Scotch bonnets (or ‘ridged bonnets’) Semicassis granulata or Phalium granulatum are a medium-sized species of sea snail found in the tropical and subtropical western Atlantic from North Carolina to Uruguay. They are predators, foraging on sandy stretches of the ocean floor for echinoderms such as sand dollars, sea biscuits, and other sea urchins (Caution: ‘Oxford comma’)

  • It takes approximately six years for a Scotch bonnet to mature
  • The shells grows 2 – 4 ins long (5 – 10 cm), showing distinct growth stages
  • Scotch bonnets live on sand, usually in fairly shallow water (but see below)
  • The more a Scotch bonnet eats the more elaborate its shell, the glossier its sheen & the brighter its colours (research suggests this doesn’t work for humans)
  • Divers frequently find Scotch bonnets at depths of 50 – 150 feet (15 to 46 m). Specimens have been found in depths up to 308 ft (94 m)
  • Shipwrecks provide a good habitat for this species
  • Crabs are its main predators, crushing the shell to get at the occupant. Since the snails’ main defence mechanism is to withdraw into their shells, they urgently need to evolve a new tactic
  • The empty shell of this sea species is often used by hermit crabs
  • In 1965 the state of North Carolina made the Scotch bonnet its official state shell, in honor of the Scottish settlers who founded the state

The ridge on my shell, below, may be somewhat unusual. I haven’t found any images showing such a very distinct dorsal growth, though many show a sort of fault line there. STOP PRESS shell expert Colin Redfern explains: The dorsal ridge on your shell is a varix, indicating a previous position of the outer lip during the growth process. Varices on Scotch Bonnets are usually thicker (as in the image above).”

dear wiki: how kind to help

CASSIS RUFA (Cypraecassis rufa)

There are many different sorts of Phalium worldwide. By way of comparison, here is another type, Cassis Rufa, from the Pacific (commonly, east Africa to New Guinea). It’s colloquially known as a Bullmouth, Red Mouth or Grinning Mouth Helmet –  and also as a ‘Cameo Shell’, because it is often used for making cameos (see eBay for examples)

        [rh provenance / historical note: it’s not an area I’ve ever been to, nor am I likely to go. This shell was collected by my late father-in-law when he oversaw the building of the original Gan airstrip on Addu Atoll (Maldives) in… in…. many years ago, as a naval project. It is now ‘Gan International Airport’ and sells giant Toblerone & ‘Parfum de Jordan’ from the Katie Price ‘Scentsless’ range]

3 thoughts on “SCOTCH BONNET SHELLS (Phalium / Semicassis) ON ABACO

    • Hi Jess. Excellent question, and not one I had researched. I’ve done a quick bit of digging and the answer seems to be that these ridges are ‘denticles’, integral to the shell, usually at the aperture or just inside the shell. These are often, erroneously, referred to as ‘teeth’. In fact it is thought that the denticles of a gastropod act as aids in shell positioning (possible in ‘mooring’, predator deterrence (because they resemble teeth) , or calcium provisioning (but I can’t think how or why!). Not sure if that helps more than a little bit… RH


      • Thanks. I’m a high school oceanography teacher and one of my students asked me this when I was passing around this shell as we talked about marine gastropods. Still not sure I can give him a clear answer, but thanks for helping! 🙂



Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s