Acoelomates: Phylum Platyhelminthes and Nemertea - Biosciweb.net

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Acoelomates: Phylum Platyhelminthes and Nemertea and Pseudocoelomates: Phyla Nematoda and Rotifera & Parasitism 6.4 Lab #6 - Biological Sciences 102 – Animal Biology Classification & Adaptations of Pseudocoelomate Animals Phylum Nematoda (roundworms) More than 25,000 species. Roundworms. Nematodes are an extensive group with worldwide distribution. They include terrestrial, freshwater, marine, and parasitic forms. They are elongated roundworms covered with a flexible, nonliving cuticle. Circular muscles are lacking in the body wall and, in Ascaris, longitudinal muscles are arranged in four groups separated by epidermal cords (some nematodes have six or eight groups of longitudinal muscles). Cilia are completely lacking. Nematodes are found free-living in almost every conceivable habitat from arid deserts to lake bottoms, rivers, polar seas. Nematodes - both parasitic and freeliving - are incredibly abundant. A handful of good garden soil contains thousands of nematodes. Some 50 different species of nematodes occur in humans, most of them nonpathogenic. Some nematodes are plant parasites feeding on plant sap, especially roots. Body Plan Features & Characteristics of Members of the Phylum Nematoda (some of these traits are seen in other animal phyla): 1. pseudocoelomate 2. bilateral symmetry 3. triploblastic structure (endoderm, mesoderm and ectoderm) 4. psuedocoelomate = possess a pseudocoelom 5. some degree of cephalization = head with sensory organs 6. some organ systems (formed of true tissues) are present 7. vermiform (worm-like) body shape 8. complete digestive tract with three angled (longitudinal, circular and oblique) muscular pharynx, intestine lacking muscular walls, short rectum and anus 9. excretion and osmoregulation through the cuticle and by excretory canals 10. lack both cilia and flame cells/bulbs 11. body wall lined with cuticle which retains body shape 12. longitudinal muscles only, no circular muscles in body wall; body length or diameter does not change in movement 13. hydrostatic skeleton (as muscles push against parenchyma and tissue fluids) 14. dioecious; sexes separate with females larger than males; one or two tubular gonads; copulatory spicules present in males Phylum Rotifera (rotifers) There are about 2000 species of rotifers. The name "rotifer" is derived from the Latin word meaning "wheel-bearer"; making reference to the crown of cilia around the mouth of the rotifer. The rapid movement of the cilia in some species makes them appear to whirl like a wheel. Rotifers can be found in many freshwater environments and in moist soil. The habitat of rotifers may include still water environments, such as lake bottoms, as well as flowing water environments, such as rivers or streams. Rotifers are also commonly found on mosses and lichens growing on tree trunks and rocks, in rain gutters and puddles, in soil or leaf litter, on mushrooms growing near dead trees, in tanks of sewage treatment plants, and even on freshwater crustaceans and aquatic insect larvae. Most species of rotifers are about 200 to 500 micrometers long. However a few species, such as Rotaria neptunia may be longer than a millimeter. Rotifers are thus multicellular creatures who make their living at the scale of unicellular protists. Characteristic features of rotifers include the ciliated corona ("wheel organ") and the mastax. The corona is located anteriorly and functions in locomotion and food gathering. The corona is modified extensively in some species. The mastax is a muscular pharynx containing a complex set of hard jaws or trophi and is found in all rotifers. These characteristics of these structures have been used extensively in classifying rotifers.
Acoelomates: Phylum Platyhelminthes and Nemertea and Pseudocoelomates: Phyla Nematoda and Rotifera & Parasitism 6.5 Lab #6 - Biological Sciences 102 – Animal Biology Body Plan Features & Characteristics of Members of the Phylum Rotifera (some of these traits are seen in other animal phyla): 1. bilateral symmetry and triploblastic structure (endoderm, mesoderm and ectoderm) 2. psuedocoelomate = possess a pseudocoelom 3. some degree of cephalization = head with sensory organs 4. some organ systems (formed of true tissues) are present 5. complete digestive system with mouth and anus 6. well muscularized pharynx = mastax that contains trophi (jaws) for sucking and grinding food particles 7. ciliated corona helps sweep food particles to mouth 8. pair of protonephridial tubules for osmoregulation & excretion 9. syncitial (multinucleate) epidermis; some have a secreted cuticle 10. longitudinal muscles and circular muscles in body wall 11. pedal glands of foot secrete adhesive material in both sessile and creeping forms 12. hydrostatic skeleton (as muscles push against parenchyma and tissue fluids) 13. dioecious; sexes separate with females larger than males; one or two tubular gonads; copulatory spicules present in males; can be parthenogenic ‣ Reproduction in Rotifers ‣ single (male) or double set of gonads (female) and ducts in each sex ‣ sexes separate (dioecious) ‣ males unknown in class Bdelloidea and only occur a few weeks a year in the class Monogononta ‣ all females are parthenogenetic in the class Bdelloidea (diploid females produce diploid females) ‣ parthenogenesis = unisexual reproduction involving the production of young by females that are not fertilized by males; common in rotifers, aphids, bees, ants and wasps. Parthenogenetic eggs may be haploid or diploid. ‣ in the class Monogononta, most of the year, diploid females produce thin shelled diploid amictic eggs. These amictic eggs develop parthenogenetically into diploid (amictic) females. When the environment in the pond or stream changes due to crowding, diet, change in photoperiod, etc. some amictic eggs develop into diploid mictic females that produce thin shelled haploid eggs. If these eggs are not fertilized then they will develop into haploid males. If the eggs are fertilized, they become mictic eggs with a thick, resistant shell and become dormant. These “winter eggs” can survive until the environment becomes more suitable at which time they hatch and develop into amictic females (completing the cycle). Females grow and reach maturity in a few days while males rarely grow and are mature at birth.
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