The Victorian naturalist . in forDiplotaxis muralis in Cruciferae.) (To be continued) 184 Vicf. Nat. Vol. 93 Life History and Biology of a Snail Part 2. Protection, Movement and Feeding BY Brian J. Smith* Land snails are soft bodied animalsprotected from predators and therigors of the hostile terrestrial environ-ment by a hard external shell intowhich they can completely withdraw. The shell The shell is calcareous in nature,being made up of calcium/magnesiumcarbonate laid down by the leadingor outer edge of the mantle. Thus itgrows by adding on extra material tothe aperture lip only and
The Victorian naturalist . in forDiplotaxis muralis in Cruciferae.) (To be continued) 184 Vicf. Nat. Vol. 93 Life History and Biology of a Snail Part 2. Protection, Movement and Feeding BY Brian J. Smith* Land snails are soft bodied animalsprotected from predators and therigors of the hostile terrestrial environ-ment by a hard external shell intowhich they can completely withdraw. The shell The shell is calcareous in nature,being made up of calcium/magnesiumcarbonate laid down by the leadingor outer edge of the mantle. Thus itgrows by adding on extra material tothe aperture lip only and to form theshape, sculpture and colour pattern ofthe shell. The snail can repair smallbreaks or areas of damage in the bodyor outer whorl of the shell, but losesthis abihty the further away from themantle edge the break occurs. Besidesproviding physical protection for thesoft body of the snail, the shell givesprotection from predators in providingcamouflage by its colour pattern andsculpture. The pattern and sculpture are. Figure 1. Scanning electron microscopepicture of Thryasona elenescens fromGeelong. (12x) species specific and under genetic con-trol. Colour pattern in particular canhave considerable variation in somespecies with local population variantsshowing interesting environmentalmodification. The classical work onthis was carried out in Britain wherepopulations of dark shells were shownto have a protective advantage in deepshadow hedge-row situations; whilepopulations of Hght shells of the samespecies fared better in sand-dune habi-tats; the selecting factor being pre-dation by birds in each case. The most elaborate microsculptureon shells in south-eastern Australia isseen in the minute endodontoidsnails (Fig. 1). This complex sculpturemay have a function in relation to sur-face water in cracks in logs, but noth-ing is really known about this. The body of the snail occupies thewhole of the shell (see Fig. 2 in Part 1of this series, Vic. Nat. 93(4): 130).The shell is
Size: 1687px × 1480px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdec, booksubjectnaturalhistory, bookyear1884
