Biology 80 - Invertebrates

Animals without a backbone. 95% of all known animal species

Porifera

• Sponges

• No true tissues or organs

• No symmetry

• Most basal animals

  1. Filter feeders

• Hermaphrodites 

  1. Produce both eggs and sperm

  2. Sequential hermaphroditism - function as one sex first, then as the other

• Three main body types:

  1. Asconoid

  2. Syconoid

  3. Leuconoid

Cnidaria

• Jellies, hydras, corals, anemones

• Basic body plan

  1. Simple diploblastic, radial body plan

  2. Gastrovascular cavity - central digestive compartment 

     1. Functions as both mouth and anus 

  3. Two Variations:

     1. Polyp

        1. Largely sessile

        2. Hydras and sea anemones

     2. Medusa

        1. More motile

        2. Jellies

  4. Tentacles armed with cnidocytes

     1. Function in defense and prey capture

     2. Specialized cnidae called nematocysts contain a stinging thread that can penetrate prey

Ctenophora

• Comb jellies

• Possess anal pores - more complex digestive tract than Cnidarians

• Movement accomplished with rows of “combs” comprised of cilia

Lophotrochozoa

• Bilateral symmetry

• No one unifying trait

  1. Lophophore (Brachiopoda and Ectoprocta) - crown of ciliated tentacles that functions in feeding

  2. Trochophore larva (Annelida and Mollusca) - a distinct larval stage

  3. Neither (Rotifera and Platyhelmenthes)

Platyhelminthes

• Flatworms (flukes, tapeworms, free living flatworms, ectoparasites)

• Acoelomates

• Triploblastic

• Possess gastrovascular cavity

• Feed with pharynx

• Many are sexual and hermaphroditic 

  1. Penis fencing flatworms

Ectoprocta

• aka Bryozoans

• Coelomates 

• Lophophore

• “Moss” animals

• Colony encased in a hard exoskeleton – studded with pores through which lophophore extends

Brachiopoda

• Lamp shells

• Coelomates

• Lophophore

• Resemble clams but shells are dorsal and ventral instead of lateral

Rotifera

• Phylum Syndermata

• Pseudocoelomates 

• Tiny animals that inhabit fresh water, the ocean, and damp soil

• Smaller than many protists but are multicellular and have specialized organ systems (alimentary canal)

• Parthenogenesis

  1. Asexual reproduction

  2. Only females

Annelida

• earthworms, leeches, polychaete worms

• Segmented lophotrochozoan invertebrates

• Coelomates

• Bodies composed of fused rings

Mollusca

• Soft-bodied + similar body plan

  1. Three parts:

     1. Muscular foot – usually for movement

     2. Visceral mass – containing most of the internal organs

     3. Mantle – fold of a tissue that drapes over the visceral mass and secretes a shell (if one is present)

  2. Many feed with a radula to scrape up food

• Most secrete a hard protective shell made of calcium carbonate

  1. Squids, slugs, and octopuses have a reduced internal shell or have lost their shell completely during evolution

Polyplacophora

• Chitons

• Shell with 8 plates

• Foot used for locomotion

• Radula

• No head

Gastropoda

• Snails and slugs

• Marine, freshwater, or terrestrial

• Head

• Usually with coiled shell or shell reduced/absent

  1. Torsion - causes animal’s anus and mantle to end up above its head

•  Foot for locomotion

• Radula

Bivalva

• Clams, mussels, scallops, oysters

• Marine and freshwater

• Flattened shell with two valves

• Head reduced

• Paired gills

• No radula

Cephalopoda

• squids, octopuses, cuttlefishes, chambered nautiluses

• Marine

• Head surrounded by grasping tentacles

  1. Usually with suckers

  2. Shell external, internal, or absent

  3. Mouth with or without radula

  4. Locomotion by jet propulsion

• Carnivores

• Beak-like jaws

• ONLY CLOSED CIRCULATORY SYSTEM in molluscs

Ecdysozoa

• Most species-rich animal group

• Covered by a tough coat called a cuticle

  • Cuticle is shed or molted through a process called ecdysis

Nematoda

• Roundworms

• Found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals

• Alimentary canal but lack a circulatory system

• Usually sexual reproduction, by internal fertilization

• Oldest known fossil parasite

Arthropoda

• Insects, spiders, crabs, lobsters, shrimp, scorpions, centipedes, millipedes

• ⅔ of every known species of animals

  1. Most diverse animal phylum

  2. Found in every habitat + capable of flight

• Body plan:

  1. Segmented body

  2. Hard exoskeleton

  3. Jointed appendages

• Body is completely covered by the cuticle, an exoskeleton made of layer of protein and the polysaccharide chitin

• Open circulatory system in which a fluid called hemolymph is circulated into the spaces surrounding the tissues and organs

• Variety of gas exchange mechanisms

  1. Trachea in insects

  2. Book lungs in arachnids

Chelicerata

• Scorpions, spiders, ticks, mites, sea spiders, horseshoe crabs

• Named for clawlike feeding appendages called chelicerae

• Earliest forms were once eurypterids (water scorpions)

• Arachnids

  1. Gas exchange through book lungs, stacked platelike structures contained in an internal chamber 

• Body has one or two main parts

• 6 pairs of appendages

  1. Chelicerae, pedipalps, and four pairs of walking legs

• mostly terrestrial or marine

Crustacea

• Isopods, decapods (crabs, lobsters, crayfishes, shrimps), copepods, barnacles

• Body of two or three parts

• Antennae

• Chewing mouthparts

• Three or more pair of legs

• Mostly marine and freshwater

Myriapoda

• Centipedes (Chilopoda)

  1. 1 pair of walking legs for each body segment

  2. Carnivorous

• Millipedes (Diplopoda)

  1. 2 pairs of walking legs for each body segment

  2. Eat decaying leaves and organic matter

Hexapoda

• Insects and springtails

• Very diverse!

  1. Powered flight

  2. Complex array of specialized mouthparts

• Body plan

  1. 3 tagmata

     1. Head, thorax, abdomen

  2. 3 pairs of walking legs

  3. 1 pair of antennae

  4. 1 pair of compound eyes

  5. Tracheal system with spiracles that open to the atmosphere

• Metamorphosis

• Most are sexual (but asexuality exists as well)

Coleoptera

• “sheath-wing”

• Beetles

Orthoptera

• “straight-wing”

• Katydids, grass-hoppers, crickets

Diptera

• “two-wing”

• True flies

Lepidoptera

• “scale-wing”

• butterflies, moths, skippers

Hymenoptera

• “married-wing”

• Ants, bees, wasps

• 2 sets of wings

  • hooks hold them together

Hemiptera

• “half-wing”

• True bugs

Deuterostomes

• Radial and indeterminate cleavage

• Formation of the mouth at the end of the embryo opposite of the blastopore

Chordata

• Notochord

• Dorsal hollow nerve chord

• Postanal tail

• Pharyngeal gill slits

Urochordata

• Sea squirts

• Non-vertebrate chordate

• Larva has notochord

• Adult is filter-feeder with degraded nervous system and no notochord

Cephalochordata

• Sea lancelet

• Non-vertebrate chordate

• No vertebrae but a notochord

Echinodermata

• 5-part radial symmetry

Asteroidea

• Sea Stars

• Central disk with 5 radiating arms

  1. Can regrow arms

• However, sea daisies (only 3 species known) lack arms

Crinoidea

• Sea lilies

  • live attached to the substrate by a stalk

• Feather stars

  • can crawl using long, flexible arms

Echinoidea

• Sea urchins, sand dollars

• No arms but 5 rows of tube feet

Holothuroidea

• Sea cucumbers

• Very reduced endoskeleton

• 5 rows of tube feet

  1. Some developed as feeding tentacles

Ophiuroidea

• Brittle stars

• Distinct central disk and long, flexible arms

• If attacked, can detach own arms