Helmets (family Cassidae) feed on sea urchins and sand dollars (Abbott 1968), including Diadema antillarum (Snyder and Snyder 1970).
The King Helmet feeds on several kinds of sea urchins and heart urchins (Rehder 1981).
In their investigation of Cassis tuberosa feeding choices when presented with various species of sea urchins, Hughes and Hughes (1971) found that when C. tuberosa were presented with equal numbers of similarly sized Echinometra lucunter (L.) and Tripneustes ventricosus (Lamarck), significantly more E. Lucunter were eaten. Diadema antillarum (Phillipi) Eucidaris tribuloides (Lamarck), Meoma ventricosus (Lamarck), and Mellita quinquiesperforata (Leske) were not eaten.
The King Helmet (Cassis tuberosa) is one of around 60-70 species in the gastropod mollusk family Cassidae (Helmet and Bonnet Shells), most of which (including the King Helmet) are found in shallow, tropical waters. Cassids feed on sea urchins and sand dollars that they encounter as they creep over the sand. (Abbott 1968; Rehder 1981)
The King Helmet (Cassis tuberosa) is found from North Carolina (U.S.A.) to Brazil; it is rare in Florida and northward, but common in the West Indies (and the most common of the true helmets in the Caribbean). (Abbot 1968; Rehder 1981)
The King Helmet (Cassis tuberosa) is found in sandy, shallow water habitats (Abbott 1968; Morris 1973; Rehder 1981).
The King Helmet (Cassis tuberosa) closely resembles the Flame Helmet (Cassis flammea), but when viewed from below it is more triangular than the Flame Helmet. The Flame Helmet (which occurs in the Lesser Antilles and only as far north as the Florida Keys) has a smooth, almost polished surface, whereas the King Helmet is marked with fine but sharp longitudinal lines. Unlike the Flame Helmet, the King Helmet shell has large dark markings on its outer lip and dark markings between the teeth on the outer lip. (Abbott 1968; Morris 1973; Rehder 1981)
The King Helmet shell is buffy or rufous yellow, mottled and blotched with various shades of brown. In addition to the brown stain between the folds of the inner lip, and the strong teeth lining the outer lip, there is a conspicuous patch of bright chestnut toward the posterior end of the aperture. The outer lips are rolled over and strongly marked with brown patches. (Morris 1973)
The shell of the King Helmet is 10-23 cm high. It is triangular, large and heavy, and yellowish-brown, with irregular, dark brown, zigzag, or crescent-shaped markings. The spire is low. The body whorl is large, with three spiral rows of triangular knobs, and a strongly latticed pattern of fine axial and spiral threads. The parietal shield is thick and the outer lip wide, together forming a strongly triangular apertural shield; the shield is pale brownish to pinkish white, with a large brown spot near the aperture. The inner side of the outer lip has 11 strong, short teeth; the spaces between the teeth are dark brown; the outer lip has squarish reddish-brown spots. (Rehder 1981)
The King Helmet feeds on sea urchins at night, apparently detecting its prey by chemoreception. It generally bores a single hole into the urchin test (the urchin's external skeleon) by cutting out a disc with its radula (a finely toothed feeding structure common to many mollusks, including gastropods, such as Cassis). All the internal tissue of the urchin except the gut contents is consumed. Afterwards, varying proportions of the spines and tube feet are eaten. (Hughes and Hughes 1971)
Despite its toxic sharp spines, even the black sea urchin (Diadema antillarum) is attacked and eaten by the Helmet Shell (Cassis tuberosa). Cassis tuberosa actively pursues the urchin and appears to overwhelm it physically, despite the phalanx of spines that Diadema brings to bear on any point of attack. Even for the tough-footed Cassis, this is an impressive feat, since the microneedle points of the spines are extremely sharp. When feeding on an urchin, Cassis tuberosa uses its long proboscis to probe among the spines to reach the urchin's body. Cassis also everts its proboscis when it is broken from its shell, and then usually squirts a jet of clear fluid in different directions, while thrashing its proboscis. This saliva is toxic to numerous marine organisms and conceivably could be used offensively as well as defensively. (Schroeder 1962; Cornman 1963)
