Sea hare
A sea hare is a soft-bodied marine mollusc related to sea slugs, capable of releasing ink when threatened.
Also known as: Aplysia, sea slug
How big is it?
20 cm long
Also 7.874 in
Defined body length · defined specimen
Typical recorded range: 12 cm to 30 cm.
A little perspective
About the same scale as Basket star.
Basket star: A basket star is a marine echinoderm related to brittle stars, with repeatedly branching arms adapted for filter feeding.
Measurements, assumptions & sources +
Sea hare
A defined 20 cm Aplysia sea hare measured along the relaxed body. Species, maturity and posture vary greatly; extended oral tentacles are excluded.
Monterey Bay Aquarium — California sea hare
The marked defined body length is calibrated. Unmeasured illustration details are representative.
Basket star
A defined 20 cm expanded basket star measured across the branching arm tips. Species and posture alter the projected span dramatically; the central disc is much smaller.
Smithsonian Ocean — Basket stars
The marked defined arm-tip span is calibrated. Unmeasured illustration details are representative.
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Why this measurement?
Why we use 20 cm
For comparison, this page uses defined body length. This is labelled defined specimen: an explicit comparison model rather than a claim that every example has the same value. The recorded range is 12 cm to 30 cm.
A defined 20 cm Aplysia sea hare measured along the relaxed body. Species, maturity and posture vary greatly; extended oral tentacles are excluded.
The marked horizontal span follows the named feature; transparent margins and unmeasured details do not alter it. How calibrated comparisons work →
Recorded properties
Sea hare dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 20 cm | 12 cm to 30 cm | defined specimen |
Around this scale
Go smaller. Go bigger.
These links use compatible length records, ordered around the selected value.
Nearest lower value · Living thingsGeoduck17 cmA geoduck is a large burrowing marine clam with a comparatively small shell and a very long siphon.
Around the same scale · Living thingsBasket star20 cmA basket star is a marine echinoderm related to brittle stars, with repeatedly branching arms adapted for filter feeding.
Nearest higher value · Living thingsBrown rat25 cmA brown rat is a medium-sized rodent that adapts easily to urban and rural environments.Sources and method
Want to check the number?
The source records and measurement method remain available for inspection.
- Monterey Bay Aquarium — California sea hareSea-hare anatomy and broad size variation; the atlas uses a smaller defined Aplysia specimen.
There’s always another scale
Follow your curiosity.
Living thingsNudibranch10 cmA nudibranch is a soft-bodied marine mollusc, often brightly coloured, commonly known as a sea slug.
Living thingsSea angel2 cmA sea angel is a small, transparent swimming sea slug with wing-like appendages, found in cold ocean waters.Living thingsBasket star20 cmA basket star is a marine echinoderm related to brittle stars, with repeatedly branching arms adapted for filter feeding.
Everyday thingsCabbage head20 cmA cabbage head is the compact, leafy, edible part of a green cabbage plant, commonly used as a vegetable.
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SpaceVanguard 116.5 cmVanguard 1 is an early American satellite launched in 1958, notable for being the oldest human-made object still in orbit.
PeopleHand span20 cmHand span is the distance measured from the tip of the thumb to the tip of the little finger when the hand is fully extended.
Built worldBrick21.5 cmA brick is a rectangular block made from clay or concrete, commonly used in building walls and structures.