Sars, 1905
Short Description:
Pseudochirella obtusa is an aetideid calanoid copepod known after both sexes (female 5.25-6.50 mm and male 4.80-5.50 mm in length) from the Atlantic, Pacific oceans and Antarctic, mainly bathy-mesopelagic.
Taxonomic Description:
Female. Total length 5.25-6.50 mm. Cephalothorax about 3-4 times longer than abdomen. Th5 posterior corners rounded, sometimes covered with hairs, symmetrical. Genital segment of barrel-like shape, symmetrical, it is widest in about its midlength, its length and width nearly equal. Abd 1-3 are covered with hairs to different degree in different specimens. Length of A1 varies from slightly longer than cephalothorax, to reaching the end of caudal rami. Ri1 A2 with 1, often with 2 setae. Re1 A2 with very small seta, placed on a knob, Re2 A2 with 1 distal seta. Ri1 Md with 2, Ri2 Md with 9 long terminal and 2 posterior setae. Re P1 3-segmented with indistinct separation of Re1 and Re2. Ri P2 2-segmented. P4 coxopodite with 8-15 spines.
Male. Total length 4.80-5.50 mm. Cephalothorax slightly less than 3 times longer than abdomen. Cephalon and Th1, as well as Th4-Th5 fused, line of fusion sometimes visible dorsally. Posterior Th5 corners rounded, with spines removed to the back side of specimen (lateral view). Oral parts setation reduced. Re P1 3-segmented, external spine of Re1 P1 not exceeding the midlength of Re2 P1. Ri P2 2-segmented. Left Re2 P5 with 2 teeth; left Re3 P5 more than 3 times longer than wide.
Remarks. The first description of P. obtusa (Sars, 1905) and subsequent redescription (Sars, 1924-1925) are brief and inadequately documented. This misled Brodsky (1950) in his assumption to originate P. polyspina from the north-western part of the Pacific Ocean. I have examined P. polyspina type series and disclosed that Re P1 of P. polyspina is indistinctly 3-jointed, not 2-jointed as considered earlier (Brodsky, 1950). Ri P2 indistinctly 2-jointed and not 1-jointed (Brodsky, 1950). On the basis of these data (the vast material from numerous geographical sites) and the literature (Sars, 1905, 1924-1925; Park, 1978; Bradford and Jillett, 1980). I have come to the conclusion on the identity between P. obtusa and P. polyspina . It should be pointed out that the figures of male identified by Vervoort (1949) as P. obtusa and later adduced in the report on aetideids from New Zealand region (Bradford and Jillett, 1980) should evidently be attributed to the male of P. dubia (Sars, 1905). The male described under the name P. spinifera Brodsky (1950) and later synonymized with P. polyspina (Park, 1978) should probably be considered as a male of P. obtusa.
Vertical distribution:
Bathy-mesopelagic species: in hauls more often occurs between 1000 and 2000 m (Grice and Hulsemann, 1967; Deevey and Brooks, 1977; Ferrari, 1980; etc; Markhaseva, 1996), found in considerable numbers in total hauls from depths from 5000 m (Sars, 1925; Bjornberg, 1973; Park, 1978; Bradford and Jillett, 1980; etc.; Markhaseva, 1996), there are single findings in epipelagic (Vervoort, 1963; Minoda, 1971).
Geographical distribution:
The species recorded to the North to 62°N in the Atlantic Ocean (With, 1915; Jespersen, 1934), in the Pacific: up to the Bering Sea (Motoda and Minoda, 1974; Markhaseva, 1996), to the South down to 67-68°S circumpolar (Park, 1978; Markhaseva, 1996).
Type locality: North Atlantic (Sars, 1925).
Material examined:
More than 500 females and 50 males from samples: 5, 18, 20, 21, 61, 63, 65, 69-73, 81, 86, 92-94, 102, 103, 119-121, 126-128, 132, 134-137, 145, 146, 156-163, 171, 173, 174, 181, 189-191, 195, 199, 218, 226, 246, 267, 269-273, 275, 276, 280, 282, 283, 285, 287, 293-297, 300-302, 304, 306, 310, 312, 314, 316, 317, 322, 334, 336, 338, 341, 363, 376, 379, 474, 569. See examined samples module.