140 



D.G. REID AND C. OSORIO 



down to 40 m by Soot-Ryen (1959), 65 m (Ramorino, 1968), 5-10 

 m (Urban & Tesch, 1996) and to 219 m (Linse, 1997). 



RECORDS. Stations 7, 14. Elsewhere Coquimbo to Tierra del 

 Fuego (Fischer-Piette & Vukadinovic, 1977). Range: 30-56°S. 



Family HIATELLIDAE 



Hiatella solida (Sowerby, 1 834) 

 (Figure 5L) 



Saxicava solida Sowerby, 1834: 88-89. 



Hiatella solida- Soot-Ryen, 1959: 67-68. Olsson, 1961: 425, pi. 77, 

 fig. 6, 6a. Dell, 1964: 224—226 (synonymy). Osorio & Bahamonde, 

 1970: 206. Dell, 1971: 177-178. Marincovich, 1973: 14-15, fig. 

 22. Bernard, 1983: 59. Gordillo, 1995: 193-195, fig. 5. 



Description. Shell 12 mm (to 46 mm, Dell, 1964); irregularly 

 elongate rectangular, often distorted by nestling habit, sometimes 

 with a strong keel running from umbo to postero-ventral margin, 

 gaping posteriorly; sculpture of irregular growth lines; hinge often 

 weak, ligament external; colour white with thin periostracum. 



HABITAT. Single specimen in Macrocystis holdfast at 3-5 m depth. 

 This species has been reported from a wide range of habitats. In the 

 Beagle Channel, it is found attached by byssus on rocky shores, 

 among Mytilus clusters, nestling in sand and gravel at low water and 

 subtidally in Macrocystis holdfasts (Gordillo, 1995). On hard rock 

 substrates it adopts a nestling habit in crevices, but on soft rock and 

 on calcareous shells (e.g. of Concholepas concholepas) it becomes 

 a shallow borer (Gallardo & Osorio, 1978). In the Falkland Islands 

 it has been recorded from the sublittoral fringe to depths of over 350 

 m (Dell, 1964). 



Records. Station 22. Elsewhere the distribution is unclear owing 

 to taxonomic uncertainty, but Soot-Ryen (1959) gives Ecuador to 

 Cape Horn, and Olsson (1961) has a record from the Pearl Islands 

 (Panama). Range: 8°N-56°S. 



Remarks. As discussed by Dell (1964) the taxonomy of this 

 genus is confused, because of variation in shell outline and hinge 

 development. Although he concluded that H. antarctica (Philippi, 

 1845) was a synonym of//, solida, others have maintained the two 

 as distinct taxa (Osorio & Bahamonde, 1970; Bernard, 1983). 

 During this study abundant fossil specimens (up to 36 mm), were 

 found in the eroding clay cliff of a raised beach on the southwestern 

 side of Isla Rojas. 



Family TEREDINIDAE 



Bankia (Bankia) martensi (Stempell, 1899) 



(Figure 5N-P) 



Teredo (Xylotrya) martensi Stempell, 1899: 240, pi. 12, figs 24-27. 

 Bankia martensi - Turner, 1966: 109, pi. 48, fig. D, pi. 61, figs A- 

 C, pi. 62, figs A, B (synonymy). 



Bankia (Bankia) martensi - Soot-Ryen, 1959: 70. Osorio & 

 Bahamonde, 1970: 207. Osorio, Atria & Mann, 1979: 36, fig. 44. 

 Bernard, 1983: 62. 



Description. Animal to approx. 150 mm, shell to 8 mm, pallets to 

 35 mm; body elongate, worm-like, enclosed in calcareous tube 

 bored into wood; shell (Fig. 5N) at anterior end, reduced, file-like 

 surface, white with thin brown periostracum; pair of calcareous 

 pallets protect siphons at posterior end; pallet (Fig. 50) composed of 

 central stalk with numerous cone-like elements with fringed border, 

 each cone extending laterally as a point. 



Habitat. A wood-boring species, abundant in logs in the inter- 

 tidal zone, recorded down to salinity of 20%c. Reported from the 

 intertidal to a depth of 55 m (Soot-Ryen, 1959). 



Records. Stations 1, 7, 20, 25. Elsewhere Seno Reloncavi to 

 Magellan Strait (Soot-Ryen, 1959). Range 41-54°S. 



DISCUSSION 



Ecology and distribution of molluscs in the study 

 area 



During our survey we recorded a total of 62 species of molluscs 

 during shore collecting and dredging from depths of 5 to 15 m. For 

 a region at this latitude (46°S) this is not a large number. In part, this 

 paucity may be explained by the pronounced salinity gradient along 

 the length of the fjord system. Within the Laguna San Rafael, subject 

 to meltwater from the San Rafael Glacier, we recorded surface 

 salinities of 14-15%o (to 17%c, Davenport et al., 1995), and found 

 but three mollusc species. In the higher and more variable salinity 

 regime of the Golfo Elefantes (surface salinity 15-21%c, at 15 m 

 almost certainly greater) the records rose to 18 species. Only in the 

 main Estero Elefantes were fully marine habitats present (27-33%o) 

 and in such habitats our total was 56 species. The most euryhaline of 

 the species was Mytilus edulis chilensis, occurring abundantly at 

 almost all stations, down to a salinity of 5%c (station 28). Other 

 euryhaline species were those found on the shore (and therefore 

 subject to the low surface water salinity) in the Golfo Elefantes: 

 Plaxiphora aurata, Nacella magellanica, Siphonaria lessonii, 

 Perumytilus purpuratus,Aulacomya atra, Mulinia edulis and Bankia 

 martensi. The only species restricted to areas of low salinity were 

 Chilina patagonica (5-15%c) and Malletia magellanica (14-21%c). 

 A striking aspect of this molluscan fauna was the dominance of 

 mytilid bivalves in a range of intertidal and shallow sublittoral 

 habitats. Most abundant was the euryhaline Mytilus edulis chilensis, 

 forming dense beds in the mid to lower eulittoral on both exposed 

 and sheltered shores, and on exposed shores providing a microhabitat 

 for the limpets Scurria parasitica and Siphonaria lessonii. Peru- 

 mytilus purpuratus generally occurred with Mytilus edulis chilensis 

 on the upper shore, and was most common in sheltered sites with 

 freshwater influence. Aulacomya atra also formed dense beds in the 

 low eulittoral and sublittoral on wave-exposed coasts, and was 

 probably common in the sublittoral of shelted sites (where 



Fig. 8 Compilation of known geographical ranges for the molluscs recorded in our survey of the Laguna San Rafael, Golfo Elefantes and Estero Elefantes 

 (see text for sources; 46°S latitude of survey area indicated as LSRNP). Superimposed are the biogeographical provincial boundaries of Brattstrom & 

 Johanssen (1983). Antarctic species are those extending south of the Antarctic convergence; Magellanic species are those found only between Cape Horn 

 and the northern limit of the transitional zone (56-30°S); Peruvian species are those found only within the Peruvian Province and transitional zone (2- 

 46°S); widespread species are those found in both Magellanic and Peruvian Provinces and (in two cases) extending north of the equator. Arrows indicate 

 ranges extending beyond the limits shown. Species occurring in the littoral zone and sublittoral fringe are indicated by dots. Note that Xymenopsis 

 cancellinus is a junior synonym of X. subnodosus 



