Comprehensive Description

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Description

Penion benthicola n.sp. Figs. 125, 130, 131.

 

 

Shell small for the genus, rather like chathamensis Powell but with much finer sculpture. Whorls 7½ in holotype, protoconch missing; the smaller paratype has a protoconch of 3½, slightly convex, white whorls followed by 6 shell whorls. Height of aperture plus canal, 1.14 to 1.19 times the height of the spire (holotype 1.17). Whorl outline strongly convex, slightly subangled below the suture. The sculpture consists of very fine spiral grooves which are comparatively equally developed, there being no primary spirals. These spirals number from 20 to 30 per centimetre on the penultimate whorl. There are also low, regular, vertical axial folds on the spire whorls, becoming obsolete across the body whorl. The larger paratype is somewhat worn and loses these axials earlier. There are 16 to 19 axials on the penultimate whorl. The columella is strongly twisted. Colour chalky white in the holotype (living shell) and larger paratype, light orange in the smaller paratype. Colour of aperture and the inner lip orange in the smaller paratype. The holotype has a raised tooth-like callus high up on the parietal wall, but this is obviously the result of an injury. Spire angle 42° (holotype), 40° and 41° in paratypes.

                            
 

 
 

Height

 
 

Diameter

 
 

Spire

 
 

Holotype

 
 

102 mm.

 
 

38 mm.

 
 

47 mm.

 
 

Paratype

 
 

96 mm.

 
 

37 mm.

 
 

44 mm.

 
 

Paratype

 
 

75 mm.

 
 

29 mm.

 
 

35 mm.

 
 

 

Holotype (M. 9775) and paratype in Dominion Museum, paratype in Can­terbury Museum.

 

Localities: C.I.E. Station 6, Chatham Rise, in 220 fathoms (type); C.I.E. Station 7, Chatham Rise, in 280 fathoms.

 

Although this species agrees with the ormesi series in sculpture and shape, it has an operculum without the white callus along the outer margin of the muscle scar, and apparently has a white protoconch. Thus it collies between the two series of Powell (1947). Fleming (1954, p. 1057) has shown that Penion should be used for the group of shells previously known as Verconella.

 

The radula of benthicola (Fig. B, 1) proves to be rather different from that described for any other species of the genus. The ribbon bears a row of centrals flanked on each side by a row of laterals, but the base of the central is much deeper than in other species and the laterals bear four cusps. This suggests that the new species would be better placed in another genus (and almost certainly a new one would be required). However, the radulae of some species of Penion from southern waters are variable. For example, Penion dispar Powell, from off Cape Campbell, has a peculiar central with a bifid central cusp flanked by a greatly reduced cusp on each side (Fig. B, 11). Penion jeakingsi Powell, from off Kapiti Island, has a central with a squarish base (as in benthicola) bearing a single cusp, near the base of which a vestigial cusp may be developed on one side or on both (Fig. B, 7). Such variation in radular characters within the group indicates that, although such forms as dilatata (Q. & G.), mandarina (Duclos), adusta (Philippi), and ormesi (Powell) may conform to a simple, fairly consistent pattern, such southern shells as dispar (Powell), jeakingsi (Powell), and possibly benthicola n.sp. present more discordant features. Before the problem can be fully considered, the radulae of fairfieldae (Powell), worthyae (Powell), and the elongata series must be studied.

 

The general features of the animal of P. benthicola are shown in Fig. 261.”

 

 

(Dell, 1956: 96-97)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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