“Halystes n. gen.
Type species. Halystes chimaera n. sp.; Recent, abyssal Tasman and southern South Pacific Basins.
Diagnosis. Shell turbiniform, umbilicate, nacreous through translucent outer shell layer, spire whorls rather shallowly convex, periphery rounded. Teleoconch sculptured with fine reticulating spiral and axial threads. Aperture subquadrate, lips thin, inner lip simple, posterior notch very shallow and broad, basal notch shallow and broad, no peripheral notch. Animal of female with head inclined to the left, a slender tentacle extending from base of right cephalic tentacle. Male with centrally-placed head: Penis stout, laterally compressed, extending from base of right cephalic tentacle, grooved along outer face. No eyes or accessory cephalic process. Radula c. 6 + 1 + 1 + c. 6, similar to that in Seguenzia Jeffreys. Operculum multispiral.
Description. As for the type species (see below).
Remarks. Halystes differs from other nominate seguenziid genera in combining a rounded and turbiniform shell, fine and reticulate sculpture, and broad and shallow apertural notches. This genus has shell shape similar to that in Guttula Schepman, sculpture similar to that in Seguenzia Jeffreys, and apertural notches as in Basilissa Watson. By comparison, the holotype (BMNH) of Rotellenzia lampra (Watson, 1879), type species of Rotellenzia Quinn, 1987, is larger, flatter, more widely umbilicate, and has a more angulate shoulder notch and weaker sculpture on the early teleoconch. Seguenzia siberutensis Thiele, 1925 and S. simplex Barnard, 1963 (Seguenzia Group III of Quinn, 1983) are probably related, but differ in being both absolutely smaller and smaller relative to the number of whorls, with deeper and narrower shoulder notches.
The inclination of the female's head, which does not seem to be an artifact of preservation, and the presence, in the female, of a tentacle in a similar position to that of the penis, are characters hitherto unknown from the family. The latter structure indicates the need for caution when sexing seguenziid animals.
Etymology. Anagram of generic name Thelyssa Bayer (feminine).”
(Marshall, 1988: 238-240)
Halystes is a genus of extremely small deep water sea snails, marine gastropod mollusks in the family Seguenziidae.[1]
Species within the genus Halystes include:[1]
Halystes is a genus of extremely small deep water sea snails, marine gastropod mollusks in the family Seguenziidae.
