All gastropods feed by using a radula , which is a tongue-like structure covered by rows of rasping teeth. Helix aspersa common garden snail. Habitat Gastropods are found in a variety of habitats across Australia but favour moist environments. Most native species can be found hiding under logs and rocks, in leaf litter or under the bark of trees. During humid weather or times of rainfall they can be seen foraging for food or looking for mates.
Slugs are particularly susceptible to drying out and some snails may wait out a dry period by sealing themselves to a hard surface with dried mucus and staying inactive, this is sometimes known as aestivation.
In some agricultural areas of South Australia aestivation by introduced snail species causes problems as huge numbers congregate in crops to aestivate over the hotter months contaminating the harvest. Entomology Home. About this Site. Alamy charges you a fee for access to the high resolution copy of the image. Natural history of animals;. The term Gastropod means stomach-footed, and is eiven to these animals because the lower side serves them as a sort of foot, by means of which they creep along.
Most of the Gastro- pods have a shell; and, as this is made of only one piece, or valve, they are often called Univalves. Some, however, have no shell in the adult state, though all have a shell when first hatched. Most Gastropods have a lid or door, called the opcrculuiii, with which they close the opening to the shell when they with- draw within. It is a horny plate, sometimes strength- ened by shelly matter. Their eyes are two, and often on long stalks, as seen in Figure Many of the I Spire.
Eyespots are absent in these animals. A single pair of nephridia for excretion is present. Figure 3. These mussels, found in the intertidal zone in Cornwall, England, are bivalves. Members of this class are found in marine as well as freshwater habitats. The overall morphology is laterally flattened, and the head region is poorly developed. Eyespots and statocysts may be absent in some species.
These animals are suspension feeders—they eat material, such as plankton, that is suspended in the water around them. Due to their diet, this class of mollusks lacks a radula. Respiration is facilitated by a pair of ctenidia, whereas excretion and osmoregulation are brought about by a pair of nephridia.
Bivalves often possess a large mantle cavity. In some species, the posterior edges of the mantle may fuse to form two siphons that serve to take in and exude water. One of the functions of the mantle is to secrete the shell.
This property has been commercially exploited to produce pearls. Gastropoda includes shell-bearing species as well as species with a reduced shell. These animals are asymmetrical and usually present a coiled shell Figure 4. Shells may be planospiral like a garden hose wound up , commonly seen in garden snails, or conispiral , like a spiral staircase , commonly seen in marine conches.
Figure 4. The visceral mass in the shelled species displays torsion around the perpendicular axis on the center of the foot, which is the key characteristic of this group, along with a foot that is modified for crawling Figure 5. Most gastropods bear a head with tentacles, eyes, and a style. A complex radula is used by the digestive system and aids in the ingestion of food. Eyes may be absent in some gastropods species. The mantle cavity encloses the ctenidia as well as a pair of nephridia.
Figure 5. During embryonic development of gastropods, the visceral mass undergoes torsion, or counterclockwise rotation of anatomical features. As a result, the anus of the adult animal is located over the head. Torsion is an independent process from coiling of the shell.
Figure 6. Members of the genus Conus produce neurotoxins that may one day have medical uses. Marine snails of the genus Conus Figure 6 attack prey with a venomous sting. The toxin released, known as conotoxin, is a peptide with internal disulfide linkages.
Conotoxins can bring about paralysis in humans, indicating that this toxin attacks neurological targets. Some conotoxins have been shown to block neuronal ion channels. These findings have led researchers to study conotoxins for possible medical applications.
Conotoxins are an exciting area of potential pharmacological development, since these peptides may be possibly modified and used in specific medical conditions to inhibit the activity of specific neurons. For example, these toxins may be used to induce paralysis in muscles in specific health applications, similar to the use of botulinum toxin.
Since the entire spectrum of conotoxins, as well as their mechanisms of action, are not completely known, the study of their potential applications is still in its infancy. Most research to date has focused on their use to treat neurological diseases. They have also shown some efficacy in relieving chronic pain, and the pain associated with conditions like sciatica and shingles.
The study and use of biotoxins—toxins derived from living organisms—are an excellent example of the application of biological science to modern medicine.
Cephalopods are a class of shell-bearing animals as well as mollusks with a reduced shell. They display vivid coloration, typically seen in squids and octopi, which is used for camouflage.
All animals in this class are carnivorous predators and have beak-like jaws at the anterior end.
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