Slipper Snail, Slipper Limpet, or Boat Shell
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Calyptraeidae, Genus: Crepidula, Species: Crepidula aculeata · Calyptraeidae (Slipper snails and Cup-and-saucer shells) · Gastropod (univalve); Cap-shaped shell. This specimen is a whole shell with a common acorn barnacle (Crustacea) attached to the exterior dorsal surface.
Species
Crepidula cf. aculeata (with attached Barnacle)
Shell Type
Gastropod (univalve); Cap-shaped shell. This specimen is a whole shell with a common acorn barnacle (Crustacea) attached to the exterior dorsal surface.
Family
Calyptraeidae (Slipper snails and Cup-and-saucer shells)
Size
Approximately 15-25mm in length. This is a standard size for adults of this species in the Moreton Bay region.
Color & Pattern
Dull white to grayish-brown with subtle mauve or purple radiating streaks and speckling. The interior typically features a white shelf or 'deck'. The attached barnacle is a chalky white color.
Rarity
Very Common. These are frequently found on beaches in the Brisbane area, especially after tides wash up debris from the seagrass beds and mudflats.
Habitat
Intertidal and shallow subtidal zones. These are sedentary mollusks often found attached to rocks, other shells (like oysters), or debris in muddy-sandy environments like those found around Sandgate.
Geographic Range
Found throughout the Indo-Pacific, including the coastline of Queensland, Australia; common in sheltered bays like Moreton Bay.
Description
An oval, cap-like shell with a small, slightly coiled apex shifted to one side. The exterior is rugose and bumpy, often covered in prickly scales or spines (though these are eroded in this specimen). The interior contains a horizontal, shelf-like platform called a septum, which resembles the deck of a boat or the inside of a slipper.
Key Features
Distinguished by the horizontal internal septum (shelf) covering roughly half of the aperture and the slightly asymmetrical, coiled apex. The presence of a symbiotic or hitchhiking barnacle on the exterior is a common feature for these sedentary shells.
Collector Value
Low. This is a common 'beach-find' shell in Brisbane. While interesting due to the attached barnacle, it is not a high-value collector's piece and is usually kept as a representative specimen of local intertidal life.
Condition Notes
Fair to Good. The shell shows significant environmental wear (erosion), which has smoothed down its characteristic prickles. The attachment of a barnacle adds biological interest but technically obscures the shell's natural sculpture. Collectibility grade: Fair.
Interesting Facts
Slipper shells are protandric hermaphrodites; they start their lives as males and later transition into females. They often live in 'stacks' where the larger individuals at the bottom are female and the smaller ones on top are male.
Ecological Role
Suspension feeders; they filter plankton and organic detritus from the water. They provide substrate for other organisms (like the barnacle seen here) to grow upon. They have no major conservation concerns.
Similar Species
Crepidula convexa (usually smoother and more convex) or Crepidula fornicata (larger and smoother). It can be distinguished from true limpets by the internal shelf.
Beach Finding Tips
Look along the high tide line at Brighton Beach or Sandgate during low tide. They are often found attached to discarded oyster shells or tucked into the crevices of rocky groynes.
Notes
Brighton beach Sandgate Brisbane