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Read online Crawfishes of Louisiana PDF, azw (Kindle)

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However, ev- idence indicates that even the antennae arose postorally during embryogenesis, migrating to a preoral position later in development. Hawaiians used to smear their spear tips with this cnidarian, the toxin from which is called palytoxin. There are no antennae, but all six segments of the prosoma usually bear appendages. Other groups possess excretory organs that may represent highly modified nephridia or secondarily derived (“new”) structures. We have seen some examples of such activity in the preceding section.

Download online Structure and Function of Invertebrate Respiratory Proteins: EMBO Workshop, 1982 (Life Chemistry Reports Supplement Series) PDF, azw (Kindle), ePub, doc, mobi

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The functions of homologous struc- tures may be similar or different, but this has no bearing on the underlying homology of the structures involved. As depicted in Figure 2.4, a clade is a monophyletic group or branch of a tree, which may undergo very little or a great deal of diversi- fication. The reproductive systems of scorpions lie within the mesosoma, and both testes and ovaries are in the form of interconnected tubules (Figure 19.24).

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Gemmules are asexual reproductive bodies of most of the freshwater and a few marine sponges. Occurrence of teleplanic pelago- sphera larvae of sipunculans in tropical regions of the Pacific and Indian Oceans. Little is known about digestion in brachiopods, but some work on Lingula (Chuang 1959) indicates that it occurs intracellularly in the digestive gland. When swallowed, the cysts of E. histolytica pass through the stomach unharmed. We reserve our discussion of the origins of spe- cific taxa for later chapters.

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They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as Antarctica and oceanic trenches. Proceedings of the National Academy of Sciences of the United States of America 104: 16204-16208. Nuclear division occurs by semi-open pleuromito- sis in all except gregarines, which show much diversity in their mitoses: mitotic spindle organiz- ers are either disks, plugs, or electron-dense cres- cents on nuclear envelope in the location of fenes- trae.

Read Millipeds in Captivity: Diplopodan Husbandry and Reproductive Biology (Millipede Husbandry) PDF, azw (Kindle), ePub

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Note that there is no "the" before Crustacea. Tim Stebbins ************************************************************************** Timothy D. Fluid nutrients are transported by capil- lary action along minute surface channels from the la- bellae to the mouth. Minute arachnids with prosoma divided into protero- soma, covered by the carapace-like propeltidium, fol- lowed by two free segments and joined to opisthoso- ma by a narrow pedicel; opisthosoma segmented and divided into broad mesosoma and short narrow meta- soma, the latter bearing a long multiarticulate telson; eyes absent.

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Molecular cloning and biological activity of ecdysis-triggering hormones in Drosophila melanogaster. Monomorphic, without alternation of generations and without any kind of an attached sessile life stage 9. Nervous system is a simple nerve net(s), com- posed of naked and largely nonpolar neurons 9. The presumed primitive condition is shown in Figure 12.2A. William of Ockham (Occam), the fourteenth-century English philosopher, stated the principle as, “Plurality must not be posited without necessity.” Modern render- ings would read, “An explanation of the facts should be no more complicated than necessary,” or, “Among competing hypotheses, favor the simplest one.” Scientists in all disciplines follow this rule daily, and it can be viewed as a consequence of deeper principles that are supported by statistical inferences.

Download online Nematoda (Handbook of Zoology) PDF, azw (Kindle), ePub

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Gastropods comprise over 35,000 living species of marine, ter- restrial, and freshwater snails and slugs. Beyond these gen- eralities, a great deal of variation occurs in molluscan cleavage. The story is based on the comparison of DNA sequences (which relies on many assumptions as discussed earlier) between organisms and a presumed common ancestor. Raup goes on to say that “we still have a record which does show change, but one that can hardly be looked upon as the most reasonable consequence of natural selection.” In comparing fossil forms with modern forms, we do see change all right, but it’s not the kind of change associated with evolution by natural selection.

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Slugs, squids, and octopuses have reduced or lost their shells completely during their evolution. An interesting predatory strategy is that of New Zealand glowworms (Arachnocampa luminosa), which live in caves and in bushes along river beds. We saw a hint of this process in our examination of the polychaetes, but nothing of the magnitude evident among the arthro- pods, in which segment and appendage diversification has reached its zenith.

Download online Aquatic Oligochaetes: Proceedings of the 7th International Symposium on Aquatic Oligochaetes held in Presque Isle, Maine, USA, 18-22 August 1997 (Developments in Hydrobiology) PDF, azw (Kindle)

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It is not known whether this is a develop- mental oddity or an indication that a taxonomic reassignment is warranted for this species. It also occurs in dogs, cats, and other primates. Evidence for a transitory diges- tive tract in Vestimentifera. Look for feeding damage and dark fecal pellets. I am especially interested in understanding the costs and benefits associated with these different patterns.

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With a dorsal groove that functions in gas exchange. Food particles drawn in by the cilia are captured by the jaws (trophi) in the pharynx and ground up. In bedbugs (order Hemiptera, fami- ly Cimicidae) males use the swollen penis to pierce a spe- cial region of the female’s body wall; sperm are then de- posited directly into an internal organ (the organ of Berlese). Many superficially similar insects represent different species, which exhibit great differences in habits, distribution and economic importance.

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