Protostome Animals Notes

Protostomes

  • Protostomes: "mouth first"
    • Anterior brain around the digestive tract entrance.
    • Ventral nervous system with paired/fused nerve cords.
    • More species than deuterostomes.
  • Arthropods: lost coelom, hemocoel (blood chamber).
  • Mollusks: open circulatory system, coelom vestiges.

Lophotrochozoans

  • Lophophore: ciliated tentacles for food/gas exchange; sessile adults.
  • Trochophore: ciliated larval form, lost in some lineages.
  • Many have wormlike bodies, bilaterally symmetrical.

Lophotrochozoans - Flatworms

  • Lack specialized organs for oxygen transport; dorsoventrally flattened.
  • Digestive tract: mouth to blind gut, often branched to increase surface area.
  • Most are parasites (tapeworms, flukes) absorbing host's digested food.

Lophotrochozoans - Annelids

  • Segmented wormlike bodies for independent movement.
    • Each segment has a ganglion.
  • Most lack external protection; thin body wall for gas exchange.
  • Polychaetes: mostly marine, many in soft sediments; use eyes/tentacles for prey or filter food; some have parapodia for gas exchange/movement.
  • Clitellates: freshwater, marine, terrestrial; no parapodia, eyes, or anterior tentacles.
    • Oligochaetes: 4 pairs of setae bundles per segment; hermaphroditic, exchange sperm; earthworms ingest soil.
    • Leeches: coeloms not divided; suckers; ectoparasites feeding on blood.

Lophotrochozoans - Mollusks

  • Diverse group.
    • Foot: locomotion/support, modified in groups.
    • Visceral mass: digestive, reproductive, excretory, respiratory systems within the shell.
    • Mantle: covers visceral mass, secretes shell; forms mantle cavity with gills for gas exchange.
  • Gills used for filter feeding.
  • Radula: scrapes food.
  • Open circulatory system, blood to hemocoel.

Lophotrochozoans - Mollusks - Classes

  • Chitons: 8 overlapping plates, girdle; marine omnivores, cling to rocks with foot.
  • Gastropods: snails, slugs, etc.; glide on foot, some swim; nudibranchs/slugs lack shells.
  • Bivalves: hinged two-part shell; clams, oysters, etc.; burrow with foot; filter feeders with incurrent siphon.
  • Cephalopods: squid, octopus, etc.; modified excurrent siphon for "jet propulsion"; predators with complex sensory organs; foot = arms/tentacles.

Ecdysozoans

  • Cuticle: external covering, molted and replaced for growth.
    • New cuticle forms under the old one.

Ecdysozoans - Nematodes

  • Nematodes (roundworms): thick, multilayered cuticle.
    • Cuticle is shed 4 times as the organism grows.
  • Gas/nutrient exchange through cuticle/gut.
  • Many are microscopic scavengers; some are plant/animal parasites.

Ecdysozoans - Arthropods

  • Arthropods: Ecdysozoans with paired appendages.
    • Most diverse animal group.
  • Segmentation: jointed appendages for complex movements and specialized functions.
  • Exoskeleton: support on land/water
    • Impedes movement and gas exchange.

Ecdysozoans - Arthropods - Relatives

  • Exoskeletons thickened by protein and chitin.
  • Jointed appendages for walking/swimming/gas exchange/feeding/sensory.
  • Muscles attach to inside of exoskeleton.
  • Tardigrades (water bears): fleshy, unjointed legs, hydrostatic skeleton; resilient to extreme conditions.
  • Velvet worms: soft, fleshy, unjointed legs.

Ecdysozoans - Arthropods - Chelicerates

  • Chelicerates: chelicerae (grasping mouthparts).
  • Two-part body: cephalothorax and abdomen; four pairs of walking legs.
    • Sea spiders: marine
    • Horseshoe crabs: changed very little over history
    • Arachnids: terrestrial

Ecdysozoans - Arthropods - Arachnids

  • Arachnids (spiders, scorpions, mites, ticks): terrestrial.
  • Simple life cycle: miniature adults hatch from eggs.
    • Spiders: predators with venomous chelicerae, webs.
    • Ticks/mites: mostly parasites.

Ecdysozoans - Arthropods - Myriapods

  • Myriapods (centipedes, millipedes): long, segmented trunk with many legs.
    • Centipedes: 1 pair of legs/segment, predators.
    • Millipedes: 2 pairs of legs/segment, scavengers.

Ecdysozoans - Arthropods - Crustaceans

  • Crustaceans: dominant marine arthropods.
    • Decapods: shrimps, lobsters, crabs.
    • Isopods: woodlice.
    • Barnacles.
  • Body regions: head, thorax, abdomen.
  • Head: 5 pairs of appendages.
  • Thorax/abdomen: 1 pair of appendages/segment.
  • Carapace: exoskeleton fold over head/thorax.

Ecdysozoans - Arthropods - Insects

  • Insects (hexapods): dominant terrestrial arthropods.
  • Body regions: head, thorax, abdomen.
    • Head: single pair of antennae.
    • Thorax: three pairs of legs.
    • Abdomen: no appendages.
  • Gas exchange: tracheae and spiracles.
  • Relatives: wingless hexapods (springtails, etc.).
  • Pterygota: winged insects, sometimes wings are lost.
  • Metamorphosis:
    • Incomplete: gradual changes between instars.
    • Complete: dramatic changes between stages; different stages have different functions/food sources.

Ecdysozoans - Arthropods - Insects - Wings

  • Flying insects: 2 pairs of wings on thorax.
    • True flies: 1 pair of wings, stabilizers.
    • Winged beetles: 1 pair hardened.
  • Mayflies/dragonflies: cannot fold wings.
    • Aquatic larvae.
    • Adult dragonflies: predators.
    • Adult mayflies: lack digestive tracts, short-lived.
  • Neopterans: can fold wings.
    • Incomplete metamorphosis: grasshoppers, roaches, etc.; gradual adult organ development.
    • Complete metamorphosis: beetles, butterflies, flies, bees, etc.