
Subfamily Haementeriinae Autrum, 1939
Genus Helobdella Blanchard, 1896
Diagnosis. Small, two eyes, transparent papillae on segment, nuchal gland or scute on dorsum on VIIIa1/a2, gonopores separated by one annulus, compact salivary glands, crop with less developed first pair and unbranched second to sixth pairs of caeca, liquidosomatophagous (Blanchard, 1896; Sawyer, 1986).
 |
| Helobdella viridoclypus, new species, live holotype (ZRC.ANN.1623). A, dorsal view; B, ventral view. |
Helobdella viridoclypus, new species
Diagnosis. Rice-shaped, transparent body; cephalisation; a pair of large, distinctly separated, dark eyes on somite III; anterior sucker twice as large as prostomium without pits inside; central mouth in anterior sucker; triangular nuchal scute pointed backward with yellowish-green colouring around mid-dorsal region (VIIa1–a3, annuli 11–13); smooth surface without dorsal papillae; rich dark-green pigmentation on dorsum, particularly around crop caeca; lesser or almost absent pigmentation along crop; one male gonopore on XIIa1/XIIa2 (annuli 26/27); one female gonopore on XIIa2/ a3 (annuli 27/28); six pairs of crop caeca with unbranched posterior caeca; maximum body width wider than anterior and posterior suckers by four and two times, respectively.
Etymology. The species epithet refers to the description of the nuchal scute on the neck region, which resembles a shield and is a yellowish green colour.
The following common names are suggested: “Emerald-charm leech” (English), “Pling soi mor ra kot” (ปลิงสร้อยมรกต) (Thai), and “Der Smaragdt-charm Plattegel” (German).
Krittiya TRIVALAIRAT, Poramad TRIVALAIRAT, Tashfia RAQUIB and Watchariya PURIVIROJKUL. 2026. Helobdella viridoclypus (Hirudinea: Rhynchobdellida: Glossiphoniidae), A New free-living Leech Species from Chiang Mai, Thailand. RAFFLES BULLETIN OF ZOOLOGY. 74: 124–141. [23 March 2026]