Crustaceans (lat. Crustacea) form a large group of arthropods, which includes such familiar animals as crabs, lobsters, crayfish, shrimps, wood lice and mollusks. There are more than 67,000 species described. From the smallest crustaceans, 0.1 mm in size, to the Japanese spider crab, 3.8 meters in size and weighing 20 kg. Like all arthropods, crustaceans have an exoskeleton, from which pairs of limbs depart. How many cancers have walking legs?
Exoskeleton structure and body structure
The body of a crustacean consists of segments that are grouped in three places: head, chest, and abdomen, or stomach.
The head and chest can be fused together, forming the cephalothorax, which can be covered with one large carapace. The body of the crustacean is protected by a solid exoskeleton. The shell around each paired formation of the embryo (somite) can be divided into dorsal and thoracic. Different parts of the exoskeleton can be fused together. How many cancers have walking legs? This amount may vary, depending on the classification of the creature.
Each segment of the body can carry a pair of appendages: on the segments of the head, they include two pairs of antennae, mandibles on the jaws; the thoracic segments carry legs, which can be specialized as walking legs (pereiopods) and jaws (lactating legs). The abdomen has a swimming limb, and ends with a large posterior fin (telson), which carries the anus, and is often surrounded by the last pair of limbs (uropods), forming a tail fan. The number and variety of appendages may be partially responsible for the large group size.
Body systems of crustaceans
The main body cavity is an open circulatory system, where blood is pumped with the help of a heart located near the back. Malacostraca has hemocyanin as an oxygen-containing pigment. While copepods, ostracods, mollusks, and toad-like mollusks have hemoglobin. The digestive canal consists of a straight tube, in which there is often a gastric mill, similar to the stomach, to grind food and a pair of digestive glands that absorb food. Structures that function like kidneys are located near antennas. The brain exists in the form of ganglia, that is, in the form of a cluster of nerve cells such as axons, dendrites and glial cells.
How many legs do crayfish have? Many crustaceans have ten. The first (and sometimes second) pair of swimming limbs specializes in sperm transfer. Many terrestrial crustaceans (such as the red Christmas crab) mate seasonally and return to sea to release eggs. Others, such as wood lice, lay their eggs on land, albeit in humid conditions. In most decapods (decapod crustaceans), females retain eggs until they hatch in freely floating larvae.
Crustacean habitats
Most crustaceans are aquatic, living either in a marine or in a fresh environment. Several groups have adapted to life on land, such as land crabs, land hermit crabs, and wood lice.
How many legs do crayfish live in the sea? Marine crustaceans are as widespread in the oceans as widespread as insects on land. Most of them are mobile and move independently, although some are parasitic and live attached to their owners (including marine, fish, whale lice, language worms, which may be referred to as “crustacean lice”). Adult shells live a sedentary life - they are attached to the surface of the substrate and cannot move independently.
Crustacean life cycles
Crustaceans have 3 life cycles: mating, eggs and larvae.
Most crustaceans reproduce sexually. But there are a small number of hermaphrodites, including shells, remipeds, and cephalocarids. Some may even change their sex during their lifetime. Parthenogenesis is also widespread among crustaceans, where the female produces viable eggs without the need for male fertilization. This occurs in many toad-like, in some shells (ostracods), in some large crustaceans (isopods), and in some “higher” crustaceans, such as Marmorkrebs.
In many groups of crustaceans, fertilized eggs just fall into the water column, while others have developed a number of mechanisms to hold the eggs until they are ready for hatching. Most decapod crayfish carry eggs attached to the swimming legs (pleopods), while others lay eggs by attaching them to the chest limbs. Sometimes the female does not carry eggs in the external eggs, but glues them to stones and other objects.
Most krill carry eggs between the chest limbs; some copepeds carry their eggs in special thin-walled sacs, while others tie them in long, tangled strings. How many legs do crayfish that carry eggs have? There are more than 10 pairs, which means that the brood will be large.
Crustaceans exhibit a number of larval forms. The earliest and most characteristic is nauplii. He has three pairs of appendages that come out of the head of a young animal. In most groups, there are further larval stages, including zoia. This name was given when naturalists considered it a separate species. It follows the nauplius stage and precedes the post-larva. Zoia larvae swim with breast appendages, unlike nauplii, which use the head limbs. How many feet have crayfish just born? The amount is not very different from an adult. Larvae often have shell-like spikes that can help in directional swimming. In many decapod crustaceans (decapods), due to their accelerated development, zoya is the first larval stage. In some cases, it is followed by the stage of misis, and in others, by the stage of megalope, depending on the group of crustaceans.
Output
Crustaceans are very ancient and interesting creatures. How many legs does the crayfish we meet most often have? He has over 19 pairs of limbs. This is a very large amount for such a small creature.