8 U.S. NiATIONAl, MUSEUM BULLETIN 271 



Six or seven families of amphipods construct dwelling tubes. The 

 cylindrical or flattened tubes are spun from strands of material 

 secreted and probably manipulated by pereopods 1-2. The tubes may 

 be limp (Ampelisca) and lay prone on the bottom or they may be 

 stiff and erect and attached to rocks (Photis). Mud is occasionally 

 used to reinforce the walls of the erect tubes. 



Glands of domiciliary Amphipoda appear to be concentrated mainly, 

 if not exclusively, in pereopods 1-2. They are found most heavily 

 concentrated in article 2, often in article 4 and occasionally in other 

 articles. Glands usually appear to be composed of densely packed, 

 ''yolky" tissue, often posterior to the main muscles of article 2, often 

 composed of morula-like bodies, and often of different color than the 

 muscles or other tissues, even in specimens preserved in alcohol; they 

 are frequently yellow, ochre, orange, or purple. Apparently a duct 

 carries the secretion to a meatus located subterminally on the dactyl. 

 The meatus is very difficult to see and not definitive of Gammaridea 

 known to be domiciliary because many other Amphipoda seem to 

 have a dactylar meatus but lack conspicuous glands. The presence of 

 these glands may be a useful clue by assisting in the identification of 

 several genera in Isaeidae, Ischyroceridae, Corophiidae, and Am- 

 pithoidae that otherwise resemble nondomiciliary Amphipoda. Com- 

 plete reliance cannot be made on them as familial characters, for all 

 members of domiciliary familes do not necessarily have glandular 

 pereopods 1-2 and very few species have actually been examined for 

 their presence. Some phoxocephalids, haustoriids, and argissids have 

 conspicuous glands in pereopods 3-5. 



Most domicihary amphipods except for the Ampeliscidae have 

 somewhat depressed bodies, shortened pereopods, and have better 

 crawling abihty than do nontube builders. They can be observed 

 emerging from their closely crowded tubes, their antennae appar- 

 ently being used digitally in a search for particles of food. Ampeliscid 

 amphipods he upside down in their tubes and project their strongly 

 setose antennae as filtering organs. Only one benthic gammaridean has 

 been reported as a predator but some pelagic amphipods catch prey. 



After hatching, young amphipods are like adults (Gammaridea do 

 not have larvae as do most crustaceans) and are carried about for 

 a few hours or days in the brood pouch. In the early stages molting 

 and growth are rapid; a young amphipod may first molt while still 

 in the brood pouch, within a day or two after hatching. As growth 

 proceeds rates of molting and growth decrease, so that adults may 

 molt every 20-30 days and in some striking instances only every 

 six months or so. Few amphipods have been studied for their molting 

 rates; of those examined it has been determined that sexual ma- 

 turity is reached at about the sixth molt (commencing the seventh 



