Shell trochoid, spire conical, base generally flattened, umbilicate or imperforate; interior of shell nacreous, exterior sculptured and calcareous, with nacreous sheen often showing through. Aperture rounded or oblique, smooth or lirate within, outer lip thin, base of columella thickened. Sculpture usually of smooth or beaded spiral cords. Operculum thin, corneous, circular, multispiral.
Swainson (1840) introduced the name Calliostoma without any designation of a type-species. His mention of Trochus zizyphinus as an example of the genus has been considered by some subsequent authors as monotypy. However, Swainson later in the same work (p. 351) listed 7 additional species with Trochus zizyphinus under Calliostoma, obviously not considering it a monotypic genus. I therefore agree with Woodring (1928) and Olsson (1971) that this does not constitute monotypy and that the subsequent designation of Trochus conula Martyn (=T. conulus Linnaeus) by Herrmannsen (1846) should stand.
The classification of Calliostoma has depended greatly on differences in shell morphology, especially the presence or absence of an umbilicus. This character has been used not only at the subgeneric level, but also to separate genera. However, Clench & Turner (1960) discarded this approach in favor of subgeneric groupings using jaw morphology and radular characters, since some species are umbilicate when young and become imperforate with maturity. They based their study on the jaws and radulae of 20 North Atlantic species, but since these characters have been recorded for so few species from other geographic areas, we must await further work along these lines to determine whether these groupings are valid.
What little is known of the natural history of this genus has been summarized by Clench & Turner (1960). Most authors have considered species of Calliostoma to be strict herbivores or detrital feeders. Perron (1975), in a study of 3 shallow-water species of Calliostoma, established that at least some members of the genus are carnivorous, feeding on hydroids. It is still probable that deep-water species are primarily detrital feeders but may be opportunistic predators of hydroids.
Calliostoma is widely distributed in tropical and temperate waters. As strictly defined it does not seem to enter Arctic or Antarctic waters, being replaced in the Antarctic by closely related genera such as Photinula Adams & Adams and Photinastoma Powell (Powell, 1951). The Calliostoma fauna of the western North Atlantic is rich, probably comprised of about fifty species.
Bathymetric range: From the intertidal zone to over 2000 m. The deepest Atlantic record is 2330 m for Calliostoma suturale (Phillipi) collected west of Morocco by the TALISMAN. In the western North Atlantic C. occidentale (Mighels & Adams) was taken alive in 1792 m by the BLAKE off Georges Bank, and several species were collected by the BLAKE in 1472 m in the Straits of Florida off Havana, Cuba.

Shell trochiform or turbiniform, 8-100 mm high, umbilicate or anomphalous, internally nacreous. Protoconch sculptured with network of threads that enclose roughly hexagonal spaces. First teleoconch whorl convex, subsequent whorls flat to convex or angulate; sculpture rarely absent, usually consisting of nodular spiral cords that multiply by intercalation (rarely by fission) and
axial riblets, the axials generally restricted to earliest whorls, though in some species persistent throughout. Operculum chitinous, thin, multispiral. Radula (adult) with the formula
oo + 1-17 + l + 17-l + oo, tooth morphology very diverse (see subfamily diagnoses); lateral teeth added incrementally by intercalation in the central field in Calliostomatinae, and by morphological transformation of marginal teeth in Fautricini. Jaw plates large, buccal musculature very strong. Cephalic tentacles elongate, tapered, papillate, well developed eyes on swellings at their outer bases in all species examined. Snout tip papillate, ventral lip split and rolled to form an incomplete tube (pseudoproboscis), dorsal lip with a cuticularised lining that extends into buccal cavity. Epipodium well developed with prominent neck lobes. Cephalic lappets large, small or absent. Up to five prominent epipodial tentacles on each side, side of foot papillate. Sexes separate. (See FRETTER & GRAHAM, 1962, 1977 for more detailed anatomical data).

SCULPTURAL FEATURES OF CALLIOSTOMA
PROTOCONCH. The calliostomatid protoconch is highly distinctive in having a sculptural network of crisp threads that enclose more or less hexagonal spaces, and in having a thickened apertural rim. Thread thickness, enclosed space size, overall protoconch size, and degree of exsertion (tilting) are interspecifically variable and intraspecifically highly stable. The shape of the tip of the apical fold may be rounded or tightly pinched, an obese protoconch evidently reflecting a large yolk supply. BANDEL (1982) has shown that the surface sculpture is secreted after deformation (folding) of the protoconch, presumably via solute transmission through the semipermeable outer shell layer at an early stage of mineralisation. The fully mineralised shell is almost perfectly bilaterally symmetrical, and so far no species have been noted in which the tip of the apical fold bulges abapically as in some trochids (HADFIELD & STRATHMANN, 1990). Incidentally, these latter authors misinterpreted trochids with abapically bulging protoconch tips as having "heterostrophic" shells. This is incorrect, because the archaeogastropod protoconch is asymmetrically (in this case) or symmetrically folded about an axis, and there is no accretionary shell growth.
TELEOCONCH I. All known calliostomatines exhibit a pronounced growth scar on the first quarter teleoconch whorl, the position of which is interspecifically variable though intraspecifically rather stable (Figs 2-3). Sculpture before the scar comprises 4-6 fine, crisp, similar spiral threads, and usually 1, 2 or more varices. Sculpture immediately after the scar is usually discordant (Fig. 2), though a few species exhibit a rather fluid transition to succeeding teleoconch sculpture, usually accompanied by a sudden increase in the strength of the spiral sculpture (Fig. 3). From descriptions of calliostomatids reared in aquaria (LEBOUR, 1936; HOLYOAK, 1988; RAMON, 1990; K. BANDEL pers. comm.), teleoconch accretion commences immediately or soon after formation of the terminal varix of the protoconch (here interpreted as the point of settlement). During the period of initial teleoconch formation the young evidently subsists on residual yolk, the resorbed velum, and perhaps dissolved organic matter, probably increasingly supplemented by detritus ingested from the substratum. It seems clear that the postlarval scar represents a growth pause or a crisis period and I suggest that it may denote the transition to exclusive detritivory (later transitional to carnivory). It may actually mark the transition to carnivory, at least in some species, though the radula may be insufficient to deal with Cnidaria or sponges at such an early stage of development. This interpretation is at variance with that of HICKMAN (1992: fig. 5G) who identified the terminal protoconch varix and the varix following it as denoting the times of hatching and settlement respectively. Note that the postlarval scar in the species illustrated by HICKMAN is situated immediately on the adapertural side of the varix following that denoted as time of "settlement".
TELEOCONCH II. With the exception of a few more or less smooth species, the majority of calliostomatids are sculptured with prominent (usually nodular) spiral cords and axial costae, the latter generally confined to the early spire whorls. There are usually four primary spiral cords (P1-P4, Fig. 1) on the early spire whorls, to which others are added by intercalation (rarely fission) of secondary spirals (SI-S3) and sometimes one or more tertiary spirals that may enlarge to resemble the primaries or secondaries. The number, spacing, relative size, rate of enlargement, position, point of origin, and cross-sectional shape of spiral cords are primary criteria for discrimination of species group taxa. Sculpture tends to be intraspecifically highly stable on the early spire whorls, and increasingly variable on later whorls, due primarily to intercalation of varying numbers of tertiary spirals at varying positions with varying rates of enlargement. Accordingly, for descriptions and discrimination of taxa, careful attention must be paid to the origin and development of individual
elements of the spiral sculpture by tracing them from the beginning of the teleoconch — mere counting of the number of spiral cords on particular whorls is virtually useless. Unequivocal objectivity can only be achieved through rigorous application of the excellent spiral designation system initiated by IKEBE (1942), which is reproduced here for convenience .

Sculptural features combine to produce an infinite variety of distinctive, intraspecifically stable gross shell fades, particularly on the early teleoconch. Natural (phylogenetic) groups segregated on the basis of highly distinctive radular morphology (e.g. Asteley Laetifautor, Fautrix gen. nov. and Thysanodonta) tend also to have distinctive early teleoconch facies. Nevertheless, even highly distinctive shell facies are typically impossible to quantify and very difficult to describe objectively (especially with verbal economy), so illustrations (SEM) are an integral component of my genus group diagnoses.

Diagnosis. Moderately high-spired, whorls flat-sided or rounded; final lip not thickened. Peristome incomplete, columella lacking folds or denticles, although somewhat thickened and truncate toward base; base usually with umbilical depression or open umbilicus. Early sculpture of beaded spiral cords, cords and beading either persisting or lost in later growth stages. Protoconch with reticulate sculpture and rounded pits. Color patterns often variegated; interior iridescent, exterior surface often showing metallic luster.
Remarks. All Calliostoma have a reticulate protoconch and early sculpture of three spiral cords. Although there are many generic-level taxa available as subgenera, efforts to arrange the worldwide members of the group into a meaningful scheme have not been successful.