NO. 5 BARNARD: AMPHIPODA 23 



Eleven of the 15 important canyon species are in the abundancy list 

 from the slope. Here Paraphoxus bicuspidatus occurs in its expected 

 high density. 



The most common amphipods in each depth interval in the canyons 

 are shown in Table 16. The most important is the eurybathic Hetero- 

 phoxus oculatus, occurring from the shallow shelf through most of the 

 depth range that has been sampled. Ampelisca macrocephala exists as an 

 oculate subspecies in depths shallower than 300 m, becoming largely the 

 blind subspecies unsocalae in greater depths. Deep-water influence starts 

 at 301 m with harpinias commencing to predominate. Protomedeia ar- 

 ticulata and Paraphoxus daboius^ in depths of 701-1000 m, are enclosed 

 in parentheses to indicate that the former species is restricted largely to 

 Monterey Canyon and that the latter species represents a possible ab- 

 normal depth displacement. Indeed, Paraphoxus obtusidens in 401-500 

 m is abnormally displaced, but P. calcaratus is truly a cold-water form 

 not found in shallow waters of southern California. The families Phoxo- 

 cephalidae and Ampeliscidae predominate; they are burrowing and 

 tube-dwelling organisms dominating most open-sea sublittoral and bathy- 

 al substrates. 



The occurrence of Maera simile in depths of 201-300 m is an unusual 

 record of a primarily eulittoral phycophilous organism. 



A partially subjective assessment of the optimal environment of the 

 taxa has been made in order to place each canyon species in the scheme 

 of Table 17, showing the dech'ne of shelf species and the increase of 

 slope species in relation to depth intervals in the canyons. Between 400 

 and 600 m the faunal balance is shifted from its primarily sublittoral 

 character to its primarily bathyal condition. 



Some species that have been assigned to the shelf fauna occur pri- 

 marily on its deeper margin. Many of those listed below live in shallow 

 waters in colder latitudes and have been displaced to the shelf edge 

 in southern California, but do not descend far into the slope environ- 

 ment: Monoculodes norvegicus, Orchomene pacifica, Ericthonius hun- 

 teri, Haploops spinosa and probably all of those species listed in Table 18 

 between Bathymedon roquedo and Monoculodes norvegicus. 



Ascent and'Descent of Species in the Canyons and Basins 



That canyons cutting the full width of the shelf might afford path- 

 ways for shelf animals descending to greater depths than normal was 

 suggested when the spoon-worm Listriolobus pelodes (see Barnard and 



