Why are crayfish classified as protostomes

Worms have many segments. Crayfish are classified as arthropods, because of their characteristic segmented bodies, chitinous exoskeleton, and joint appendages. Yes, molluscs fit into the group known as protostomes.

All animals are protostomes, save for starfish, sea urchins, sea cumcumbers all Echinodermata and vertebrates, those are deuterostomes. Neither are protostomes. Chordates, Hemichordates, and Echinoderms are all deuterostomes in that the blastopore forms the anus first.

In protostomes, the blastopore forms the mouth first. Protostomes along with other Athropods. They are Deuterostomes. Starfish are deuterostomes. Log in. Zoology or Animal Biology. Study now. See Answer. Best Answer. They have remote nipples, that are used for warmth.

Study guides. Biology 22 cards. Espinosa, C. Parr, T. Jones, G. Hammond, and T. The Animal Diversity Web online. Disclaimer: The Animal Diversity Web is an educational resource written largely by and for college students.

ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe.

Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

Additional Information Encyclopedia of Life. Decapoda Facebook. Kingdom Animalia animals. Animalia: information 1 Animalia: pictures Animalia: specimens Animalia: sounds Animalia: maps Eumetazoa metazoans. Eumetazoa: pictures Eumetazoa: specimens Eumetazoa: sounds Eumetazoa: maps Bilateria bilaterally symmetrical animals. Bilateria: pictures Bilateria: specimens Bilateria: sounds Bilateria: maps Protostomia protostomes.

Protostomia: pictures Protostomia: specimens Protostomia: sounds 13 Protostomia: maps Ecdysozoa: pictures Ecdysozoa: specimens Ecdysozoa: sounds Arthropoda arthropods.

Arthropoda: information 1 Arthropoda: pictures Arthropoda: specimens Arthropoda: sounds Crustacea shrimps, crabs, lobsters, water fleas, and relatives. Crustacea: information 1 Crustacea: pictures Crustacea: specimens 7. Class Maxillopoda. Maxillopoda: information 1 Maxillopoda: pictures Maxillopoda: specimens 5.

Class Malacostraca. Malacostraca: information 1 Malacostraca: pictures Malacostraca: specimens 5. Order Decapoda. Decapoda: pictures Decapoda: specimens 1. Superfamily Alpheoidea. Alpheoidea: pictures 3. Superfamily Astacoidea.

Astacoidea: pictures Superfamily Atyoidea. Superfamily Axioidea. Family Belliidae. Superfamily Bresilioidea. The crustacean body plan resembles that of other arthropods in some respects nervous system, for example , but most crustaceans have three body sections— head , thorax , and abdomen —as do insects; in comparison, chelicerates have two body sections fused cephalothorax and abdomen.

In some crustaceans, the head is fused with various thoracic segments to form a cephalothorax. The crustacean coelom is small and the main body cavity—a hemocoel, or cavity in which blood circulates—is part of the circulatory system, as in other arthropods. The crustacean mode of gas exchange, however, differs from that in other arthropods; gills —evident in crabs and lobsters—exchange gases with the water or air.

A tube-shaped heart with ostia is the circulating pump for blood. In lobsters, one of the mouthparts is modified as a gill bailer, which the animal uses to generate a current of water through its gill chamber , enhancing gas exchange through the gills. Crustaceans that are semiterrestrial for example, the hermit crab Clibanarius inhabit the intertidal zone of the sea beach, a habitat that provides at least occasional moisture to their respiratory surfaces.

Some crustaceans have blood vessels; others have no vessels and pump blood only to the hemocoel. A dorsal brain, ventral nerve cords with ganglia in each body segment , and sensory organs such as the compound eyes of Daphnia and statocysts constitute the nervous system. Krill chemically produce light in luminescent organs on their legs and eyestalks; their light displays may function in mating or in protecting them from predators, such as penguins, that are below them in the sea.

All crustacean muscle is striated, typical of arthropods, and quicker to contract and relax than the smooth muscle that predominates in other invertebrates. Crustaceans may be dioecious, often with sexual dimorphism that ranges from a difference in size between females and males to sexual dimorphism of appendages males may have appendages used in mating to the extreme sexual dimorphism of some isopods. Barnacles are hermaphrodites; the long penis of one barnacle fertilizes another nearby but permanently attached barnacle.

A three-segmented, free-living larva called a nauplius is a characteristic crustacean larva. Some barnacles brood embryos to the nauplius larval stage. Some highly specialized crustacea are so bizarre in form that they can be classified only upon observation of their nauplius larvae.

Diverse larvae having forms as exotic as their names—zoea, megalops, phyllosoma, mysis—are present in decapod custaceans, an order of Class Malacostraca that includes crabs, some shrimp, hermit crabs, lobsters, and crayfish.

Other species in Class Malacostraca lack a larval stage; young hatch as juveniles. Some freshwater copepods and members of Class Branchiopoda are parthenogenetically reproducing females. The cuticle of Nematodes is rich in collagen and a carbohydrate-protein polymer called chitin.

The cuticle also lines many of the organs internally, including the pharynx and rectum. The epidermis can be either a single layer of cells or a syncytium, which is a multinucleated cell formed from the fusion of uninucleated cells.

The overall morphology of these worms is cylindrical, while the head is radially symmetrical. A mouth opening is present at the anterior end with three or six lips. Teeth occur in some species in the form of cuticle extensions. Some nematodes may present other external modifications such as rings, head shields, or warts. Rings, however, do not reflect true internal body segmentation. The mouth leads to a muscular pharynx and intestine, which leads to a rectum and anal opening at the posterior end.

In addition, the muscles of nematodes differ from those of most animals; they have a longitudinal layer only, which accounts for the whip-like motion of their movement. Nematode shape : Scanning electron micrograph of soybean cyst nematode and its egg. Nematodes are cylindrical in shape, often looking like thin hairs.

They possess an exoskeleton that prevents them from drying out. It must be shed a process called ecdysis in order for them to grow. In nematodes, specialized excretory systems are not well developed. Nitrogenous wastes may be lost by diffusion through the entire body or into the pseudocoelom body cavity , where they are removed by specialized cells.

Regulation of water and salt content of the body is achieved by renette glands, present under the pharynx in marine nematodes. Most nematodes possess four longitudinal nerve cords that run along the length of the body in dorsal, ventral, and lateral positions. The ventral nerve cord is better developed than the dorsal or lateral cords. Nematodes employ a variety of reproductive strategies that range from monoecious to dioecious to parthenogenic, depending upon the species under consideration.

The uterus has an external opening known as the vulva. Specialized structures at the tail of the male keep him in place while he deposits sperm with copulatory spicules.

Fertilization is internal with embryonic development beginning very soon after fertilization. The embryo is released from the vulva during the gastrulation stage. The embryonic development stage lasts for 14 hours; development then continues through four successive larval stages with ecdysis between each stage L1, L2, L3, and L4 ultimately leading to the development of a young male or female adult worm. Adverse environmental conditions such as overcrowding and lack of food can result in the formation of an intermediate larval stage known as the dauer larva.

Arthropods are the largest grouping of animals all of which have jointed legs and an exoskeleton made of chitin. Arthropods dominate the animal kingdom with an estimated 85 percent of known species included in this phylum; many arthropods are as yet undocumented. The principal characteristics of all the animals in this phylum are functional segmentation of the body and presence of jointed appendages. Arthropods also show the presence of an exoskeleton made principally of chitin, which is a waterproof, tough polysaccharide.

Phylum Arthropoda is the largest phylum in the animal world; insects form the single largest class within this phylum. Arthropods are eucoelomate, protostomic organisms. Phylum Arthropoda includes animals that have been successful in colonizing terrestrial, aquatic, and aerial habitats. This phylum is further classified into five subphyla: Trilobitomorpha trilobites, all extinct , Hexapoda insects and relatives , Myriapoda millipedes, centipedes, and relatives , Crustaceans crabs, lobsters, crayfish, isopods, barnacles, and some zooplankton , and Chelicerata horseshoe crabs, arachnids, scorpions, and daddy longlegs.

Trilobites are an extinct group of arthropods found chiefly in the pre-Cambrian Era that are probably most closely related to the Chelicerata.

These are identified based on fossil records. Trilobite fossil : Acadoparadoxides , possibly A. A unique feature of animals in the arthropod phylum is the presence of a segmented body and fusion of sets of segments that give rise to functional body regions called tagma.

Tagma may be in the form of a head, thorax, and abdomen, or a cephalothorax and abdomen, or a head and trunk. A central cavity, called the hemocoel or blood cavity , is present; the open circulatory system is regulated by a tubular, or single-chambered, heart. Respiratory systems vary depending on the group of arthropod. Insects and myriapods use a series of tubes tracheae that branch through the body, open to the outside through openings called spiracles, and perform gas exchange directly between the cells and air in the tracheae.

Other organisms use variants of gills and lungs.