AMBLER: SPECIES OF Aff/MDOPS/S OFF OREGON 



In all specimens examined, the ocular peduncle 

 extends beyond the eye as a blunt spine, although 

 Benedict ( 1902) does not consider it an eyespine in 

 his key. On the carina of the second, third, and 

 fourth abdominal somites, there are slight median 

 projections. Benedict (1902) considers these pro- 

 jections "armature on the abdomen confined to the 

 median line." 



The main variation of the Oregon and A /6a^ross 

 specimens is in the shape of the apex of the ros- 

 trum. Henderson (1888, plate XIX, figure 1) de- 

 scribes the rostrum as ending in an "acute apex," 

 which is true for USNM 21285 and some of the 

 Oregon specimens. In most of the Oregon speci- 

 mens and MCZ 4563, the rostrum ends as a spine 

 (Figure 9). 



Rhizocephalan parasites occurred under the ab- 

 domen in 40 of 444 Oregon specimens; 23 hosts 

 were females and 17 were males. 



Distribution. — Munidopsis latirostris is the most 

 abundant Munidopsis species found in Cascadia 

 Basin, with a wide depth range, 1,900-3,021 m. 

 This species has also been found in the tropical 

 Pacific Ocean at 280 and 3,243 m off Panama 

 (Faxon 1895) and at 1,958 m between Papua and 

 Admiralty Islands (Henderson 1888). 



VERTICAL AND GEOGRAPHIC 

 DISTRIBUTION OF THE SPECIES 



Twelve species o{ Munidopsis were captured in 

 51% or 146 of the total number of tows. Collections 

 from both otter and beam trawls are included in 

 the distributional analysis for more complete 

 coverage. Although samples from otter trawls 

 have been considered quantitative (number per 

 hour trawled, Haedrich et al. 1975), beam trawls 

 were designed to be more quantitative, giving 

 number per square meter (Carey and Heyamoto 



u. 



I I I 



I cm 



Figure 9. — Munidopsis latirostris, variation in rostrum, left 

 rostrum ends as spine, right rostrum ends as acute apex. 



1972). Carney (1976) questioned the reliability of 

 beam trawl data for area covered and expressed 

 abundance as number per trawl for samples with 

 similar wheel readings. In this paper, abundances 

 are expressed as average number per trawl 

 (number of specimens/number of trawls towed) 

 because beam and otter trawls were towed for 

 approximately the same time. Some specimens 

 which can escape through 1.3 cm mesh liners are 

 not sampled adequately. Adult densities of small 

 species such as M. ciliata, M. quadrata, and M. 

 yaquinensis , and immature individuals of the 

 other species are probably underestimated. Imma- 

 ture specimens included M. subsquamosa, M. 

 latirostris, M. bairdii,M. tuftsi, and M. beringana. 

 Cascadia Basin off Oregon was probably the 

 only area trawled adequately enough to sample all 

 the species, since most species were collected at 

 least several times there. The most abundant 

 species, M. latirostris, contributed 73.0% of the 

 total number of specimens. Three species together 

 contributed 20.2% of the total: M. bairdii (7.5%), 

 M. ciliata (6.2%), and M. subsquamosa (6.5%). 

 These four species together represented 93.2% of 

 all specimens, and were only found in Cascadia 

 Basin. At the deepwater dumpsite stations in 

 northern Cascadia Basin, all of the above except 

 M. ciliata were collected. Five additional species 

 (32 specimens) were also found on Cascadia Basin. 

 Although 106 tows were taken on the continental 

 slope off Oregon, only 5 tows yielded a total of 

 three species (six specimens). Three species (17 

 specimens) were found on Tufts Plain (Table 7). 

 Abundances (number per trawl) for all 

 Munidopsis species were about the same for the 

 base of the continental slope (CP-1 line) and the 

 CP-2 line (Table 7). However, the relative abun- 

 dance of species changed from east to west. 

 Munidopsis latirostris was the most abundant on 

 both the CP-1 and CP-2 lines. On the CP-1 line, M. 

 subsquamosa was second in rank, but on the CP-2 

 line, M. subsquamosa was fourth, M. ciliata was 

 second, and M. bairdii was third (Table 7). 



Eight of the 12 Munidopsis species were col- 

 lected in Cascadia Basin, especially below 2,250 m 

 (Figure 10). The single sample from Gorda Ridge, 

 south of Cascadia Basin, contained one specimen 

 of the rare, deepwater form, M. verrucosus. Muni- 

 dopsis quadrata was the only species occurring 

 over a wide depth range on the continental slope. 

 A single tow on the lower part of the continental 

 slope contained Munidopsis sp. and M. subsqua- 

 mosa. 



29 



