Invertebrates Class Notes

Invertebrates Notes

• Phylum Ctenophora (Comb Jellies):

  • First animal phylum to diverge from other animals
  • All marine, abundant
  • Cilia for locomotion, arranged into combs
  • Most have 2 long tentacles with sticky hairs
  • Gastrovascular cavity for digestion and circulation of digested nutrients
  • Hermaphrodites (both male and female reproductive organs)
  • Bioluminescent
  • Unique embryonic development and nervous system compared to bilateral animals

• Phylum Porifera (Sponges):

  • Mostly marine
  • Mostly no symmetry
  • No tissues, potentially a degenerative condition
  • Adults sessile, anchored in one place
  • Filter feeders (suspension feeders) filtering matter and plankton
  • Many specialized cells (flagellated choanocytes) draw water through pores
  • Amoebocytes absorb food, digest, and distribute nutrients
  • Intracellular digestion (limits food size)
  • Sponges have an inner and outer layer of cells with gelatinous material in between
  • Mostly hermaphrodites
  • Can reproduce asexually and sexually
  • Contain a tough protein (spongin) and spicules (silica/calcium carbonate/protein)

• Phylum Cnidaria:

  • Jellyfish, corals, hydras, sea anemones, box jellies, etc.
  • Radial symmetry
  • Two tissue layers (ectoderm and endoderm)
  • Mostly marine, some in freshwater
  • Gastrovascular cavity
  • Jelly-like acellular material (mesoglea) between the tissue layers
  • Have cells called cnidocytes containing nematocytes that release venom

• Phylum Platyhelminthes (Flatworms):

  • Acoelomates
  • Free-living and parasitic species
  • Gastrovascular tract with a single opening
  • Free-living forms include planarians
  • Most have a distinct head and ventral nerve chords
  • Include flukes (parasites) and tapeworms (parasites with no digestive tract—absorb food)

• Phylum Rotifera (Rotifers):

  • Very small
  • Mostly freshwater
  • Pseudocoelomates
  • Have a crown of cilia directing food into the mouth
  • Have jaws to grind food
  • Complete digestive tract (mouth and anus)

• Phylum Nemertea (Ribbon or Proboscis Worms):

  • Coelomates
  • A complete digestive tract
  • Closed circulatory system (blood in vessels)
  • Some are venomous

• Phylum Mollusca:

  • Soft bodies, many with protective shells of calcium carbonate
  • Visceral mass contains most organs
  • Mantle folds over visceral mass, secretes shell
  • Radula (rasping feeding organ in many, not all)
  • Most have an open circulatory system (hemolymph bathes organs)
  • Ventral nerve cords
  • Includes snails, slugs, clams, oysters, mussels, scallops, squids, octopuses, cuttlefish, and nautiluses
  • Most have internal shells
  • Have a closed circulatory system
  • Have a complex brain

• Phylum Annelida (Segmented Worms):

  • Coelomates (protostomes)
  • Closed circulatory system
  • Metanephridia (paired excretory tubules)
  • Brain-like cerebral ganglia
  • Earthworms are cross-fertilizing hermaphrodites, tubeworms are sessile as adults
  • Polychaetes are marine worms with parapodia (structures that look like legs)

• Phylum Nematoda (Unsegmented Roundworms):

  • Pseudocoelomates
  • Important members of zooplankton and important parasites. Very abundant.

• Phylum Arthropoda (Jointed Feet):

  • Crustaceans, spiders, insects, millipedes, centipedes, many others

  • Coelomates (protostomes)

  • Jointed legs, hard exoskeleton, segmentation

  • Exoskeleton made of chitin and protein (protection and water resistance)

  • Molting (shedding old exoskeleton)

  • Many sensor organs concentrated on heads. Many appendages. Open circulatory system.

  • 4 major subphyla

    • Chelicerata
    • Myriapoda
    • Crustacea
    • Hexapoda

  • Chelicerata: arachnids, sea spiders, horseshoe crabs

  • Myriapoda: centipedes, millipedes

  • Crustacea: crabs, lobsters, shrimp, etc.

  • Hexapoda: Insects, have 3 body regions (head, thorax, abdomen), 3 pairs of legs, one pair of antennae.

• Phylum Echinodermata (Spiny Skin Animals):

  • Deuterostomes
  • Starfish, brittle stars, sea urchins, sand dollars, sea lilies/cucumbers
  • Water vascular system (hydraulic canals connected to tube feet) for locomotion, feeding, and respiration
  • Have a hard skeleton
  • Radial symmetry as adults
  • Larvae are bilateral
  • Closely related to our own phylum. Important members of zooplankton (marine + freshwater).

• Phylum Hemichordata (Marine Worms):

  • Related to echinoderms and chordates
  • Some are burrowing sediment feeders, some are colonial filter feeders
  • Features of chordates
  • Acorn worms (formerly considered chordates)

• Phylum Chordata (include vertebrates):

  • This is not an invertebrate phylum.

• Other phyla (Lophophorates, Ecdysozoa, Deuterostomia):

  • Lophophorates have ciliated feeding structures (lophophore)
  • Ecdysozoa have molting outer covering (ecdysis)
  • Deuterostomia share similar developmental pattern

• Metamorphosis:

  • Incomplete: young (nymphs) resemble adults, several molts
  • Complete: larval stages, transformation during pupal stage
  • Tardigrada (water bears) can suspend metabolism during extreme conditions, such as periods of drought

Explore the fascinating world of invertebrates with notes on Phylum Ctenophora and Phylum Porifera. Learn about their unique characteristics, such as locomotion using cilia, filter feeding methods, and their developmental differences compared to bilateral animals. This quiz will test your knowledge of invertebrate biology and their ecological roles.