Crustaceans (lat. Crustacea) form a large group of arthropods that includes such familiar animals as crabs, lobsters, crayfish, shrimp, woodlice and mollusks. There are more than 67,000 described species. 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 extend. How many walking legs do crayfish have?
Exoskeleton structure and body structure
The body of a crustacean consists of segments that are grouped in three places: the head, thorax and abdomen, or belly.
The head and thorax can be fused together to form a cephalothorax, which can be covered by one large carapace. The body of the crustacean is protected by a hard exoskeleton. The membrane around each paired formation of the embryo (somite) can be divided into dorsal and thoracic. Various parts of the exoskeleton can be fused together. How many pairs of walking legs do crayfish have? This number may vary, depending on the creature's classification.
Each body segment can carry a pair of appendages: onsegments of the head they include two pairs of antennae, mandibles on the jaws; the thoracic segments bear legs, which may be specialized as walking legs (pereiopods) and jaws (feeding legs). The abdomen has a swimming limb, ending in a posterior large fin (telson) that carries the anus, and is often surrounded by the last pair of limbs (uropods) to form a tail fan. The number and variety of appendages may be partly responsible for the large size of the group.
Crustacean body systems
The main body cavity is an open circulatory system where blood is pumped by the heart located near the back. Malacostraca has hemocyanin as an oxygenated pigment. Whereas copepods, ostracods, mollusks and toad-like mollusks have hemoglobin. The alimentary canal consists of a straight tube that often contains a stomach-like mill to grind food, and a pair of digestive glands that absorb food. Structures that function like kidneys are located near the antennae. The brain exists in the form of ganglia, that is, as a collection of nerve cells such as axons, dendrites, and glial cells.
How many legs do crayfish have? Many crustaceans have ten. The first (and sometimes the second) pair of swimming limbs is specialized for transporting sperm. Many terrestrial crustaceans (such as the red Christmas crab) mate seasonally and return to the sea to release their eggs. Others, such as woodlice, lay their eggs on land, albeit in humid conditions. In most decapods (decapods), females retain their eggs until they hatch into free-swimming larvae.
Crustacean habitats
Most crustaceans are aquatic, either marine or freshwater. Several groups have adapted to life on land, such as land crabs, land hermit crabs and woodlice.
How many legs do sea crayfish have? Marine crustaceans are as common in the oceans as insects are on land. Most are motile and move independently, although some are parasitic and live attached to their hosts (including sea lice, fish lice, whale lice, tongue worms, which may be referred to as "crustacean lice"). Adult barnacles live a sedentary life - they are attached to the surface of the substrate and cannot move on their own.
Life cycles of crustaceans
Crustaceans have 3 life cycles: mating, eggs and larvae.
Most crustaceans reproduce sexually. But there are a small number of hermaphrodites, including barnacles, remipeds, and cephalocarids. Some may even change gender during their lifetime. Parthenogenesis is also widespread among crustaceans, where the female produces viable eggs without the need for fertilization by the male. This occurs in many toad-like, some barnacles (ostracods), some large crustaceans (isopods), and some "higher" crustaceans such as Marmorkrebs.
Many groups of crustaceansfertilized eggs simply fall into the water column, while others have developed a number of mechanisms to hold the eggs until they are ready to hatch. Most decapods lay their eggs attached to swimming legs (pleopods), while others lay their eggs by attaching them to their thoracic limbs. Sometimes the female does not lay eggs in the outer eggs, but sticks them to stones and other objects.
Most krill carry their eggs between their thoracic limbs; some copepods lay their eggs in special thin-walled sacs, while others tie them into long, tangled strings. How many legs do crabs have that lay eggs? There are more than 10 pairs, which means that the brood will be large.
Crustaceans exhibit a range of larval forms. The earliest and most characteristic is the nauplius. It has three pairs of appendages that emerge from the young animal's head. In most groups, further larval stages exist, including the zoya. This name was given when naturalists considered it a separate species. It follows the nauplial stage and precedes the post-larva. Zoya larvae swim with thoracic appendages, unlike nauplii, which use head limbs. How many legs do newborn crayfish have? The number is not very different from the adult. The larva often has carapace spines that can aid in directional swimming. In many decapod crustaceans (decapods), due to their accelerated development, zoia is the first larval stage. In somein some cases it is followed by a mysis stage and in others a megalopa stage, depending on the crustacean group.
Conclusion
Crustaceans are very ancient and interesting creatures. How many legs does the most commonly seen crayfish have? It has over 19 pairs of limbs. This is a very large number for such a small creature.
