Range: W. and Central Pacific; probably also Indian Ocean (Mascarenes, Seychelles).

Description: Medium-sized to moderately large, moderately solid to solid; form vitulinus (Pl. 21, Figs. 16-19, see below) slightly heavier than typical form but its relative weight may vary by 50% among specimens of similar size. Last whorl conical or ventricosely conical; outline convex at adapical fourth, almost straight below. Shoulder angulate. Spire low, usually lower in form vitulinus; outline slightly concave, sigmoid or convex. Larval shell of about 3 whorls, maximum diameter about 0.8 mm. Teleoconch sutural ramps flat, often concave in late whorls, with 1 increasing to 5-7 spiral grooves; spiral sculpture occasionally weak on last 2 ramps. Last whorl with variably raised and granulose spiral ribs on basal third or fourth, sometimes weakly ribbed above; ribs variably spaced but usually more closely set toward base.

Ground colour white, sometimes suffused with cream to tan on last whorl, but rarely so on sutural ramps. In typical form (Pl. 21, Fig. 15), last whorl with a broad yellowish to dark brown spiral band on each side of centre, sometimes blending with adjacent areas but usually leaving a groundcolour band at centre and below shoulder; subshoulder band may be very narrow and interspersed with brown axial markings. In form vitulinus (Pl. 21, Figs. 16-19), last whorl with a broad tan to dark brown band on each side of centre, either solid or reduced and split into axial streaks and flames. Dark brown axial streaks or flames cross brown and intervening ground-colour bands; the latter spiral bands vary in width and are sparsely to heavily interspersed with dark brown axial markings. Both colour forms intergrade in numerous geographic localities. In both forms as well as intermediates, overlying dotted, dashed or solid brown to dark brown spiral lines may extend from base to shoulder, varying from few to numerous and from closely to widely spaced. Base and siphonal fasciole violet, often obscured by overlying dark brown. Apex cream. Late sutural ramps with variably numerous brown radial markings, often extending to subshoulder area in form vitulinus and intermediates. Aperture white, violet to brown at base.

Periostracum grey, yellow or brown, thin and translucent to thick and almost opaque, with tufted spiral lines on last whorl and sutural ramps; shoulders with slightly longer fringes (Kohn, 1959a; Cernohorsky, 1964; Chaberman, pers. comm., 1981; Pearson, unpubl. observ.).

Animal yellow. Dorsum of foot lighter medially, sometimes dotted with white laterally and anteriorly; marginal zones maculated with brown to black markings large and confluent at anterior end and clustered or absent at posterior end. Sole of foot dark yellow with pale flecks, sparsely mottled with brown. Rostrum dark yellow, proboscis somewhat paler. Siphon pale yellow, edged with darker yellow, with a blackish brown ring 1/3 or 1/2 the length from the tip (Pl. 75, Fig. 38; Pl. 79, Fifth row, left) (form vitulinus; Kohn, 1959a; Chaberman, pers. comm., 1981; Pearson, unpubl. observ.)

Radular teeth of form vitulinus small, with an adapical barb opposite a long second barb; a double row of prominent denticles forms a serration as long or twice as long as second barb; base with a distinct spur (James, 1980; Kohn, unpubl. observ.).

Habitat and Habits: Intertidal to about 60 m; on reef rock beneath dead coral, sand bottom with algae, and on coral and rubble. In Hawaii, form vitulinus epifaunally in 0.6-55 m, uncommonly on subtidal reef flats and more commonly in 16-40 m (Kohn, 1959a, b; Cernohorsky, 1964; Kay, 1979; Estival, 1981; Tirard, pers. comm., 1989). In Hawaii, form vitulinus feeds on eunicid polychaetes (Kohn, 1959b). Its egg capsules are deposited in irregular clusters affixed to the underside of rocks by confluent basal plates. Capsules of about 23 x 16-17 mm contain eggs 225 µm in diameter, suggesting a minimum pelagic period of about 21 days (Kohn, 1961a; Perron & Kohn, 1985).

Discussion: This species is closely allied to C. ferrugineus, C. striatellus, C. circumactus and C. swainsoni; for comparison with the latter three species, see the Discussions of those species. Form vitulinus sometimes also resembles C. litoglyphus; for the distinctions see the Discussion of the latter species. C. planorbis is not distinguishable from C. ferrugineus by size and shape of the shell. The only reliable difference is the uniformly white aperture of C. ferrugineus, in contrast to the violet to violet brown base of the aperture in C. planorbis. In addition, the white subshoulder band of C. planorbis rarely occurs in C. ferrugineus, and the granulose ribs on basal part of last whorl are often light coloured in C. planorbis but usually overlaid with a dark spiral line in C. ferrugineus. The violet colour of the basal end of the shell (most pronounced within the aperture) is a distinctive character of this species. It is present in the lectotypes of both C. vitulinus and C. planorbis. As specimens intermediate in colour pattern between C. planorbis and C. vitulinus occur in most populations that consist primarily of one of these variants, we consider both to represent forms of the same species. For the assignment of C. vulpinus Hwass to C. planorbis, see the Discussion of C. ferrugineus. A local population from Kwajalein, Marshall Is. (Pl. 21, Fig. 20), characterized by Pearson (1988) as "golden cones," has very similar shell characters and animal colouration to C. planorbis form vitulinus. The shells are 34-56 mm long. They differ from the sympatric form vitulinus in the light yellowish brown rather than dark brown pattern on both last whorl and spire, and in the absence of the violet brown colour of base, siphonal fasciole, and anterior end of the aperture. The thin and very translucent periostracum bears spirally arranged bristles on the last whorl and has fringed shoulders. The animal shades from light to dark yellow. The dorsum of the foot bears many white and scattered brown spots that are larger and more closely spaced along the lateral margins and across the anterior part. The sole of the foot has a brown mottling that is heavier laterally and forms a broad transverse band of axial stripes close behind the distal edge. The rostrum is dark yellow, while the tentacles are pale except for their tips. The siphon grades to cream or white distally, has a yellow distal edge and a black transverse band halfway back from the tip (Pl. 79, Fourth row, right). The animals occur epifaunally among living and dead coral in 1-3 m in the lagoon (Pearson, unpubl. observ.). We provisionally assign this population to C. planorbis. Similar shells are also known from W. Samoa (Plate 21, Fig. 21).

C. planorbis range map

This section contains verbatim reproductions of the accounts of 316 species of Conus from the Indo-Pacific region, from Manual of the Living Conidae, by Röckel, Korn and Kohn (1995). They are reproduced with the kind permission of the present publisher, Conchbooks.

All plates and figures referred to in the text are also in Röckel, Korn & Kohn, 1995. Manual of the Living Conidae Vol. 1: Indo-Pacific Region.

The range maps have been modified so that each species account has it own map, rather than one map that showed the ranges of several species in the original work. This was necessary because each species account is on a separate page on the website and not confined to the order of accounts in the book.