THE AUSTRALIAN MUSEUM MAGAZINE. 



Ill 



LIMPETS. 



The limpets are proverbial for stick- 

 ing to the rocks, and, as a matter of 

 fact, no amount of ordinary pulling in 

 a straight line will remove one from its 

 holding. The central part of the foot 

 is raised from the rock by muscular ac- 

 tion, forming a kind of sucker with a 

 partial vacuum between the foot and 

 the rock, and, since the edges of the 

 foot tit the support perfectly, the ex- 

 ternal atmospheric pressure helps the 

 animal to resist being detached. The 

 limpets are always easily known by their 

 dome-shaped or tent-shaped shells, a 

 shape on which the battering waves can 

 get no purchase to dislodge them. 



The limpet, which also has a ribbon 

 tongue, is a vegetarian and feeds on the 

 green sea growths on the rocks. A re- 

 markable thing about these animals is 

 their homing instinct. A limpet hol- 

 lows out a depression in a rock to ac- 

 commodate itself nicely, and, though it 

 leaves this at feeding time in search of 

 food, it will return again and again to 

 its old home, and never seems to settle 

 in the wrong hollow by mistake. 



CHITONS. 



Occasionally gliding over the rock, but 

 more often as still as the stone itself. 



may be seen those curious molluscs, the 

 chitons, often called mail-shells. Instead 

 of one solid shell like a limpet, these 

 animals have developed a hard calcareous 

 armour composed of eight separate trans- 

 verse pieces, which fit one over tlie other 

 something after the manner of tiles on 

 a roof. You can see this well if you 

 detach a chiton from its rock and place 

 it on its back, when it will proceed to 

 roll itself up into a ball with the shell 

 on the outside. A leathery band or 

 girdle runs around the outside of the 

 eight plates. The chitons have no eyes 

 or tentacles, whereas the periwinkles and 

 their kind, have two tentacles and also 

 eyes on very short stalks, at the base of 

 the tentacles. 



The chitons are vegetable feeders, liv- 

 ing on minute seaweeds and those very 

 tiny marine plants called diatoms. If 

 you place one of these molluscs on a 

 piece of glass wet with sea water and 

 watch its movements from the underside, 

 you will see that its foot extends nearly 

 the whole length of its body, while the 

 moutli is plainly visible just above the 

 foot. Behind the mouth is a long, 

 toothed, ribbon tongue like that of the 

 periwinkle. 



In spite of its very simple appearance 

 the chiton has a well developed three- 



Mussels (Brachyodontes hirsutus). 

 Portion of a colony fitted together into a mass of epidermis and 'byssus (hairy 

 filaments). This species is to be found clustering on wharf-piles or in rock 

 crevices in sheltered waters. The top of the picture shows a number of 



barnacles. 



Photo. — A. Musgrave 



