THE ROBINSON LIBRARY
|The Robinson Library >> Science >> Zoology >> Mollusks >> Class Gastropoda|
The abalone somewhat resembles a snail, the body being little more than a muscular foot with a head at one end, bearing a pair of eyes and sensory tentacles. The body is also fringed with tentacles. Over the top of the shell lies a line of holes, through which water is exhaled after it has been drawin in under the shell and over the gills to extract oxygen. New holes are formed as the shell grows forward, while the old holes become covered over, so that only a few younger holes are open at any one time, the rest appearing as a line of bumps. Abalones range in size from the 1-inch-long Haliotis pourtalese to the red abalone (H. rufescens), which is a foot across.
Distribution and Habitat
Abalones are found along the coasts of the Mediterranean, Africa, Australia, New Zealand, the Pacific islands, and the western coast of North America. Except for two species, abalones live between the extreme low-water mark and a depth of about 60 feet along rocky shores where there is no sand to clog the gills or in rocky pools large enough not to be heated too quickly by the sun. H. pourtalese is the deepest-living abalone, living at depths of 350 to 1,200 feet. The black abalone (H. cracherodii) lives in the splash zone where waves breaking against rocks alternately cover and expose it.
Abalones have no particular place to which they return after feeding. They simply hide up in a crevice or under a rock, avoiding the light and coming out at night. When disturbed, an abalone grips the rock face, using its foot as a suction pad -- the two main muscles of the body can exert a force up to 400 pounds in a 4-inch specimen.
Movement is achieved by waves of muscular contractions that pass along the foot, pushing the animal forward. As each part expands it is fixed to the ground by slimy mucus -- the part in front, expanding in turn, is pressed forward and then itself stuck down. Alternate waves of movement pass down either side of the foot, so that as a part of one side is moving the corresponding part on the other side stays fixed. The rate of travel is actually quite rapid for a shellfish -- up to 5 or 6 yards per minute is possible, but rarely actually achieved.
Abalones are vegetarians, crawling over rock faces and browsing on seaweeds that they seek out with their tentacles. Their favorite foods are red weeds and green sea lettuces, but they will also scrape tissue off fragments of kelp that have been torn away by waves. Food is scraped up and chewed into small pieces by the rasp-like action of the radula, a "tongue" made up of large numbers of small, chalky teeth.
A female releases 100,000 or more eggs directly into the sea, but only after a male has released a cloud of sperm around her. The fertilized eggs are covered by a gelatinous coat and float freely in the sea until they hatch a few hours later as minute trochophore larvae. These larvae are top-shaped and swim around by means of a band of hair-like cilia around the thickest part. Within a day the trocophore develops into a veliger -- a miniature version of the adult complete with shell but still with the band of cilia. Two days later it loses the cilia, sinks to the bottom and starts to develop into an adult, a process that takes several weeks. Sexual maturity is reached at about six years.
|The Robinson Library
>> Zoology >> Mollusks >> Class Gastropoda
This page was last updated on October 30, 2017.