1997 Volume 63 Issue 1 Pages 81-89
Morphological development of veliger larvae and juveniles of the hatchery-rearedsurf clam was examined. Larvae settled by 0.26mm shell length (SL) with the gills and the siphons remaining scarcely differentiated. Although the inner demibranch began to develop just after settlement, the outer one did not do so until about 1.3-1.5mm SL. After settlement, the primary exhalant siphon arose at first by 0.3mm SL. The inhalant siphon appeared between 0.4 and 0.6mm SL, and the exhalant one between 2.2 and 2.5mm SL. Although distinct in early juveniles, the byssal gland degenerated by 5.0mm SL. Digestive organs developed rapidly, once a shell length of 3-5mm SL was reached.
The juvenile stage consists of four substages that differ in their mode of life.Newly settled juveniles depend on interstitial seawater because of the lack of the inhalant siphon. Development of the inhalant siphon enables the juveniles to draw in seawater lying above the bottomsurface. Elongation of the siphons enables the juveniles to burrow deeper into the seabed. Juveniles almost completely attain the adult features and mode of life by 15mm SL.
The organs do not develop harmoniously in the surf clam. Some morphological changes tend to trigger transitions in the mode of life before there has been sufficient development of organs and functions required for the subsequent life style. Such inharmonious organogenesis probably results in deficiencies in adaptation at the transitions.
