7.2. INVERTEBRATE ANIMALS

General characteristics of invertebrates:

1. Skeleton: invertebrates have not spinal column, but they can present an external skeleton (exoskeleton), an internal skeleton or no skeleton.
2. Movement: some can move around; others are sessile.
3. Eight groups: porifera, cnidarians, platyhelminthes, nematodes, annelids, molluscs, arthropods and echinoderms.

PORIFERA (sponges)
Habitat: marine Nutrition: filter feeders Motion: sessile (stationary) Body: no symmetry; full of pores Skeleton: internal hard structures

CNIDARIANS
Habitat: marine Nutrition: carnivorous Body: radial symmetry Motion: sessile and motile Skeleton: no skeleton

PLATYHELMINTHES
Habitat: aquatic and damp soils Body: bilateral symmetry Nutrition: carnivores and parasites Motion: cilia and muscle contraction Skeleton: no skeleton Reproduction: asexual (fragmentation) and sexual (hermaphrodites: ovaries and testis)

NEMATODES
Habitat: aquatic, damp soils and parasites Skeleton: no skeleton Reproduction: sexual Body: bilateral symmetry; thin and cylindrical Nutrition: free-living (some parasites) Motion: muscle contractions Size: small or microscopic

ANNELIDS
Skeleton: no skeleton Motion: setae Reproduction: sexual Habitat: sea, fresh water and damp soils Body: bilateral symmetry; metameres (segmented worms) Nutrition: free-living and parasites

MOLLUSCS
Habitat: aquatic or damp soils Body: bilateral symmetry; head, visceral mass and foot CEPHALOPDS: internal shell; beak BIVALVES: external shell (2 valves) GASTROPODS: external shell (spiral shaped)

PRÁCTICA DE LABORATORIO Nº 11:
Disección de un mejillón.

ARTHROPODS
Habitat: ocean, damp and dry soils Nutrition: carnivorous Motion: legs (jointed appendages) Body: bilateral symmetry; head, thorax and abdomen; cephalothorax (head+thorax) in crustaceans and arachnids Skeleton: external

ECHINODERMS
Habitat: ocean Nutrition: carnivorous Skeleton: internal skeleton Body: radial symmetry; mouth on the underside Movement: water vascular system Reproduction: asexual (fragmentation) and sexual

YouTube: Jonathan birds’s blue world “Sponges!”

YouTube: National Geographic “Corals collaborating to eat jellyfish”

YouTube: BBC Earth “Jellyfish sunbathing”

YouTube: BBC Earth “Fluorescent corals”

YouTube: WillDiv serie Animales Fantásticos

YouTube: TED-Ed “La vida secreta del plancton”