Leodamas marginatus Ehlers 1897

Leodamas marginatus (Ehlers, 1897)

Figures 28–29 A–C

Aricia marginata Ehlers, 1897: 95 –97, pl. 6, figs. 150–156; 1908: 116; 1912: 23; Willey 1902: 275, pl. 45, fig. 4; Benham 1921: 77; Monro 1930: 144.

Aricia ohlini: Gravier 1911: 105 –107, pl. 6, figs. 70–73. Not Ehlers 1900, 1901.

Naineris marginata: Fauvel 1916: 445, pl. 8, figs. 26–33.

Aricia marginata mcleani Benham, 1921: 78, pl. 9, fig. 90; 1927: 96–97. New synonymy.

Scoloplos (Scoloplos) marginatus: Mesnil & Caullery 1898: 142.

Scoloplos marginatus: Augener 1932a: 109; 1932b: 40; Monro 1936: 159; 1939: 123–124; Fauvel 1951: 762; Bellan 1972: 76; 1975: 789; Arnaud 1974: 557, 561, 638.

Scoloplos (Leodamas) marginatus: Hartman 1952: 232; 1953: 38; 1957: 289; 1966: 11, pl. 2, figs. 6–7; 1967: 108; Rozbaczylo 1985:131; Hartmann-Schröder 1986: 82; Hartmann-Schröder & Rosenfeldt 1988: 53 –54; 1990: 107; Knox 1962: 345; 1998: 465, figs. 133–134.

Scoloplos (Leodamas) marginatus mcleani: Hartman 1966: 11; Averincev 1982: 26 –27, Pl. III, figs. 9–13. New synonymy.

Scoloplos marginatus mcleani: Hardy 1977: 209 –226. New synonymy.

Scoloplos (Leodamas) naumovi Averincev 1982: 37 –38, Plate IV, figs. 1–7. New synonymy.

Scoloplos (Leodamas) sp. Hartman 1967: 108 (in part); 1978: 156.

Material examined. Chile, Patagonian region, Straits of Magellan, Eltanin Sta. 11-960, 64 m (1, USNM 60649).— Tierra del Fuego, Hero Sta. 656, 18 m (2, USNM 60676); Staten Island, Hero Sta. 71-2-6, 0–1 m (2, USNM 60675).— Falkland Islands, Hero Sta. 672, 50 m (1, USNM 60677); Sta. 676, 18 m (1, USNM 60678).—Drake Passage, Eltanin Sta. 9-740, 384– 494 m (1, USNM 56459); Sta. 12-1089, 641 m (1, USNM 56461). — South Orkney Islands, Eastwind Sta. 1966-028, 188–192 m (2, USNM 67615). —N. of Elephant Island, ANDEEP I, R/ V Polarstern, Sta. PS-61/045-1, Otter trawl, 196–269 m (1, SEM, JAB); South Shetland Islands, Hero Sta. 700, 38 m (1, USNM 60682); Sta. 1064, intertidal (2, USNM 60681); Eastwind Sta. 0 8, 97– 113 m (3, USNM 67614); Eltanin Sta. 6-410, 220– 240 m (12, USNM 56463, 60648); Sta. 12-1003, 210– 230 m (1, USNM 56466).—Antarctic Peninsula, off Anvers Island, Hero Sta. 957, 190 m (1 USNM 60679); Sta. 972, 40 m (1, USNM 60680); Sta. 1101, 360– 370 m (1, USNM 60683); Arthur Harbor, Sta. 1897 (1, USNM 69382).—Ross Sea, western sector, Eltanin Sta. 32-2075, 568 m (1, USNM 60670); Sta. 32-2085, 468– 482 m (1, USNM 60671); Sta. 32-2088, 430– 433 m (USNM 60672); Staten Island Sta. 1, 201 m (1, USNM 67613); off Ross Ice Shelf, Eltanin Sta. 32-2065, 473 – 475 m (1, USNM 60669).—Ross Sea, eastern sector, Eltanin Sta. 27-1869, 1565– 1674 m (4, USNM 60651); Sta. 27- 1870, 659– 714 m (9, USNM 60652); Sta. 27-1885, 311– 328 m (6, USNM 60653); Sta. 27-1896, 70– 81 m (2, USNM 60654); Sta. 27-1897, 362– 375 m (1, USNM 60655); Sta. 27-1901, 445– 448 m (1, USNM 60656); Sta. 27- 1903, 640– 646 m (1, USNM 60657); off McMurdo Sound, Eltanin Sta. 27-1907, 891 m (2, USNM, 60658); Sta. 27-1916, 728 m (1, USNM 60659); off Moubray Bay, Eltanin Sta. 32-1995, 344 – 348 m (3, USNM 60660); Sta. 32-1996, 348– 352 m (1, USNM 60661); Sta. 32-1997, 523– 528 m (7, USNM 60662); Sta. 32-2012, 589– 608 m (1, USNM 60663); Sta. 32-2014, 567 m (1, USNM 60664); Sta. 32-2031, 535 m (9, USNM 60665); off Terra Nova Bay, Eltanin Sta. 32-2035, 876 m (1, USNM 60666); Sta. 32-2036, 334– 335 m (1, USNM 60667); Sta. 32-2039, 565– 569 m (1, USNM 60668); off Cape Adare, Sta. 32-2125, 160 – 164 m (1, USNM 60673); Deep Freeze III, Atka Sta. 23, 392 m (1, USNM 67609); Robertson Bay, Deep-Freeze I, Edisto Sta. 3, 27 m (1, USNM 67605); Moubray Bay, Deep Freeze IV, Northwind Sta. 8, 134 m (1, USNM 67612).—McMurdo Sound, Deep Freeze I, Edisto Sta. 8, 321 m (5, USNM 67604); Deep Freeze II, Glacier Sta. 2, 384 m (1, USNM 67606); Sta. 6B, 250 m (2, USNM 67607); Deep Freeze III, Glacier Sta. BL- 16, 140 m (2, USNM 67611); Burton Island Sta. 3, 433 m (8, USNM 67608); off Cape Royds, Ross Island, U.S. Navy Antarctic Expedition, Sta. 99, Jan 29, 1948, 106 m, coll. D.C. Nutt (11, USNM 23869); Sta. 104, 106 m (5, USNM 23853–4); near shore Cape Evans, off Scott’s Hut, 16 Jan 2000, 9 m, coll. S. Kim (1, JAB, SEM).—Budd Coast, Vincennes Bay, near Wilkes Station, Deep Freeze III, Atka Sta. 29, 135 m (1, USNM 67610).—Weddell Sea, Glacier Sta. 69- 1, 513 m (6, USNM 46612).— South Pacific Ocean, SE of New Zealand, near Antipodes Island, Eltanin Sta. 32-2143, 2010 – 2100 m (3, USNM 60674).

Description. Largest specimens posteriorly incomplete, 62 mm long, 3 mm wide for 54 setigers; type specimens reported to be 80 mm long for 102 segments (Ehlers, 1897). Color of larger specimens brown; smaller specimens opaque white to light tan.

Thoracic region with peristomium and first three setigers only slightly flattened, thereafter dorsoventrally flattened; abdominal region cylindrical in cross section. Thorax with 14–20 setigers, 11–19 according to Hartman (1966); transition to abdominal region abrupt.

Prostomium triangular in shape, narrowing to pointed anterior end (Fig. 28 A), appearing somewhat flattened in lateral view (Fig. 29 A); nuchal organ a broad curving slit or groove on either side (Fig. 29 A). Peristomium with one simple asetigerous ring, distinctly separated from setiger 1 (Figs. 28 A, 29A).

Thoracic parapodia all similar; notopodia with cirriform, postsetal lamellae (Fig. 28 A); notopodial lamellae short on setiger 1, becoming full size by setiger 6–8 (Fig. 28 A); thoracic neuropodia with swollen lobes from which rows of uncini emerge (Fig. 28 B); a small triangular-shaped neuropodial postsetal lobe sometimes present from middle body segments. Abdominal parapodia lacking ventral and interramal cirri; each notopodium with long, cirriform postsetal lamella (Fig. 28 D); neuropodium elongated truncate (Fig. 28 D).

Notosetae including crenulated capillaries in thoracic and abdominal notopodia; furcate setae (Fig. 28 E) present in abdominal notopodia. Furcate setae with unequal tynes connected by web of fine needles (Fig. 28 E). Thoracic neuropodia with three long dorsoventral rows and one short, curved fourth transverse row of yellow uncini (Fig. 28 C) curving ventral to first three rows; first and fourth row sometimes appearing to merge into Ushape ventral to rows 3 and 4; uncini thick, blunt-tipped, with lateral notch or groove (Fig. 28 F–G); with SEM groove broad and flattened, continuing from rounded apex and merging with low transverse crenulated ribs extending around shaft, these not seen in light microscopy (Fig. 29 C); with small group of crenulated capillaries sometimes present superior to three rows of uncini, especially in juveniles. Abdominal neuropodia with few smooth, non-crenulated capillaries; embedded acicula present in notopodia; single emergent acicula with curved tip present in neuropodia.

Branchiae from setiger 6, continuing to end of body; each branchia thick, cirriform, tapering to rounded tip, with thick rows of cilia on medial side (Figs. 28 C, 29B).

Biology. Leodamas marginatus is one of the few species of Antarctic polychaetes to be the subject of an investigation of its reproduction, life history, and ecology. Hardy (1977) studied two populations occurring between the littoral zone and 35 m depth on Signi Island in the South Orkney Islands (60°42′S; 45°39′W). Hardy (1977) considered his specimens of L. marginatus to be small, but they were larger than any encountered in the present study, being up to 99 mm long for 185 segments.

Hardy (1977) found the male: female ratio to be 1:1.85, with 38% of the population being juveniles. In midwinter (July) the species was found to spawn a single cocoon containing an average of 551 eggs with an average diameter of 600 µm. Embryos develop slowly to the 3–4 segment stage by September. At that time the larvae hatch and burrow into the substratum where they complete their development, with metamorphosis occurring in December and January. Development is therefore direct, without any planktic larval stage. Another 30 months are required before this cohort spawns. Hence, Hardy (1977) was able to determine that three years are required for one generation of this species to develop and reproduce. Mature females live at least five years and may produce a single cocoon in each of two or three spawning seasons.

Averincev (1982) working in shallow waters in the Davis Sea found the species on rock faces with a thin layer of silt at a depth of about 25 m.

Remarks. Leodamas marginatus is reported to have only uncini in thoracic neuropodia (Hartman, 1957). Some specimens in the present collection, however, have a superior group of long crenulated capillaries located dorsal to the uncini. These capillaries normally occur in the smaller specimens and juveniles. Leodamas marginatus mcleani was distinguished from the stem form by Benham (1921) because a separate group of uncini was present posterior to the three main rows. This character appears to be typical of the species as a whole, however, and a subspecies is not supported; further in some instances, the shorter fourth row merges ventrally with the first row forming a U-shape of uncini ventral to rows 2 and 3. This arrangement is similar to several other species of Leodamas. See further comments with L. cirratus and L. hyphalos (below). Scoloplos (Leodamas) naumovi described by Averincev (1982) from shallow waters of the Davis Sea is not well described, but agrees with the characters reported here for L. marginatus.

Distribution. South America, Straits of Magellan and Patagonian regions; Falkland Islands; sub-Antarctic latitudes off SE Argentina and SE New Zealand; Antarctic Peninsula; Ross Sea; Weddell Sea; Intertidal to 1674 m.