Unit 04 · Marine Invertebrates
Most animals in the sea have no backbone. This unit works through the great marine invertebrate phyla — sponges, cnidarians, mollusks, arthropods, and echinoderms — and the traits that define each. You learn to read body plans and symmetry, radial versus bilateral, and the adaptations that make these animals work: filter feeding, stinging cnidocytes, jointed exoskeletons, and the echinoderm water-vascular system. Along the way you settle a common mistake — coral is an animal, a polyp living with symbiotic algae, not a rock or a plant. Mastery means you can take an unknown specimen and place it by its structure.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Major phyla & defining traits | Groups all “sea bugs” together without distinction. | Names some phyla but mixes up their defining traits. | Identifies Porifera, Cnidaria, Mollusca, Arthropoda, and Echinodermata and gives a defining trait for each. |
| Body plans & symmetry | Cannot describe an animal’s symmetry. | Uses “radial” and “bilateral” but applies them to the wrong animals. | Distinguishes radial from bilateral symmetry and links each body plan to how the animal lives and moves. |
| Adaptations & feeding | Describes marine invertebrates as simple or all alike. | Names an adaptation but cannot tie it to survival. | Explains filter feeding, stinging cnidocytes, exoskeletons, and the water-vascular system as adaptations that solve real problems. |
| Coral as an animal | Calls coral a rock or a plant. | Knows coral is alive but not what kind of organism it is. | Explains that a coral is an animal — a cnidarian polyp — living with symbiotic zooxanthellae that feed it through photosynthesis. |
| Lab technique (invertebrate dissection & ID) | Damages the specimen or cannot use the key. | Dissects carefully but keys the animal to the wrong group. | Dissects an invertebrate cleanly and identifies it to phylum with a dichotomous key, recording the traits that got it there. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“This one’s bilateral with a jointed exoskeleton, so it’s an arthropod — the key took me straight there off the legs. The sea star next to it is radial, an echinoderm, and it moves on a water-vascular system. And coral isn’t a rock; it’s a cnidarian polyp living with algae inside it.”
“It’s some kind of sea bug. Symmetry means it’s the same on both sides, I think. Coral is a colorful rock.”
You demonstrate this unit through an invertebrate dissection where you identify the specimen to its phylum with a dichotomous key and defend the call aloud — not a multiple-choice test. A criterion counts as mastered only when you can both handle the dissection and explain the traits that place the animal. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.