Shells, also known as molluscs, are widely distributed, including 7 major categories, including bivalves, snails, multi-platens, excavators and cephalopods, only because most of the species have one, two or more calcareous shells or plates.
Bivalves have a 2-petal shell, no obvious head, well-developed foot roots, axe-shaped, also customarily called axe-footed, such as clams, bamboo clams. The snail is a spiral shell, such as the crown snail, bao also belongs to this class, but its shell spiral part is not obvious. Multi-plated species such as stone turtles, there are 8 bone plates, arranged in an orderly manner on the back, not covered by the whole body. There are few species of foot diggers, and it has an ivory shell with openings at both ends, such as the large horned shell. The most specialized or evolved is the cephalopods, which have developed heads and eyes, and the feet are toe-shaped (wrist), located at the front of the head, so they are called cephalopods. This issue focuses on the crown snail and the nautilus.
Crown snail
Taxonomic status: Gastropods, Heterogaschidae, Coccomedae
Morphological characteristics: the shell is large and thick, slightly spherical or oval. The spiral part is short, and the body snail layer is very large, accounting for almost all of the shell. The tip of the snail has nodule protrusions on the shoulders of each spiral layer, especially the nodules of the body snail layer are particularly developed, with 5 to 7 horn-like protrusions. The surface of the shell is off-white with irregular reddish-brown markings, and the inner surface of the shell mouth is dark orange-red.
Biological and ecological characteristics: warm sea benthic large shellfish, common individual shell height of about 300 mm. Meat is edible, shells are peculiar, and can be used for ornamental purposes or processed into ornaments.
Status quo and protection: The "Red List of Species in China" is listed as an endangered species and is now a second-class protected animal in China.
nautilus
Taxonomic status: Cephalopods, Nautilus, Nautilus
Morphological characteristics: there is a dorsal-ventral spiral-shaped calcareous shell on the outside of the body, and the shell surface is smooth, with 15 to 20 orange-red, brownish red or brownish yellow wavy horizontal stripes. From the shell mouth inward, about 30 shell chambers. The first chamber is huge, inhabited by the flesh part of the animal, called the "living room"; the remaining chambers are gradually reduced to store air, called the "gas chamber". There are small holes in the center of each gas chamber, and many small holes form a "string pipe", which can usually adjust the sinking and floating in the water body with the help of the filling and release of the air in the air chamber.
Biological and ecological characteristics: it is a warm-water large shellfish endemic to the Indian and Pacific oceans, with a water depth of 5 meters to 400 meters. Usually lurking on the coral reefs and rocks on the seabed, the movement is fast and agile.
Status quo and protection: beautiful shells, precious ornamental shellfish, meat edible, but also the oldest surviving cephalopods, known as activated stones, is now listed as China's first-class protected animals.
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(Author: Zhao Shenglong)