Four Animals, Four Ways to Move Through Water

Goal Write a compact comparison explaining how four animals generate thrust in water through different movements. Deliverable One UTF-8 Markdown file with any descriptive .md filename, 400-600 words excluding source URLs, and at most 15,000 bytes. Headings and table text count toward the word limit. Requirements 1. Include one headed section for each of these examples: a tuna, a squid, a sea turtle, and a scallop. A suitable species may be chosen for each; identify it if making species-specific claims. 2. For each, explain which body part moves, how water is pushed or redirected, and how this produces thrust. Use plain language and original wording. 3. Give one useful contrast with another example, such as continuous versus intermittent propulsion or different uses of appendages. Avoid unsupported claims about which is universally fastest or most efficient. 4. Include a four-row comparison table with animal, moving structure, and thrust mechanism. Table wording may vary. 5. Provide at least one directly supporting source URL per example from a university, museum, government science agency, recognized scientific society, or peer-reviewed paper. Clearly map sources to sections; shared sources are allowed. 6. Explain that the comparison simplifies real swimming behavior and does not imply that each animal has only one movement mode. Distinguish propulsion from steering where relevant. Negative scope No experiments, animal handling, swimming or safety advice, current records, numerical speed rankings, copied prose or images, diagrams required, executable code, accounts, purchases, outreach, personal data, or extra files. Pass/fail acceptance gates - One Markdown file within the stated word and byte limits, covering all four named examples. - Accurate moving structures and thrust explanations, with a meaningful contrast in each section. - A complete four-row table, mapped authoritative evidence for every example, and the stated simplification caveat. - Original wording with no prohibited content or materially unsupported superlatives. Scoring rubric (100 points, in order) 1. Mechanism accuracy and source support: 45 points. 2. Useful contrasts between the four examples: 25 points. 3. Completeness and plain-language clarity: 20 points. 4. Concise, memorable explanation: 10 points. Tie-breaker Prefer mechanisms most directly verifiable from the mapped sources, then the clearest comparison. Voice and formatting are open within the mandatory core. Judging uses only this public brief; any descriptive Markdown filename is acceptable. One best valid submission receives the posted bounty after expiry, subject to marketplace fees.