PHYLUM ANNELIDA PDF
Phylum Annelida In: Atkinson LJ and Sink KJ (eds). Field Guide to the Ofshore Marine Invertebrates of South Africa,. Malachite Marketing and Media, Pretoria, pp. PHYLUM Annelida. CLASS Polychaeta. A. Note parapodium w/ setae & acicula ( A). Parapodia are used for locomotion, sensory purposes & respiration. [fig. Oligochaeta - “few chaetae” a subclass of Clitellata. • many terrestrial and freshwater but few marine species. – mostly thread-sized. – mostly deposit- feeders.
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Phylum Annelida. (segmented worms, bristle worms). 15, species large successful phylum in water & on land include earthworms, sand worms, bristle. Phylum Annelida. Segmented Worms. Characteristics. - Segmentation. - Chaetae (Hairs made of Chitin. - 3 Cell Layers. - True Coelom. - Head develops first. Annelida. Arthropoda. Bryozoa. Phoronida. Brachiopoda. Echinodermata. Chordata phyla. Pseudocoelomates. Coelomates. A Phylogeny of the Animal Phyla.
Annelids include segmented worms, such as leeches and earthworms; they are the most advanced worms as they possess a true coelom. Phylum Annelida contains the class Polychaeta the polychaetes and the class Oligochaeta the earthworms, leeches, and their relatives. These animals are found in marine, terrestrial, and freshwater habitats, but a presence of water or humidity is a critical factor for their survival, especially in terrestrial habitats. The name of the phylum is derived from the Latin word annellus, which means a small ring. Animals in this phylum show parasitic and commensal symbioses with other species in their habitat. Approximately 16, species have been described in phylum Annelida.
Approximately 16, species have been described in phylum Annelida.
Phylum Annelida: General Characteristics and Classification
The phylum includes earthworms, polychaete worms, and leeches. Annelids display bilateral symmetry and are worm-like in overall morphology. They have a segmented body plan where the internal and external morphological features are repeated in each body segment.
This metamerism is thought to arise from identical teloblast cells in the embryonic stage, which develop into identical mesodermal structures. The overall body can be divided into head, body, and pygidium or tail. The clitellum is a reproductive structure that generates mucus that aids in sperm transfer and gives rise to a cocoon within which fertilization occurs; it appears as a fused band in the anterior third of the animal.
The clitellum is the reproductive structure of an annelid. It creates mucus that aids in sperm transfer and gives rise to a cocoon within which fertilization occurs. It can be seen in this image as the enlarged band around the animal.
The epidermis is protected by an acellular, external cuticle, but this is much thinner than the cuticle found in the ecdysozoans and does not require periodic shedding for growth. Circular as well as longitudinal muscles are located interior to the epidermis. Annelids show the presence of a true coelom, derived from embryonic mesoderm and protostomy.
Hence, they are the most advanced worms. A well-developed and complete digestive system is present in earthworms oligochaetes with a mouth, muscular pharynx, esophagus, crop, and gizzard being present. The gizzard leads to the intestine and ends in an anal opening. Each segment is limited by a membranous septum that divides the coelomic cavity into a series of compartments.
Annelids possess a closed circulatory system of dorsal and ventral blood vessels that run parallel to the alimentary canal as well as capillaries that service individual tissues. In addition, these vessels are connected by transverse loops in every segment. These animals lack a well-developed respiratory system; gas exchange occurs across the moist body surface.
Annelids show well-developed nervous systems with a nerve ring of fused ganglia present around the pharynx. The nerve cord is ventral in position, bearing enlarged nodes or ganglia in each segment. Annelids may be either monoecious, with permanent gonads as in earthworms and leeches , or dioecious, with temporary or seasonal gonads that develop as in polychaetes.
However, cross-fertilization is preferred in hermaphroditic animals. These animals may also show simultaneous hermaphroditism, participating in simultaneous sperm exchange when they are aligned for copulation. The many chetae of polychaetes are also arranged within fleshy, flat, paired appendages that protrude from each segment.
These parapodia may be specialized for different functions in the polychates. A significant difference between leeches and other annelids is the development of suckers at the anterior and posterior ends and an absence of chaetae. Additionally, the segmentation of the body wall may not correspond to the internal segmentation of the coelomic cavity.
This adaptation possibly helps the leeches to elongate when they ingest copious quantities of blood from host vertebrates. Unlike earthworms, leeches lack chaetae and have suckers at both ends of the body. The clitellum is a structure on the anterior portion of the worm that generates mucus to aid in sperm transfer from one worm to another; it also forms a cocoon within which fertilization occurs.
Most annelids have chitinous hairlike extensions in every segment called chaetae that are anchored in the epidermis, although the number and size of chaetae can vary in the different classes.
Annelids possess a closed circulatory system, lack a well-developed respiratory system, but have well-developed nervous systems. Annelids can either have distinct male and female forms or be hermaphrodites having both male and female reproductive organs.
Phylum Annelida: General Characteristics and Classification
Earthworms are hermaphrodites and can self-fertilize, but prefer to cross-fertilize if possible. Phylum Annelida Phylum Annelida contains the class Polychaeta the polychaetes and the class Oligochaeta the earthworms, leeches, and their relatives. Morphology Annelids display bilateral symmetry and are worm-like in overall morphology. Anatomy The epidermis is protected by an acellular, external cuticle, but this is much thinner than the cuticle found in the ecdysozoans and does not require periodic shedding for growth.
Provided by: October 23, OpenStax CNX. Located at: CC BY: Attribution Lophotrochozoa. Attribution-ShareAlike cephalization.
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Annelid - Wikipedia
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