Scientific Name and Authority

Tortanus dextrilobatus   Chen and Zhang, 1965


Both sexes of Tortanus dextrilobatus have some asymmetry in the urosome and caudal rami. The feeding appendages are claw-like and prominent, indicative of predatory feeding. Adult females have an oblong cephalothorax, with a somewhat triangular forehead. The head is not fused with the 1st thoracic segment, but the 4th and 5th thoracic segments are fused. There is a single median eye, which is red. The corners of the last thoracic segment form curved, symmetrical protuberances. The urosome has 3 segments. The genital segment is about as long as it is wide, with the genital operculum located ventromedially. The operculum is semicircular, with the posterior margin slightly concave. The 2nd urosomal segment has a posterior-dorsal process on the right side, while the 3rd segment has a larger thorn-like dorso-lateral process. The right caudal ramus is slightly longer than the left one. The two antennules are symmetrical, have 17 segments, and when folded back, reach to the 3rd urosome segment. The exopod and endopod of the 5th leg (P5) consist of only one segment each. The tip of the endopod is bifurcated, and the exopod is claw-like. The length of Chinese specimens was 2.00-2.25 mm (Chen and Zhang 1965), while Korean specimens measured 1.75-1.79 mm, and San Francisco Bay females were 1.58-1.61 mm in size (Ohtsuka et al. 1992; Ohtsuka and Reid 1998; Hoof and Bollens 2004).

Adult males have a much more slender body than the female's. The 4th and 5th thoracic segments are partially fused, and the corners of the 1st thoracic segment are rounded, without protuberances. There are 5 urosome segments, but the posterior segment is very short. As in the female, the right caudal ramus is slightly longer than the left. The right 1st antenna is geniculate (hinged) between the 14th and 15th and comprises 16 segments, but two of these are partially fused. The 5th legs (P5) are each composed of 3 segments, and are asymmetrical. The left leg has broad 1st and 2nd segments, and the distal end of the 3rd segment is curved inwardly. It has setae on the inner surface and 9-10 transverse ridges on the outer surface. The right P5 leg is clawlike. The 1st segment is very broad, with a blunt triangular process on the inner border and a spine at the apex. The distal segment is curved, with 5 denticles and 19-21 fine transverse ridges on the inner surface. Males in China were 2.00-2.25 mm in size (Chen and Zhang 1965) and 1.53-1.76 mm in Korea (Chen and Zhang 1965; Ohtsuka et al. 1992).

The copepodite and naupliar stages of this copepod have not been described, but probably resemble those of Tortanus discaudatus (Johnson 1934). Tortanus dextrilobatus is characteristic of brackish waters (Ohtsuka et al. 1992).

Taxonomic Classification:

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Maxillopoda
Subclass: Copepoda
Order: Calanoida
Family: Tortanidae
Genus: Tortanus
Species: dextrilobatus

Potentially Misidentified Species:

Tortanus discaudatus

Native to the NW Atlantic and N Pacific, found in poly-euhaline waters

Tortanus forcipatus

Native to NW Pacific, found in poly-euhaline waters