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Crustaceans vs. Mollusks: The Basic Split
Understand the two broad groups this guide covers, and why the distinction matters before identifying an exact species.
Requiredquick-read
Why it matters
Every species page, regulation, and recipe in this guide is organized around this basic split — crustaceans (crabs, shrimp) have jointed exoskeletons and molt to grow, while mollusks (oysters, clams, mussels, whelks) have hinged or coiled shells and grow their shell continuously.
Steps
- Crustaceans (crabs, shrimp) have a jointed, armor-like exoskeleton they must periodically molt (shed) to grow — this is exactly why blue crab has distinct 'peeler' and 'soft crab' legal categories tied to that molt cycle.
- Bivalve mollusks (oysters, clams, mussels, scallops) have two hinged shell halves and filter-feed — they don't move much as adults and grow their shell continuously rather than molting.
- Gastropod mollusks (whelks, periwinkles) have a single coiled shell and are mobile predators or grazers, distinct from both crustaceans and bivalves.
- This guide also includes a cephalopod (longfin squid) and several protected/non-target species (horseshoe crab, ghost crab) specifically so you can recognize what you're NOT looking at, not just what you are.
Beginner tip: Start with the broad group, not the exact species — see this guide's own Species directory, filterable by group.