Effects of larval eyestalk extirpation on morphogenesis and molting in the snapping shrimp Alpheus heterochaelis say

Zoea larvae of Alpheus heterochaelis were reared in isolation in the laboratory at selected temperature levels (17, 22, 25, and 27°C) and 32‰ salinity. One or both eyestalks were removed from some animals (experimentals), or antennae from others (operated controls), at various times during larval development. In all experiments virtually all unoperated animals (controls), operated controls, and zoeae lacking one eyestalk exhibited the same abbreviated pattern (three larval “stages” or instars) typical of this species. Ablation of both eyestalks during Stage II always produced an extra “Stage IV” zoea with postlarval features in the abdomen. These animals usually molted again without undergoing substantial structural changes. Ecdyses into the two supernumerary instars occurred significantly earlier than comparable ecdyses (to postlarva and juvenile) among all other experimentals and controls. Bilateral eyestalk removal a few hours before or after the molt to Stage III often generated forms ranging from precocious zoeae to postlarvae (megalopae) with some residual larval features. Some of these individuals subsequently molted into normal postlarvae and juveniles, as did all animals whose eyestalks were removed 12 or more hours into Stage III. Juveniles that developed from eyestalkless larvae were consistently darker (red) than stalked animals. These results suggest that the larval eyestalk contains a factor that promotes metamorphosis, a molt‐inhibiting hormone, and a chromatophorotropin. © 1994 Wiley‐Liss, Inc.