segment 3. Left Bl reaching one-fifth to one-fourth 

 length of right B2; left B2 reaching one-half length of 

 right Rel. Left leg longer than right by length of Re3. 

 Left Re longer than right. Order of length, longest to 

 shortest, of Re segments: left 2, 1, 3; right 1 = 2 = 3. 

 Right Re3 not small. Each Rel probably with short 

 flat seta on outer distal edge. Right Re 1-2 more or less 

 fused. Inner edge of left Re3 with long hairs. Each Re 

 with short bladelike terminal process. 



Male stage V,— Length 2.04-2.08 mm (Fig. 212). 

 Ce sclerotization about as on adult female. P5 (Fig. 

 213) uniramus, symmetrical. Re incompletely 2- 

 segmented; Rel with outer distal seta; Re2 with short 

 bladelike terminal process. 



Remarks 



Mimocalanus nudus and M. sulcifrons females are 

 similar, while the males are more distinct. Both 

 species are found in the North Atlantic, but M. sul- 

 cifrons has not been found in the Pacific, nor M. 

 nudus in the Arctic. The present study considers the 

 larger male Arctic Mimocalanus species to be con- 

 specific with M. sulcifrons; therefore, the larger Arctic 

 female is most likely also M. sulcifrons, described for 

 the first time. The large North Pacific female 

 Mimocalanus species is considered identical to M. 

 nudus; the corresponding Pacific male is, therefore, 

 most likely to be male M. nudus, described for the 

 first time. 



Wheeler (1970) found one male specimen on which 

 he based the description of M. sulcifrons. His descrip- 

 tion of the "horn-shaped esthetes" was of the esthete 

 bases only. Th4 and Th5 of the hoiotype are separate, 

 as on other male Spinocalanidae. Wheeler stated that 

 PI Ri had "1 subterminal, and 2 terminal setae," 

 however his illustration (fig. 17) correctly shows a 

 total of 4 setae. The anterior depression was much 

 more pronounced on the hoiotype, and the hoiotype 

 did not possess the conspicuous dorsolateral spines of 

 the Arctic males. However, the other characteristics 

 of the hoiotype of M. sulcifrons were consistent with 

 those of the Arctic males. Perhaps the "sulcus" and 

 the dorsolateral spines are characteristics of age of the 

 adult male (see Spinocalanus dorsispinosus Brodsky, 

 1950). 



Grice and Hulsemann (1965) reported one male M. 

 nudus from the northeast Atlantic. Their description 

 is generally consistent with that of male M. sulcifrons. 

 The illustration of dorsal view (fig. 6a) clearly shows a 

 depressed anterior, while male M. nudus has a 

 protruding anterior margin, and is more robust. 



Distribution 



Johnson (1963a), Minoda (1967), Hughes (1968), 

 and Dunbar and Harding ( 1968) reported M. distinc- 

 tocephalus from the Arctic; these records will be con- 

 sidered as M. sulcifrons in the present study. 



Arctic Ocean 



Eurasian Basin: Minoda (1967), 0-520 m. 

 Canadian Basin: Johnson (1963a), 0-2,000 m. 



—Hughes (1968), 80-90 m. —Dunbar and 



Harding (1968), 0-2,000 m. — Vidal (1971). — 



Present study, 100-2,500 m. 

 Atlantic Ocean 

 Northeast: Grice and Hulsemann (1965), 2,000- 



4,000 m. 

 West: Wheeler (1970), 2,000-4,000 m. 



10. Mimocalanus heronae, new species 



(Figures 163, 216-223) 



Mimocalanus cultrifer. — Tanaka, 1956, p. 387-389, 

 fig. 13. Not M. cultrifer Farran, 1908. 



Mimocalanus distinctocephalus. — Boucher and de 

 Bovee, 1970, p. 527-534, fig. 1-2. Not M. distincto- 

 cephalus Brodsky, 1950. 



Type Specimen; Hoiotype, female (1.23 mm), USNM 



142702. 



Type Locality: Central and Northeast Pacific, 0- 



1,000 m. 



Material Studied: Hoiotype, female (1.23 mm), 



sample 31 (Table 3); 2 paratypes, females (1.25, 1.27 



mm), sample 32, SIO XVIII-779; 1 paratype, female 



(1.28 mm), sample 32, USNM 142703. 



Description 



PI Ri with 2 inner setae; P2 Ri2 with 1 outer seta; 

 P3-P4 Ri3 with 1 outer seta. 



Female.— Length 1.23-1.95 mm (Figs. 216, 217). 

 Prosome in dorsal view slender ovoid; head rounded. 

 In lateral view with irregular, fairly abrupt forward 

 slope. Th4 and Th5 partly fused. Prosome length 

 nearly 4 times urosome. Genital segment slightly 

 wider than long, protruding ventrally one-third depth 

 of rest of urosome. Caudal rami length slightly greater 

 than width. Inner caudal seta small, not reduced. 



Al exceeding caudal rami by nearly 1 segment; ter- 

 minal segments (Fig. 163) relatively wide. Segment 9 

 partly fused with segment 10. Armature as Table 4. 



Mn B2 with 2 short inner setae; proximal seta thick, 

 nude, distal seta plumose. Blade (Fig. 218) with large 

 ventral bicuspid, followed by 4 hi- or tricuspids of 

 decreasing length, 2 narrow bicuspids, 1 thin sharp 

 process, and dorsal seta. 



Mxl gnathobase without proximal posterior setae; 

 left and right with short distal anterior seta. Proximal 

 part of Ri with 3 proximal and 3 distal setae. 



Mxp (Fig. 219) Bl distal knob with long anterior 

 surface hairs, 3 subequal setae, and short truncate 

 process. B2 anterior surface with proximal row of 

 short hairs and row of denticles. Ri2-5 inner setae 

 nude; Ri4-5 outer setae moderately long with long 

 plumes each side; terminal seta plumose. 



80 



