catseyeoperculums

CAT’S EYE OPERCULA
(Singular nouns: Fr-œil de chat opercule; Ger-Katzenauge Kiemendeckel; Nor-lokk/gjellelok; Rus-крышка)

A. Cat's Eye Operculum (diameter - 2.4 cm) from the turban gastropod Turbo petholatus Linnaeus, 1758: A. side originally attached to gastropod's foot; B. reverse side; C. view from side to show plano-convex shape of a cross-section. Collected by RVD from dredgings on the lagoon side of Kwajalein of the Marshall Islands during WWII. (© photos by Dick Dietrich)

B. Turban shell, tapestry or cat's eye turban (Turbo petholatus Linnaeus,1758) and cat's eye operculum (diameter - 2.4 cm) collected by RVD from dredgings on the lagoon side of Kwajalein of the Marshall Islands during WWII. (© photo by Percy A. Morris, taken 1947)

DESCRIPTION:   Operculum (plural, operculums or opercula) is the name given the door, sometimes designated plate or shield, that is attached to a gastropod's foot and serves, when the animal withdraws itself into its shell, as closure of the aperture of its shell; when closed, this virtually seals the animal within its shell thus protecting it from its predators and from physical and chemical stresses. Although most opercula are proteinaceous (i.e., they consist of "horny material"), those used as cat's eyes consist largely of the calcium carbonate mineral aragonite (Adegoke, 1973; verified by Henk K Mienis, personal communication, February, 2006). These calcareous opercula, which are from the gastropod Turbo petholatus Linnaeus, 1758 (class, Gastropoda; subclass, Prosobranchia; ... family Turbinidae; subfamily Turbininae) have shapes that resemble relatively low domes (Figure A-c). Their convex sides are multi-colored and glossy; their flat sides are chiefly white and porcelaneous.
   Colors - Typically, the just alluded-to multi-colored convex side is green, orange and white with color patterns similar to those shown on the photograph (Figure A-a); the chiefly white planar side has a thin brown spiral with its origin near the center (Figure A-b).   According to Yronwode (1995-2003), some reddish opercula from the western Pacific have also found widespread use in jewelry and decorative pieces. (To date, I have been unable to verify this.)
   H. 3; 3½ (Webster, 1975)
   S.G. 2.69-2.71; 2.70 - 2.76 (Webster, 1975)
   Light transmission - opaque
   Luster - convex side - waxy to subvitreous (almost mirror-like); planar side - porcelaneous.
   Breakage - irregular
   Miscellaneous - Most of those used in jewelry range between 1.25 and 2.5 cm in diameter. An ill-defined marginal flange occurs on some of these opercula. Being larbely CaCO₃, they effervesce (fizz) -- i.e., form bubbles of because of the liberation of CO₂ -- when dilute HCl (hydrochloric acid) is placed on them; and if the acid is placed on convex side the reaction modifies the luster. Some of these opercula exhibit a slight luminescence under long-wave ultra violet radiation.

OTHER NAMES: I have seen the following in the marketplace; I suspect there are others.

ambiliman - Tamil name (≃ 'the disc of the moon') -- See fifth paragraph under Remarks subheading.
Chinese cat's-eye - This name, perhaps the most common of the geographic based names, is also recorded in the literature (e.g., Webster, 1975, p. 507).
Guadalcanal cat's-eye - This name is sometimes given in lieu of shell cat's-eye; it does not, however, necessarily indicate that all so-named cat’s-eyes are from Guadalcanal.
"Moon-eyes" - See fifth paragraph under Remarks subheading.
New Guinea cat's-eye - another name sometimes given in lieu of shell cat's-eye -- This name does not, however, necessarily indicate that all so-named cat’s-eyes are from the New Guinea region.
Pacific cat's eye - widely applied general designation.
Pupu - Maori name for these cat's eyes -- According to Omeka (2005), which uses the coiled side of one of these "eyes" as its logo, "In Maori tradition, the spiral is seen as growth and new life, and is often ... represented through the unfurling of a new frond of a native fern.”
Shell cat's-eye - This name, in my opinion, is the best rather widely applied designation for these “cat’s eyes;” alternatively, they should be called cat's-eye opercula. Among other things, its use reduces possible confusion of these “cat’s eyes” and mineral cat’s-eyes – e.g., chrysoberyl and other minerals the cabochons of which exhibit well-defined light lines and have been designated cat’s-eyes for at least 300 years.

USES: These so-to-speak natural cabochons have found use in bracelets, charms, cuff links, pendants, earrings and even finger rings. Some jewelry -- e.g., pendants and bracelets -- has been fashioned with back to back pairs of these cat's eyes; and, rather surprisingly (at least to me), some earrings, finger rings and pendants feature the coil sides of these "eyes" (Figure C). Also, Webster (1975, p. 509) mentions another calcareous operculum "encountered in jewellery" -- it is "coloured white with a central eye of red colour, and in some cases the surface is covered with raised 'pimples'." -- (To date, I have been unable to determine any information about these opercula.) See the fifth paragraph under the REMARKS subheading for other uses of calcareous opercula from Turban shells.

C. Cat's Eye Operculum (diameter ~ 2.85 cm) pendant: This operculum was collected from a dead silver mouth turban shell (Turbo argyrostoma Linneaus, 1758) from Tonga. The pendant, fashioned by Marcus Bulstrode of Densizen Designs, is now in the National Gallery of Australia, Canberra. (© photo by Marcus Bulstrode (http://www.denizendesigns.com.au), from http://www.ArtsKuranda.asn.au)

D. Cat's eye Operculum?. The focus of this attractive piece, identified as a catseye (longer diameter ~ 4 cm), was found on the beach at Seal Rocks, New South Wales, Australia. It is described as “just as picked up” – i.e., neither polished nor having any coating. Considering its overall appearance, I suspect it is part of a gastropod shell rather than an opercula. (© photos by Stuart C. Bryce)

OCCURRENCES & NOTEWORTHY LOCALITIES: Gastropods of the Turbinidae family occur throughout the world. Their most common environments are relatively shallow water in subtropical and tropical seas. The local inhabitants of the Cocos-Keeling Islands, Eastern Indian Ocean, used to gather these opercula for preparing jewelry (Orr Maes, 1967, p.106). In a statement about turban snails and their opercula, Ruppert, Fox and Barnes (2004, p.309) note that they are "a common tropical Pacific and Indian Ocean taxon. [and] The heavy, calcareous operculum of the South Pacific species ... often washes up on beaches in large numbers.” [I suspect that here they are talking about turban snails in general.] However, such abundance for cat's eye opercula is recorded by statements such as “Turbos have a distinctive operculum (cat’s eye) that is harder than the shell. ... [which] means that it tends to survive well in middens. In some circumstances the opercula can form wave-washed concentrated drifts.” (Aboriginal Affairs..., post-2002); [and] "The shells ... are used in the mother-of-pearl industry... [whereas] the opercula ... are thrown away." (van Benthem Jutting, 1950). The fact that one can purchase these opercula for as little $.50 each in lots of 100 or more also seems permissively supportive of this abundance.

REMARKS: The word operculum comes from the Latin, operire meaning to cover.

Opercula such as those used as shell cat's-eyes are classified as spiral; other categories are concentric and lamellar. Of the spiral type, those from dextral gastropods spiral counter-clockwise, whereas those from sinistral gastropods coil clockwise. A large percentage of the shell cat's eyes used for jewelry and decorative items are from the typically sinistral gastropod Turbo petholatus Linnaeus, 1758 (class, Gastropoda; subclass, Prosobranchia; ... family Turbinidae).

Because of the relatively low hardness of shell cat's eyes, some potential uses – e.g., their use as ring stones -- have led to their being coated with some more durable material to make their exposed surface harder and less likely to be scratched. Unfortunately, when mounted with the eye side up, such coatings tend to diminish the natural luster, which is one of the desirable characteristics of these cat’s eyes.

"During the Victorian era, cat's eye shells were made into jewelry which was worn to ward off the evil eye ... Such jewelry was especially popular among sea-trading people like the British. It is likely that most of the cat's eye jewelry of this era was made by or for sailors and given as gifts to female relatives and lovers." (Yronwode, 1995-2003).

Opercula of Turbo species have had diverse uses other than those mentioned under the Uses subheading. A few examples follow: Small calcareous opercula have been used as eyes in masks and fetishes -- e.g., one "aus Holz geschnitzer Kopf des Nashornvogels mit enem turbodeckel as Auge" is illustrated by Pfeiffer (1914, Figure 12, p.15). Relatively large ones from Turbo marmoratus Linnaeus, 1758, which are sometimes called "moon-eyes," were used to ”pave” an ornamental garden path in Sabang, Pulau Weh Island, Sumatra -- photographs are shown by van Benthem Jutting (1950). "Some are so large as to be heavy enough for use as paper weights, quite two inches [= 5 cm] in diameter[;] ... in former days the Maoris of New Zealand used [opercula similar to those illustrated here] ...as eyes for their idols[;] ... [and] in booths within the main entrance to Rameswaram temple, [India, shell opercula are] for sale to the pilgrims and devotees ... [as] ambiliman, 'the disc of the moon'." (Hornell, 1951, p.6). "In beautiful Stewart Island [south of South Island, New Zealand] opercula are used for money." Webster, 1975, p. 509)

SIMULANTS: None, so far as I know. However, I cannot but believe there must be some on the marketplace, especially in the south Pacific and Pacific-ring areas.

REPLICAS: N/A

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