Lecture 13 - Animals: Cnidarians, Platyhelminthes, & Annelids

General characteristics of the members from phylum Cnidaria

-Eumetazoans (true animals) have embryonic germ layers

-Diploblastic (ectodermis and gastrodermis)

-Radial symmetry

What is the gastrovascular cavity in a cnidarian?

-A central cavity w/ a single opening

-functions as both a mouth and an anus

Cnidarian medusa form

-oral surface faces down

-moves by drifting freely or body contractions

Cnidarian polyp form

-mostly sedentary

-can detach from surface

-oral surface faces up

Oral surface of cnidarian

surface where mouth is located (tentacles)

Aboral surface of cnidarian

surface opposite to mouth

Cnidocytes

-stinging cells that contain cnidae (nettle), capsules capable of exploding outward

-found on tentacles

-used for defense and capture of prey

Nematocysts

organelle in Cnidocytes that ejects a stinging coiled thread to entangle or paralyze prey

Medusozoans

-spend majority of life in medusa form

-jellies, box jelly

Anthozoa

-exist only in polyp form

-sea anemone, corals

Coral colony structure: presence of algal endosymbiont

Form symbiosis with zooxanthellae algae

-photosynthetic algae provides sugar to coral

Coral colony structure: formation of exoskeleton

Secret and build exoskeleton of calcium carbonate

-build on top of previous generations’ skeletons

General features of Lophotrochozoans

-Bilateral symmetry

-Protostome development

Either:

~Lophophore: ciliated feeding structure around mouth

~Trochophore: a type of developmental larval stage

General characteristics of Platyhelminthes?

-Protostome

-Acelomates (no internal body cavity)

-Live in aquatic and damp terrestrial environments

-Lack a circulatory system

-Some species are free-living (class Turbellaria), others are parasites (class Cestoda)

-Monoecious

Why are platyhelminthes flat?

-Minimizes surface area

-Gas exchange and waste removal all via diffusion across body

Planarian features: Eyespots

light detection

Planarian features: Ganglia

dense nerve cell clusters at front end, centralized nervous system

Planarian features: Pharnyx

extended through mouth to feed and take up food, undigested waste ejected here

Planarian features: Gastrovascular cavity

highly branched to deliver nutrients to cells

Features of the group Turbellaria

-phylum Platyhelminthes

-free-living

-carnivores

-aquatic and terrestrial flatworms

-move by undulation or gliding along secreted mucus layer

Features of the group Cestoda

-phylum Platyhelminthes

-parasites of vertebrates

-scolex on anterior end has hooks and suckers to attach to intestinal lining of host

-body made of proglottids

-ex: tape worm

What are proglottids

repeating sacs containing sex organs, sexual reproduction fills up proglottids w/ fertilized eggs and proglottids are shed in feces

What are rotifers

-Microscopic wheel animals

-plylum Syndermata

General features of rotifers?

-Live in freshwater, marine, and damp soil environments

-Psudocoelomates (hemocoel with hemolyph)

-Protostome

-Multicellular but smaller than most protists

-Reproduce via parthenogenesis

-Dioecious

How do rotifers obtain nutrients

-Have ring of cilia around mouth to draw in food via vortex

-Jaws grind up food and digestion and excretion occurs in rest of alimentary canal (GI tract)

What is parthenogenesis

When females produce unfertilized eggs that develop into new females (asexual), some species lack males entirely

General features of Annelids?

-Protostome

-Coelomates

-Have closed circulatory system and alimentary canal

-well developed nervous system

-segmented internally and externally

-most have chaetae

What are chaetae

external bristles made of chitin (polysaccharide), used for moving and gripping the ground

What are the two made clades of the phylum Annelida?

Errantians and Sedentarians

Errantians

-Annelida

-Highly mobile marine worms

-Predators and grazers

Sedentarians

-Annelida

-Less mobile worms

-Include earthworms and leeches

-Filter feeders or feed on sediment/soil

-Some burrow slowly through marine sediments or soil while others live in tubes

Purpose of parapodia

Lateral paddles with several chaetae used for movement and gas exchange

What are leeches? What’s hirudin used for?

-Parasitic annelid (sedentarians)

-Hirudin (anticoagulant) thins blood and they feed on the blood

Digestive system in earthworms

Mouth, esophagus, crop (temporary food bag), gizzard (grind food), intestine, and anus

Nervous system of earthworms

Cerebral ganglia (brain) coordinates movement towards or away from light, temp, touch, etc

Circulatory system of earthworms

Closed (blood is contained with in blood vessles) and has a heart

What are metanephridia used for by earthworms?

Waste removal and osmoregulation (invertebrate kidney)

How do earthworms reproduce?

By aligning themselves in opposite directions and exchanging sperms (monoecious)