APLYSIA. 193 



ENEMIES. , 



Despite the ancient fables concerning them (vide History), 

 Aplysiae are absolutely harmless and appear to possess few 

 enemies. No other animals are known to attack them,* and 

 they are singularly free from parasites or epizoic organisms. 

 There is no record of any parasite, but on young specimens 

 in the " red " stage, small colonies of Obelia and Pedicellina, 

 etc., are occasionally found attached to the mantle. 



In all stages Aplysia is protectively coloured, and the 

 resemblance to the weed on which it is feeding is so close that 

 detection may be difficult except when it is moving. If 

 attacked it has two means of defence. f It can exude a rich 

 purple dye, which forms an effective screen under cover of which 

 it can escape, from glands situated on the under side of the 

 mantle, and an acrid fluid from the sub-pallial opaline or poison 

 gland. It might be supposed that the dye would have been 

 employed by the ancients, to whom Aplysia was well known, 

 but there is no evidence that they utilised this particular 

 animal. The unstable character of the dye coupled with 

 abhorrence of the creature that produced it were quite sufficient 

 to prevent its use. 



FOSSIL REMAINS. 



There are no authentic fossil remains of Aplysia, whose 

 soft body and delicate shell do not lend themselves to pre- 

 servation. The supposed fossil shells of Aplijsia from the 

 Pliocene are probably flakes from Pelecypod shells. (Zittel, 

 Text-book of Palaeontology, Vol. 1, p. 568.) 



* Rondelet states that the Mullet eats the Sea-hare. As, however, 

 he also says that Aplysia feeds on " water, mud, and filth," he cannot have 

 investigated very thoroughly either its habits or its anatomy. 



f As Sir Charles Eliot says of the Nudibranch : "It cannot fight and 

 it cannot run away." 



