Comprehensive Description

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Description

Eucominia olsoni n.sp. Fig. 124.

 

Shell large, of similar build to nassoides (Reeve), but with deeply channelled sutures. Whorls 9, including a large, dome-shaped protoconch of 3 whorls. Sculp­ture of strong axial folds with fine, smooth growth lines crossed by rather wavy, microscopic spiral grooves, the axials becoming obsolete across the last half of the body whorl. Twelve axials on the penultimate, 18 on the body whorl. A short distance below the suture on the spire whorls a shallow groove separates a single series of large, rounded subsutural nodules from the lower axials. Subsutural nodules becoming stronger on the penultimate and body whorl. Antepenultimate and penultimate with two rows of strong nodules on the axials, around the centre of the whorls, and on the body whorl. Basic colour reddish-brown, with the nodules clear white. Dots of white continue across the body whorl corresponding to the position of the nodules, where the nodules themselves have become obsolete. On the body whorl a row of white, rather elongate spots runs from the sutural level, with a second, smaller row below. A few deeper spiral grooves around the base. A longitudinally striated fasciole is separated from the body whorl by a very narrow raised rib. A deep, oblique, anterior siphonal notch. Suture deeply chan­nelled.

 

 

                                 
 

 
 

Height

 
 

Diameter

 
 

Height of spire

 
 

Holotype

 
 

55.4 mm.

 
 

28.0 mm.

 
 

27.5 mm.

 
 

Paratype

 
 

37.8 mm.

 
 

20.0 mm.

 
 

19.2 mm.

 
 

Paratype

 
 

34.0 mm.

 
 

20.5 mm.

 
 

16.0 mm.

 
 

Paratype

 
 

32.1 mm.

 
 

17.2 mm.

 
 

15.5 mm.

 
 

 

Holotype (M. 9776) and paratypes in Dominion Museum, paratypes in Can­terbury Museum.

 

Localities : C.I.E. Station 2, Mernoo Bank, in 61 fathoms (type); C.I.E. Station 3, Mernoo Bank, in 41 fathoms.

 

This species is amply distinguished from all other species of Eucominia by the channelled suture and the shoulder. Well-preserved specimens show the distinctive colour pattern. The holotype is the only specimen obtained from Station 2. Four paratypes were collected at Station 3. One of these (the largest, though much smaller than the holotype) has a thin outer lip and definitely appears subadult. The other three specimens (32 to 34 mm. in length) all have a thickened outer lip and appear to be adult. Two of these are proportionately much wider in the shell than the three other known specimens. The matter is stressed because of the very variable shell characters in other Eucominia populations and because it supplies another probable example of nanism in deep-water mollusca.

 

This species, one of the finest in the genus, is named in memory of the late Mr O. P. Olson, Paleontologist to the New Zealand Geological Survey. Radula (Fig. B, 4) of the usual Eucominia type with a tricuspid central tooth (the cusps of which are subequal) and a bicuspid lateral on either side.”

 

(Dell, 1956: 95-96)

Trusted

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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