134 



D.G. REID AND C. OSORIO 



Perumytilus purpuratus (Lamarck, 1819) 



(Figure 5C) 



Modiola purpurata Lamarck, 1819: 113. 



Brachidontes purpuratus - Soot-Ryen, 1955: 45, pi. 4, fig. 18, 



textfig. 30. Soot-Ryen, 1959: 28. Dell, 1971: 172. Bernard, 1983: 



18 (synonymy). 

 Perumytilus purpuratus - Olsson, 1961: 117, pi. 12, fig. 1, pi. 14, 



fig. 1, la, lb (synonymy). Osorio & Bahamonde, 1970: 192. 



Marincovich, 1973: 9, fig. 6. Osorio, Atria & Mann, 1979: 24, fig. 



25. 



Description. Shell to 50 mm; beaks almost terminal, rounded; 

 shell solid; several small tooth-like crenulations within umbo; resilial 

 ridge adjacent to ligament not pitted by pores; posterior adductor 

 and retractor scars continuous; fine radial ribs present, crenulating 

 margin; periostracum thick, glossy; shell white, purplish posteriorly, 

 overlaid by dark brown to black periostracum, eroded at umbos, 

 interior nacreous, silvery to purplish brown. 



Habitat. Frequent in a range of intertidal habitats : under stones in 

 mid to upper eulittoral on sheltered boulder shores, forming partly 

 buried accretions on upper shore of muddy shingle beaches, and 

 sometimes together with Mytilus edulis chilensis in dense beds of 

 small shells at top of Mytilus zone in mid-eulittoral on exposed 

 rocky coasts. The species is especially abundant in sheltered habitats 

 where there is a moderate freshwater input from streams or runoff, 

 and was found at salinities down to 15-20%o. This is a strictly 

 intertidal species (Soot-Ryen, 1959; Dell, 1971), but can be found 

 throughout the intertidal zone in both southern and northern parts of 

 its distribution (Marincovich, 1973; Brattstrom, 1990; Benedetti- 

 Cecchi & Cinelli, 1997). In central and northern Chile P. purpuratus 

 is the dominant organism in the mid-eulittoral on both sheltered and 

 exposed shores, forming dense beds (Guiler, 1 959a; Romo & Alveal, 

 1977; Ruiz & Giampaoli, 1981; Santelices, 1991; Alvarado & 

 Castilla, 1996). The great abundance of this species may be a 

 consequence of the removal of its major predator, the edible 

 Concholepas concholepas, by humans (Castilla & Duran, 1985). 



RECORDS. Stations 1, 5, 6, 10, 11, 12, 14, 17, 20, 21, 22, 25, 26. 

 Elsewhere Yasila near Paita (Peru) (Olsson, 1 96 1 ) to Magellan Strait 

 (Soot-Ryen, 1955; Benedetti-Cecchi & Cinelli, 1997). Range: 5- 

 54°S. 



Remarks. Discrimination from the only other ribbed mussel, 

 Aulacomya atra, has been described earlier. Perumytilus purpuratus 

 is seldom found in pure colonies, but almost always together with 

 Mytilus edulis chilensis. When shells are well preserved, the two are 

 easily separated by the fine radial ribs of the former. When shells are 

 severely eroded (as is often the case in habitats of low salinity), the 

 crenulated margin and purplish shell of P. purpuratus differentiate it 

 from the blue, smooth-margined shells of M. edulis chilensis. The 

 proportions of these two species in the mytilid zone appear to vary 

 with exposure, tidal level and salinity. On exposed shores and at 

 lower levels P. purpuratus is replaced by M. edulis chilensis. 

 Perumytilus purpuratus becomes more frequent on sheltered shores, 

 and wherever there is limited freshwater inflow. However, in estua- 

 rine areas of the lowest salinity (5-15%o, stations 28, 29, 30, 31) it is 

 absent and here the presumably more euryhaline M. edulis chilensis 

 occurs alone. 



Family PECTINIDAE 



Zygochlamys patagonica (King & Broderip, 1832) 



(Figure 40) 



Pecten patagonicus King & Broderip, 1832: 337. 



Chlamys patagonica - Soot-Ryen. 1959: 29. Osorio, Atria & Mann. 



1979: 28, fig. 30. Waloszek, 1984: 207-276, pis 1-3, pis 5-9 



(synonymy). 

 Chlamys patagonica patagonica -Beu, 1985b: 1-11, pi. l,figs 1-4. 

 Chlamys (Zygochlamys) patagonica -Dell, 1964: 178-179. Osorio 



& Bahamonde, 1970:193. 

 Zygochlamys patagonica - Waller, 1991: 28-30, pi. 2, figs 13, 14. 

 Chlamys patriae Doello Jurado, 1918 - Soot-Ryen, 1959: 29-31. 



Osorio & Bahamonde, 1970: 193. 

 Chlamys amandi Hertlein, 1935 - Soot-Ryen, 1959: 29-31, pi. 1, 



figs 7, 8. Osorio & Bahamonde, 1970: 193. 



Description. Shell 16 mm (to 90 mm, Waloszek, 1984); a round, 

 almost equivalved scallop; sculptured by 30-32 (22-41, Waloszek, 

 1984) primary radial ribs (excluding ears), with secondary ribs 

 between, crossed by fine concentric laminae which may form 

 minute scales on ribs or in interspaces; right (lower) valve pink, 

 orange or brown, with darker ribs; left valve white with pink to 

 orange ribs; interior white, flushed with pink or purple. 



Habitat. Single small specimen dredged from 10-15 m, among 

 cobbles with encrusting calcareous red algae, in sheltered bay. 

 Although occasionally taken in the shallow sublittoral, the typical 

 habitat of this species is in deeper water, 25-100 m in the vicinity of 

 I. Chiloe (Soot-Ryen, 1959), 15 to over 200 m off eastern Patagonia 

 and the Falkland Islands (Dell, 1964; Waloszek & Waloszek, 1986). 



RECORDS. Station 7. Elsewhere I. Chiloe to Magellan Strait, Tierra 

 del Fuego and Cape Horn (Waloszek, 1984). Range: 42-56°S. 



Remarks. A detailed taxonomic study of this and other Magellanic 

 scallops has revealed that the three species discriminated by Soot- 

 Ryen (1959) are extremes of the range of a single taxon with variable 

 microsculpture (Waloszek, 1984). The generic assignment has been 

 discussed by Beu (1985b) and Waller (1991). This species is fished 

 commercially in the Magellan Strait (Osorio et al., 1979) and in 

 1997 the catch was 2598 tonnes (SERNAP, 1998). During the 

 present study fossil specimens of an additional pectinid species, 

 Chlamys vitrea (King & Broderip, 1832), were found in a clay cliff 

 of an eroding raised beach on the southwestern shore of Isla Rojas. 

 This species has a more delicate shell, transparent when young, with 

 less distinct, rounded ribs and in life is associated with Macrocystis 

 (Waloszek, 1984: pi. 4, fig. 5). 



Family UNGULINIDAE 



Felaniella inconspicua (Philippi, 1845) 



(Figure 4N) 



Diplodonta inconspicua Philippi, 1845: 53. Hupe, 1854: 357, 

 malacologiapl. 8, fig. 4. Soot-Ryen, 1959: 43 (synonymy). Herm, 

 1969: 115, pi. 3, figs 5-7. Osorio & Bahamonde, 1970: 199. Dell, 

 1971: 173. 



Fig. 6 Scanning electron micrographs of Polyplacophora. A, C. Leptochiton (Leptochiton) medinae (C, detail of girdle spicules). B, D. Ischnochiton 

 (Ischnochiton) stramineus (D, detail of girdle scales). E. Ischnochiton (Haploplax) pusio, detail of girdle scales. F. Chiton (Amaurochiton) magnificus 

 bowenii, detail of girdle scales. (All specimens from study area; NHM collection). 



