Deuterostome Animals Summary

Deuterostome Animals

• Historically distinguished by:
  • Radial cleavage
  • Blastopore develops into the anus
  • Coelom develops from mesoderm
• All deuterostomes:
  • Triploblastic, coelomate animals
  • Internal skeletal elements
  • Less obvious segmentation than protostomes
• Major groups:
  • Echinoderms: sea stars, sea urchins, etc.
  • Hemichordates: acorn worms and pterobranchs
  • Chordates: tunicates, lancelets, and vertebrates

Echinoderms

• Body symmetry changes during development.
  • Larva: Bilateral symmetry
  • Adults: Pentaradial symmetry
• No head, move equally well in many directions.
• Oral side (mouth) and aboral side (anus).
• Unique structural features:
  • Calcified internal plates covered by skin/muscles form internal skeleton.
  • Water vascular system: gas exchange, locomotion, feeding.
    • Seawater enters through madreporite to ring canal, then to radial canals and tube feet.

Chordates

• Principal clades:
  • Lancelets: all marine
  • Tunicates: all marine
  • Vertebrates: diversified in marine, then fresh waters
    • Tetrapods: four-legged vertebrates.
• Chordate characteristics:
  • Dorsal hollow nerve cord
  • Tail extends beyond the anus
  • Notochord: dorsal supporting rod, replaced by skeletal structures in most vertebrates
• Lancelets:
  • Notochord extends entire body length
  • Pharyngeal basket for filter feeding
• Tunicates:
  • Sea squirts form colonies via asexual budding
  • Use pharyngeal basket for filter feeding

Chordates - Vertebrates

• Vertebral column replaces notochord.
• Key features:
  • Anterior skull enclosing brain
  • Rigid internal skeleton with vertebral column
  • Internal organs in coelom
  • Well-developed circulatory system with ventral heart
• Structural features support large, active animals.
  • Internal skeleton supports muscular system, oxygen from circulatory, controlled by central nervous system.
• Hagfishes:
  • Weak circulatory systems with three small accessory hearts, a partial cranium, no jaws but have a tongue-like structure with toothlike rasps, no stomach, no vertebrae and skeletons composed of cartilage.
  • Produce slime for defense; use sensory tentacles around the mouth to detect food.
• Lampreys:
  • Complete cranium and cartilaginous vertebrae
  • Undergo complete metamorphosis from filter-feeding larvae
  • Adults of many species are parasitic, attach to fish and rasp away flesh

Vertebrate Diversity - Gnathostomes

• Gnathostomes evolved jaws from modified skeletal arches.
• Jaws improved feeding efficiency and prey capture.
  • Evolution of teeth: grasping and breaking up prey; chewing aids digestion.
• Chondrichthyans:
  • Cartilaginous fishes (sharks, skates, rays, chimaeras).
  • Flexible, leathery skin with sandpaper-like scales.

Bony Vertebrates

• Bony vertebrates have internal skeletons of calcified, rigid bone.
• Gas-filled sacs supplemented gills; evolved into swim bladders in ray-finned fishes.
• Ray-finned fishes:
  • Covered with thin, flat scales.
  • Gills open into operculum.
• Lobe-limbed vertebrates:
  • Gas-filled sacs evolved into air-breathing organs, enabling movement onto land.
  • Pelvic and pectoral fins developed into muscular fins joined to the body by a single enlarged bone.
  • Modern representatives: coelacanths, lungfishes, tetrapods.
• Coelacanths:
  • Skeletons composed mostly of cartilage derived feature because it had bony ancestor.
• Lungfishes:
  • Have lungs and gills, can burrow in mud during dry seasons.
  • Have lungs and gills.
• Early aquatic lobe-limbed vertebrates evolved into tetrapods (four-legged vertebrates).
  • Tetrapod legs evolved from jointed fins.
• Amphibians:
  • Confined to moist environments due to water loss through skin.
  • Eggs susceptible to water loss; some have internal fertilization.
  • Caecilians, Anurans, and Salamanders.

Amniotes

• Amniotes became dominant terrestrial tetrapods due to the amniote egg.
  • Impermeable to water, allows embryo to develop in aqueous environment.
  • Shell halts evaporation but permits gas exchange.
  • Large yolk stores food.
• Innovations:
  • Tough, impermeable skin reduces water loss.
  • Kidneys eliminate nitrogenous wastes without much water loss.
• Amniotes split into Reptiles and Mammals during the Carboniferous.

Reptiles and Birds

• Lepidosaurs:
  • Squamates
  • Tuataras
  • Covered with horny scales to reduce water loss.
• Lizards:
  • Mostly insectivores; some herbivores/carnivores.
  • Snakes are limbless
• Turtles have dorsal and ventral bony plates forming a shell.
• Archosaurs:
  • Crocodilians (crocodiles, caimans, gharials, alligators).
• Birds are specialized theropods (predatory dinosaurs):
  • Bipedal, hollow bones, furcula, elongated metatarsals/forelimbs, backward-pointing pelvis.
  • Feathers are lightweight, help with insulation, flight is metabolically expensive.

Mammals

• Small/medium mammals coexisted with dinosaurs.
• Increased in numbers/diversity after dinosaur extinction.
• Key features:
  • Sweat glands
  • Mammary glands secrete milk
  • Hair and a four-chambered heart that completely separates the oxygenated blood from the deoxygenated blood.
  • Internal fertilization, embryos develop inside the female uterus.
• Two primary groups:
  • Prototherians, Therians further divided into the marsupials and the eutherians.

Mammalian Diversity

• Prototherians:
  • Duck-billed platypus and echidnas, found in Australia and New Guinea.
  • Lay shelled eggs, have sprawling legs, supply milk without nipples.
• Marsupials:
  • Carry young in pouches.
  • Restricted mostly to Australasia and the Americas.
• Eutherians:
  • More developed at birth than marsupials
  • Divided into 20 major groups
• Primates:
  • Grasping limbs with opposable digits.
  • Wet-nosed (Strepsirrhines: lemurs, lorises, galagos), and Dry-nosed (Haplorrhines: tarsiers, monkeys, apes).
• Hominins:
  • Modern humans and extinct relatives.
  • Bipedal locomotion, increased brain size, decreased jaw size