3. Meet the Lower InvertebratesKingdom-Animalia

Major Phyla – 1st Notes

• A) Phylum Porifera-Unit 6

• B) Phylum Cnidaria-Unit 6

• C) Phylum Annelida-Unit 6

• D) Phylum Echinodermata-Unit 6

• E) Phylum Mollusca-Unit 7

• F) Phylum Arthropoda-Unit 7

A) Phylum Porifera

• The Sponges

• Most primitive animals – no symmetry, few systems

• Kept upright by spicules, glassy or chalky needles inside them

B) Phylum Cnidaria• Jellyfish (AKA Sea Jellies), sea

anemones, and corals

• Members of this group have stinging cells called cnidoblasts containing toxins

• Radially symmetrical – like spokes on a wheel

• Live with symbiotic dinoflagellates: zooxanthellae

• Have 2 forms: medusa & polyp

Cnidaria Life Stages: Medusa vs. Polyp

C) Phylum Annelida• The Worms!• Bilateral symmetry• Three important

marine worms:– Platyhelminthes -

flatworms– Nematodes -

roundworms– Polychaetes –

bristly, segmented worms

D) Phylum Echinodermata

Echinoderm Water Vascular System

Movement – Hydraulic Pressure System

Class – Stelleroidea – the Stars!

Subclass Asteroidea(sea stars-a.k.a. starfishes)

As it changes from being meroplanktonic to benthic a

young starfish’s typical meals may consist of 56 small mussels during its first 6 days (about 25-

30 % of its own weight)

In some reefs (Australia, Queensland) Crown-of-Thorn outbreaks have reduced coral cover by

95%

Some seastars have “issues”

Subclass Ophiuroidea(basket stars, brittlestars, and snake

stars)

Class Holothuroidea(sea cucumbers)

Class Echinoidea(heart urchins, sand dollars, and sea

urchins)

References

• http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20102/Bio%20102%20lectures/Animal%20Development/starfish_development.jpg

• http://animaldiversity.ummz.umich.edu/site/accounts/pictures/Echinodermata.html