118 



D.G. REID AND C. OSORIO 



lateral triangles often indistinct, but sometimes marked by a raised 

 and nodulose diagonal line, and lateral triangles sometimes bearing 

 small radial pustules; mucro of tail valve near anterior margin, post- 

 mucronal slope concave; shell colour variable, pale pink, orange, 

 pale green or turquoise, with fine red or purple longitudinal and 

 radial lines, or finely marbled pattern; girdle macroscopically smooth, 

 flesh pink. 



HABITAT. Under stones in calcareous red algal zone of sublittoral 

 fringe in large, sheltered, rock pool; dredged from 10-15 m in 

 sheltered bay, on substrate of cobbles encrusted with calcareous red 

 algae. At intertidal sites in central Chile this species was also mainly 

 found submerged in pools (Otafza & Santelices, 1985). Leloup 

 (1956) recorded it from intertidal habitats both sheltered and ex- 

 posed, and to a depth of 1 3 m. 



RECORDS. Stations 7, 12. Elsewhere Tumbes (Peru) to Tierra del 

 Fuego (Leloup, 1956; Dell, 1971). Range: 12-54°S. 



Remarks. Both colour and sculpture of this species are highly 

 variable, resulting in a complex synonymy. Of the forms differenti- 

 ated by Leloup (1956), the present specimens correspond with f. 

 lineolata (Frembly, 1827), by virtue of their striking colour pattern 

 and mainly smooth valves, although the sculpture sometimes ap- 

 proaches f. grayii Sowerby, 1832. 



Class Gastropoda 

 Family NACELLIDAE 



Nacella (Nacella) mytilina (Helbling, 1779) 



(Figure 2P, Q) 



Patella mytilina Helbling, 1779: 104-106, pi. 1, figs 5, 6. 

 Nacella mytilina -Dell, 1971: 201-202 (synonymy). Castellanos& 



Landoni, 1988: 27, pi. 4, figs 9, 10. 

 Nacella (Nacella) mytilina - Powell, 1973: 192, pi. 73, fig. 9, pis 



173, 174 (synonymy). Ubaldi, 1985: 11-12, 17-18, figs 1^. 



Description. Shell to 32 by 24 mm, height 13 mm; shell thin, 

 translucent; apex one third from anterior edge; surface almost 

 smooth, but with faint radial riblets; horn colour, with radiating 

 white streaks; interior silvery iridescent. 



Habitat. On fronds of Macrocystis growing from depth of 1 0- 1 5 

 m near shore; rare, only 3 specimens found despite examination of 

 many plants. It is a common member of the epibiotic community on 

 Macrocystis further south in the Magellanic region (Castilla, 1985). 



RECORDS. Stations 1,14. Elsewhere I. Wellington, Magellan Strait 

 and Tierra del Fuego (Dell, 1971; Powell, 1973). The present 

 records are the northernmost. Range: 46-55°S. 



Remarks. The shell of this species is highly variable, ranging 

 from semitransparent to moderately solid, and from smooth to 

 ribbed. The position of the apex is also variable; in typical speci- 

 mens (Powell, 1973: pi. 173, figs 1, 2) it is at the anterior end, 

 whereas in the present material it is at about one third of the shell 

 length from the anterior margin. It is notable that the Nacellidae are 

 presently accorded full familial status in the superfamily Patelloidea 

 (Sasaki, 1998: 208-209). 



Nacella (Patinigera) magellanica (Gmelin, 1791) 



(Figure 2L-0) 



Patella magellanica Gmelin, 1791: 3703. 



Patinigera magellanica - Dell, 1971: 204. Osorio, Atria & Mann, 



1979: 14-15, fig. 8. Castellanos & Landoni, 1988: 2, pi. 3, figs 1- 



3. 

 Nacella (Patinigera) magellanica magellanica - Powell, 1973: 198, 



pi. 73, figs 14, 15, pi. 178, figs 1, 2 (synonymy). 

 Patella venosa Reeve, 1854: sp. 18, pi. 10, figs 18 a-c. 

 Nacella (Patinigera) magellanica venosa -Powell, 1973: 198-199, 



pi. 180. 



Description. Shell to 71 by 63 mm, height 37 mm; shape vari- 

 able, from smooth, low-conical (height/length 0.32), round (width/ 

 length 0.98) (form venosa, Fig. 2N, O) to radially ribbed, high- 

 conical (height/length 0.77), oval (width/length 0.87) (typical 

 magellanica, Fig. 2L, M); external colour also variable, typically 

 grey with dark brown radial stripes, but form venosa may in addition 

 be black, or cream with sparse streaks or chevrons; interior silvery 

 iridescent with exterior pattern showing through, spatula always 

 dark coppery iridescent. 



Habitat. This is an abundant species in a wide range of intertidal 

 rocky habitats, on exposed and moderately sheltered shores, on cliffs 

 and stones, from the lower barnacle zone, through the Mytilus zone, to 

 the low water mark. The species does not occur subtidally. On 

 moderately exposed vertical rock faces it is most common in a super- 

 ficially bare zone between the Mytilus zone above, and the calcareous 

 red algal zone below; in this intermediate region other herbivorous 

 molluscs are also common (Chiton granosus, Tegula atra, Fissurella 

 picta), and grazing pressure may maintain the bare rock surface. 

 Nacella magellanica was found at stations with salinity down to 15- 

 20%o. Larger specimens were found on open rock surfaces, smaller 

 animals beneath stones and in crevices. After 2-3 days of diurnal low 

 tides and clear sunny weather, animals towards the upper limit of 

 distribution were observed (2-3 Feb. 1998) to suffer heat coma, 

 dropping off the rock and dying. The distribution and density of this 

 species have been studied in the Magellan Strait (Guzman, 1978). 



RECORDS. Stations 1,5,6,7,8, 13, 14, 17,20,21,22,25.Else-where 

 I. Chiloe to Tierra del Fuego and Magellan Strait (Powell, 1 973; Dell, 

 1971). The northern limit of this species is uncertain. Brattstrom & 

 Johanssen (1983) mention 'Patinigera deaurata (Gmelin, 1791)' 

 from six locations between Laguna San Rafael and Seno Reloncavi 

 (41°29'33"S), and mention P. magellanica from Valparaiso to the 

 Magellan Strait. Brattstrom ( 1 990) recorded N. magellanica com- 

 monly in Seno Reloncavi and listed a single occurrence of A 7 , aenea 

 Martyn, 1784(aninvalidnameforA^. deaurata). N. Nacella deaurata 

 is a species recognized by Powell (1973), who gave its range as the 

 Magellan Strait, Tierra del Fuego and the Falkland Is.; in the Beagle 

 Channel this species is common intertidally, together with N. 

 magellanica (DGR, pers. obs.), but it was not seen in our study area. 

 It seems likely that the records by Brattstrom & Johanssen (1983) of 

 deaurata from the Chilean archipelago arose from misidentification 

 of the ribbed form ofN. magellanica, and accordingly we assign their 

 record from Seno Reloncavi to that species. The source of their record 

 of N. magellanica from Valparaiso is unknown, and we consider this 

 unreliable. Range: 41-55°S. 



Remarks. The systematics of the genus Nacella are still some- 

 what confused. In the most recent monograph, Powell (1973) 

 recognized the smoother, more round and more brightly coloured 

 examples from Isla Chiloe as the geographical subspecies N. m. 

 venosa, contrasting these with the more strongly ribbed, taller, more 

 oval shells of the typical forms from the southern part of the range. 

 In the present study the majority of specimens conformed to the 

 northern subspecies (Fig. 2N, O), but at station 25 in the lower 

 salinity (and perhaps colder) environment of the Golfo Elefantes, 

 the shells were mainly of the typical form (Fig. 2L, M). Inter- 





