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Pseudocoelomate vs. Coelomate

Phylum Nematoda

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Pseudocoelomate vs. Coelomate

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    1. Pseudocoelomate vs. Coelomate Phylum Nematoda and Phylum Annelida

    3. Nematodes

    5. More nematodes! Nematodes are almost unbelievably abundant. One study reported around 90,000 individual nematodes in a single rotting apple. Another reported 236 species living in a few cubic centimeters of mud. The number of described species is around 12,000, but too little attention has been paid to these animals and the true number may be closer to 500,000. Some species are generalists, occurring across wide areas and in many habitats; others are much more specialized. A good example of the latter is a species of nematode that is known only from felt coasters placed under beer mugs in a few towns in Germany. Many nematodes are free living and play critical ecological roles as decomposers and predators on microorganisms.

    8. Trichinella larvae encysted in muscle

    9. Funky Nematode Sex! The male nematode is usually smaller than the female. The posterior end of the male is curled like a hook to hold onto the female during copulation. Fertilization takes place when males use special copulatory spines to open the females' reproductive tracts and inject sperm into them. The sperm are unique in that they lack flagellae and move by pseudopodia, like amoebas. Development of fertilized eggs is usually direct.

    12. Annelids

    13. Phylum Annelida The segmented worms. Annelids have a closed circulatory system with blood vessels running the length of the body and branching into every segment. Closed circulatory systems are more efficient than open ones for moving materials within a body. The annelid nervous system consists of a brain connected to a ventral solid nerve cord, with a ganglion in each segment. Annelids have a complete digestive system that include a pharynx, stomach, intestine, and accessory glands.

    14. Annelids are coelomate animals. Segments allow for increased specialization. A true coelom allows for expansion of the internal organs. The coelom and the body wall acts as a hydroskeleton. While Oligochaetes and polychaetes typically have spacious coeloms; in leeches, the coelom is reduced to a system of narrow canals. There are about 12,000 marine, freshwater, and terrestrial species usually divided into three taxonomic classes. Annelids can be told by their segmented bodies. Polychaetes (meaning "many bristles") have, predictably, many bristles on the body, while earthworms and leeches have fewer bristles.

    15. Annelid Classification Class Polychaeta – ex. Clamworms, sandworms. Class Oligochaeta – ex. Earthworms, freshwater worms. Class Hirudinea – leeches!

    16. Polychaetes Class Polychaeta - Most polychaetes are marine and possess parapodia and setae. Parapodia are paddlelike appendages used in swimming that also serve as respiratory organs. Setae are bristles, attached to parapodia, that help anchor polychaetes to the substratum and also help them move. Only during breeding do polychaetes have reproductive organs. \ Polychaet zygotes develop into a type of larva similar to that produced by marine clams. Many have well-developed cephalization, with a head having well-developed jaws, eyes, and other sense organs. Sedentary filter feeders possess tentacles with cilia to create water currents and to select food particles.

    17. Oligochaetes Class Oligochaeta - earthworms. Earthworms tend to have their few setae protruding in clusters directly from their body. Earthworms have poorly developed heads or parapodia. Earthworms reside in moist soil where a moist body wall facilitates gas exchange. Earthworms are scavengers that extract organic remains from the soil they eat. Locomotion is by coordinated movement of the body muscles and assistance of their setae.

    18. Earthworms cont. A muscular pharynx draws food into the mouth. Ingested food is stored in a crop and ground up in a muscular gizzard. The earthworm excretory system has coiled nephridia tubules in each segment with two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall. Red blood is moved anteriorly by a dorsal blood vessel and pumped by five pairs of hearts (sometimes referred to as aortic arches) to a ventral vessel. Earthworms are hermaphroditic, having both testes with seminal vesicles, and ovaries with seminal receptacles. Mating involves the worms lying parallel to each other facing opposite directions and exchanging sperm. Each worm possesses a clitellum that then secretes a mucus, protecting sperm and eggs from drying out. Embryonic development lacks a larval stage. The ability of earthworms to feel pain is of interest to people whouse them for bait. We often assume that a "primitive" organism like an earthworm with a tiny brain and ganglia would feel no pain when being threaded on a hook. Studies have shown that when damaged, earthworms produce natural opiates as our brains do in response to pain.

    20. Class Hirudinea Although leeches are known as “bloodsuckers”; many are scavengers or predators of small aquatic invertebrates. Approx. 500 species Most are freshwater organisms. Most adults are 2 – 5 cm. long. Lack appendages and setae. Have a reduced coelom. Most are hermaphrodites, however there is copulation between different individuals, No larval stages. Embryos develop within a coccon secreted by the clitellium.

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