Rock Shells (muricidae)

There are over 1300 species of muricid shells worldwide. They are very popular with shell collectors because of their sculptured shells.

Murexs are one of the best-known and distinctive mollusc families. Many species make good food. Empty shells become homes for hermit crabs. The murexs are bizarre in shapes and covered with coralline algae (which acts as a camouflage). Vermitid worms also inhabit the surface of the murex shell often boring their way in. Shell dealers clean these coverings off with hydrochloric acid to make the shells more appealing to buyers. The tips of large adult shells are often eroded. The area around the aperture of the murexs is often beautifully coloured. The cover to the shell opening (called the periostracum) protects the animal from predators and from desiccation.

A purple dye is secreted by some Mediterranean species and used to dye tunics for royalty during the height of the Roman Empire. The dye is toxic to many marine animals except mammals and provides protection.

The first fossil records are from the Cretaceous Period (about 146-65 million years ago). Shell sizes vary from 6mm to 300mm or more. The largest Murex is Chicoreus ramosus which is featured on the $2 stamp.

The murexs belong to the Animal Kingdom in the phylum Mollusca, Class Gastropoda, subclass Prosobranchia and family Muricidae. The taxonomy is based on radula shape (teeth shape) and the shell morphology.

The shell colour can be purple, brown or orange. The degree of bizarre sculpturing is influenced by environmental and genetic factors.

Murexs have a single shell, which is formed by the mantle. Coiled body with a flat sole-like foot, developed sensory organs, a well-developed radula feeding apparatus. The radula (modified teeth) is used to bore tiny cylindrical holes through the shell of the prey and bring the proboscis (tongue) to it.

The life history is simple. The larval stage is a free-swimming planktonic veliger, which then settles out as an adult to a benthic way of living. The larval stage aids in its dispersal. Murexs are slow moving.

The reproductive cue is activated by rising water temperature. Internal fertilisation takes place. There are male and female. Sexual dimorphism is indicated by teeth shape.

Murexs live on rocky or rubble bottom or mud ooze or coarse sand. Murexs avoid soft oozy muddy bottom because they cannot move or feed freely in this habitat.

69 cents: Murex sauli (Sowerby, 1841). Common name: Saul’s Murex. It is up to 100mm long. Light rusty orange-brown. Heavily sculptured. Found from Japan to Fiji. It is uncommon and is sought after by shell-collectors.

96 cents: Murex tribulus (Linnaeus, 1758). Common name: Caltrop Murex Creamy white to pale tan. Shows polymorphism in spine length. They live in muddy areas and feed on mussels but will climb on gill nets to eat gilled fish and often get caught themselves. Murex tribulus is dangerous to step on. It is a voracious predator, using its rasping organ to feed. Shell-collectors are always seeking the perfect specimen (with unbroken spines), which is difficult to find.

$1.00:. Drupa morum (Roding, 1798). Common name: Purple Pacific Drupe. It is a purple aperture, 18-49mm long. Found on the windward or exposed reef flats, associated with algal ridges and constantly moistened by the breaking surf. It is omnivorous and common. Encrusted with algae, coralline algae and vemetid worms. Well blended into the substrate. It is preyed on by Conus textile. It is found in the Indo-Pacific from the Red Sea to Galapagos Islands. This species was put in the family Thaidinae previously (now Thaidinae is a subfamily of Miricidae). There is a subspecies found in eastern Polynesia.

$2.00: Chicoreus ramosus (Linnaeus, 1758). Common name: Ramose Murex Massive. Low spire. Large body whorl. Big aperture. Periostracum is corneous and brown. White shell often encrusted with algae. Found in the Indo-West Pacific. Popular with shell-collectors and decorators. It is common and is a popular food species for humans. Up to 300mm long.

If you are interested in further information on Fiji’s shells, please contact me by e-mail. I would be happy to communicate with you. E-mail: seeto_j@usp.ac.fj