“3.1. Nautilus pompilius Linnaeus, 1758
Mature shell size variable, but typically about 165 mm (Philippines), with a total weight (body plus shell) of about 850 g. Shell has a small umbilicus (≈ 5% of shell diameter), filled with a callus (with rare exceptions); shell coloration variable, but generally comprises irregularly radiating brown stripes that extend from umbilicus to venter.
The type species of the genus (and the most common and widely distributed), N. pompilius appears to exhibit the greatest range in variation (Fig. 4). The diameters of 234 mature specimens caught during the 1979 ALPHA HELIX Expedition to the Tañon Straits, the Philippines, ranged from 150 mm (mature female) to 188 mm (barely mature male), with a mean of 165 mm. Sexual dimorphism is shown by slightly smaller females (mean diameter 160 mm) compared to males (mean 170 mm). Specimens of this species (provided by D. Dan) purported to have been caught live, off Tubbataha Reef, central Sulu Sea, the Philippines (Fig. 3C and D), are the smallest known representatives of this species, ranging from 103 to 126 mm in mature shell diameter, with a mean of 114 mm (N = 29). In Papua New Guinea, the average mature size of geographically isolated populations of N. pompilius varies considerably, from 144 mm (Lae, on the north coast of Papua New Guinea) to 169 mm (Kavieng, New Ireland Province), with an overall range in individual (mature) size of 124-199 mm in diameter (Saunders and Davis, 1985). Specimens of this species from Queensland average 153 mm in diameter (N = 5). The cause for the wide range in variation in mature size is not known; it may be genetic, or it may be related to ecological factors.
Variation in the pattern of shell coloration is manifest as differences in the amount of coloration, hue, degree of coalescence of banding over the venter, and development of color bands in the vicinity of the umbilicus. There appears to be a trend toward an increased proportion of shells with a white umbilical region, going southward through Papua New Guinea toward Australia (compare Fig. 2B, C, D).
The number of specimens with an open umbilicus (i.e., lacking an umbilical callus) does not appear to vary systematically; typically, fewer than 0.025% of live-caught N. pompilius in the Philippines and in Papua New Guinea show this curious abnormality (see also Mapes et al., 1979). In N. pompilius, the umbilical callus is secreted during the growth of the second whorl, at approximately 75- mm diameter in Philippine specimens.
In his description of N. pompilius, Linnaeus stated only that it "inhabits the Indian and African Ocean" (Turton, 1806, p. 305). However, because his reference to an illustration was that of Rumphius (1741, Plate 17, Figs. A–C), Amboina (Ambon), Indonesia (the source of the specimens illustrated by Rumphius), is the type locality for the species. Nevertheless, this species is best known from the Philippines, and it has been the subject of a number of studies (e.g., Griffin, 1900; Dean, 1901; Bidder, 1962; Haven 1972, 1977a,b; Hayasaka et al., 1982; Hayasaka, 1983: Cochran et al., 1981; Ward and Chamberlain, 1983; Arnold, 1985), particularly in the Tañon Straits, between Cebu and Negros, which was the site of research expeditions, based on the R/V ALPHA HELIX, in 1975 and 1979.*
Occurrences of N. pompilius in Fiji have been reported by Moseley (1892), Davis and Mohorter (1973), Ward et al. (1977), Ward and Martin (1980), Masuda and Shinomiya (1983), Zann (1984), and Hayasaka (1985). A single live animal is captured off Kagoshima Bay, south Japan (Tanabe and Hamada, 1978; JE-COLN, 1980b). Other reports substantiate the existence of living populations in the Andaman Islands (Smith, 1887) and the New Hebrides (Owen, 1832; Bennett, 1834), and this species is widely distributed in the Papua New Guinea region, including New Britain, New Ireland, Manus, Lae, and Port Moresby (Willey, 1895, 1896, 1897a,c, 1898a, 1899, 1902; Saunders and Davis, 1985; Saunders et al., 1987a). The existence of living N. pompilius from the Great Barrier Reef, Australia, has been established just recently with the capture of six specimens off Lizard Island, Queensland, at depths of 200-400 m (Saunders and Ward, 1987), and in 1986, 39 specimens were trapped outside Pago Pago Harbor, American Samoa (Saunders et al., 1987b). The even wider distribution of drifted shells of N. pompilius (see Chapter 4) makes it certain that many more occurrences remain to be discovered.
* For results of these expeditions, see the Journal of Experimental Biology, Vol. 205 (1978), and Pacific Science, Vol. 36 (1982).”
(Saunders, 1987: 39-41)