Galeodea triganceae Dell 1953

“Galeodea triganceae n.sp. (Figs. 1-4)

Shell of moderate size, rather globose, diameter about two-thirds the height, spire about one-third the height. Protoconch of two smooth whorls, limits not clearly defined. Post-nuclear whorl with about 11 spirals crossed by weak axials. Second whorl developing two stronger spiral keels, the lower at first stronger, the upper forming a definite shoulder fairly close to the suture, the lower slightly above the lower suture. Penultimate whorl with two subequal strong spirals which continue across the body whorl. On the penultimate, there are four weak spiral threads on the shoulder, six weak spirals between the two strong spirals, and three weak threads below the lower strong spiral. On the body whorl, there is a moderately strong subsutural cord, five weak spirals on the shoulder, eleven spirals between the two strong spirals, and thirty-eight across the rest of the body whorl, base, and canal, every second or third spiral being relatively more strongly developed. All whorls after the nucleus crossed by axials which render the strong spirals nodulous, 26 to 31 on penultimate, 22 to 25 on body whorl. These nodules develop into rounded knobs. Suture somewhat impressed, bordered by a spiral cord. Aperture produced into a fairly long twisted anterior canal. Outer lip as it approaches aperture thickened by a deposit of callus, but actual edge of outer lip sharp. Inner lip thin, spread across parietal wall, but projecting lower down to form an umbilical chink and on the base a fasciolar umbilicus. Columella straight and smooth. Operculum very similar to that in G. echinophora (L.). Colour very similar to the Mediterranean genotype, a light sienna, nodules, deposit of callus within the outer lip white, inner lip flecked with brownish orange.

Height mm.

Diameter mm.

Height of spire mm.

S.I.*

D.I.*

Holotype

42.6

27.5

16.4

28

65

Paratype

46.3

31.2

15.7

34

67

Paratype

41.2

26.8

14.7

36

65

Paratype (immature)

36.5

24.6

13.7

-

-

Locality, off Timaru, in 60-70 fathoms.

Holotype (M5717) anti juvenile paratype (M5718) in Dominion Museum. Adult paratype in collection of Mrs S. Trigance. Another paratype in collection of Mr and Mrs N. Gardner. Named for Mrs S. Trigance, who has discovered four of the known specimens.

Galeodea triganceae is close to the Awamoan G. apodemetes, but differs in the less thickened outer lip and in the finer sculpture (12 nodules on the penultimate in apodemetes). This latter character effec­tively separates it from the other New Zealand Tertiary members of the genus. This genus has been recorded previously in New Zealand doubtfully from the Wangaloan (Finlay and Marwick, 1937), from the Bortonian (G. modesta Suter and G. geniculosa Marwick), from the Awamoan (G. apodemetes Marwick), and the Altonian(?) (G. wylliei Marwick). It is most probable that it has been present in the New Zealand area since the Altonian, but has not been recorded in all horizons. One reason for this lack of fossil evidence may well he the restricted habitat. Its habitat at present would seem to be on the east coast of the South Island in moderate depths between Timaru and Banks Peninsula. It has not been reported from Cape Campbell or off the Moeraki–Oamaru coast, in both of which centres commercial fish-trawling would have brought such a form to light if it had been present. The discovery of this genus alive serves as a warning to those of us who try to draw zoogeographical conclusions from the lack of certain genera in the late Tertiary fossil beds of New Zealand.

The geological history and present distribution of the genus show that the peculiar scattered distribution of the living species probably represents peripheral remnants of a group which is becoming extinct.

Finlay and Marwick (1937, p. 67) have reiterated the fact that the Cretaceous record of the genus G. cretacea Muller must be disre­garded until new specimens are obtained and that the genus should be regarded as exclusively Tertiary and Recent.

In Europe and the Mediterranean, there is a continuous fossil history from Eocene to Recent, with species most plentiful numerically in the Oligocene. In North America, the strongest development was reached in Oligocene times. In Australia, two species have been described from the Balcombian (Mid-Miocene). The genus is also represented in the Tertiary of the East Indies. In New Zealand, the geological range is now known to be Eocene to Recent.

The Recent species that the writer has been able to trace comprise G. echinophora (L.) from the Mediterranean (the genotype), G. coronadoi (Crosse) from Cuba, G. deshayesii (Duval) from West Africa, G. echinophora Hirase and G. leucodoma Dall from Japan, and the present species from New Zealand. Finlay and Marwick (1937) regard the New Zealand fossil shells as representing an immigrant, world-colonizing stock. It would appear to have established its range in the early Tertiary, to have reached an early period of maximum develop­ment in the Eocene and Oligocene, and to have continued through to the Recent in a few isolated cases. The general characters of the genus seem to have remained very similar throughout its geological history, and the genus must be considered a conservative one.

The protoconch of the New Zealand Recent species is very similar to that figured by Cossman ( 1903, p. 130), except that in triganceae there are only two whorls. The New Zealand fossil apodemetes and the Recent triganceae do differ from the living Mediterranean genotype in having a sharp outer lip which is not thickened to form a flange. This apparent diversification since the Miocene in New Zealand seas may represent the development of a different line, worthy of subgeneric distinction, especially as the group is apparently very conserva­tive in shell features. This difference could, however, only be evaluated by study of a series of species that are not available in this country. It should be noted that G. wylliei Marwick does not appear to be on the direct line apodemetes—triganceac.

*S.I. and D.I. stand for the Spire Index and Diameter Index (the height of the spire and the diameter expressed as a percentage of the height) respectively.”

(Dell, 1953: 51-53)

Galeodea triganceae is a species of large sea snail, a marine gastropod mollusc in the family Cassidae, the helmet snails.