User talk:Oladeboabiola

The Polychaeta or polychaetes are a polyphyletic [1] class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000 species are described in this class. Common representatives include the lugworm (Arenicola marina) and the sandworm or clam worm Nereis. Polychaetes as a class are robust and widespread, with species that live in the coldest ocean temperatures of the abyssal plain, to forms which tolerate the extreme high temperatures near hydrothermal vents. Polychaetes occur throughout the Earth's oceans at all depths, from forms that live as plankton near the surface, to a 2–3 cm specimen (still unclassified) observed by the robot ocean probe Nereus at the bottom of the Challenger Deep, the deepest known spot in the Earth's oceans. [2] Only 168 species (less than 2% of all polychaetes) are known from freshwaters. 7 hours ago Oladebo Sheriff Abiola The Class Polychaeta (“many bristles”) is the largest group of annelids, containing over 10,000 species, most of which are Marine. Polychaete characteristics include a well-developed head and lateral appendages called parapodia, which are found on each segment. Parapodia are used for both creeping and swimming. They can also take part in gas exchange, which is possible because parapodia contain a large number of respiratory capillaries. In some forms (fanworms), the parapodia have been modified into large, feathery gills. In terms of nutrition, many polychaetes are carnivorous, seizing prey in chitinous jaws or teeth that are everted rapidly from a muscular pharynx. Some sedentary forms are particle feeders that use ciliary currents and mucus to trap organic food molecules, plankton, etc. Examples of polychaete worms include: Nereis virens (the clamworm), Amphitrite (the spaghetti worm), Glycera (the beak thrower), Chaetopterus (the parchment worm), Aphrodita (the sea mouse) and fan worms (also called feather duster worms or Christmas tree worms) 7 hours ago Oladebo Sheriff Abiola characteristics of polychaetae Major Attributes: 1. Metamerically segmented. 2. Bilateral symmetry. 3. Chitinous setae called parapodia. 4. Schizocoelic. 5. Closed circulatory system. 6. Complete digestive system. 7. Respiration through skin, gills or parapodia. 8. Nephridia for excretion. 9. Hermaphroditic, asexual reproduction in some by budding. 7 hours ago Oladebo Sheriff Abiola Oligochaete Anatomy Like the polychaetes, oligochaetes have bodies divided into segments. However, they lack parapodia and, with a few exceptions, have relatively few and inconspicuous setae. The setae are usually arranged in four bundles on each segment; those of aquatic forms are longer than those of land forms. The setae of an earthworm may be felt as a roughness if one rubs a finger along its side. Oligochaetes are less varied in their external form than the polychaetes, but are much more numerous. As many as 4,000 oligochaetes have been counted in 1 square meter of lake bottom, and about 9,000 in 1 square meter of meadow soil. In almost all oligochaetes, the head is a simple cone- shaped structure without sensory appendages. Light is detected by photoreceptor cells in the skin, usually concentrated toward the front of the animal. Oligochaete Digestion The mouth, located under the head, leads to a relatively simple, straight digestive tract consisting of a pharynx, an esophagus, and an intestine, terminating in an anal opening. Terrestrial oligochaetes tunnel through the ground, swallowing soil as they go. The digestive tract of such a worm is specially modified for this rough diet. Typically it has a thin-walled storage area, or crop, and a muscular gizzard for grinding the soil to remove the organic matter that is the actual food of the worm. Specialized calciferous glands remove excess calcium, magnesium, strontium, and phosphate and regulate the level of these ions in the blood. Solid wastes are egested and plastered against the burrow wall, or ejected from the mouth of the burrow; the ejected material is called castings. Earthworms, through their burrowing and digestive processes, are largely responsible for the mixing and aeration of the soil. Not all oligochaetes have soil diets; some of the small aquatic worms are active predators on other small invertebrates. Excretion is typically carried out by a pair of tubes in each segment. Oligochaete Circulation and Respiration The circulatory system is that typical of the annelids and has many contractile vessels, or hearts. Although a few aquatic forms have gills for respiration, most oligochaetes lack such specialized structures and use the capillaries of their body walls for respiratory exchange. Oxygen dissolved in the soil water diffuses through the moist epidermis of the worm. If earthworms are forced to the surface, as when their burrows are filled with rainwater, they suffocate as a result of desiccation. Oligochaete Reproduction All oligochaetes are hermaphroditic, and nearly all cross-fertilize by copulation. Male and female reproductive organs are located in separate segments. The copulating pair exchange sperm, which are stored in the body of the recipient worm until its eggs are mature. The worm then secretes a cocoon into which it deposits the eggs and the sperm; fertilization and development of the eggs occur in the cocoon. When the young emerge they are miniatures of the adults. The cocoon is secreted by a glandular region, the clitellum, consisting of several thickened segments. The clitellum of an earthworm is a conspicuous saddle-shaped region near its front end. 7 hours ago Oladebo Sheriff Abiola Class Oligochaeta Characteristics Have no parapodia & few setae Includes earthworms EARTHWORM Bodies may have over 100 metameres Internal partitions called septa Distinct anterior & posterior ends Cephalization (head with sense organs) shows specialization for burrowing Have both circular & longitudinal muscles for movement Have external, saddle-shaped structure called clitellum that forms a cocoon containing eggs & sperm Prostomium or lip digs through soil as earthworm feeds on organic matter Pharynx is a muscular organ behind the mouth to help suck in food Food temporarily stored in crop, ground in gizzard, and digested & absorbed in intestine Wastes called castings pass out through anus Closed circulatory system with 5 pairs of aortic arches or hearts Dorsal blood vessel carries blood posteriorly to cells & ventral blood vessel returns blood anteriorly Secrete mucus to keep skin moist so oxygen will dissolve & diffuse into body Long tubules called nephridia filter wastes from blood & excrete it through pores Simple brain, no eyes, & dorsal and ventral nerve cords Sensitive to light, touch, moisture, chemicals, temperature, & vibrations Hermaphrodites exchange sperm & cross-fertilize Sperm sacs store the worm's own sperm & seminal receptacles store exchanged sperm Class Hirudenia Characteristics No setae or parapodia Includes leeches Have anterior & posterior suckers for attachment LEECH Some suck blood from hosts, while others are scavengers or predators Mouth's of blood-sucking leeches with chitinous teeth & secrete anticoagulant Found in f reshwater Flattened dorso-ventrally Hermaphrodites that cross-fertilize Class Polychaeta Characteristics Marine Includes sandworms & clamworms Have paddle-like parapodia to move Take in oxygen through parapodia Some are free-swimming predators with strong jaws to feed on small animals Many live commensally with sponges, mollusks, & echinoderms Well-developed head with antenna & specialized mouthparts