An Antarctic collection of Latrunculia apicalis contained as its major secondary metabolite the pigment discorhabdin C as well as a previously unreported pigment, discorhabdin G. Discorhabdin alkaloids have a variety of pharmacological and ecological bioactivities, including the mediation of interactions with the potential predator Perknaster, a spongivorous sea star. Sponges of the genus Latrunculia have been the subject of several chemical investigations, leading to the discovery of the ichthyotoxic latrunculins A and B from a Red Sea L. magnifica (1), the cytotoxic discorhabdins A-F (e.g., 1), from several South Pacific Latrunculia species including the New Zealand L. cf. bocagei (2), and L. brevis from both New Zealand (3-6) and Australia (7), and terpenoid peroxides from an uncharacterized Australian Latrunculia species (8). Discorhabdins A and D have also been isolated from the Japanese sponge Prianos melanos (9,10), along with the related prianosin B (11). Discorhabdin A and its probable biosynthetic precursors, the makaluvamines (e.g., 3), have been reported from the South Pacific sponge Zyzzya sp. (12). Our collection of Latrunculia apicalis Ridley and Dendy (family Latrunculiidae, order Hadromerida), collected in McMurdo Sound, Antarctica, was found to exhibit significant bioactivity, including activity influencing sea star feeding behavior and antibiotic activity (13-15). In addition to discorhabdin C [1], bioactivity in our collections of Antarctic Latrunculia can be traced to a new discorhabdin alkaloid, discorhabdin G [2]. Sponges were collected using scuba between 6 and 40 m depth from Hut Point, Danger Slopes, and Cape Evans on Ross Island, Antarctica (77° 51.5' S; 166° 39' E). Organisms were freeze-dried, then subjected to solvent extraction of increasing polarity: hexane, CHCl₃, MeOH, and 70:30 MeOH-H₂O. The CHCl₃ and MeOH extracts of L. apicalis displayed significant activity in an ecological assay to identify extracts deterrent toward the major sponge predator on the Antarctic benthos, the sea star Perknaster fuscus (14). The MeOH extract was applied to a Sephadex LH-20 column and the first green fraction was collected. Repeated reversed-phase hplc (35% MeOH in 0.05% aqueous trifluoroacetic acid) resulted in purification of a red and a green pigment. The red pigment was identified as discorhabdin C [1] by comparison of its ¹H- and ¹³C- (Table 1) nmr data to those reported previously (3). The green pigment could not be correlated to a known discorhabdin alkaloid and was given the designation discorhabdin G [2].