What are Mollusks?

Mollusk (Latin scientific name: Granulifusus kiranus) is an invertebrate mollusc phylum animal, the largest group except arthropods, about 100,000 species. The systems are very different, but have the same characteristics: the body is soft without segmentation, and it is usually head-foot (some heads degenerate or disappear; foot muscle quality) and visceral-mantle (by the dorsal viscera, mantle And jacket cavity)).

Mollusc habitat is very vast, from the tropical continent to the North and South Arctic oceans, from high-altitude ponds above 7000 meters above sea level to more than 800 meters below the deep sea, are their paradise. There are many types of mollusks, second only to arthropods-more than 100,000 species exist. They differ greatly in form, but they all have soft bodies. Most of them live in the ocean, and only part of the bivalves and gastropods migrate to brackish and freshwater ^[1]

(Mantle)

The skin folds extend from the back of the body, often covering the entire visceral mass. Cavity formed between mantle and viscera

(Shell)

Mollusc

Mollusc

For aquatic species

The original type of nervous system has no ganglion differentiation, only the peripharyngeal nerve ring and a pair of foot cords and a pair of lateral cords protruding backwards. The higher species mainly have 4 pairs of ganglia, with nerve connections between the ganglia. The cerebral ganglion (cerebral ganglion) is located on the dorsal side of the esophagus and emits nerves to the head and front of the body.

Mollusks are mostly hermaphrodites, and many species are hermaphrodite; some are hermaphrodites. The cleavage forms are mostly completely unequal cleavage, many of which are spiral. A few for

There are two versions of the origin of molluscs: one is that molluscs originated in

Terrestrial snails and slugs eat leaves and buds of plants and endanger vegetables, fruit trees, tobacco, etc .; some carnivorous species in the ocean can kill young seedlings such as oysters and loach, causing loss of cultured bivalves; Sexual species often eat kelp, seaweed seedlings, yes

First, the shells of mollusks are formed by the calcareous secretion of the shell, and they will not molt for life, except that there are no joints at the joints. Arthropods are covered with chitinous exoskeleton, called epidermis or cuticle. The stratum corneum is very thin on the joint membrane between adjacent body segments and is prone to flexion. The joints of the appendages can also move. Arthropods molt regularly during their growth.

Second, mollusks are a class of invertebrates with soft bodies. Molluscs generally have a symmetrical body shape, but some molluscs have various peculiar shapes due to twisted bodies. They often have a shell, no somite, and most of them can be divided into 3 parts: head, feet, and visceral sac. The outer skin folds from the back into a film called the coat. The coat surrounds the body and secretes lime.

Crustaceans belong to the arthropod phylum. Arthropods are composed of a series of somites. They are divided into three sections: head, chest, and abdomen. Each body segment has a pair of segmented appendages. There are two types of appendages: single branch and single branch. The circulation system is open tube. Respiratory organs of aquatic species are gills or book gills, and terrestrial ones are trachea or book lungs or both. Primitive arthropods exchange gas on the surface. The nervous system is a centralized chain nervous system. There are sensory organs such as touch, taste, smell, hearing, balance and vision. There are two types of eyes: monocular and compound. The compound eye is composed of an eye, which can sense the movement and shape of external objects, and can adapt to the intensity of light and distinguish colors.

In addition, crustaceans vary greatly in their morphology, the smallest such as fissures, with a body length of less than 1 mm. The largest mitten crab can reach 4 meters in width when two chelates are stretched. The body is long-tube-shaped, with distinct body segments, and the entire body is divided into 3 heads, chest, and abdomen. The head is healed from 6 sores. The crustacean exoskeleton consists of two parts: one on the back and one on the ventral surface. The sides of the carapace often extend outward (lower) and are the side armor. The appendages are usually born on the sides of the plastron. It can be seen that arthropods are higher than mollusks ^[2] .