enter the Arctic Waters in low numbers, and their 

 movement out of the Arctic would be restricted. They 

 have been found in the North Atlantic, but at too 

 great depths to be transported into the Arctic. 



Mimocalanus crassus was not found in the Arctic 

 Water, and therefore probably does not leave the Arc- 

 tic. It has been found in the Atlantic (Caribbean), as 

 well as Indian Ocean, at depths sufficient to be 

 carried into the Arctic if it occurs in the North Atlan- 

 tic at similar depths. 



Therefore, the Arctic Spinocalanidae could be 

 characterized as follows: (1) Spinocalanus longicornis 

 (Arctic, North Pacific, and North Atlantic, including 

 Caribbean and Mediterranean); (2) S. antarcticus 

 (bipolar; possibly a continuous distribution); (3) S. 

 horridus (cosmopolitan); (4) S. elongatus (Arctic); (5) 

 ^'. polaris (Arctic, with some transport to the deep 

 Atlantic); (6) Mimocalanus crassus (probably 

 cosmopolitan); and (7) M. sulcifrons (Arctic, with 

 some transport to the deep Atlantic). 



In view of the great vertical ranges, and evident 

 tolerances of these Arctic species, it is interesting to 

 speculate on the limited distributions of some of 

 them. If there are no physical boundaries, perhaps 

 there are boundaries imposed by the interactions of 

 closely related species. 



To examine this possibility one must consider 

 which closely related species are present in the North 

 Pacific and North Atlantic. Of the spinocalanids not 

 found in the central Arctic, all North Pacific and 

 North Atlantic Spinocalanus species except S. 

 abyssalis. S. magnus, and S. breuicaudatus, all 

 Mimocalanus species except M. cultrifer, all 

 Monacilla species, and Teneriforma naso are reported 

 at too great depths to be transported into the Arctic. 



Five Arctic spinocalanids have limited dis- 

 tributions. Spinocalanus polaris has a rather unique 

 morphology (see systematic review) and may not have 

 an obvious counterpart in the North Atlantic. It may 

 be more widely distributed than known at present, or 

 it may, since it is deep living, be limited by interac- 

 tions with other deep-living North Atlantic 

 spinocalanids. 



The three other Arctic Spinocalanus species of 

 limited distribution, S. longicornis, S. antarcticus, 

 and ^S. elongatus, would encounter three very closely 

 related species in the North Pacific and North Atlan- 

 tic, S. abyssalis, S. magnus, and S. breuicaudatus 

 respectively. Spinocalanus longicornis and S. 

 abyssalis have overlapping distributions in the North 

 Atlantic (including the Caribbean and 

 Mediterranean), but the other species apparently do 

 not. 



The last Arctic species of limited distribution, 

 Mimocalanus sulcifrons, may, like S. polaris, be 

 restricted by interactions with other deep-living 

 North Atlantic spinocalanids, especially M. cultrifer 

 and M. nudus. 



FAMILY SPINOCALANIDAE 

 VERVOORT, 1951 



Description 



PI Bl without inner edge seta. B2 with minute seta 

 near outer distal edge; long anterior seta near Ri base. 

 Re 3-segmented; Rel with or without outer distal 

 spine, without inner seta; Re2 with 1 outer distal 

 spine and i inner seta; Re3 with 1 outer distal spine, 4 

 inner setae, and 1 bladelike terminal seta. Terminal 

 seta outer edge lightly serrate, inner edge plumose. Ri 

 1-segmented, with outer lobelike process near end, 2 

 terminal setae, and 1-3 inner setae; lobelike process 

 more or less rounded, usually tipped with open, 

 porelike points. 



P2 Bl with inner seta (except Mimocalanus 

 crassus). Surfaces (except Spinocalanus polaris) and 

 margins of B2 nude. P3 Bl with inner seta (except M. 

 crassus). B2 with surfaces and margins nude. P4 Bl 

 with inner seta in females (except M. crassus). with or 

 without inner seta in males. B2 margins nude. 



P2 Ri 2-segmented; Ril without surface armament, 

 with 1 inner seta; Ri2 with 2 inner, 2 terminal, and 0-1 

 outer setae. 



P3-P4 Ri 3-segmented; Ril without surface arma- 

 ment, with 1 inner seta; Ri2 outer distal corner 

 spiniform, 1 inner edge seta; Ri3 with 2 inner, 2 ter- 

 minal, and 0-2 outer setae. Number of setae on rami is 

 identical in P3 and P4 in any one species. 



P2-P4 Re 3-segmented; Rel without posterior sur- 

 face armament, with 1 outer spine and 1 inner seta; 

 Re2 with 1 outer spine and 1 inner seta; Re3 without 

 serrate margins, with 3 outer edge spines, 5 inner edge 

 setae, and 1 serrate bladelike terminal seta. 



Inner caudal seta small, directed ventrally; ter- 

 minal 4 setae well developed but very fragile; outer 

 seta small, minute, or, usually, apparently absent. 



Female.— Length usually 0.8-3.58 mm, two species 

 4.20-4.7 mm. Prosome in dorsal view slender to robust 

 ovoid, widest at Thl; Ce and Thl separate; Thl-Th4 

 sometimes with lateral spinules in Spinocalanus; 

 Th4-Th5 usually separate, probably never completely 

 fused; Th5 lateral corners sometimes prolonged, never 

 pointed; rostrum 2 symmetrical or asymmetrical long 

 strong points, or single long blunt cone, or absent; P5 

 absent (see Monacilla typica). Urosome 4-segmented; 

 genital segment longest, protruding ventrally one- 

 fourth to one-half depth of rest of urosome; anal seg- 

 ment length ^3-1 times caudal ramus; caudal ramus 

 length 1-2' 2 times width (one ramus sometimes 

 longer and wider). 



Al extending to anal segment or beyond caudal 

 rami by up to 4 segments (except S. angusticeps and 

 S'. validus, and Mimocalanus ovalis); segments 8 and 



9 usually fused, never completely separate; segment 



10 not fused with 9 (partly fused in M. heronae); 

 segments 24 and 2.5, terminal segments, separate. 



A2 Bl with proximal hairs or setules and 1 long 



13 



