Phoronida

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Phoronids, common name for a wormlike marine invertebrate animal, a kind of tube worm. There are about 12 species of phoronids. They are sedentary animals that can be as long as 38 cm (15 in). Most species secrete a protective tube in the mud or sand bottoms of shallow seas.

The phoronids are regarded as closely related to the bryozoans and brachiopods because they possess a lophophore, a horseshoe-shaped structure carrying ciliated tentacles (see Tentaculata). The tentacles serve to catch food materials suspended in the water, and the cilia move mucus-entrapped food to the mouth, located at the center of the lophophore. The digestive tract is U-shaped, so the anus is located near the "head" of the animal but outside the lophophore.

The phoronids possess a well-developed circulatory system. Some species are hermaphroditic, in which one individual may have both male and female organs. Fertilization generally occurs outside the body; however, in some species, the eggs develop at the base of the lophophore tentacles.

Scientific classification: Phoronids are members of the phylum Phoronida, of the kingdom Animalia.

Types of Invertebrates

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Annelida -> Segmented worms with a muscular body wall used for burrowing. External hairs called setae aid in traction during burrowing. An internal coelom is divided into compartments by walls known as septum. The digestive system stretches from the mouth to the anus, differentiated into regions, each with a different function. Reproduction is sexual. – Examples: Lugworms, earthworms, leeches

Pogonophora -> Deep-sea worms that live in chitinous tubes attached to the ocean floor. Their long, slender body has a beard of tentacles at the head end. There is no mouth or digestive system and these animals absorb all nourishment through the body surface. They reproduce sexually. – Examples: Bead worms

Vestimentifera -> Giant deep-sea worms that live in chitinous tubes attached to the ocean floor. They derive nutrition using a specialized organ called a trophosome to digest sulfide-oxidizing bacteria. – Examples: Llamellibrachs

Sipuncula -> Marine worms with a saclike body and a long proboscis. These worms withdraw their narrow head into the fatter posterior portion. The head end bears tentacles used in burrowing and gathering food particles. Lacking a cardiovascular system, they use internal fluid to transfer oxygen and food to body tissues. They reproduce sexually and some have a larval form. -> Peanut worms

Echiura -> Plump marine worms that take shelter in sand burrows or rock crevices. They use a mucous net or a scoop-shaped proboscis to capture food particles. Reproduction is sexual. – Examples: Spoon worms

Priapulida -> Cucumber-shaped, marine worms with spiny heads. During movement the barrel-shaped proboscis withdraws into the trunk of the worm. Reproduction is sexual. – Examples: Priapulus

Tardigrada -> Microscopic animals with four pairs of stubby legs that live in marine and freshwater sediments and on the surface of mosses and lichens. They use sharp stylets protruding from their mouths to suck food from plant cells. These animals have a remarkable ability to withstand extreme dryness and low temperatures. Reproduction is sexual. – Examples: Water bears

Pentastomida or Linguatulida -> Parasitic worms that live in the lungs of snakes, crocodiles, and some mammals and birds, feeding on blood and tissue. The head bears four leglike claws and a snoutlike mouth. The body is covered by a cuticle that is molted during larval development. They reproduce sexually. – Examples: Tongue worms

Phoronida -> Cylindrical, marine worms that live in a chitinous tube embedded in sand or attached to rocks, shells, or other objects in shallow water. Protruding out of the tube is the animal's lophophore, a structure of ciliated tentacles arranged in a horseshoe shape, that is used for feeding. They have a U-shaped digestive tract. Adults are sedentary and larvae are free-swimming. Reproduction is asexual in at least one species, but most species reproduce sexually. – Examples: Horseshoe worms

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