Chapter 33 Intro to Invertebrates Sunday May 10 2015 8 49 PM Ecdysozoans are the most species rich animal group Includes animals that shed a tough external coat cuticle as they grow Derives name from this process called ecdysis or molting Contains more known species than all other animal protist fungus and plant groups combined Phylum Nematoda roundworms Found in most aquatic habitats in the soil in moist tissues of plants and in the body fluids and tissues of animals No segmented bodies Cylindrical bodies range from less than 1 mm to more than 1 m long often tapering to a fine tip at the posterior end and to a blunter tip at the anterior end Tough cuticle type of exoskeleton which is shed as body grows and a new larger one is created Alimentary canal but lack circulatory system Nutrients transported via fluid in pseudocoelom Longitudinal body wall muscles Contraction produces thrashing motion Reproduce sexually by internal fertilization Zygotes of most are resistant cells that can survive harsh conditions Includes species that parasitize plants agricultural pests that attack the roots of crops parasitsize animals some benefit humans by attacking insects such as cutworms that feed on roots of crop plants Ex Trichinella spiralis worm that causes trichinosis caused by eating raw or undercooked pork Trichinella parasitizes animals controls the expression of specific muscle cell genes that code for proteins that make the cells elastic enough to house the nematode Common features Colorless round body w tapered ends w thick flexible cuticle outer coat that is shed as it grows ecdysis Anatomical features Well developed digestive tract gonads and nerve cords Pseudocoelom acts as circulatory system and respiratory system by distributing nutrients throughout gut Pseudocoelom contributes to locomotion by acting as a hydrostatic skeleton distinctive thrashing motion Gases diffuse directly Has mouth and anus for excretory Most widespread of all animals Important free living decomposers in soil Parasites in plants animals Ex Of animal parasites trichina worm causes trichinosis from eating undercook pork dog intestinal roundworm dog heart worm dog hookworm human pinworms filaria worm Phylum Onychophora velvet worms Predators in tropical forests Flexible cuticle w chitin sheds as it grows Segemented body w many legs but legs are soft and unjointed Fleshy antennae and several dozen pairs of saclike legs Linked phylogenetically to arthropods due to having an external cuticle that sheds as it grows and have a segmented body however their appendages legs are unjoined unlike the arthropoda Phylum Tardigrada water bears b c of rounded shape stubby appendages and lumbering bearlike gait Segmented w chitonous cuticle that sheds But w 4 pairs of stubby unjointed legs Segemented body w many legs but legs are soft and unjointed Fleshy antennae and several dozen pairs of saclike legs Linked phylogenetically to arthropods due to having an external cuticle that sheds as it grows and have a segmented body however their appendages legs are unjoined unlike the arthropoda Phylum Tardigrada water bears b c of rounded shape stubby appendages and lumbering bearlike gait Segmented w chitonous cuticle that sheds But w 4 pairs of stubby unjointed legs Very small 0 5 mm Live in water films on plants and soils Can survive in dehydrated dormant state of years w o water Piercing mouthparts feed on plant animal cell fluids Extreme low temperatures Hi lo Phylum Arthropoda 2 out of every 3 known species are arthropods found in nearly every habitat The diversity and success of arthropods may be attributed to their body plan their segmented body hard exoskeleton and jointed appendages May have evolved from lobopods extinct group Lobopods such as Hallucigenia had segmented bodies but most segments were identical to one another Early arthropods such as trilobites also showed little variation form segment to segment Segments tended to fuse and became fewer appendages became specialized for a variety of functions as arthropods continued to evolve Body plan allows for the division of labor among different body regions Comparison of Hox genes in arthropods and in onychoporans indicated that the arthropod body plan diversity did NOT arise from the acquisition of new Hox genes instead driven by changes in the sequence or regulation of existing Hox genes Characteristics Segmented body w hard exoskeleton cuticle constructed form layers of protein and polysaccharide chitin Segments are usually highly specialized in a variety of different functions Tough cuticle made of chitin and proteins Can be thick and hard or paper thin and flexible over joints For support protection and attachment of muscles that move appendages advantageous Hardened in marine species w CaCO3 advantageous Land species w waxes to reduce H2O dessication advantageous and its strength solved problem when arthropods left buoyancy of water But limits body size Must be shed to grow molting vulnerable to predation Well developed sensory organs Eyes olfactory smell receptors antenna that functions in both touch and smell Open circulatory system Hemolymph propelled by heart through short arteries and into spaces called sinuses surrounding tissues and organs fluid that is pumped in vessels and bathes in tissues and blood Different from blood b c blood stays in blood vessels and doesn t bathe tissues Hemolymph reenters arthropod heart through pores that are usually equipped w valves Hemolymph filled body sinuses are collectively called the hemocoel which is not part of the coelom Hemocoel becomes main body cavity in adults Gas CO2 O2 exchange varies Aquatic species hemolymph pumped thru gills w feathery extensions that place an extensive surface area in contact w water Errestrial generally have internal surfaces for gas exchange Spider s hemolymph flows thru book lungs in contact w air Insects tracheal system takes air directly to cells for gas exchange at cell level so does not need the circulatory system to take air to blood usually by RBCs Hemocoel becomes main body cavity in adults Gas CO2 O2 exchange varies Aquatic species hemolymph pumped thru gills w feathery extensions that place an extensive surface area in contact w water Errestrial generally have internal surfaces for gas exchange Spider s hemolymph flows thru book lungs in contact w air Insects tracheal system takes air directly to cells for gas exchange at cell level so does not need the circulatory system to take