Description: Moderately large to large (50-110 mm), solid to heavy. Last whorl conical; outline largely straight, variably convex adapically; in form fuscatus, outline often slightly concave at upper two-thirds and straight below. Shoulder angulate, strongly to sometimes weakly tuberculate. Spire usually low; outline slightly concave to slightly sigmoid, often with domed early postnuclear whorls and a projecting larval shell surmounting an otherwise flat spire. Postnuclear spire whorls distinctly tuberculate. Teleoconch sutural ramps flat to variably concave; 4 increasing to about 10 spiral striae on late ramps. Last whorl with weak to obsolete spiral ribs at base.
Ground colour white to bluish grey (blue tint more common in form fuscatus). Colour pattern of last whorl maximally variable in the Indian Ocean.
Pacific shells: Last whorl encircled with 2 brown or olive bands. Bands variable in width, usually distinct, occasionally split into axial streaks and blotches. Adapical band occasionally divided in two. Spiral rows of alternating blackish brown and white dashes extending from base to shoulder; rows variable in number and arrangement. Variably numerous spiral rows of fine to minute brown dots, partially alternating with white markings in irregular sequence, also extending over entire last whorl. Base, siphonal fasciole and basal part of columella dark bluish grey, occasionally suffused with brown.
Indian Ocean shells : Some specimens have a pattern typical of Pacific shells; others vary widely. Spiral bands vary from brown to blackish olive or almost black. They may either be very wide, covering entire last whorl, or be reduced to sparse flecks. Bands often split into fused or separate patches and axial flames or blotches.
Teleoconch spire immaculate white to bluish grey in early whorls; late ramps with orange to nearly black radial streaks and blotches. Pattern elements variable. Aperture white to violet, except for a dark violet to brown base, rarely extending to shoulder along outer margin. Periostracum olive to orange, thin, translucent, smooth (Hawaii; Marshall Is.; Fiji; Philippines; Madagascar).
Animal dominated by various shades of red: In the Marshall Is., anterior part of dorsum of foot purple and red; central part white, mottled with brown, with white dots. In N. Papua New Guinea, dorsum of foot white to light pink, dotted with white and radially mottled with shades of red or purple; pale blackish brown dots set off a narrow solid red marginal zone; anterior half of dorsum solid red toward front and with black dots arranged in 2 mediolateral lines.

Sole of foot pink, washed or mottled with red and brown, darker red anteriorly. Rostrum, tentacles and siphon violet, streaked and mottled with reddish brown, with white dots; rostrum and tentacles may also be solid dark pink.
Radular teeth stout, with a short adapical barb opposite a second large barb, both perpendicular to a complex row of serration; serration consists of a double (to triple) row of denticles and terminates in an internal barb slightly posterior to the second barb; base with a distinct spur.

C. imperialis is most similar to C. zonatus but cannot be confused with any congener.
Typically patterned shells from the Indian Ocean tend to have weaker shoulder tubercles and sometimes have relatively broader last whorls than shells from the Pacific. Wils (1970) and Coomans et al. (1985a) considered the latter populations as a separate subspecies, C. L compact us , but this form occurs sympatrically with specimens agreeing with the description of C. fuscatus.
The name C. fuscatus applies to shells from the W. Indian Ocean having a narrower last whorl, usually darker colouration, and irregular pattern with mainly axial orientation. This form occurs sympatrically with the typical form in Kenya and Zanzibar (in slighly greater depths) as well as Mozambique (in different micro-habitats). The two forms intergrade in colour pattern and shape (RD 0.50-0.63 in form fuscatus and 0.57-0.68 in sympatric typical shells; PMD 0.87-0.97 and 0.84-0.92). We therefore regard C. fuscatus as a form of C. imperialis and not as a sibling species or geographic subspecies. Synonyms include C. viridulus , C. coronaducalis, C. queketti (a subadult specimen), C. i.flavescens, C. i. nigrescens, C. douvilleiy and C. daulzenbergi.

Range: Entire Indo-Pacific except For Red Sea.
Habitat and Habits: Intertidal to 75 m; in Philippines, dredged to 240 m. In Hawaii, C. imperialis on subtidal coral reef platforms, on fine to coarse sand, reef limestone with or without algal turf, and on coral rubble as well as dead coral. In Fiji, in sand under coral and in sand pockets of coral reefs (Cernohorsky, 1964); in New Caledonia, in 1-25 m inside the lagoon, on coarse sand bottom and dead coral of platforms exposed to waves (Richer de Forges & Estival, 1986; Tirard,pers. comm., 1989); on the Great Barrier Reef, subtidally in lagoons (Huish, 1978); in Indonesia, subtidally on lagoon reef platforms and seaward reef platforms (Kohn & Nybakken, 1975; Kengalu, 1980) and also reported from coral rubble at low tide level. In Mozambique (Grosch, pers. comm., 1989), typical C. imperialis intertidally close to the infralittoral fringe on pure sand bottoms; form fuscatus in depressions, holes and crevices of rocky ledges and seldom on coral sand. Although both forms live syntopically in Mozambique, they do not share the same microhabitat. The rocky bottoms, on which form fuscatus occurs, are covered with crustose coralline algae, as are the shells of the living animals, whereas more typical C. imperialis exhibits hardly any encrustation. However, in Pacific localities C. imperialis often has heavy encrustations of coralline algae on its shells. In Reunion, form fuscatus ranges from slightly subtidal habitats to 50 m. C. imperialis is known to feed almost exclusively on polychaetes of the family Amphinomidae ("fireworms"); Eunicidae are rarely consumed; the radular teeth share characteristics with those of other Conns species that prey on amphinomids (Nybakken, 1970). In Hawaii, the species has been observed ovipositing in a depression in 0.3 m. Capsules are skewed to one side and are 18-20 x 12-13 mm. Each capsule contains about 6,000 eggs of 225 µm diameter, suggesting a minimum pelagic period of 21 days. In Palau, egg diameter is 265 (im, indicating a minimum pelagic period of about 18 days. In the Seychelles, dense clusters of capsules are deposited in shallow water. Capsules are affixed to the substratum by confluent basal plates and to other previously laid capsules. Number of eggs per capsule varies from 2,300 to 4,300, and capsules measure 18-19 x 11-12 mm.