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“Halystes chimaera n. sp.
Description. Shell up to 8.70 mm wide, turbiniform, broader than high, spire up to 0.76× higher than aperture, of moderate thickness, umbilicate. Nacreous beneath thin, translucent white outer shell layer.
Protoconch bulbous, 427 µm wide. Surface mostly eroded but that remaining sculptured with fine vermiculate granules.
Teleoconch of up to 5.6 convex whorls, reticulately sculptured with spiral threads and axial riblets. Spire whorls shallowly and rather evenly convex, broadly and evenly rounded around periphery to umbilical rim. Spiral threads multiplying by intercalation to total 4 on 1st whorl, 5 on 2nd, 9-10 on 3rd, 14-15 on 4th, 17-19 on 5th whorl, and at least 30 on base and outermost part of umbilical wall. Spirals thread-like on 1st 3 whorls with interspaces considerably wider than each spiral. On subsequent whorls spirals gradually broaden and interspaces narrow until as wide as or considerably narrower than each spiral in mature body whorl. Axial riblets collabral, regularly spaced, fine, crisp and thread-like, prominent at first then gradually weakening, becoming obsolete on body whorl. Umbilicus conical, diameter about 28% of shell diameter, rim narrowly rounded, inner wall with collabral growth lines and faint spiral lirae. Aperture subquadrate, outer lip thin at rim, thickened within; inner lip rather thick and simple. Posterior apertural notch very broad and shallow, its depth immediately behind apertural rim less than 2.3% of shell diameter. Lip swinging backwards to basal notch, which is deeper and narrower than posterior notch.
Animal (male holotype). Head broad. Snout quadrate and dorsoventrally flattened, concave in front with prominent lateral processes. Cephalic tentacles dorsoventrally flattened, gradually tapering, finely ciliated, the right larger. Penis long and thick, stouter than cephalic tentacles, arising immediately below base of right cephalic tentacle, laterally compressed, tapered at its tip alone, deeply medially grooved along outer face. Epipodial tentacles of moderate size, 6 on left and 5 on right. No eyes or accessory cephalic process. Operculum very thin, typical of the family. Female (paratype, Eltanin stn 346, USNM 859075) with head inclined to the left so that right cephalic tentacle extends along midline of foot of withdrawn animal. A long slender, tapering, grooveless tentacle arises immediately behind and outside base of right cephalic tentacle. Epipodial tentacles extremely large for the family and larger than in the male, tightly abutting, 7 on left and 6 on right, a group of 3 very small tentacles below base of the left cephalic tentacle. Other characters as in the male.
Radula (Fig. 4D–F) extremely small for the size of the animal, ribbon 400 µm long and 230 µm wide, cross-row formula c. 6 + 1 + 1 + 1 + c. 6. Central and lateral teeth very thin in section. Central longer than broad, subrectangular; cutting area narrowly tapered, edges smooth distally, finely serrated proximally. Laterals broad, cutting area narrowly tapered, edges smooth distally, finely serrated proximally. Marginals slender. Innermost marginal stout, outer marginals very slender with laterally expanded bases, terminal cusp very long and narrow, a few fine subterminal cusps on outer edge.
Dimensions (mm):
H
D
nW
8.6 (est.)
9.30
-
Paratype U.205
8.10
8.70
6.60
Paratype Eltanin Stn 346
7.70
8.00
6.60
Holotype
7.10
8.55
-
Paratype Eltanin Stn 1211
2.85
3.30
4.75
Paratype Eltanin Stn 364
Type data. Holotype NZOI H.456: U225, 37°39.7 'S , 162°15.5 'E, mid Tasman Sea, 4058-4077 m, 16 Oct 1982, RV Tangaroa. Paratypes (4): U.205, 35°48.6'S, 156º31.8’E, E of Sydney, alive, 4714-4548 m, 1 Oct 1982, RV Tangaroa (1 NMNZ), Eltanin Cruise 25, stn 346, 50º06'S, 127°31’W, S South Pacific Basin, alive, ♀, 3914 m (1 USNM); Eltanin Cruise 25, stn 364, 56°17'S, 156°13’W, S South Pacific Basin, alive, 3694 m, 11 Nov 1966 (1 USNM); Eltanin Cruise 14, stn 1211, 59°01’S, 159°50’W, S South Pacific Basin, dead, 3587-3816 m, 12 Aug 1964 (1 USNM).
Other material examined. A poorly preserved shell from Eltanin stn 346.
Known distribution. Tasman Sea and southern South Pacific Basin, 3587-4714 m.
Remarks. Halystes chimaera is characterised by its large size, turbinate shape, rounded whorls, fine reticulate sculpture, and broad and shallow apertural notches. See additional remarks under Halystes n. gen.”
(Marshall, 1988: 240-242)
