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38 Cards in this Set
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Phylum Arthropoda
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"jointed-foot" animals; trilobites, crustaceans, chelicerates, myriapods, insects; largest phylum of animals; found in all major environments
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Characteristics shared with other phyla not unique to arthropods
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bilateral symmetry, coelomates, triploblastic, prostomate
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Clade Panarthropoda
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phylum arthropoda, phylum onychophora, phylum tardigrada
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Phylum Onychophora
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"velvet worms", not an arthropod, possible closest living relatives of arthropods; terrestrial, mostly tropical species (live in leaf litter);numerous paired, unjointed legs that end in claws on each segment; soft outer cuticle that is molted (ecdysozoan); metameric, nephridia, open circulatory system with blood bathing organs within a hemocoel (true coelom is reduced); anterior brain; respiratory trachael system of tubes leading to surface pores for air; dioecious
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Phylum Tardigrada
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"water bears"; don't have a lot of information on them because they're so tiny and hard to study; maybe have a true coelom, but it's reduced; have primarily a hemocoel; if coelomate, enterocoelic; molecular evidence suggests affinity to arthropods; all habitats but mostly live in lichens and mosses; eutely; outer cuticle is molted; dioecious (lay eggs); 4 pairs of unjointed legs ending in claws; nervous sytem (brain, ventral nerve cord, metameric ganglia); have an excretory system and complete digestive system; complex pharynx to pierce & suck small prey & plants; no respiratory organs
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cryptobiosis
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"hidden life"; a state in which the sign's of life of an organism have weakened to the point where they are barely measurable or no longer measurable; tardigrades are capable of surviving extremes this way
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tun
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a cyst-like capsule that tardigrades exhibit during cryptobiosis; when dessicated, animal shrivels into a "tun" until water returns
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traditional (non-molecular) view of arthropod descent
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arthropods evolved from polychaete-like (metameric) annelid ancestor that developed appendages on every segment, followed by segments fusing together for specialized functions (tagmosis)
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tagmosis
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fusion of segments/metameres into distinct body regions; defines the different arthropod classes;
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Unique shared characteristics linking polychaetes & arthropods
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1. metameric segmentation & how segments develop (posterior budding zone)
2. paired appendages on segments 3. double ventral nerve cord with metameric ganglia 4. a cuticle secreted by hypodermis tissue |
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"Arthropodization"
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hard outer exoskeleton; jointed appendages moved by antagonistic muscle pairs; major body cavity is a hemocoel (persistent blastocoel, true coelom is reduced); tagmosis; open circulatory system
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Coelom formation
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locomotion becomes associated with the exoskeleton and its attached muscles and the coelom becomes greatly reduced
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open circulatory system in arthropods
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blood empties from the vessels into sinuses to bathe organs and tissues and returns directly from the hemocoel to the pumping heart through ostia
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General characteristics of arthropods
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bilateral, metameric, tagmosis; paired, jointed appendages(one pair per segment); exoskeleton; most exhibit metamorphosis; reduced "true" coelom & persistent blastocoel (hemocoel); complete digestive system (mouth, anus); open circulatory system; paired excretory organs; mostly dioecious; nervous system with ventral double nerve chain of ganglia; respiration by various specialized structures
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exoskeleton
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hard, chitinous cuticle secreted by epidermal cells that periodically molts; provides skeletal support (allowing reduction of hydrostatic coelom) & sites for muscle attachment; covers all epidermal surfaces except inner gut lining; cuticle has three layers formed of chitin (a polysaccharide), wax, tanned proteins, and minerals
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metamorphosis
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a series of distinct post-embryonic changes in body form (larva to adult)
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three layers of cuticle
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epicuticle, exocuticle, endocuticle; exocuticle & endocuticle make up the procuticle
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Challenges imposed by exoskeletal cuticle
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restricts growth, movement, gas exchange, exchange of solutes & water, sensation
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Solution to exoskeletal restriction of growth
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Molting or ecdysis
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Ecdysis
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molting; allows an animal to grow by replacing the old cuticle with a larger one; a new soft cuticle is deposited below the old one, the arthropod inflates with water or air, the old cuticle splits and is cast off in one piece, another inflation of the body expands the new cuticle before it hardens; only the epi- & exocuticle are shed, old endocuticle gets dissolved; controlled by hormones (molt-inhibiting/molt-promoting hormones)
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Solution to exoskeletal restriction of movement
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jointed exoskeleton & arthrodial membranes (movement only occurs at the joints which move in one plane only)
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arthrodial membranes
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thin, flexible membranes at joints
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apodemes
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broad (high surface area) sites for muscle attachment
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solution to exoskeletal restriction of gas exchange
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gills, book lungs, & tracheal systems
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trachea
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air tubes
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tracheal system of insect
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a system of air tubes extending from surface spiracles (openings) that carry air to inner tissues
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solution to exoskeletal restriction of exchange of nitrogenous solutes and water with environment
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excretory malpighian tubules, coxal glands, maxillary glands or antennal glands
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solution of exoskeletal restriction of sensation
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elaborate sensory receptors; "insensitivity" is overcome by either thinning the cuticle (allowing photo and acoustic reception) or using sensory bristles; most bristles are sensitive of bending (mechanoreceptors), some act as chemoreceptors
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tagmata
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functional groups formed when metameres are combined; a head tagma, thoracic tagma, and abdominal tagma; appendages also become specialized for walking, eating, swimming, breathing
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Remipedia
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a "primitive" crustacean class with little tagmosis
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serial homology
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repetitive ("serial") structures on the same organism; as evolution proceeds undifferentiated serial appendages may become specialized for various tasks
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uniramous
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1 terminal branch; in these types of limbs the 2nd exopod branch is "lost" (ex: walking legs of insects)
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endopod
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the internal or principal branch of locomotive appendages of crustacea
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exopod
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the external branch of the appendages of crustacea
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biramous
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2 branches
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phyllopodous
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flattened limbs (can be used for swimming)
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stenopodous
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tubular limbs (can be used for walking)
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Classification of Arthropoda
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Subphylum Trilobita
Subphylum Chelicerata Subphylum Crustacea Subphylum Myriapoda Subphylum Hexapoda |