Slipper Limpet, Boat Shell, or Half-Slipper
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Calyptraeidae, Genus: Crepidula, Species: Crepidula aculeata · Calyptraeidae (Slipper Limpet or Cup-and-Saucer family) · Gastropod (Univalve). Fragment of a cap-shaped shell featuring an internal shelf or deck.
Species
Most likely Crepidula aculeata (Prickly Slipper Limpet) based on local Australian distribution; 85% confidence due to erosion.
Shell Type
Gastropod (Univalve). Fragment of a cap-shaped shell featuring an internal shelf or deck.
Family
Calyptraeidae (Slipper Limpet or Cup-and-Saucer family)
Size
Approximately 20-30mm in length. This is standard for adult Crepidula species found in Queensland waters.
Color & Pattern
Dull chalky white to cream. The exterior is heavily eroded and sun-bleached, losing the typical brown mottling or radiating lines. The interior shelf (deck) is white with some yellowish calcification and visible pitting.
Rarity
Common. These shells are frequently washed up on the beaches of Moreton Bay, though often as worn fragments like this specimen.
Habitat
Intertidal and shallow subtidal zones. These are sessile animals that attach themselves to rocks, other shells (often oysters), or debris in sandy/muddy areas like Moreton Bay.
Geographic Range
Globally distributed in warm temperate to tropical waters; specifically common along the coast of Queensland, Australia, including Sandgate/Brighton Beach.
Description
A worn fragment of a slipper-shaped gastropod. The shell is characterized by its flattened, oval shape and a distinctive horizontal internal shelf (septum) that covers roughly half of the aperture. This specimen shows heavy bio-erosion (pitting) and skeletal remains of serpulid tube worms on the interior.
Key Features
The most diagnostic feature is the internal 'deck' or shelf which gives the shell its 'slipper' appearance. The apex is posterior and slightly turned to one side.
Collector Value
Negligible ($0-$1 USD). It is a common 'beach-find' rather than a high-end collector specimen. Its value lies in its biological interest and its presence as a local record of Moreton Bay fauna.
Condition Notes
Poor to Fair. The shell is a beach-worn fragment with significant erosion, sun-bleaching, and numerous sponge borings (small holes). It features encrusting tubeworm remnants. Collectibility is low as a specimen, but high as a 'beach find' curiosity.
Interesting Facts
Slipper limpets are sequential hermaphrodites; they often live in 'stacks' where the large individual at the bottom is female and the smaller ones on top are male. As the female dies, the male above her changes sex to become the new female.
Ecological Role
Suspension feeders that filter plankton from the water column. They provide substrate for other organisms (epibionts) and serve as a food source for predatory snails and crabs. No conservation concerns.
Similar Species
Crepidula convexa (usually smaller and darker) or Maoricrypta costata (ribbed slipper shell). Distinguished from true limpets by the presence of the internal shelf.
Beach Finding Tips
Look in the drift line at low tide, especially near rocky groynes or oyster beds at Brighton Beach. They are often found attached to larger dead shells or inside the apertures of hermit crab-occupied shells.
Notes
Brighton beach Sandgate Brisbane