AMBLER: SPECIES OF Mt/WDOPS/S OFF OREGON 



TUFTS 

 PL A in 



44* 44' 



134" 



—I 



O M bairdii 

 • M tafirostns 



Figure ll. — Distribution of Munidopsis species off Oregon and Washington; upper — M. cascadia, M. ciliata, M. tuftsi, M. 



subsquamosa, and M. beringana; lower — M. bairdii and M. latirostris. 



CP-4-E, the deepest and most western station on 

 Cascadia Basin. Three species — M. subsquamosa, 

 M. cascadia, and M. ciliata — occurred predomin- 

 antly on the eastern side of Cascadia Basin. Only 

 M. beringana was taken on both abyssal plains, 

 notably occurring in Cascadia Basin only at the 

 deeper, southern stations. Two species occurred 

 only on Tufts Plain — M. verrucosus and M. tuftsi. 



Carney (1976) found greater overlap in species 

 distributions between Cascadia Basin and Tufts 

 Plain for holothurians than for Munidopsis 

 species. He described three basic distribution pat- 

 terns: 1) present on Cascadia Basin but generally 

 absent from the base of the continental slope, 2) 

 present over all of Cascadia Basin extending to the 

 eastern edge of Tufts Plain, and 3) present in the 

 deepest and farthest offshore stations of Cascadia 

 Basin and on Tufts Plain. 



Two distributional studies of infauna on Cas- 

 cadia Basin have shown great variation in species 

 composition between different stations: Hancock's 

 (1969) polychaete study along the CP-E line 

 (Newport hydrographic line) and the gammarid 

 amphipod study at stations CP-l-E and CP-3-E by 

 Dickinson and Carey (1978). Carney (1976) 

 showed that the species composition of poly- 

 chaetes had greater variability between stations 

 than that of the holothurians. Of the 20 most 

 abundant gammarid amphipod species at the two 

 Cascadia Basin stations, only 6 had similar abun- 

 dances at both stations, and 10 species only oc- 

 curred at one station (Dickinson and Carey 1978). 

 Of the eight Munidopsis species I found on Cas- 

 cadia Basin, only three occurred at both CP-l-E 



and CP-3-E. In all three groups (polychaetes, am- 

 phipods, galatheid crabs), there are differences in 

 species composition between stations on either 

 side of Cascadia Basin, which Dickinson and 

 Carey (1978) suggested may be caused by decreas- 

 ing sedimentation rates with increasing distance 

 offshore, since other environmental conditions are 

 constant across Cascadia Basin. 



Of 65 known abyssal species of Munidopsis, 

 Doflein and Balss ( 1913) found that a high percent- 

 age (71%) are endemic to specific oceanic regions. 

 Since many abyssal species have been described 

 from single or few specimens, the percentage of 

 endemism declines with further collecting. My col- 

 lections off Oregon extended the geographic range 

 of seven species, three of which were previously 

 known from only one location: M. beringana from 

 the Bering Sea, M. aries from the Caribbean, and 

 M. verrucosus from off Chile. 



The number of cosmopolitan Munidopsis 

 species, those found in all three major oceans, is 

 small (Doflein and Balss 1913). Only one of the 

 Oregon species, M. subsquamosa, can be consi- 

 dered cosmopolitan. Seven of the Oregon species 

 are found only in the Pacific Ocean; one is also 

 found in the Indian Ocean (Table 8). However, four 

 of the Pacific and Indian-Pacific species have sib- 

 ling species in the Atlantic Ocean, evidence that at 

 one time the progenitors had broader distribu- 

 tions. 



The four most abundant species from Cascadia 

 Basin have tropical Pacific affinities (Table 8). 

 Only one species, M. beringana, has arctic 

 affinities and is found in the deepest parts of Cas- 



31 



