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Farran, 1929

Short description:

Aetideus acutus is an aetideid calanoid copepod known after both sexes (female 1.48-1.80 mm and male 1.22-1.58 mm in total length). The species is mainly epipelagic, notably in the upper layers of mesopelagic. Widespread in the Pacific, Atlantic and Indian oceans.

Taxonomic description:

Female. Total length 1.48-1.80 mm. Cephalothorax 3.6-4.0 times longer than abdomen. Body surface covered with chitinous thickenings. Rostrum very strong, with rami rising from wide undivided base, well visible when looking ventrally. There are two rounded projections in rostral excavation. Width of rostral excavation (when looking dorsally) is about 1.4 times more than depth. Base of rostrum well visible when looking dorsally. Crest present, well visible when looking dorsally and laterally. Th5 posterior corners extended into wing-like lobes ending into points exceeding posterior border of Abd2. Spermatheca of bag-like form, duct connecting its ventral and dorsal parts without narrow part. A1 reaching the end of Abd3 or end of caudal rami. Oral appendages and P1-P4 typical for Aetideus. Ri P2 one-segmented.

Male. (Described after Park (1974) with modifications). Total length 1.22-1.58 mm. Cephalothorax about 3.8 times longer than abdomen. Th5 posterior corners much shorter than in female, their points slightly exceeding posterior border of genital segment (when looking dorsally). A1 reaching posterior end of Abd3. A2 coxopodite and basipodite equipped as in female. Ri1 A2 with 1 very small seta, Ri2 A2 external lobe with 6 long and 1 short terminal setae, internal lobe with 6 long setae. Re1 and Re2 A2 without setae. Md palp base with 1 very small seta, Ri1 Md with 1, Ri2 Md with 8 long and 1 shorter terminal setae. Mx1 gnathobase and second internal Mx1 lobe lacking setae, third internal lobe bears 2 setae, protopodite near the base of Ri with 3 setae, Ri with 6, Re with 10 setae. Mxp protopodite supplied with 3 setae in its distal part. Ri P2 - one-segmented, reaching distal end of Re2 P2. Re3 P2 and Re3 P3 terminal spines longer than Re3 with 23 and 18 teeth respectively. Re3 P4 terminal spine shorter than Re3 with about 16 teeth. P5 second-fourth segments with width length ratio 1:(3.41-3.78); 1:(6.72-7.33) and 1:(6.00-6.60) respectively.

Vertical distribution:

Mainly epipelagic and upper mesopelagic species. Usually known above 200-500m (Farran, 1929; Tanaka, 1957a; Brodsky, 1962; Grice, 1962; Park, 1968; Tanaka and Omori, 1970a; Bradford, 1971a; etc.).

Geographical Distribution:

The species is widespread in the Pacific Ocean - from 35°N (the Izu region (Tanaka, 1957a; Brodsky, 1962; Tanaka and Omori, 1970a)) to the south to 40°S (Farran,1929), in the Atlantic Ocean - in the north-eastern part (Grice and Hulsemann, 1965; Roe, 1972a, 1972b; Brenning, 1983, 1985), in the regions off Madeira, the Canary Islands, the Caribbean Sea and the Gulf of Mexico (Park, 1970, 1974; Vives, 1982), Wheeler (1970) recorded species up to 40°N. Species is also known from the Malay Archipelago (Vervoort, 1957). It was found in the north-western (Grice and Hulsemann, 1967) and the north-eastern parts of the Indian Ocean (Markhaseva, 1996).

Type locality: to the north-west off the northernmost point of New Zealand (Farran, 1929).

Material examined :

25 females from samples 45, 49, 54, 55, 202, 407, 410, 411, 412, 413, 414, 416, 417. See examined samples module.

Aetideus acutus