MOLLUSCA OF SOUTHERN CHILE 



131 



Description. Shell to 3 1 mm (38 mm. Smith, 1881); ovate, more 

 or less pointed posteriorly, delicate; surface smooth, with growth 

 lines; periostracum thick, glossy; external ligament; hinge taxodont, 

 8-9 anterior teeth, 17-20 posterior teeth (but sometimes distorted 

 when umbos are eroded); pallial sinus large, but distant from pallial 

 line, so that meeting of the two is bluntly rounded; colour yellow 

 brown to dark or olivaceous brown, interior white. 



Habitat. Dredged from 5-15 m depth on silt bottom, abundant in 

 Laguna San Rafael at salinity of 15%c. Smith (1881) recorded this 

 species from 4-58 m depth on mud in the northwestern Magellan 

 Strait. 



RECORDS. Stations 25, 29, 30. Elsewhere Islas Otter (52°S) and 

 Caleta Cockle (Smith, 1881). Carcelles & Williamson (1951) give 

 the Magellanic region and Kerguelen Islands. Range: 46-52°S. 



Remarks. Six nominal species of Malletia are recorded from 

 southern Chile (Osorio & Bahamonde, 1970), and the chief distin- 

 guishing features are shell outline, numbers of hinge teeth and the 

 form of the pallial sinus (Soot-Ryen 1959; Dell, 1964; Ramorino, 

 1968; Villaroel & Stuardo, 1998). Both the hinge and pallial line of 

 the present specimens are identical to those of the syntypes in the 

 NHM, but the largest syntype (and the figures of Smith, 1881, and 

 Carcelles, 1950) shows a markedly more rostrate posterior. How- 

 ever, two of the three syntypes are less rostrate, and overlap with the 

 most elongate examples of the present collections (e.g. Fig. 4K). 

 Dell (1964) has observed variation in the development of the 

 rostrum in another Malletia species. The majority of the samples 

 from the Laguna San Rafael are, nevertheless, more oval in outline, 

 and additional material is necessary to confirm our identification. 



Family MYTILIDAE 



Mytilus edulis chilensis Hupe, 1 854 

 (Figure 5D, E) 



Mytilus chilensis Hupe, 1854: 309-310, malacologia pi. 5, fig. 4. 



Reid, 1974: 179-184. Osorio, Atria & Mann, 1979: 25-26, fig. 27. 

 Mytilus edulis chilensis -Soot-Ryen, 1959: 24-25. Dell, 1964: 174. 



Osorio & Bahamonde, 1970: 191. Dell, 1971: 170-171. 

 Mytilus edulis Linnaeus, 1758 -Soot-Ryen, 1955: 19-22, pi. 1 , figs 



1, 2, textfigs 1, 2, 10, 11 (anatomy, synonymy). Olsson, 1961: 



113, pi. 12, fig. 6. McDonald, Seed & Koehn, 1991: 323-333. 



Description. Shell to 105 mm; beaks terminal, pointed; shell 

 solid, but thinner and translucent in brackish habitats (Fig. 5D); 3- 

 4 small tooth-like folds within umbos; chalky resilial ridge adjacent 

 to ligament pitted by minute pores; posterior adductor and retractor 

 scars continuous; radial sculpture absent; periostracum thick, glossy, 

 with hairs in very small specimens; colour blue or sometimes pale 

 brown, overlaid by black or brown periostracum, eroded at umbos; 

 interior nacreous, silvery blue. 



Habitat. An abundant species in a wide range of intertidal habi- 

 tats; on exposed shores it forms dense beds from the middle to lower 

 eulittoral on rocks and cliffs (size increases towards lower levels and 

 in more sheltered situations); on sheltered shores it occurs also 

 among stones and boulders; in estuaries and lagoons it forms clumps 

 on hard substrates in muddy situations, occurring adjacent to fresh- 

 water streams; in a brackish inlet (station 28) the species was still 

 common on the muddy shore at a salinity of 5%c\ in the Laguna San 

 Rafael it occurred intertidally and was also dredged from 5-10 m, in 

 clumps on mud and gravel, at salinities of 15%c. Mytilus edulis 



chilensis is an important component of the ecosystem of the Laguna, 

 where its occurrence and zonation have been described by Daven- 

 port etal. (1995). Soot-Ryen (1959) notes that although the species 

 is mainly intertidal, a few living specimens have been found at 25 m 

 depth. Ecological studies of this species include those by Miranda & 

 Acuna (1979) in the Magellan Strait and by Stotz (1981) in an 

 estuary near Valdivia. 



RECORDS. Stations 5, 6, 10, 12, 13, 14, 15, 17, 20, 21, 22, 24, 25, 

 26, 28, 29, 30, 31. Elsewhere, Soot-Ryen (1959) reports specimens 

 from Iquique to Magellan Strait. The species is evidently scarce in 

 central and northern Chile, for it is not reported in ecological or 

 faunistic studies of this region (Marincovich, 1973; Romo & Alveal, 

 1977; Ruiz & Giampaoli, 1981). Range: 20-54°S. 



REMARKS. Mytilus edulis has a wide, bipolar distribution in the 

 north Atlantic and southern South America. Traditional morpho- 

 logical comparison of shells has failed to detect consistent differences 

 between the northern and southern groups (Soot-Ryen, 1955), 

 although they have often been recognized as distinct subspecies on 

 account of their geographical separation (Soot-Ryen, 1959). More 

 recently, multivariate morphometric analysis has shown that South 

 American mussels are intermediate in shell shape between the 

 northern M. edulis and M. trossulus Gould, 1 850, but since allozyme 

 analysis has revealed a closer similarity to northern M. edulis, this 

 name has been tentatively applied to the southern forms also 

 (McDonald et ai, 1 99 1 ). Reid ( 1 974) described the digestive system 

 and claimed that Chilean material differed from a published account 

 of northern M. edulis, but this requires confirmation. The presence 

 of this species in South America is apparently not the result of recent 

 human introduction from the north Atlantic, since there are some 

 genetic differences and, furthermore, the species is present in pre- 

 Colombian shell middens in Argentina (McDonald etal., 1991). The 

 modern information on classification and evolution of Mytilus has 

 been reviewed by Gosling (1992) and Seed (1992). Until the geo- 

 graphical relationships of M. edulis are resolved, we retain subspecific 

 distinction for the Chilean form. Well preserved specimens of M. 

 edulis chilensis have a smooth surface, but care must be taken to 

 distinguish eroded specimens from the longitudinally ribbed 

 Aulacomya atra and Perumytilus purpuratus, with which they may 

 occur on the same shore. Choromytilus chorus is externally similar 

 to M. edulis chilensis, but reaches much larger size and is mainly 

 found subtidally. Another large mytilid, Perna perna (Linnaeus, 

 1758), has been recorded from Conception to the Magellan Strait 

 (Carcelles & Williamson, 1952, as Chloromya achatinus; see Soot- 

 Ryen, 1955: 30); this is similar in shape to M. edulis chilensis, or 

 slightly more elongate, externally brown or green, internally purp- 

 lish or pink, with a wide separation between the posterior adductor 

 and retractor scars. Mytilus edulis chilensis is an important edible 

 species, of which the annual harvest was 13358 tonnes in 1997 

 (SERNAP, 1998) and is also cultivated commercially. 



Choromytilus chorus (Molina, 1782) 

 (Figure 5F) 



Mytulus chorus Molina, 1782: 202. 



Choromytilus chorus - Soot-Ryen, 1955: 31, pi. 2, figs 7, 8, textfig. 

 5 (synonymy). Soot-Ryen, 1959: 26. Olsson, 1961: 115, pi. 12, 

 fig. 10. Osorio & Bahamonde, 1970: 191. Osorio, Atria & Mann, 

 1979: 24-25, fig. 26. Bernard, 1983: 18 (synonymy). 



Description. Shell to 186 mm (to 300 mm, Suchanek, 1985); 

 beaks terminal, pointed; shell solid; single tooth-like fold within 

 umbo of right valve, and corresponding groove in left valve; resilial 



