Unit 02 · Sponges, Cnidarians & Worms
This unit meets the simplest animals and watches complexity switch on. Sponges filter food from water without a single true tissue; cnidarians — hydra, jellyfish, anemones, coral — add radial symmetry and stinging nematocysts, and alternate between the anchored polyp and the drifting medusa; the worms bring the next leap: bilateral symmetry, a head end (cephalization), and the first true nervous systems. Mastery means you can read an animal's body plan as a record of which problems its lineage had already solved.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Sponges & filter feeding | Thinks a sponge is a plant or names no defining trait. | Calls a sponge an animal but cannot say how it feeds or that it lacks true tissues. | Explains that a sponge is an animal with no true tissues that filters food from water pulled through its pores. |
| Cnidarians, symmetry & nematocysts | Cannot name a trait that unites hydra, jellyfish, and anemones. | Groups cnidarians together but misses radial symmetry or the stinging cells. | Identifies cnidarians by radial symmetry and nematocysts and explains how the stinging cells capture prey. |
| Polyp & medusa forms | Treats every cnidarian as one fixed shape. | Names polyp and medusa but cannot say which animals show which. | Distinguishes the anchored polyp from the free-swimming medusa and gives an example of each. |
| Worms, bilateral symmetry & cephalization | Calls all worms the same and describes no body plan. | Knows worms are bilateral but overlooks a head end or a nervous system. | Explains bilateral symmetry, cephalization, and the first true nervous systems, and tells flat, round, and segmented worms apart. |
| Lab technique (hydra & planaria observation) | Skips the microscope or records nothing about behavior. | Observes the specimen but misreads its symmetry or response. | Observes live hydra and planaria under magnification, sketches each in a field notebook, and records how it feeds or responds to a stimulus. |
| 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. |
“A hydra is a cnidarian — radial, with stinging nematocysts on its tentacles, held as a polyp. A planarian is a flatworm: bilateral, with a real head end and the first true nervous system, so it moves toward food instead of just drifting into it. A sponge does neither — it just filters the water going through it.”
“They’re all just squishy sea things. A sponge is a plant, right? Symmetry means it’s the same on both sides, maybe.”
You demonstrate this unit through live-specimen observation of hydra and planaria under magnification, describing each animal’s symmetry, feeding, and response aloud — not a multiple-choice test. A criterion counts as mastered only when you can both handle the microscope and explain the body plan behind what you see. 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.