Antarctic soft-shelled clam Laternula elliptica

Laternula elliptica is found throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Orkney Islands, South Sandwich Islands, South Georgia Island, Kerguelen Island, Marion and Prince Edward Islands at depths from 1 to 458+ meters [3,5,10,11,12,14,15]. The shell of L. elliptica can be up to twelve centimeters in length, and grows to nine centimeters in 12 - 13 years [1,17]. The shell of L. elliptica is elongated with coarse growth lines and a brownish edge along the margin [11]. The shell color of L. elliptica is white with a pinkish or greenish shell covering (periostracum) when alive [12].

Empty shells of Laternula elliptica are shown here. The primary predator of unburied L. elliptica is the seastar Odontaster validus; 12% of its diet can be L. elliptica [2,9]. Predators of damaged L. elliptica that have been unburied by iceberg scouring include the seastar Cryptasterias turqueti, the nemertean Parborlasia corrugatus, the Antarctic whelk Neobuccinum eatoni, and amphipods [9]. Other predators include the fish Trematomus bernacchii and the muricid gastropod Trophon longstaffi [16,18].

Here, two Laternula elliptica have dug themselves into the seafloor so that only their sparkling greenish siphon pairs show above the gravel bottom.

Laternula elliptica lives buried in gravelly or soft mud (infaunal) with a large siphon that cannot be fully retracted into its shell; there is a large gape where the two valves do not close. L. elliptica filter feeds through these siphons and its food includes benthic diatoms [13]. Its fecal material creates a sediment of organic and terrigenous mineral particles which enriches the benthic environment [6]. L. elliptica can burrow into the sediment over fifty centimeters [9]. L. elliptica is found in greatest density in water shallower than thirty meters [5,10]. Population density ranges up to 140 individuals per square meter [4,5,12]. In shallower depths where its food is more plentiful, the deep burrowing of L. elliptica keeps it safe from seafloor scouring by pack ice and icebergs and, secondarily, from predation [5,13]. L. elliptica can re-burrow itself when exposed and is unusual among burrowing bivalves because it is capable of surface movement powered by its siphon muscles and by siphon water jetting [7]. Surface mobility combined with the ability to re-burrow are adaptations by this deep burrowing bivalve to periodic natural environmental disturbances like ice scouring [7]. L. elliptica has a protected mode of development where its embryo develops through larval stages within a protective capsule which facilitates dispersal in the environment [8].

Laternula elliptica is considered to have been a member of an earlier Antarctic fauna when the climate was more genial; it is a common fossil found in beach formations in Antarctica [3,5]. The Laternula genus is widely distributed in the subtropical and tropical Indo-Pacific. Its deep burrowing lifestyle may have given a warm-water mollusc sufficient insulation to adjust to a cold-water habitat [3].

1: Marine Biology 42(2):171-175, 1977; 2: Ecological Monographs 44(1):105-128, 1974; 3: Biogeography and Ecology in Antarctica. J Van Mieghem and P va Oye, eds. The Hague : W. Junk, 1965. Monographiae Biologicae. Volume 15. pp.333-380; 4: Report of the Underwater Association 4:91-95, 1969; 5: Holocene Environmental Changes in Antarctic Coastal Areas : Proceedings of International Workshop held at the National Institute of Polar Research, Tokyo, October 20-22, 1993. PA Berkman and Y Yoshida, eds. Tokyo : National Institute of Polar Research, 1994. Memoirs of National Institute of Polar Research. Special Issue, no. 50 . pp.1-10; 6: Journal of Experimental Marine Biology and Ecology 171(1):75-90, 1993; 7: Journal of Molluscan Studies 63(1):109-111, 1997; 8: Journal of Molluscan Studies 63(2):285-286, 1997; 9: Polar Biology 6(3):139-143, 1986; 10: Antarctic Mollusca : with Special Reference to the Fauna of the Ross Sea. RK Dell. Wellington, NZ : Royal Society of New Zealand, 1990. Bulletin 27, Royal Society of New Zealand; 11: Korean Journal of Polar Research 5(2):15-28, 1994; 12: FAO Species Identification Sheets for Fishery Purposes : Southern Ocean (Fishing Areas 48, 58 and 88) (CCAMLR Convention Area). W Fischer & JC Hureau, eds. Rome: Food and Agriculture Organization of the United Nations, 1985; 13: Antarctic Communities: Species, Structure, and Survival. B Battaglia, J Valencia, and DWH Walton, eds. Cambridge: Cambridge University Press, 1997; 14: South African Journal of Antarctic Research 21(1):45-64, 1991; 15: Polar Biology 20(4):229-247, 1998; 16: Polar Biology 13:291-296, 1993; 17: Ross Sea ecology : Italiantartide Expeditions (1987- 1995). FM Faranda, L Guglielmo, A Ianora, eds. Berlin : Springer, 2000; 18: Polar Biology 26(3):208-217, 2003

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