classification of annelida

06/12/2020 Uncategorized

In Oligochaeta the large perivisceral coelom is divided into compartments by septa lying inter-segmentally from the body wall to the alimentary canal. Body bears segmentally arranged setae or chetae. Further the annelids can be classified in to three classes. Annelida is a group commonly referred to as segmented worms, and they are found worldwide from the deepest marine sediments to the soils in our city parks and yards. Our mission is to provide an online platform to help students to share notes in Biology. Aulophorus, Tree worm, and Leech are common Annelida Examples.triploblastic and bilateral symmetry is common characteristics of annelids. Parapodia, provided with cirri, are equally developed throughout. Blood vascular system haemocoelomic type. Excretion by nephridia, each segment bears a pair of nephridium. The youngest segments occur at the posterior end, and new segments are formed in front of the last segment or pygidium. As previously mentioned, the segments are prominent on earthworms, giving them a ringed appearance. 9. There are 8,700 species described in this phylum. There are over 22,000 living annelid species, ranging in size from microscopic to the Australian giant Gippsland earthworm and Amynthas mekongianus (Cognetti, 1922), which can both grow up to 3 metres (9.8 ft) long. 1. 11. Later in 1909, Lamarck coined the name Annelida. Chaetopterus, Terebella, Sabella, Arenicola, Serpula, Amphitrite, Spirorbis. In Polygordius sexes are separate, the ovaries or testes develop in a few posterior segments, there are no ducts. Phylum ANNELIDA Annelids are vermiform, bilaterally symmetrical, triploblastic and schizocoelomate animals whose body is metamerically segmented and covered with a layer of cuticle. Yeast: Origin, Reproduction, Life Cycle and Growth Requirements | Industrial Microbiology, How is Bread Made Step by Step? Respiration occurs through general body surface, in some cases by gills also. But in many Polychaeta and Oligochaeta the nephridia are of the open type, each having a ciliated nephrostome opening into the coelom, they are called metanephridia, e.g., Neanthes, Lumbricus. Usually monoecious, i.e., hermaphrodite; dioecious or unisexual forms also present. Fertilization internal, development direct, and are hermaphrodite. General Characters of Annelida 3. Most of them are hermaphrodite, some are unisexual, development direct or through larval stage, larva is known as trochophore larva. Anterior sucker is absent but posterior sucker is well developed and composed of four segments. The gonads are patches of coelomic epithelium and are repeated in most of the segments. Nereis, Aphrodite, Glycera, Polynoe, Syllis. In some Polychaeta the coelomic peritoneum gives rise to excretory yellow cells. 1. One of which, the Clitellata, could really be called a Superclass. Share Your PDF File 6. Alimentary canal more or less straight, anus and mouth at opposite ends, digestion extracellular. The family classification below includes placement of 29 families excluded from the analysis. In Oligochaeta certain features of reproductive organs are salient characters, they are almost all hermaphrodite. Female genital apertures are always on the fourteenth segment and the male pore lies a few segments behind them. Body wall is covered with glandular epidermis, below which are muscles forming an outer layer of circular muscles and an inner layer of longitudinal muscles. Coelom is divided by septum into many chambers. They are the first coelomate animals and as regarded as metamerically segmented animals. The scheme of classification of the phylum annelida described here follows the same as appeared in the “Invertebrate Zoology”, Vol. Another class is Oligochaeta which are freshwater and terrestrial worms, like the common earthworm 30. (c) In all segments after the fourteenth there are enteronephric meronephridia which open into supra-intestinal excretory ducts having segmental opening into the intestine. All annelids are segmented. Appendages when present are un-jointed. Each typical body segment consists of five rings or annuli. 1. Mouth is small median aperture situated in the anterior sucker. Their nephridia may open to the outside of the body and are called exonephric nephridia (e.g., Lumbricus) or they may open into the gut and are known as enteronephric nephridia (e.g. 9. There are three classes within phylum Annelida. Clitellum is composed of two or more layers of cells and never begins before twelfth segment. Setae are arranged in lumbricine manner. These appendages are known as parapodia and parapodium bears many setae. Head with distinct prostomium which is provided with eyes, tentacles and palps. Setae are usually arranged segmentally. Annelid have segmentally repeated tubes called segmental organs, they are nephridia and coelomoducts. All segments are equal. In one species, the body surface is divided into 102 annuli, but the body consists of 33 segments, a number constant across all leech species. Syllis forms many branches by budding, some of which form a head, develop sex organs, notopodia are formed to reconstruct the parapodia, these sexual forms may remain attached to the parent for long or they may separate from the colony. The annelids were by early zoologists included with other worms in the group … 5. Introduction to the Annelida Everybody's favorite, worms. Before sharing your knowledge on this site, please read the following pages: 1. Body consists of definite number of segments, each segment breaks up into 2 to 4 rings or annuli. Anterior sucker with three jaws, one median dorsal and two ventro-lateral. Annelida (Clitellata, Polychaeta (Scolecida, Palpata (Canalipalpata (Sabellida, Spionida, … The coelomic chambers are serial and they communicate through spaces around the alimentary canal where the septa are not complete. What is its function? 7. in length and variously coloured. Blood vascular system is closed type, blood is red due to the presence of haemoglobin or erythrocruorin found dissolved in the plasma. Welcome to BiologyDiscussion! Gills, when present, localised to the anterior segments. But in Pheretima there is large number of small-sized nephridia in each segment, they are called meronephridia or micronephridia. In metamerism not only is there a serial repetition of homologous parts (e.g., nephridia, blood vessels, nerves, reproductive organs, muscles), but each of these parts works in cooperation with all the others, the segments being integrated into a single functional unit, the segmental structures are interdependent. Mostly parasitic on the fins of salmon fishes. 8. Sexes separate, fertilisation external, free swimming larval stage trochophore. Examples- Acanthobdella, Pontobdella, Hirudo. Head poorly developed with tentacles, pulps and feeding appendages. 4. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. 2. Share Your PPT File. Some Polychaeta have compound excretory organs formed by the union of nephridia and coelomoducts, they are called nephromixia. Phylum: Annelida (Annelids) Class: Oligochaeta (Earthworms, Leeches) Class: Polychaeta (Marine Annelids) Oligochaeta (Earthworms, Leeches) Earthworms Segmentation. Sexes united, gonads few, permanent, development direct. Setae and Para podia are usually absent. Body with conspicuous external and internal segmentation. 4. Some forms reproduce asexually by budding, but in Autolytus there is a proliferating region at the end from which a chain of sexual zooids is budded off which detach one by one. Nephridial opening situated on the surface between the segments. Annelida is derived from Latin word ‘anellus’ meaning little ring. This group contains species like earthworms, leeches, and marine worms. Body triploblastic, bilaterally symmetrical, elongated and vermiform. The clitellum is a thickened part of the body wall secretes a cocoon-like sac around the eggs. The coelomic fluid in the longitudinal channels and their branches is red due to dissolved haemoglobin, but it is not coloured in other coelomic spaces. Coelom is spacious usually divided by inter-segmental septa. First, we will take a look at Oligochaeta, the class containing the ever-popular earthworm (as well as many aquatic worms). Nephridia remove waste from the coelom, but their original function was probably removal of water from the body. All body segments are similar except at anterior and posterior ends. The first septum in Pheretima lies between segments 4 and 5, so that the coelom of the first four segments is continuous. Well developed blood vascular system, blood vascular system closed. (c) Mixonephrium or Nephromixium, coelomoduct is attached to a nephridium in such a way that they form a single organ, the funnel being coelomoduct and the duct is nephridial, e.g., Capitellidae, Arenicola. In some tubicolous worms, e.g., Serpula there is a division of labour, the nephridia of the anterior region are large and carry on excretion, and those of the posterior region are small and act as genital ducts exclusively. Ventral nerve cord gives off ganglia in each segment. One major class is the Polychaeta, which are marine worms. Through most of the 20th century Annelida was split into three major groups; Polychaeta, Oligochaeta (earthworms etc.) 5. In Hirudinaria the nephridia are coiled tubes opening into a bladder which leads to the exterior by a nephridiophore, the other end lies in a coelomic space but it has no nephrostome. They show segmented body.The annelids are distributed all over the world. Organs of excretion are metameric ectodermal nephridia, besides which there are tubular mesodermal coelomoducts used for passage of reproductive cells. Some Oligochaeta possess special copulatory setae. The spermatozoa unite in bundles to form permatophores. 12. The walls of the coelom give rise to reproductive cells and to coelomoducts which carry sperms or eggs from the coelom to the exterior. External segmentation is slightly marked by faint, while internal segmentation is marked by coelomic septa. In some Polychaeta, e.g., Neanthes, a part of the coelomoduct separates from the metanephromixium and becomes attached to the dorsolateral muscles as a dorsal ciliated organ, this keeps the coelomic fluid in circulation. Annelids exhibit bilateral symmetry and ar… In most annelids sea or cheaeta and parapodia are locomotory are locomotory organs, some move by muscles, i.e., seta or parapodia absent. Excretory organs are segmentally paired nephridia. Each typical body segment consists of 3, 6 or 12 rings. Annelid - Annelid - Classification: Classification of free-living and sedentary polychaetes relies almost exclusively on external characters, such as the shape of the head, and on the number and nature of structures, such as appendages (including anal ones), parapodia, and setae, and on tube construction. Development direct in monoecious forms but indirect in dioecious forms. 3. 9. (b) Metanephromixium, coelomoduct is attached to an open metanephridium, e.g., Hesione. 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