Gastropods

The gastropods are one of the groups of animals different , both in shape , habits and habitat . They are the largest group of mollusks , with more than 62,000 living species, and comprise about 80% of living mollusks. They have a long fossil record and their presence is recorded from the Early Cambrian Period, which shows periodic extinctions of subclasses, followed by the diversification of new groups.

Gastropods have figured prominently in paleobiological and biological studies , and have served as study organisms in numerous evolutionary , biomechanical, ecological, physiological, and behavioral investigations . They are extremely diverse in size, body and shell morphology, and habits, and occupy the widest range of ecological niches of all mollusks , being the only group that has managed to invade land.

Characteristics of gastropods

The main characteristics of gastropods are the following:

• Its most common representatives are snails and slugs .
• Their diet is quite varied.
• They have a heart with a ventricle and one or sometimes two atria.
• Your skin is rich in glands secreting mucus that helps them move from one place to another.
• They are able to stick their head into the shell when they feel in danger.
• They can live on land or in water sweet or salty.

Types of gastropods

There are marine and terrestrial gastropods . Most are considered to be those that inhabit the sea and are herbivores , detritivores and carnivores . Many of them are also excavators and have siphons to get oxygen and food. They breathe through gills and some have developed lungs .

Terrestrial ones also have shells and most have lungs , usually they can be found in humid or wet environments . Their muscles are strong and use the mucus they release to get up rough surfaces. They have tentacles on their heads and a primitive brain . In addition, they are hermaphrodites and lay nests on the ground.

Classification

The classification of gastropods is as follows:

• Opisthobranchs : they are marine and have the gills behind the heart.
• Prosobranchs : They can live in marine or fresh water.
• Sistelomatophores : They are terrestrial and in this group are terrestrial slugs.
• Lung : They are terrestrial, with shell and lung respiration.

Feeding

Their type of nutrition or diet is highly variable, for this reason, many of them can be carnivores , herbivores , scavengers , some can eat particles that are in suspension, and also parasites .

They usually feed on algae or tiny animals . Some mollusks live fixed in the substrate, and have the ability to move close to where they are fixed to look for their food.

Some carnivorous gastropods can eat echinoderms , bivalves , other gastropods, fish, and crustaceans . Those belonging to the group of scavengers can eat dead fish that are in suspension. Slugs and land snails are completely herbivorous .

Habitat

The favorite habitat of gastropods is the rocky coast as it is an inhospitable place , as it is there where the waves break on the rocks.

They are distributed from the intertidal zone to the abyssal depths , to the fresh waters of rivers and lakes to which they have been able to adapt and there are also those who have managed to learn to live on land . Some of them are also able to stay out of the water for long periods, which helps them cope with low tides.

Reproduction of gastropods

Almost all gastropods have an ovary or a testicle and the type of fertilization can be external or internal . Most of them expel sperm and eggs that have not been fertilized to the water where a type of external fertilization occurs . Some of them may be unisexual or hermaphroditic . These changes in sex depend largely on the number of females there are when fertilization occurs.

Breathing

Their breathing can be air or water . In the case of aquatic respiration, this is carried out by means of gills that are located in the paleal cavity and depending on the species, this will be the number of gills it has.

In the case of beings that have air respiration, this is carried out through the paleal cavity, which is a highly vascularized cavity and which functions in the same way as a lung .

Fossils

In Mesozoic times, the ancestors of today’s gastropods evolved. One of the first known is the Maturipupa , which was found in Europe . In Mesozoic rocks , gastropods were found in greater abundance and were better preserved. Its fossils appear in marine and freshwater sediments . In southern England , fossils of the Viviparus lake snail have been found.

Cenozoic rocks have fossil gastropods, related to current forms. Diversity increased markedly at the beginning of this era, along with that of bivalves . Gastropods are one of the groups that best provide information on the changes in fauna caused by the advance and retreat of the ice during the Pleistocene .

Examples of gastropods

The most common gastropods that we can find are:

• Snails : they have a shell and are terrestrial. They are moved by muscle contractions.
• Slugs : they are marine mollusks, some have shells and others do not. Some of them have their dorsal surface covered with tentacles.
• Sea shells: they have a fairly developed shell and can close it. It has gills in the paleal cavity and its nervous system is well developed. They have tactile eyes and tentacles.
• Sea hares : their skin resembles that of a leopard and their size is medium. They live near the coasts of tropical and subtropical seas.