Invertebrates
Scallop
Pectinidae · also called scallops
Most bivalves stay put or burrow, but a scallop has an actual escape plan. Rows of simple eyes along its shell’s edge watch for danger, and when a slow-moving predator such as a sea star gets too close, the scallop claps its ribbed, fan-shaped shell together and jets away, a genuine swimming ability almost nothing else in its family shares.
Overview
The scallop, family Pectinidae, is a swimming bivalve mollusk found on sea floors in oceans worldwide. Rows of simple eyes along its mantle edge detect approaching predators, triggering a jet-propelled escape by rapidly clapping its shell.
An escape most bivalves never developed
While the majority of bivalve mollusks simply endure whatever comes their way, the scallop’s combination of light-sensing eyes and shell-clapping propulsion gives it a genuine, active defense most relatives in its own broader group never evolved.
Status
Least Concern collectively — common and widespread across suitable sea floor habitat in oceans worldwide, supported by managed commercial fisheries in many regions.
Scallop: common questions
How does a scallop actually swim?
A scallop swims by rapidly clapping the two halves of its shell together, using its powerful adductor muscle to force water out and jet the animal a short distance away, a genuinely unusual form of active movement compared with most other bivalve mollusks, which remain largely stationary or simply burrow into sediment.
Does a scallop really have eyes?
Yes, a scallop has numerous simple eyes arranged along the edge of its mantle, capable of detecting light, movement, and shadow, an unusual sensory feature among bivalves that helps the scallop detect an approaching predator early enough to trigger its jet-propelled swimming escape.
Why can a scallop escape a sea star but many other bivalves cannot?
A scallop's ability to swim by rapidly clapping its shell provides a genuine active escape option not available to most other bivalve mollusks, allowing it to put meaningful distance between itself and a slow-moving predator such as a sea star, which simply cannot match the scallop's sudden burst of jet-propelled speed.
What part of the scallop do people typically eat?
The part of a scallop most commonly eaten is its adductor muscle, the same powerful muscle responsible for rapidly clapping the shell together during swimming, valued commercially for its sweet, tender texture and forming the basis of a significant global fishery.