GASTROSTOMOBDELLIDAE RICHARDSON, 1971

FAMILY GASTROSTOMOBDELLIDAE RICHARDSON, 1971

Emended diagnosis: Body firm and muscular, elongate, with constant width in caudal direction, dorsoventrally compressed. Somite I completely merged with prostomium. Somite II uniannulate, not separated from I. Mid-body somite annulation, variable, basically sexannulate. Post-anal annuli present. Male gonopore in posterior part of somite XI to anterior part of somite XII. Female gonopore in posterior part of somite XII to anterior part of somite XIII. Papillae numerous, minute, hardly visible, one row on every annulus, and two rows on annuli with secondary furrow. Pharynx agnathous, euthylaematous. Pharyngopore, when present, dorsally in posterior part of somite XIV. Pharyngoporal duct simple, straight, descending to pharynx terminal end. Crop tubular, acaecate. Gastropore, when present, ventral in posterior part of somite XIV to somite XIV/ XV. Gastroporal duct columnar, running vertically from ventral surface of crop to gastropore; two pores open to crop; canal Y-shaped; penetrated by nerve cord. Intestine tubular, acaecate. Rectum tubular, thin walled, straight. Testisacs multiple. Ejaculatory bulbs absent. Epididymides absent. Pre-atrial loops absent. Male median reproductive system in posterior part of somite XI to anterior part of somite XII, without penis or penis sheath. Ovisacs tubular, directly descending to female gonopore.

Remarks: Both the Southeast Asian family Gastrostomobdellidae and the East Asian monogeneric family Orobdellidae are characterized by an agnathous and euthylaematous pharynx in the digestive tract. According to taxonomic studies ( Nakano et al., 2012; Nakano, 2016), Gastrostomobdellidae is distinct from Orobdellidae in the following characteristics: post-anal annuli present (absent in orobdellid species), and ovisacs tubular, directly descending to female gonopore (globular with oviducts in orobdellid species). Moreover, gastrostomobdellid species lack epididymides in their male genital system, whereas most orobdellid species possess them. The characteristics of the gastrostomobdellid ventral gastropore and gastroporal duct are also clearly different from those of the orobdellid leeches: in Gastrostomobdellidae , when present, the gastropore opens in the posterior part of somite XIV to somite XIV/XV (in the anterior part of somite XIII in Orobdellidae ). The gastroporal duct is columnar, and runs vertically from the ventral surface of the crop to the gastropore (tubular, lying on the female organ in Orobdellidae ). A dorsal pharyngopore and the duct connecting it to the pharynx have never been described for species within the other erpobdelliform families, i.e. Erpobdellidae , Orobdellidae , and Salifidae .