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Download Lecture 14, Ecdysozoa - Cal State LA
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Phylum Nematoda ~25,000 species Nematode muscles run the long way down body (longitudinal), but no circular muscles go around the middle - can’t squeeze itself to get fatter or thinner on one end, the way an earthworm can Covered in a cuticle, tough outer covering shed in a series of 4 molts during growth - helps worms survive in hostile environments C. elegans is a model organism for developmental biology Phylum Nematoda Ecological importance of nematodes: - very abundant and important decomposers - 200 per ml of coastal mud - 90,000 per rotting apple - 9 billion per acre of soil Medical importance: - parasitic forms cause diseases: river blindness elephantiasis trichinosis ~25,000 species Phylum Arthropoda over 1,000,000 species! Segmented bodies organized into specialized regions: head, thorax, abdomen Each body segment has paired, jointed appendages Cuticle forms a well-developed exoskeleton covering outside; -molting (ecdysis) is required for growth Coelom is very reduced; not needed because muscles attach to the exoskeleton - main body cavity is a hemocoel (open circulatory system, like molluscs) Keys to Arthropod Success #1: Exoskeleton Arthropods are encased in a hard external covering made of proteins + chitin, coated with waxy fats - gives protection from predators - major pre-adaptation for life on land: they don’t dry out (analogous to the cuticle of plants) In crustaceans (crabs, lobster), cuticle is hardened by calcium carbonate (like mollusc shells, coral skeletons) Coelom is unnecessary as a hydrostatic skeleton (and wouldn’t even work, since the body is so rigid) replaced w/ open circulatory system + hemocoel Arthropod muscles anchor to inside of the exoskeleton... Molting Living inside a cuticle is like being trapped in a suit of armor: how would you grow bigger? Molting is a process of shedding the cuticle, allowing growth - process is controlled by hormone ecdysone (hence the group name, Ecdysozoa) Cuticle is weakened by enzymes, then animal crawls out all soft & naked - animal sucks in air/water to inflate itself - then secretes a new cuticle, which quickly hardens - this leaves space inside the new cuticle for growth Keys to Arthropod Success #2: Jointed appendages Appendages have muscles connected to the exoskeleton Have multiple joints and branches, giving incredible flexibility Appendages are adapted for different functions -antennae, mouthparts, claws, legs, flippers for swimming, even gills for breathing, are all modified appendages 2-branch limb of a crab 1-branch limb of an insect Keys to Arthropod Success #3: Specialized body regions Annelid worms are segmented, but don’t usually have clumps of segments specialized into different body regions Arthropods have body regions made of segments grouped together and specialized for a function - head, thorax and abdomen are regions specialized for performing different tasks - appendages on different segments do different things - antennae on head for sensory perception - claws on thorax for grabbing food, fighting - legs on abdomen for walking + swimming Body regions of an insect Head Thorax Abdomen Phylum Arthropoda SUB-PHYLA: Trilobitomorpha: Trilobites (extinct, 350 mil yr ago) Myriapoda: Centipedes Cheliceriformes: Spiders, scorpions Crustacea: Crustaceans Hexapoda: Insects Phylum Arthropoda SUB-PHYLA: Trilobitomorpha: Trilobites (extinct) Myriapoda: Centipedes + millipedes - many identical segments - body is not separated into thorax + abdomen the way it is in insects 12,000 species Phylum Arthropoda SUB-PHYLA: Trilobitomorpha: Trilobites (extinct, 350 mil yr ago) Myriapoda: Centipedes Cheliceriformes: Spiders, scorpions 65,000 species - 2-part body: cephalothorax & abdomen - 1st pair of appendages = tiny feeding claws (can’t really see them on spiders) - instead of legs, appendages on abdomen are modified as spinnerets that spin silk proteins into webs SubPhylum Cheliceriformes SubClass Merostomata Horseshoe crabs cephalo- abdomen thorax - once very common - over-harvested, now rare SubPhylum Cheliceriformes SubClass Merostomata Horseshoe crabs cephalo- abdomen thorax SubClass ArachnidaScorpions, spiders, ticks SubClass Arachnida 65,000 species spider silk is 5x stronger than steel yet more flexible than rubber scorpion spiders spin liquid proteins into solid strands that may be sticky for catching prey, or just strong spider orb weaver spider + web many chelicerates are parasites, including harmless mites and blood-sucking ticks mites tick Phylum Arthropoda SUB-PHYLA: Trilobitomorpha: Trilobites (extinct) Myriapoda: Centipedes Cheliceriformes: Spiders, scorpions Crustacea: Crustaceans – crabs, lobster, shrimp 75,000 species - body = 5-segmented head + thorax + abdomen - one of the most successful groups of marine animals, with 2 different groups that also colonized dry land SubPhylum Crustacea Body = 5-segmented head + thorax + abdomen A pair of limbs is found on every segment, but modified: - head: antennae & pincers for eating - thorax: claws and walking legs - abdomen: swimming legs Some legs are flattened + used as “gills” for respiration - like how parapodia of annelids can act as gills! Shrimp: body of 19 segments: head, 5 segments thorax, 8 segments abdomen, 6 segments + tail Thorax segments Abdomen swimming legs walking legs Crustacean Head Each of the 5 head segments has its own unique appendages 1 2 3 4 5 Class Maxillopoda: Barnacles 26,000 species start life as a swimming larva, which glues its head onto a rock at metamorphosis adult secretes a hard shell, uses modified legs for filter-feeding swimming larva (looks like a crustacean) adult cemented to rock (doesn’t look crustacean-y) Class Malacostraca 25,000 spp. Decapods (“10-legs) Isopods - 14,000 species: crabs, shrimp, lobster - 10,000 species - mostly marine but includes terrestrial “pill bugs” - 5 pairs of walking legs, 1st pair modified as claws - carapace = protective shield over head + thorax carapace Lobsters Crabs Carapace Abdomen powerful tail used to scoot backwards - abdomen is folded under thorax - 5th walking leg flattened for swimming Crustaceans on Land Pill bugs (isopods) are the most successful crustaceans on land Land hermit crabs must still return to the ocean to spawn no swimming larvae = no need for water Phylum Arthropoda SUB-PHYLA: Trilobitomorpha: Trilobites (extinct) Myriapoda: Centipedes Cheliceriformes: Spiders, scorpions Crustacea: Crustaceans Hexapoda: Insects ~1,000,000 species so far… SubPhylum Hexapoda: Insects - Head with one pair of antennae, chewing mouthparts - 3 segment on thorax = 6 legs (2 per segment) - Wings often present, made of dorsal cuticle - Head Thorax Abdomen compound eye with many facets spiracles Insects decouple gas exchange and circulation - air moves in through spiracles, little holes in the cuticle - piped directly to each cell of the body through a system of tubes (like air ducts) for efficient delivery of oxygen - overcomes inefficient open circulatory system... The Power of Flight Wings contribute to the ecological dominance of insects by providing a very efficient means of dispersal - locate mates, new patches of food - ladybug preparing to fly Most groups have 2 pairs of wings - in beetles, first pair is modified as a covering to protect back pair, actually used for flying Butterfly migration Monarch butterfly migrates 2000 miles each fall from the northeast to forests in Mexico for the winter - it congregates by the thousands in trees there; is endangered by clear-cutting of forests Monarch caterpillar Batesian mimicry Monarch caterpillar eats milkweed plant, stores toxic chemicals which make adult butterfly taste bad to predators Viceroy butterfly mimics the Monarch, but tastes fine ! Coevolution of herbivorous insects and plants: generating earth’s biodiversity Most species on earth, by the numbers, are herbivorous insects - half of all insect species are beetles that eat angiosperms Studies suggest that when a population of angiosperms divided into 2 different species, the beetles feeding on them also divided into 2 new beetle species - you have to be specialized to handle the toxic chemicals most plants produce to defend themselves Specialization allows many related species to co-occur in the same habitat without competing Biodiversity: Insect Orders The Apterygota Protura Collembola Springtails The Exopterygota Ephemeroptera Mayflies The Endopterygota Odonata Dragonflies Coleoptera Beetles Plecoptera Stoneflies Thysanura Silverfish Grylloblatodea Ice Bugs Diplura Bristle-tails Orthoptera Crickets + Grasshoppers Neuroptera Lacewings Strepsiptera Stylops Mecoptera Scorpionflies Phasmida Stick-Insects Siphonaptera Fleas Dermaptera Earwigs Diptera True Flies Embioptera Web Spinners Lepidoptera Butterflies + Moths Dictyoptera Cockroaches + Mantids Trichoptera Caddis Flies Isoptera Termites Zoraptera Psocoptera Bark and Book Lice Mallophaga Biting Lice Siphunculata Sucking Lice Anoplura Biting + Sucking Lice Hemiptera True Bugs Homoptera Cicadas + Hoppers Thysanoptera Thrips Hymenoptera Ants, Bees + Wasps Who is related to whom? Mollusc Annelid Arthropod share obvious segmentation Who is related to whom? Mollusc Annelid share trochophore larval stage Arthropod DNA sequences re-wrote the book Lophotrochozoa Molluscs Based on analysis of DNA, gene order… Annelids ancestor with trochophore larva Ecdysozoa Arthropods Nematodes ancestor with a cuticle …Protostomes are now divided into 2 major sub-groups
