FISHER V BULLETIN; VOL. 69. NO. 4 



in the collection. (Siiecimens of Pseiidomma sp. 

 have not yet been measured.) They have been 

 classified as small, medium, or large. Two cri- 

 teria were used for determining the appropriate 

 size category: (1) the maximum length of spec- 

 imens of each species rei)resented in the col- 

 lection and (2) the length of the smallest adult 

 of each species. 



Small species are those with a maximum 

 length of 6.6 mm or less and with the smallest 

 adult 4.5 mm or less. There are four species 

 in this category: Anchialina typica, Mysidopsis 

 bigelou'i, M. furca, and Pro»(2/.s/.s athnificu. My- 

 sidopsis bic/elowi is the smallest species encount- 

 ered; it matures at a body length of 3.5 mm. 



Medium size species are those having a max- 

 imum length between 8.9 and 16.2 mm and with 

 the smallest adult 4.6 to 13.0 mm long. There 

 are nine species in this category: Bowynuniella 

 portoricensis, Erythrops erythrophthalma, Me- 

 tei-ythrojis robnsta, Hypererythiops caribhaea, 

 Psendommn affine. Amblyops abbreviata. Bathy- 

 mysis renocidata, Neomysis americana, and 

 Heteromysis formosa. 



Large species are those with a maximum 

 length of 25.0 mm or more and with the smallest 

 adult more than 15.0 mm long. There are five 

 species in this category: Eucopia grimaldii, 

 Boveomysis tridens. Mysis mixta. M. stenolepis, 

 and Praunus flexuosiis. 



RELATION TO BOTTOM SEDIMENTS 



A large majority of mysid species in the 

 NMFS collection live on bottom sediments com- 

 posed of sand or silty sand. They were least 

 abundant and seldom encountered in gravel and 

 rocky areas. (Eucopia giimaldii is excluded 

 from this discussion of mysids in relation to bot- 

 tom sediments, because it is a bathypelagic spe- 

 cies.) Eleven of the 18 benthic species were 

 most commonly associated with sand and silty 

 sand. The sand-dwelling species are: Bowma- 

 niella, po)'forirensis, Avchialina hjpica, Enj- 

 throps erythrophthalma, Hypererythrops carib- 

 haea, Mysidopsis bigelowi, M. furca, Promysis 

 atlantica, and Neomysis americana. The two 

 most common species are both included with the 

 sand-dwelling inhabitsints, but there are signifi- 



cant differences in the habitats they occupy. 

 Neom.ysis americana are occasionally taken on 

 silty sand bottoms, but typically inhabit sand 

 sediments that are silt free or contain very little 

 silt. Conversely, PJrythro/is erythrnjihthalina 

 have their center of abundance in areas of sand 

 sediments that contain small to moderate quan- 

 tities of silt. However, the silt content of the 

 sands they occupy is usually insufficient to classi- 

 fy them as silty sands according to the standard 

 classification established by Shepard (1954). 

 Silty sand inhabitants are: Boreomysis tridens, 

 Pseudomma affine. and Pseudomma sp. The 

 only species that is frequently associated with 

 gravels and other coarse substrates is Metery- 

 throps robusta. 



Species associated with fine-textured sedi- 

 ments or with various tyiies of bottom materials 

 were usually less abundant and present at fewer 

 localities than the species listed above. Species 

 that were associated with silt-clays are: .Ambly- 

 ops ahbreriafa and Bafhymysis renocidata. Both 

 species are deepwater inhabitants. Their over- 

 ail depth range is 183 to 366 m. Fine-grained 

 sediments blanket a large portion of the sea floor 

 at these de])ths. S]iecies that were found occu- 

 pying a wide variety of difl^erent kinds of bottom 

 sediment types are: Mysis mixta, Praunus 

 flexuosus, and Heteromysis formosa. These are 

 shallowwater species and the most common 

 bottom types they inhabited were: sand, 

 gravel, silt-clay, glacial till, algae, and eelgrass 

 {Zostera) . 



CO-OCCURRING SPECIES 



The catch records reveal a high incidence of 

 co-occurrence of the Atlantic coast mysids. 

 Listed in Table 14 are 15 species, 79''f of the 

 total number of species collected, taken in the 

 same sample with one or more other species of 

 mysids. The presence of difl'ei-ent species of 

 mysids in dredges, trawls, ring nets, and similar 

 sami>liiig instruments that are towed along the 

 ocean bottom for relatively long distances 

 (hundred meters to several kilometers) reveals 

 a rea.sonably close spatial occurrence. Unfortu- 

 nately, the spatial separation between specimens 

 of the different species in such samples prior to 



744 



