Chapter 33A: Introduction to Invertebrates

Invertebrate are…

…animals that lack a backbone

Eumetazoa characteristics

true animals with tissues

exception = Porifera

Bilateria characteristics

animals with two-sided (bilateral) symmetry and three tissue layers

most animals

Invertebrate characteristics

no backbone

97% of all animal species

morphologically diverse

occupy almost every habitat on earth

Phylum Porifera

Metazoan

closest living species = choanoflagellates (protists)

basal animals

sessile

filter feeders

Ex: sponges

Filter Feeders

Phylum Porifera;

filter out food particles from the water for nutrition as they draw it through epidermal pores and then pump out the water

Spongocoel

filter feeders;

central cavity

Osculum

filter feeders;

large opening in the top where filtered water exits

more complex = have branched corals and several osculum

Basal animals

Phylum Porifera;

most basic

lack tissues but still have different types of cells

Mesohyl

Phylum Porifera;

two layers of cells separated by a gelatinous matrix

“middle matter”

amoebocytes and spicules found here

Epidermis

Phylum Porifera;

outer layer of tightly packed epidermal cells

Pores

Phylum Porifera;

water enters through here

formed via doughnut-shaped cells spanning the body wall

Choanocytes

Phylum Porifera;

lines Spongocoel with flagellated cells

beats to create currents that draws water in through pores and out the osculum

Amoebocytes

Phylum Porifera;

cells that transport nutrients to other cells of the sponge body

produce materials for skeletal fibers (spicules)

can become any sponge cell needed

Phylum Cnidaria

Eumetazoa;

oldest Eumetazoans = true animals

radial symmetry

gastrovascular cavity

two body plans/forms

Ex: jellyfish, corals, hydras, sea anemones, stinging-celled animals

Radial symmetry of Phylum Cnidaria

Phylum Cnidaria;

no head or brain, but have a “nerve net” that respond to stimuli

Gastrovascular cavity

Phylum Cnidaria;

Stomach: digestion, one opening, food enter→feces leave

opening surrounded by crown of tentacles (contains stinging cells)

Two body plans/forms of Phylum Cnidaria are…

Polyp and Medusa

Polyp

body plan/form of Cnidaria;

usually asexual

mostly sessile

Ex: corals, sea anemone, hydra

Medusa

body plan/form of Cnidaria;

motile

sexual reproduction

medusa release egg/sperm into water→mix and fertilize→Planula larva

Ex: jellyfish, sea wasp

Nematocysts

Phylum Cnidaria;

found in cnidocytes

harpoon-like structures used for prey capture and defense

allows these animals to paralyze and kill prey much larger than them

Cnidocytes

Phylum Cnidaria;

cells unique to Cnidarians

contain "explosive" organelles called cnidocysts, used for prey capture and defense

Process of feeding for Cnidarians

prey hits “trigger” on tentacles →

coiled thread inside nematocysts release sting and can kill →

tentacles bring prey to mouth/anus

Hydrozoa

Phylum Cnidaria;

colonial

Ex: Hydra

Scyphozoa

Phylum Cnidaria;

cup animals

Ex: jellyfish

Cubozoa

Phylum Cnidaria;

highly toxic cnidocytes

respiratory failure, cardiac arrest, and death within minutes if stung

Ex: sea wasp

Anthozoans

Phylum Cnidaria;

sessile

secrete and hard exoskeleton

contain zooxanthellae (photosynthetic algae)

produce colorful proteins

Ex: sea anemone, corals (coral reefs)