What is a Crustacean?

Any member of the Crustacea subphylum (phylum Arthropoda), a group of invertebrate animals of over 45,000 species found all over the planet. The crustaceans meaning is an arthropod of the large, mainly aquatic group Crustacea, such as a shrimp, crab, lobster, or barnacle.

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Crabs, lobsters, crabs, and woodlice are some of the most well-known crustaceans examples, but the group also contains a large number of other species that go by different names. Crustaceans are aquatic and have two pairs of appendages (antennules and antennae) in front of the mouth and paired appendages near the mouth that act as jaws, unlike other arthropods. However, since there are so many variations to the basic characteristics, a comprehensive classification of all Crustacea is extraordinarily difficult to come up with.

The crustacean group can be considered a subphylum of the clade Mandibulata however, recent molecular studies have established that the crustacean group is paraphyletic and that it includes all species in the clade Pancrustacea except hexapods. Few crustaceans have a closer relationship with insects and other hexapods than with other crustaceans.


Crustaceans Characteristics

The majority of crustaceans are free-living, but others are sessile or parasitic.

The majority of people eat with their maxillae and mandibles. The walking legs, which have adapted chelipeds, may be used to aid in prey capture. Some crustaceans filter microscopic plankton or even bacteria from the water, while others are predators and scavenge nutrients from detritus.

The vast majority of crustaceans are dioecious. Fertilization is accomplished through a variety of processes. Some crustaceans produce miniature adults, while others go through a larval stage known as a nauplius.

They are insect relatives.

Insects and crustacea would be phyla if the Arthropods were considered a superphylum (see List of animal phyla). The group has a long fossil record that dates back to the Cambrian period.

The majority of crustaceans are aquatic, mostly marine. Some people have permanently relocated to the property. Crabs and woodlice are examples of land-based crustaceans. Crustacea vary in size from 0.1mm parasites to the Japanese spider crab, which has a leg span of up to 14 feet (4.3 metres) and weighs 44 pounds (20 kg). The North Atlantic lobster will grow to be over 40 pounds in weight.

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Most crustaceans are mobile, but after their larval stage, some become sessile.

Barnacles are crustaceans that stick themselves to seashore rocks. Fish lice and tongue worms, for example, are parasitic. While most Crustacea have different sexes, others are hermaphroditic. Eventually, their eggs hatch into larvae.


Arthropoda Crustacea

Crustaceans are members of the Arthropoda phylum and the Crustacea subphylum so it’s also called Arthropoda crustacea. Crustaceans are named after the Latin word crusta, which means "shell."

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Crustaceans are a complex group of invertebrates that includes active animals like crabs, lobsters, shrimp, krill, copepods, amphipods, and barnacles, as well as more sessile species like barnacles.

The majority of big crustaceans crawl along the bottoms of lakes, rivers, and the ocean, sometimes reaching shore.

Benthic animals are named so because they float around the earth under the sea. Even though lobsters and shrimp can swim a little, they prefer to walk around the bottom of the water they live in.

Fishing and farming produce over 10 million tonnes of crustaceans for human consumption, the majority of which are shrimp and prawns. While krill and copepods aren't as common as other fish, they have the most animal biomass on the planet and are an important part of the food chain.

The bulk of crustaceans are free-living marine species, but others are terrestrial (e.g., woodlice), parasitic (e.g., Rhizocephala, fish lice, tongue worms), and sessile (e.g., Rhizocephala, fish lice, tongue worms), and others are sessile (e.g. barnacles).

Triops cancriformis, a living fossil that has lived seemingly unchanged since the Triassic era, belongs to the genus, which has a long fossil record dating back to the Cambrian. Fishing and farming produce more than 7.9 million tonnes of crustaceans for human consumption per year, the majority of which are shrimp and prawns. Krill and copepods are less often fished, but they can have the highest biomass on the planet and are an important part of the food chain.

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Structure of Crustaceans

A crustacean's body is made up of segments that are divided into three regions: the cephalon (head), pereon (thorax), and pleon (abdomen).

A cephalothorax, which is protected by a single wide carapace, may be formed by fusing the head and thorax. The hard exoskeleton protects the crustacean body, which must be moulted for the animal to rise. Each somite's shell is divided into three parts: a dorsal tergum, a ventral sternum, and a lateral pleuron. Various exoskeleton components can be fused.

Each somite, or body segment, may have two pairs of appendages: two pairs of antennae on the head segments, mandibles and maxillae on the mandibles and maxillae on the thoracic segments, and pereiopods (walking legs) and maxillipeds on the thoracic segments (feeding legs).

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Pleopods are found on the belly, which leads to a telson, which carries the anus and is often flanked by uropods to form a tail fan. Part of the group's popularity may be due to the number and variation of appendages in various crustaceans.

Crustacean appendages are usually biramous, which means they have two parts.

The second pair of antennae are used, but not the first, which is normally uniramous, except the Class Malacostraca, where the antennules may be biramous or even trigamous. It's uncertain if the biramous syndrome is a derivative state that originated in crustaceans, or whether all other species have lost the second branch of the limb. Trilobites, for example, had biramous appendages as well.


Reproduction System of Crustaceans

In crustaceans, the sexes are usually, but not always, apart.

Simultaneous hermaphroditism means that most barnacles have both males though female reproductive organs, though the males of some species are much smaller than the hermaphrodites. 

These "dwarf" males fertilise the eggs of the larger individuals by attaching themselves to the interior of their mantle cavity. Few members of the order Notostraca (tadpole shrimps) are also hermaphrodites, with sperm-producing lobes dispersed among the developing eggs in their ovaries. A change in sex during an individual's life is a common occurrence in certain shrimps.

In the Crustacea, structural or behavioural variations between the sexes are common and may be extreme; males in certain classes can be so small that they are difficult to see on the much larger female. This is particularly true for some parasitic copepods.

Normal sexual reproduction entails the union of a sperm and an egg, but certain crustaceans are parthenogenetic, meaning that they contain eggs that mature without being fertilised by a sperm. Many branchiopods, as well as certain ostracods and isopods, will do this.

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Mating System

The majority of crustaceans have two sexes and reproduce sexually.

In reality, recent research explains how male crustaceans, T. californicus, choose which females to mate with based on dietary variations, choosing algae-fed females over yeast-fed females. Barnacles, Remipedes, and Cephalocarida are among the few hermaphrodites. Some people can also alter their sex during their lives. In crustaceans, parthenogenesis occurs when a female produces viable eggs without the need for fertilisation by a male. Many branchiopods, some ostracods, some isopods, and some "upper" crustaceans, such as the Marmorkrebs crayfish, show this feature.


Life Cycle of Crustaceans

Eggs

Many crustaceans easily release the fertilised eggs into the water column, while others have evolved a variety of strategies to keep the eggs until they can hatch.

Peracarids, notostracans, anostracans, and many isopods form a brood pouch from the carapace and thoracic arms, while most decapods bear the eggs attached to the pleopods. Female Branchiura does not use external ovisacs to hold their eggs; instead, they tie them in rows to rocks and other items. The eggs are carried by most leptostracans and krill between their thoracic limbs; some copepods bear their eggs in unique thin-walled sacs, while others have them strung together in long, tangled strings.

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Larvae

Crustaceans have a variety of larval stages, the earliest and most distinctive of which is the nauplius.

This creature has three pairs of appendages that emerge from the head of the young animal, as well as a single naupliar eye. There are additional larval stages in most groups, including the zoea. It was assigned this name by naturalists who thought it was a distinct genus.  It comes after the nauplius stage and before the post-larva stage. Unlike nauplii, which swim with their cephalic appendages, and megalopa, which swim with their abdominal appendages, Zoea larvae swim with their thoracic appendages.

The zoea is the first larval stage in several decapods due to their rapid growth.

Based on the crustacean group involved, the zoea stage is followed by the mysis stage in some cases and the megalopa stage in others.

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Size Range of Crustaceans

The largest crustaceans belong to the Decapoda, a broad order of around 10,000 species that includes the 20-kilogram (44-pound) American lobster and the 3.7-metre-long Japanese spider crab (12 feet).

At the other end of the spectrum, certain water fleas (class Branchiopoda), such as Alonella, grow to be less than 0.25 millimetres (0.009 inches) long, and many members of the Copepoda subclass grow to be less than one millimetre long. The group's complex grouping reflects the diversity of composition.

As adults, certain parasitic types have been so transformed and advanced that they can only be identified as crustaceans based on their life histories.


Features of Crustaceans

  • Crustaceans are hard with flexible exoskeleton or shell.

  • It has two pairs of antennae.

  • A pair of mandibles which are used for eating food.

  • There are two pairs of maxillae on their heads.

  • Crustaceans are either oviparous or ovoviviparous.

  • Crustaceans have two compound eyes, often on stalks

  • The body of crustaceans is segmented with appendages on each body segment.

  • Crustaceans have gills.

  • Crustaceans are members of the Arthropoda Phylum and the Crustacea Subphylum.

  • Crustacean’s growth type is by moulting which sheds old skeleton and secretes a large one.

  • Branchiopoda (branchiopods), Cephalocarida (horseshoe shrimp), Malacostraca (the class that is potentially most important to humans, which includes crabs, lobsters, and shrimps), Maxillopoda (which includes copepods and barnacles), Ostracoda (seed shrimp), Remipedia (remipedes), Pentastomida (seed shrimp), Remipedia (Remi (tongue worms).

  • Crustaceans come in a wide range of shapes and sizes, and they can be found in a variety of environments, including on land.

  • Crustaceans can be found in a variety of habitats, from shallow intertidal zones to the deep sea.

Origin and Application of Crustacean

Crustaceans have significant economic, ecological, and aesthetic qualities, and they can also be admired from a bi-level functionality standpoint.

Larger crustaceans, such as shrimp, lobsters, and crabs, are important food sources, whereas smaller crustaceans, which are mostly considered a division or superclass rather than a subphylum, play an important role in many food webs. Crustacean carcinology is the biomedical study of crustaceans. Carcinology is also known as malacostracology, crustaceology, and crustalogy, and a carcinologist, crustaceologist, or crustalogist is a scientist who works in this field. The oldest crustaceans, including the well-known Burgess Shale fauna, have been discovered in Cambrian sediments. These primitive crustaceans are worm-like in form, but they have many of the main characteristics of crustaceans that can be seen in modern crustaceans like shrimps.

 

Conclusion

Crustaceans (Arthropods) are a group of animals with a body that is armoured on the outside (called an exoskeleton), The portion of the exoskeleton that is retained as a fossil is a strong exoskeleton. Arthropod is derived from the Greek words "arthro" (joint) and "poda" (foot or leg).

Arthropoda crustacea are the Animal Kingdom's largest phylum. It contains about 11,340,000 species in all ecosystems. Heteronomous metamerism, a chitinous exoskeleton, and jointed appendages are all characteristics of Arthropoda. The exchange of breathing gases happens across the general body surface in very small crustaceans. Gills and book gills are used by large aquatic arthropods, while trachea and book lungs are used by terrestrial arthropods. The oldest crustaceans have been discovered in Cambrian sediments.

FAQs (Frequently Asked Questions)

Q1. Is a Crustacean a Fish?

Answer: An allergy to shellfish is not the same as an allergy to seafood.

Fish (such as tuna or cod) and shellfish are examples of seafood (like lobster or clams). Fish and shellfish are scientifically distinct, even though they are all classified as "seafood." So, unless the individual already has a fish allergy, fish would not induce an allergic reaction in anyone with a shellfish allergy.

Q2. Define Crustaceans.

Answer: Crustaceans meaning is, arthropods that belong to the large, mostly aquatic Crustacea family, such as crabs, lobsters, shrimp, and barnacles.

Q3. What is the Largest Class of Crustaceans?

Answer: Clade Multicrustacea

Crabs, lobsters, shrimps, woodlice, prawns, krill, barnacles, crayfish, copepods, amphipods, and other crustaceans belong to the clade Multicrustacea, which is the largest superclass of crustaceans, including roughly four-fifths of all described crustacean species.