Vermetids are recognized by their coiled, wormlike shells which are cemented to hard substrates. The shells of gregarious species may be so numerous as to form vermetid reefs which have been described in the Cape Verde Islands (Crossland, 1905), along the Mediterranean shore of Israel (Safriel, 1966), and along the coastline
of Brazil (Kempf and Laboriel, 1968). In Hawaii one species, Dendropoma gregaria, which as its name implies is gregarious, is an intertidal zone former, veneering solution benches and boulders with a mat of shell several centimeters in thickness. Densities of D. gregaria on a bench at Diamond Head, Oahu, were estimated at 60,000/m2 (Hadfield and others, 1972). Four solitary species are also common in the intertidal; their coiled shells may be more than 40 mm in diameter. At least three small species of Dendropoma are associated with subtidal coral communities where they seem to be almost exclusively associated with coralline algal substrates.
Vermetids, because of their sessile habit, feed either by mucous net or by ctenidial cilia. In Dendropoma the pedal tentacles spin small droplets of mucus into fine threads which attach to the substrate near the aperture and become laden with diatoms and detritus. The food-laden threads are then rasped by the radula and jaws and ingested. Ciliary feeding involves the production of an inhalant current in the mantle cavity by the ctenidia; plankton and detritus are removed from the water current by mucus produced in the mantle cavity and the food-laden bolus of mucus is ingested.
Despite the sessile habit, sexes are separate and fertilization is internal, by large eupyrene sperm which enter the mantle cavity of the females. The eggs are brooded in capsules either in the mantle cavity or attached to the shell from which they hang suspended in the mantle cavity through a cleft in the pallial wall of the female. Hawaiian vermetids appear to reproduce continuously throughout the year and most produce small, hatching juveniles rather than swimming veligers.
The four genera recognized in Hawaiian waters may be keyed as follows:
1. Operculum present 2
Operculum absent; foot large, brightly colored Serpulorbis
2. Operculum small, concave; tubes tending to be loosely coiled
and rising above the substrate 3
Operculum elaborate, filling the tube and with an axial mamilla; shell entrenched or partially embedded in
the substrate Dendropoma
3. Shell with an internal lamella Petaloconchus
Shell without an internal lamella Vermetus