Comprehensive Description

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Description

 

Nacella concinna (Strebel, 1908)

 

(Pl. 176, figs. 1-5)

 

 

Range—South Georgia, South Orkneys, South Shetlands, Bouvet Island, Seymour Island, Paulet Island, Wandel Island, Anvers Island and Petermann Island.

 

Remarks—Unfortunately the well-known name of this species, Patella polaris Hombron & Jacquinot, 1841, falls as a homonym of the same combination of Röding, 1798. However there is a substitute name available, in Patinella polaris concinna Strebel, 1908, from South Georgia, and this name, concinna, may be used specifically, since there appears to be no real difference between the shallow-water 'polaris’ and the deeper- water concinna, other than a gradual tendency towards lower profile, lighter build, more clear‑cut ribbing and paler coloration as the depth increases. Strebel's concinna, described as a Patinella, does not conflict with the Japanese acmaeid that was originally described as Patella concinna Lischke. The species lives from the intertidal zone down to 110 metres.

 

 

Description (shallow-water 'polaris' form)— Shell moderately large, up to 60 mm. (2⅜ inches) in length, elongate ovate, rather thin, moderately elevated, with the apex between central and the anterior third. Sculptured with distant weak radial ribs in young shells, but the ribbing be­comes subobsolete to obsolete in the adult. Col­our, externally pale brownish; internally very dark bronzy-brown, almost black, the spatula sometimes a paler chestnut-brown.

 

Description (deeper-water typical form)—Shell usually small, 20 to 32 mm. (¾ to 1¼ inches) in length, thin and fragile, elongate ovate, moder­ately elevated and with the apex at about the anterior third. Sculptured with about 28 to 30 narrow radial (ribs, crossed by dense fine lamel­lose growth lines. Colour buff, sparingly blotched in reddish brown; interior cream, shining, vary­ingly maculated with pale reddish brown. Some larger examples, approaching the larger shallow-water form in size, tend to flatten out at the margin, towards which the radial sculpture be­comes subobsolete.

 

 

Measurements (mm.)—

                                              
 

length

 
 

width

 
 

height

 
 

 
 

58.0

 
 

42.0

 
 

19.0

 
 

Palmer Archipelago, 4-10 metres; (‘polaris’ form)

 
 

44.0

 
 

31.0

 
 

18.5

 
 

S. Orkneys (‘polaris’ form)

 
 

42.0

 
 

29.0

 
 

9.0

 
 

S. Georgia, 27 metres: (intermediate form)

 
 

31.0

 
 

21.5

 
 

11.0

 
 

S. Georgia (‘polaris’ form)

 
 

29.0

 
 

20.0

 
 

8.0

 
 

S. Georgia, 18 metres: (typical concinna)

 
 

25.0

 
 

17.0

 
 

6.25

 
 

S. Georgia (typical concinna)

 
 

 

Synonymy—

 

1841 Patella polaris Hombon & Jacquinot, Ann. Sci. Nat. Zool., vol. 16, p. 191 (non Röding, 1798).

 

1886 Patella polaris H. and J. Martens and Pfeffer, Moll. Süd-Georgien, J. hamb. wiss. Anst., vol. 3, p. 101, pl. 2, figs. 11-13.

 

1891 Nacella (Patinella) polaris H. and J. Pilsbry, Man. Conch., vol. 13, p. 120, pl. 49, figs. 21-27.

 

1908 Patinella polaris H. and J. Strebel, Wiss. Ergeb. schwed. Südpolar-Exped. (1901-3), vol. 6, p. 81, pl. 5, fig. 77.

 

1908 Patinella polaris concinna Strobel, Wis. Ergeb. schwed. Südpolar-Exped. (1901-3), vol. 6, p. 82, pl. 5, figs. 76 a-e, 78 a, b.

 

1951 Patinigera polaris H. and J. Powell, Discovery Rep., vol. 26, p. 82.

 

1951 Patinigera polaris concinna Strebel, Powell, Discovery Rep., vol. 26, p. 83.

 

 

Records—SOUTH GEORGIA (type of ‘polaris’): Cumberland Bay, 15-25 metres (type of concinna); East Cumberland Bay 18-110 metres; Moltke Harbour, in rock pool; Stromness Harbour, 26-35 metres; Undine Harbour, 18-27 metres. SOUTH ORKNEYS: Signy Island, 18-27 metres; Normanna Strait, 24-36 metres (`Discovery II'; Powell, 1951). SOUTH SHETLANDS: Deception Island, 5-60 metres; Nelson Island, shore; Livingston Island, shore; Wilhelmina Bay, Danco Land, 1-8 fathoms (‘Discovery II’; Powell, 1951). PALMER ARCHIPELAGO: Melchior Island, 4-10 metres. Bouvet Island, 40-45 metres (‘Discovery II’; Powell, 1951). Seymour, Paulet, Wandel, Anvers and Petermann Islands (Strebel, 1908; Lamy, 1911).”

 

 

(Powell, 1973: 193-195)

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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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