Phylum Annelida Metamerism Have an anterior prostomium in addition to posterior pygidium; b

Phylum Annelida Metamerism Have an anterior prostomium in addition to posterior pygidium; b

Phylum Annelida Metamerism Have an anterior prostomium in addition to posterior pygidium; b

Musick, Mecca, News Anchor has reference to this Academic Journal, PHwiki organized this Journal Phylum Annelida Metamerism Have an anterior prostomium in addition to posterior pygidium; both nonsegmented Body is divided into a linear series of similar parts or segments, in addition to each segment is called a metamere The pattern of repeated segmentation is called metamerism Each metamere is separated from the next by a transverse septum Each metamere acts as a hydrostatic skeleton Each metamere has longitudinal in addition to circular muscles; longitudinal muscle contraction causes segments to shorten; circular muscle contraction causes segments to elongate Each segment usually bears one or more chitinous bristles called setae; help anchor segments Nervous System Consists of a brain, which is connected to a pair of ventral longitudinal nerve cords, with a ganglion in each segment (metameric) Circulatory System Closed circulatory system, in which the blood is always enclosed within blood vessels that run the length of the body in addition to branch to every segment Several hearts (5 in earthworms) are used to pump blood through the closed circuit

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Excretory System Consists of paired (metameric) metanephridia Excretory tubes with ciliated funnels that remove waste from the coelomic fluid; open to the outside via excretory pores. Note: Not all organ systems are metameric For example, the digestive system extends the length of the organism in addition to is differentiated along its length Reproductive System Most annelids are hermaphroditic, but they are usually cross fertilizers. Earthworms in addition to leeches as long as m pairs in addition to reciprocally fertilize one another Some annelids (e.g. marine s in addition to worms) are dioecious in addition to they release eggs in addition to sperm into the marine environment, where gametes unite to as long as m trochophore larvae Class Polychaeta (“many bristles”) General Characteristics Marine worms, including s in addition to worms in addition to clamworms. Each segment is equipped with a pair of fleshy paddle-like structures – parapodia; used in locomotion Parapodia contain a large number of chitinous bristles – setae; anchor the worms

Polychaetes: General Characteristics cont. Prostomium is well equipped with sensory in addition to feeding structures Polychaetes: General Characteristics cont. Mouth is located just below the prostomium, but in front of the modified segments – peristomium Digestive system includes a muscular pharynx that can be everted through the mouth Pharynx is equipped with pincer-like jaws Although many of the smaller polychaetes lack respiratory structures, the larger one do possess gills Gills are usually modifications of the parapodia Class Polychaeta: Diversity Although a number of polychaetes are active predators, some are sedentary in addition to burrow into mud or live in protective tubes in the mud In several of these species filter feeding has evolved A good example is the fan worm Sabella, with their feather-like head structures called radioles

Class Polychaeta: Diversity cont. Chaetopterus is tube dweller; lives in a U-shaped tube Parapodia are highly modified into 3 fan-like structures that bring water into the tube The notopodium secretes a mucous bag that traps food from the water flowing through the tube; the bag is periodically passed anteriorly toward the mouth Class Polychaeta: Diversity cont. Arenicola lives in a J-shaped burrow It employs peristaltic movements to generate a water flow Food is filtered out from the front of the burrow Class Oligochaeta (“few bristles”) Many of the morphological structures are reduced when compared to the polychaetes Prostomium lacks sensory structures Parapodia are absent; each segment usually contains one or more pairs of setae; used in locomotion Aquatic as long as ms usually have larger setae than the terrestrial as long as ms

Class Oligochaeta cont. Earthworms feed on vast quantities of soil that contains living in addition to decaying organic material. Digestive tract of the annelids shows specialization along its length: mouth, pharynx, crop (food storage), gizzard (grinding), calciferous gl in addition to s (accessory gl in addition to s that excrete excess calcium from the food) Remainder of the gut is the intestine – as long as digestion in addition to absorption Its surface area is increased because of a dorsal longitudinal fold called the typhlosole Class Oligochaeta cont. Lack respiratory organs; gas exchanges occurs across the body wall Hermaphroditic, but exchange sperm during copulation During copulation, worms join their anterior ends; held together by mucous secretions from a clitellum After reciprocal copulation, sperm is stored in seminal receptacles Clitellum then secretes a mucous tube that serves as a cocoon The cocoon moves anteriorly in addition to eggs from the oviduct in addition to sperm from the seminal receptacles are poured into it; fertilization occurs in the cocoon Cocoon eventually slips off the anterior end of the worm In time, young worms emerge from the cocoon Class Hirudinea Body is dorso-ventrally flattened Anterior segments are modified as a small sucker which surrounds the mouth; posterior segments as long as m a larger sucker Setae are completely absent Evidence of segmentation externally, but no internal septa There is serial repetition of many of the organs (e.g., nephridia in addition to testes)

Class Hirudinea cont. Leeches crawl over the surface in a loop like fashion, with the use of 2 suckers. Body is extended due to circular muscle contraction in addition to the attachment of the anterior sucker to the substrate. Posterior sucker is subsequently released, in addition to longitudinal muscles contract bringing the posterior part of the body as long as ward. Class Hirudinea con’t Most leeches are active predators; however, some are the parasitic, bloodsucking as long as ms. Blood suckers have blade like jaws that they use to penetrate the skin of a host. Blood is prevented from clotting because they secrete a powerful anticoagulant; anesthetics are also released A muscular pharynx subsequently pumps blood into the gut. Medicinal Leeches

Class Hirudinea con’t Leeches are hermaphroditic but engage in cross-fertilization; some use hypodermic impregnation Leeches have a clitellum in addition to are capable of generating a cocoon

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