Lathonura Lilljeborg, 1853

Genus: Lathonura Lilljeborg, 1853

Type species.

Lathonura rectirostris (O. F. Müller, 1785) .

Emended genus diagnosis.

Parthenogenetic female. Body length 0.5–1.3 mm. Body elongate, oval, slightly flattened laterally, valves with a low dorsal keel. Head lacking a rostrum, depression between head and valves weakly expressed or absent. Anterior headshield margin straight to slightly convex. A single dorsal head pore, resembling a large oval or rounded ‘ fenestra’. Ventral valve margin weakly convex, bears lanceolate setae bilaterally armed by short spinulae. Gut with no loops. Abdomen lacking processes. Postabdomen small, bilobed in cross-section, with a large dorsal process bearing postabdominal setae; anal opening terminal. Preanal and anal portions are covered by transverse rows of spinulae. Postabdominal claws large, incurved, lacking basal spine; both outer and inner surfaces bear a longitudinal row of short spinulae. Antenna I long, cylindrical, ornamented by wide triangular scale-like spinulae; anterior surface bearing two scale-like serrate setae in its distal part; basal antennular seta located at a low prominence. Nine aesthetascs with acute, slightly incurved tips and subapical pores; one aesthetasc much longer than others. Antenna II long; basipodite with very short distal burrowing spine. Antenna II seta formula 0–1 – 1 – 3 / 1 – 1 – 3, spine formula 0–1 – 0 – 1 / 0 – 0 – 0. Five thoracic appendages. IDL of the limb I bearing four setae, each seta with unilateral armature of flattened setulae. Anterior setae of the limb I inner portion long, not forked. Ejector hooks small, one of them reduced to a tubercle. Limb II exopodite with one seta; inner portion with eight scraping setae in anterior row and three setae in posterior row. Limb III exopodite with four setae; distal endite with three long posterior setae and one long anterior seta. Limb IV exopodite with one seta; inner portion with three setae. Limb V with a total of four setae.

Ephippial female. Body length 1.1–1.2 mm. General body shape similar to that of parthenogenetic female, compressed laterally, dorsal keel low. Dorsal valve margin angulate in the anterior half, widely rounded posteriorly. Ephippium transparent to weakly melanized, ornamented by polygons or wrinkles. Two to eight eggs in the ephippium.

Male. Body length 0.5–0.8 mm. General body shape similar to that of young parthenogenetic female, body compressed laterally. Postabdomen shape similar to that of the female; gonopores slit-like, located subdistally on lateral surface of the postabdomen. Antenna I bearing an additional basal seta at the anteromedial side and six or seven transverse rows of more or less flattened setae along its anterior side. Antenna II basipodite with two additional distal setae at the outer side. Thoracic limb I with a prominent subdistal lobe and a hook at IDL base; anterior surface of the SDL bearing transverse rows of spinulae; posterior surface of the hook tip with three transverse cuticular ridges. IDL of the limb I and endite 3 both with one additional anterior seta.