Scotch Bonnet (also known as the Banded Tun or Bonnet Shell)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Cassidae, Genus: Semicassis, Species: Semicassis granulata · Cassidae (Helmet and Bonnet family) · Gastropod (univalve) whole shell, spiral shape with a rounded, inflated body whorl
Species
Semicassis granulata
Shell Type
Gastropod (univalve) whole shell, spiral shape with a rounded, inflated body whorl
Family
Cassidae (Helmet and Bonnet family)
Size
Approximately 3 to 4 inches in length, which is a very typical and mature size for this species. Adults generally range from 2 to 5 inches.
Color & Pattern
Cream to light golden-tan base color adorned with distinct rows of square or rectangular reddish-brown spots creating spiral bands. The surface shows some weathering and sun-bleaching typical of beach specimens, muting the brightness of the pattern.
Rarity
Common to Uncommon. While beach specimens can be found by dedicated beachcombers after storms, pristine live-taken or high-grade specimens are less frequently encountered.
Habitat
Found in shallow subtidal waters down to moderate depths of about 150 feet, typically inhabiting sandy bottoms, offshore sand bars, and areas near coral reefs or seagrass beds.
Geographic Range
Western Atlantic Ocean, ranging from North Carolina through Florida, the Gulf of Mexico, the Caribbean, and down to Brazil.
Description
A sturdy, globular shell featuring a short spire and a remarkably large, inflated body whorl. The surface is finely sculptured with low spiral cords and faint vertical grooves, giving it a granular or textured feel. The outer lip is slightly thickened and often toothed internally, though the aperture is hidden in this viewing angle.
Key Features
Inflated, rounded body whorl, a relatively low and pointed spire, and distinctive spiral rows of square reddish-brown spots on a light background, combined with a finely beaded or granulated surface texture.
Collector Value
Moderately valued by collectors. While common beach finds have low monetary value (a few dollars), large, gem-grade specimens with exceptional color contrast and intact lips can be desirable for regional collections.
Condition Notes
Good condition for a beach-found specimen. It is largely intact with a solid structure, though it exhibits moderate surface wear, minor pitting, and sun-bleaching with some loss of vibrant color contrast. Collectibility grade is Good.
Interesting Facts
Bonnet shells are specialized predators that feed almost exclusively on sea urchins and sand dollars, using their acidic secretions and radula to drill into or pry open their prey.
Ecological Role
Acts as a key marine carnivore controlling sea urchin populations, thereby helping to maintain the balance of benthic ecosystems and preventing overgrazing of algae and seagrasses.
Similar Species
Other helmet and bonnet shells such as the Yellow Helmet (Cypraecassis testiculus) or the Smooth Bonnet (Semicassis cicatrosa), which can be distinguished by differences in size, sculpture details, and exact spot patterns.
Beach Finding Tips
Look along sandy ocean beaches in the southeastern United States, particularly after heavy offshore storms or tropical weather events. Low tide and the wrack line are ideal times and locations for discovery.