Chlanidota signeyana Powell 1951

"Chlanidota (Chlanidota) signeyana
Powell, 1951
Figs. 9-11; Table 5

Chlanidota signeyana Powell, 1951:141, fig. F, 194, fig L74, 196, fig. N129, pl. 8, figs. 34-35; Carcelles, 1953:191, pl. 3, fig. 59; Powell, 1960:150; Kaicher, 1990: 5801; Dell, 1990:177, fig. 307.

Cominella (Chlanidota) vestita var. elon­gata Lamy, 1910:319; Lamy, 1911:6, pl. 1 fig. 6.

Chlanidota elongata Powell, 1951:140, 194, fig. L76; Carcelles, 1953:191, pl. 3, fig. 56; Powell, 1960:150; Cernohorsky, 1977:110; Horikoshi et al., 1979: 22, fig. 8: Hain, 1989:71, Taf. V/4, Taf. XXIII/1; Numanami, 1996: 160-162, figs. 106- 107.

Chlanidota lamyi Dell, 1990:182, fig. 310, new name for Cominella (Chlanidota) elongata Lamy, 1910, not Cominella elongata Dunker, 1857.

Chlanidota pyriformis Dell, 1990:182, fig. 309.

Chlanidota cf. lamyi Dell, 1990:182, fig. 315.

Description.-Shell (Fig. 9) large for genus (to 42.6 mm), thin, fragile, elongate to ovate in outline, with medium to high, rounded to turreted spire. Protoconch unknown, early whorls heavily eroded. Teleo­conch of up to 5+ evenly-rounded convex whorls, deeply eroded where periostracum damaged or missing. Suture deeply im­pressed, sharply abutting. Spiral sculpture typically of distinct, sharp, narrow cords (7-14 on penultimate whorl, 15-35 on body whorl) equal or subequal in prominence, that may be reduced or nearly absent in some specimens (Fig. 9F, K). In specimens with pronounced cords (Fig. 9H-I), includ­ing the holotype (Fig. 9A-C), 4-5 adapical cords on body and penultimate whorls usu­ally more widely spaced, giving the illusion that they are more pronounced. Spaces be­tween cords equal to cord width on early whorls, at least twice cord width on body whorl. Axial sculpture limited to fine, weakly recurved, prosocline growth lines. Aperture elongate to broadly ovate, deflected from shell axis by 14-17°. Outer lip thin, evenly rounded, fragile. Columella 1/3-1/2 AL, weakly convex, with strong siphonal fold. Callus of thin, silver-edged or thick, brownish glaze overlying parietal region, siphonal fasciole. Siphonal notch broad, dorsally recurved, with straight columellar and rounded apertural margins that form borders of fasciole. Ridge margin of fasci­ole extends from apertural margin of si­phonal notch. Shell color chalky-white to brownish or orange-tan. Aperture weakly glazed. Periostracum (Fig. 10E) thin to moderately thick, orange-tan to greenish-tan, smooth in weakly sculptured speci­mens, forming low, axial lamellae with short, hairlike projections on intersections with spiral cords of strongly sculptured specimens. Operculum (Fig. 9L) small (0.25-0.37 AL), broadly ovate, weakly coiled, with terminal nucleus rotated nearly perpendicular to long axis. Operculum may be thin, yellowish, translucent, but usually opaque, brownish to dark brown. Attach­ment area oval, spanning about 4/5 of inner surface, posterior and left margins thick­ened, abraded.

Ultrastructure.-(Fig. 10F) Outermost layer prismatic (≈38 µm), middle layer comarginal crossed-lamellar (≈60 µm), in­ner layer radial crossed-lamellar (≈20 µm).

Anatomy.-Gross anatomical features of C. signeyana very similar to those of C. densesculpta, but left and right salivary glands of C. signeyana separate, not fused. Radular ribbon long, 9.6-12.2 mm (0.48- 0.55 AL), 790-910 µm wide (0.04 AL), triserial (Fig. 10A-D), consisting of 65-75 rows of teeth, posteriormost 5-6 rows na­scent. Rachidian teeth with arched base, straight lateral sides, 3 large, robust cusps of equal length. Lateral teeth with 3 cusps, outer cusp longest, intermediate cusp short­est, situated close to inner cusp.

Type locality.-[Chlanidota signeyana] Off Signy Island, South Orkneys, 60°50'30"S, 46°15'00"W, in 244-344 m (R/V Discovery II, Sta. 167); [Cominella (Chlanidota) vestita var. elongata Lamy, 1910] King George Island, South Shet­lands, in 420 m; [Chlanidota pyriformis Dell, 1990] Off South Shetland Islands, 63°00'S, 60°32'W, in 26 m (R/V Westwind: Sta. W.10).

Type material.-[Chlanidota signeyana] Holotype, BMNH 1961512 (fig. 9A-C), and 2 paratypes; [Cominella (Chlanidota) vestita var. elongata Lamy, 1910] The holotype (Fig. 9D) was not found in MNHN; [Chlanidota pyriformis Dell, 1990] Holotype, USNM 613075 (Fig. 9E-F) paratypes 1-6, USNM 860181, Paratype 7, ME 47204.

Material examined.-R/V Eltanin: Sta. 426, South Shetland Islands, Bransfield Strait, 62°27'S, 57°58'W, in 809-1116 m, 5 Jan 1963, 3 shell fragments, USNM 870290, 7 shells or fragments, USNM 870291, 4 specimens, USNM 886204; Sta. 428, South Shetland Islands, Bransfield Strait, 62°41'S, 57°51'W, in 662-1120 m, 5 Jan 1963, 1 shell fragment, USNM 870293; Sta. 432, South Shetland Islands, 62º52'S, 59°27'W, in 884-935 m, 7 Jan 1963, frag­ments of 2 shells, USNM 870303; Sta. 439, Antarctic Peninsula, 63º51'S, 62º38`W, in 128-165 m, 9 Jan 1963, 1 shell, USNM 870313, 1 specimen, USNM 881919; Sta. 444, South Shetland Islands, 62º56'S, 62°02'W, in 750-732 m, 11 Jan 1963, 1 specimen, USNM 881923; Sta. 538, South Orkney Islands, Bransfield Strait, 60º30'S, 47°34'W, in 616-662 m, 6 Mar 1963, frag­ments of 2 shells, USNM 870330; Sta. 993, South Shetland Islands, Elephant Island, 61°25'S, 56º30'W, in 300 m, 13 Mar 1964, 1 specimen, USNM 881970; Sta. 997, South Shetland Islands, Bransfield Strait, Gibbs Island, 61°44.18'S, 55°56.06'W, in 769 m, 14 Mar 1964, 1 specimen, USNM 881971; Sta. 1079, Scotia Ridge, 61°26'S, 41°55'W, in 593-598 m, 13 Apr 1964, frag­ments of 3 shells, USNM 870627, 2 spec­imens, USNM 881983; Sta. 1084, Scotia Ridge, 60°22'S, 46°50'W, in 298-403 m, 15 Apr 1964, 3 shells, USNM 870641, 7 shells and fragments, USNM 870642, 1 specimen, USNM 881988; Sta. 1997, Ross Sea, 72°00'S, 172°28'E, in 530-549 m, 2 shells, USNM 898205; Sta. 2124, Ross Sea, 71°38'S, 172°00'E, in 606-622 m, 1 shell, USNM 898202; Sta. 2127, Ross Sea, 71°23'S, 171°36'E, in 515-521 m, 1 shell, USNM 898040.

R/V Eastwind: Sta. EW66-009, Palmer Peninsula 62°43.1'S, 62°17.5'W, in 561 m, 31 Jan 1966, 1 specimen, USNM 678473; EW66-012, Palmer Peninsula 63°23'S, 60°51'W, in 405 m, 3 Feb 1966, 2 speci­mens, USNM 678475; EW66-021, off South Orkney Islands, 60°21'S, 45°55'W, in 102 m, 9 Feb 1966, 1 specimen, USNM 678396; EW66-022, off South Orkney Is­lands, 60°26.5'S, 45°53.3'W, in 168 m, 9 Feb 1966, 1 specimen, USNM 678476; EW66-029, off South Orkney Islands, 61°06'S, 44°57'W, in 290 m, 15 Feb 1966, 1 specimen, USNM 678398; EW66-036, off Elephant Island, 61°16'S, 54°45'W, in 300 m, 17 Feb 1966, 2 shells, USNM 678480; off beach wrack, Collins Pt., De­ception Island, 4 Jan 1966, 4 specimens, USNM 678378.

R/V Hero: Cruise 691, Sta. 23, off Ant­arctic Peninsula, Palmer Archipelago, Bra­bant Island, 64°12.06'S, 62°39.36'W, in 93­-95 m, 9 Feb 1969, 1 specimen, USNM 896260; Cruise 691, Sta. 31, South Shet­land Islands, Deception Island, 62°58.25'S, 60°45.40'W, in 37-51 m, 13 Feb 1969, 7 specimens, USNM 897557; Cruise 721, Sta. 751, off Antarctic Peninsula, 64°46'28"S, 64°04'20"W, in 33 m, 31 Dec 1971, 1 shell, USNM 901659; Cruise 721, Sta. 765, off Antarctic Peninsula, 64°47.3'S 64°07.4'W, in 55 m, 3 Jan 1972, 1 shell, USNM 901671; Cruise 721, Sta. 1058, off Antartic Peninsula, 62°19.0'S, 59°11.4'W, in 44 m, 19 Dec 1971, 1 shell, USNM 901657; Cruise 731, Sta. 1806, 64°46'31"S, 64°04'52"W, in 47-75 m, 18 Feb 1973, 1 specimen, USNM 901686; Cruise 824, Sta. 32-1, Antarctic Peninsula, Anversa Island, 64°37'S, 62°50.48'W, in 640-670 m, 23 Mar 1982, 1 shell, USNM 881583; Cruise 824, Sta. 7-1, Antarctic Peninsula, Adelaide Island, 66°40.40'S, 67°31.23'W, in 510-730 m, 17 Mar 1982, 1 specimen, USNM 896309; Sta. 32-1, Antarctic Peninsula, 64°37'S, 62°50.80'W, in 640-670 m, 25 Mar 1982, 1 shell, USNM 901658.

R/V Islas Orcadas: Sta. 39, South Sand­wich Islands, 57°01.2'S, 26°44.3W, in 97­-100 m, 23 May 1975, 1 shell, USNM 901663; Sta. 40, South Sandwich Islands, Kadlemas Island, 57°06.8'S, 26°43.36'W, in 15-33 m, 23 May 1975, 1 specimen, USNM 901660; Sta. 42, South Sandwich Islands, Kadlemas Island, 57°06.8'5, 26°43.6'W, in 22-44 m, 24 May 1975, 12 specimens, USNM 901669; Sta. 46, South Sandwich Islands, Kadlemas Island, 57°06.2'S, 26°44.5W, in 26-60 m, 25 May 1975, 2 specimens, USNM 901665; Sta. 48, South Sandwich Islands, Kadlemas Island, 57°06.3'S, 26°44.2'W, in 27-62 m, 23 May 1975, 4 specimens, USNM 901670; Sta. 55, South Sandwich Islands, Saunders Island, 57°47.12'S, 26°22.30'W, in 64-88 m, 27 May 1975, 1 specimen, USNM 901664; Sta. 57, South Sandwich Islands, 27 May 1975, 5 specimens, USNM 901656; Sta. 80, South Sandwich Islands, Zavodovski Is­land, 56°20.0'S, 27°38.8'W, in 351-393 m, 4 Jun 1975, 13 specimens, USNM 901667; Sta. 110, Inaccessible Island, 60°28.1'S, 46°27.2'W, in 115-132 m, 16 Feb 1976, 2 specimens, USNM 901666; Sta. 115, Inac­cessible Island, 60°32.4'S, 47°22.7'W, in 567-671 m, 17 Feb 1976, 2 shells, USNM 901655; Sta. 118, off South Orkney Islands, 62°01.5'S, 43°06.2'W, in 759-857 m, 20 Feb 1976, 1 specimen, USNM 901661; Sta. 121, off South Orkney Islands, 61°47.00'S, 43°40.00'W, in 616-642 m, 21 Feb 1976, 1 specimen, USNM 901662.

R/V Westwind: Sta. W-10, off South Shetland Islands, 63°00'S, 60°32'W, in 159 m, 26 Jan 1958, 6 shells, paratypes of C. pyriformis Dell, 1991. USNM 860181, 4 shells, USNM 890897.

R/V Polar Duke: off Palmer Peninsula, 65°36'S, 67°21'W, in 200 m, 6 Sep 1985, 1 shell, USNM 846179.

R/V Deepfreeze IV: Sta. TD2-ED 14, off Cape Norwegia, Weddel Sea, 71°50'S, 15º50'W, 1028-1122 m, 18 Jan 1959, 1 shell and fragments, USNM 638862.

Published records.-R/V Discovery II, Sta. 162, Off Signy Island, South Orkneys 60°48'00"S, 46°08'00"W, in 320 m; Sta. 170, off Cape Bowles, Clarence Is., 61°25'30"S, 60°28'00"W, in 342 m; Sta. 175, Bransfield Strait, South Shetlands, 63°17'20"S, 59°48'15"W, in 200 m; Sta. 1952, between Penguin Island and Lion's Rump, King George I, South Shetlands, in 367-383 m; Sta. 1957, off south side of Clarence Island, South Shetlands, in 785-­810 m (Powell, 1951). R/V Eltanin: Sta. 426, off South Shetland Islands, 62°27'S, 57°58'W, in 1116-809 m; Sta. 439, west of Antarctic Peninsula, 63°51'S, 62°38'W, in 128-165 m; Sta. 1084, north of South Ork­ney Islands, 60°22'S, 46°50'W, in 298-403 m, R/V Hero: Sta. 23, Antarctic Peninsula, 64°12.1'S, 62°39.6'W, in 93-95 m; Arthur Harbor, Anvers Island, Antarctic Peninsula, 30 m (Dell, 1990:180). PS ANT 111/3: Sta. 345, Weddel Sea, 73°27'S, 21°37'W, in 617 m (Hain, 1989). Syowa Sta., Enderby Land, in 98 m (Horikoshi et al., 1979). JARE Sta. 9, Breid Bay, Queen Maud Land, 70°13.7'S, 24°25.7'E, in 276-289 m, Sta. 10, 25 (Numanami, 1996); NZOI: Sta. A463, 72°20'S, 174°50'E, in 460 m; Sta. A464, 72°20'S, 174°00'E, in 376 m (Dell, 1990, as C. cf. lamyi).

Distribution.-South Orkneys, South Shetlands, Antarctic Peninsula, and Queen Maud Land, and the eastern margins of the Ross Sea. Living specimens were taken in 30-1116 m (Fig. 11).

We include records for this species re­ported from the area of Queen Maud Land (as C. elongata). Figured specimens from this region (Numanami, 1996:fig. 106A-B, E-F). appear to have weaker, more numer­ous spiral cords. One specimen from Syowa station has rachidian teeth with narrower cusps and additional serrations, features that had not previously been observed in spec­imens of C. signeyana. Powell (1951:142, fig. L78) reported and illustrated similar ad­ditional serrations in a specimen of Chlan­idota (Pfefferia) elata.

We have examined and also include re­cords from the eastern margin of the Ross Sea, which had been listed as Chlanidota cf. lamyi by Dell (1990:310). Dell (1990) noted that these broken and worn speci­mens closely resemble C. signeyana (as C. lamyi) from the South Shetland Islands, but differed only in having more numerous spi­ral cords on their body whorl.

Remarks.-Lamy (1910) was the first to recognize this species, proposing the taxon Cominella (Chlanidota) vestita var. elon­gata, without realizing that the name was preoccupied by Cominella elongata Dun­ker, 1857. Powell (1951:141) considered Chlanidota elongata to be restricted to the South Shetland Islands and erected the taxon C. signeyana based on material from the South Orkney Islands. He recognized that C. signeyana was closely related to C. elon­gata, but distinguished it as being "con­stantly broader and of ovate rather than cy­lindrical outline." Cernohorsky (1977:110) noted that Cominella (Chlanidota) vestita var. elongata Lamy, 1910 was preoccupied, but questioned whether this taxon was dis­tinct from C. vestita. After examining a broader range of specimens than were available to Powell, Dell (1990:180) noted that both ovate and cylindrical phenotypes co-occurred in South Shetland and South Orkney samples, but that specimens could be sorted into one or the other phenotype on the basis of the ratio of shell width (SW) to shell height (SH). He regarded Chlani­dota signeyana to be limited to the ovate phenotype with SW/SH ratios ranging from 0.60 to 0.66 and proposed the new name Chlanidota lamyi (for Cominella elongata Lamy, 1910, non Dunker, 1857) for the elongate phenotype, with SW/SH ratios be­tween 0.55 and 0.60. He did, however, recognize the possibility that "these two forms are but extremes of the same species."

Dell (1990) also described C. pyriformis based on a single lot (11 specimens) collected off the South Shetland Islands, which he regarded to be a morphologically consistent shallow-water form allied to both C. signeyana and C. lamyi, but distinguished by its tapering, conical spire.

We examined and measured a large series of specimens from throughout the ranges of the three nominal species, but were unable to differentiate between them in any reproducible manner. Larger samples from sev­eral stations (e.g., USNM 901669, USNM 897557, USNM 860181) revealed that each population spans the range of morphologies of at least two, and sometimes all three of these nominal species. Chlanidota signey­ana is highly variable in shell outline and spiral sculpture, and encompasses the phe­notypes of Chlanidota lamyi and C. pyri­formis.

There does appear to be a clinal gradient in shell shape, with northern specimens tending to be more inflated, while popula­tions from the southern portion of the spe­cies' range, including the Antarctic main­land, have a higher proportion of narrower and more cylindrical shells. Numanami (1996:146) recognized a similar gradient in shell morphology in the taxon Neobuccin­urn eatoni, noting that specimens from the Kerguelen and South Shetland Islands tend­ed to be more elongated, while the samples from Enderby Land tended to be more in­flated and shorter spired. However, his large sample (n=98) from Enderby Land showed a wide variability in shell form, and included examples from the entire range of variation for the species.

Chlanidota signeyana is most similar to C. (C.) paucispiralis Powell, 1951, but differs in having more numerous and weaker spiral cords. Moreover, C. (C.) signeyana has not been recorded off South Georgia, while C. (C.) paucispiralis is endemic to South Georgia Island.

Table 5. -Chlanidota (Chlanidota) signeyana (Powell, 1951). Measurements of shell characters. Linear measurements in mm (n=10, holotype not included).

Character

Mean

σ

Range

Holotype of C. signeyana

Holotype of C. pyriformis

Holotype of C. elongata (from Lamy, 1911)

Shell Length (SL)

29.8

6.7

21.4-42.2

37.4

28.6

30.0

Body Whorl Length (BWL)

24.5

5.1

17.8-33.4

31.9

24.4

26.5

Aperture Length (AL)

19.3

3.5

14.1-25.7

25.3

20.1

20.7

Shell Width (SW)

18.2

3.2

13.5-22.8

23.6

18.6

16.9

Operculum Length ( OL)

5.9

1.5

4.5-9.4

6.4

-

-

BWL/SL

0.83

0.02

0.79-0.86

0.86

0.85

0.87

AL/SL

0.65

0.04

0.58-0.70

0.68

0.70

0.69

SW/SL

0.61

0.06

0.54-0.71

0.64

0.65

0.56

OLAL

0.30

0.04

0.25-0.37

0.27

-

-

No. spiral cords on:

Penultimate whorl

10.1

2.2

7-14

11

7

7

Body whorl

25.0

6.2

15-35

26

21

21

"

(Harasewych & Kantor, 1999: 267-274)

Chlanidota signeyana is a species of sea snail, a marine gastropod mollusk in the family Buccinidae, the true whelks. It was described by Harold Powell in 1951.

Chlanidota signeyana là một loài ốc biển, là động vật thân mềm chân bụng sống ở biển trong họ Buccinidae.