. The Australian Museum magazine. Natural history. Some of the periwinkles have almost deserted the sea as a home, and especial- ly is this the case with a very small bluish-grey periwinkle {Meieraphe maii- ritiana), which is found in clusters in hollows well up on the rocks. It is only covered by the highest tides and some- times .only by the spray of them. It is well on the way to becoming a land ani- mal ; the land snail is a periwinkle which has completed the change. The general internal structure of the whelks and periwinkles is much the same, the internal organs being gathered together i
. The Australian Museum magazine. Natural history. Some of the periwinkles have almost deserted the sea as a home, and especial- ly is this the case with a very small bluish-grey periwinkle {Meieraphe maii- ritiana), which is found in clusters in hollows well up on the rocks. It is only covered by the highest tides and some- times .only by the spray of them. It is well on the way to becoming a land ani- mal ; the land snail is a periwinkle which has completed the change. The general internal structure of the whelks and periwinkles is much the same, the internal organs being gathered together in a twisted hump which is covered by the shell. The tongue is a long ribbon working to and fro behind the mouth opening. It is covered like a file with rows of teeth—an enormous number of them; some species of sea snails have over 500,000 teeth. The foot on which the animal glides is just a flat creeping disc, and the creatures move by a series of wave-like undula- tions which flow along it. Limpets (Cellana variegata). To be found high and dry on the rock flats when the tide is out. Photo.—A. Musgrave. hon acts. This is a spout-like projec- tion which enables the animal to re- ceive the aerated water for breathing. The opening of the shell can be en- tirely closed by a tightly fitting door called the operculum, which the creature draws into it. This operculum is a characteristic feature of those Gastro- poda (snail-like shell-fish with only one shell). In the ease of the land snail, the opening is closed in winter by a hard layer of mucous matter called the epiphragm. PERIWINKLES. Periwinkles may always be found crawling about in the rock pools. In the periwinkles, or sea snails, there is no notch in the margin of the shell such as is possessed by the whelks. The pre- sence or absence of this notch is a fairly sure guide to the feeding habits of these creatures, for if the notch be present the animal is almost certain to be carnivor- ous, while, if it is absent, the animal
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectnaturalhistory, booky
