Hatching occurs at nighttime (Paulij et al., 1991). The hatchlings hide during the day and actively seek prey in the water column during the night, as do the adults. Laboratory reared hatchlings of Sepia officinalis released into the sea are difficult to locate as their camouflage is very effective (Hanlon and Messenger, 1988; Roper & Hochberg, 1988). The chromatophoric system, as well as the chromatophore lobes of the brain, are well developed in hatchlings. In hatchlings there are 400 to 500 chromatophores per mm2 of skin; in large adults, ahowever, there are only 35 to 50 per mm2 of skin (Hanlon & Messenger, 1988). During daytime hatchlings bury in the sand or they fix themselves on a substrate by means of a "sucker" formed by the antero-ventral surface of the mantle and the postero-ventral surface of the large ventral arms (Boletzky, 1974; Hanlon and Messenger, 1988) as do the adults.
Wells (1958, 1962) has shown in learning experiments that hatchlings attack mysids presented behind a glass, although there is no reward. Prey recognition is innate which gives the hatchlings a built-in-mechanism that assures attacks on mysids. Also, like the adults, hatchlings do not follow a prawn that passes out of sight (Messenger, 1973). There is no evidence of learning in hatchlings and very young animals. At two months of age there is improvement but retention is still poor. At four months of age, learning, retention and hunting behaviour are exhibited (Messenger, 1973, 1977). The vertical lobe system which is concerned with learning and memory (see Young, 1965) is less developed in hatchlings that it is in adults (Froesch, 1971; Wirz, 1959).
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