Amphictene auricoma

Amphictene auricoma (O.F. Müller, 1776)

Figs 1A, 2A, 3A, 4 A–B, 5 – 7

Amphitrite auricoma O.F. Müller, 1776: 216.

Amphictene auricoma – Malmgren 1865: 357. — Hutchings & Peart 2002: 103, table 1.

Pectinaria auricoma – Hessle 1917: 78. — Jirkov & Leontovich 2013: 220, key.

Pectinaria (Amphictene) auricoma – Fauvel 1927: 222. — Holthe 1986: 22. — Hartmann-Schröder 1996: 480. — Kirkegaard 1996: 280.

Material examined (117 specimens, 11.0% of all specimens identified, in 18 samples)

ICELAND – North Western Fjords • 3 specs; BIOICE station 489, sample 2946; 65º47′90″ N, 25º38′70″ W; 28 Aug. 1996; 6.20ºC; 35.05 ppm; 228 m depth; sandy silt; IINH-40181 • 1 spec.; BIOICE station 489, sample 2947; 65º47′91″ N, 25º38′68″ W; 29 Aug. 1996; 6.20ºC; 35.05 ppm; 227 m depth; sediment unknown; IINH-40211. – South West to South East coast • 1 spec.; BIOICE station 968, sample 2209; 63º59′01″ N, 23º34′13″ W; 3 Sep. 1992; 7.29ºC; 35.07 ppm; 137 m depth; fine mud; IINH-40117 • 3 specs; BIOICE station 553, sample 2388; 63º30′10″ N, 22º03′70″ W; 30 Jun. 1993; 7.13ºC; 35.10 ppm; 171 m depth; silty sand; IINH-27841 • 1 spec.; BIOICE station 564, sample 2417; 63º09′90″ N, 21º11′80″ W; 2 Jul. 1993; 7.08ºC; 35.11 ppm; 259 m depth; sandy silt; IINH-40113 • 5 specs; BIOICE station 572, sample 2440; 63º20′21″ N, 19º49′55″ W; 4 Jul. 1993; 6.87ºC; 35.10 ppm; 228 m depth; sandy silt; MNCN 16.01/17982 • 1 spec.; BIOICE station 572, sample 2441; 63º20′17″ N, 19º49′60″ W; 4 Jul. 1993; 6.87ºC; 35.10 ppm; 228 m depth; sandy silt; IINH-40119 • 1 spec.; BIOICE station 582, sample 2460; 63º29′65″ N, 21º39′10″ W; 5 Jul. 1993; 7.10ºC; 35.08 ppm; 125 m depth; sediment unknown; IINH-40127 • 42 specs; BIOICE station 583, sample 2463; 63º25′40″ N, 21º39′89″ W; 5 Jul. 1993; 7.12ºC; 35.08 ppm; 133 m depth; silty sand and gravel; IINH-40155 • 4 specs; BIOICE station 715, sample 2817; 63º14′75″ N, 17º50′62″ W; 24 Aug. 1995; 7.18ºC; 35.14 ppm; 204 m depth; sediment unknown; IINH-40165 • 5 specs; BIOICE station 717, sample 2824; 63º30′12″ N, 17º42′07″ W; 25 Aug. 1995; 7.24ºC; 35.13 ppm; 120 m depth; gravelly sand; IINH-40166 • 6 specs; BIOICE station 723, sample 2837; 63º16′66″ N, 16º53′52″ W; 26 Aug. 1995; 6.74ºC; 35.12 ppm; 601 m depth; sandy gravel and corals; IINH-40170 • 18 specs; BIOICE station 275, sample 2998; 63º38′20″ N, 14º43′50″ W; 5 Jul. 1997; 7.76ºC; 35.19 ppm; 264 m depth; silty sand; IINH-40213 • 5 specs; BIOICE station 275, sample 2999; 63º38′20″ N, 14º43′60″ W; 5 Jul. 1997; 7.76ºC; 35.19 ppm; 269 m depth; sediment unknown; IINH-40293 • 14 specs; BIOICE station 299, sample 3061; 63º59′49″ N, 14º09′21″ W; 10 Jul. 1997; 7.59ºC; 35.16 ppm; 221 m depth; sediment unknown; IINH-40461 • 4 specs; BIOICE station 725, sample 3257; 63º20′10″ N, 19º52′20″ W; 11 Sep. 2001; 7.92ºC; 35.19 ppm; 221 m depth; sediment unknown; IINH-40462 • 1 spec.; BIOICE station 734, sample 3275; 63º23′10″ N, 16º16′20″ W; 15 Sep. 2001; 7.97ºC; 35.20 ppm; 305 m depth; sediment unknown; IINH-40463 • 1 spec.; BIOICE station 407, sample 3610; 63º58′80″ N, 25º30′48″ W; 12 Sep. 2003; 7.43ºC; 35.17 ppm; 188 m depth; silty sand; IINH-40464.

From off West and South of Reykjanes Peninsula to Höfn at SE; two additional samples from off northwestern fjords (Fig. 1). Depth range: 120 to 305 m (sample 2837: 601 m, not shown); bottom temperature range: 6.20 to 7.97°C (Fig. 2A). Water mass/es: MNAW.

Species of Amphictene bear a characteristic crenulated opercular rim, that is not present in other genera (Figs 4A, 5A). Amphictene auricoma – type locality: Denmark (Holthe 1986) – has been the only species of the genus reported in North Atlantic waters and also bears thick paleae with sharp tips (Fig. 5A), scaphe with crenulated margins (Fig. 6D), 17 uniramous and 13 biramous chaetigers, and distally curved scaphal hooks (Fig. 6E). However, Hutchings & Peart (2002: table 1) pointed out that there is “a considerable variation recorded for this species” in the North Atlantic. General morphology of BIOICE specimens agree well with previous descriptions and the aforementioned characters; however, SEM examination revealed that several pygidial and uncini features differ from what was described for A. auricoma. First, Holthe (1986: fig. 4c) and Hartmann-Schröder (1996: fig. 234c) mentioned a long “anal tongue” and “anal cirrus”, corresponding to the “anal lobe” and “anal papilla” (after Hutchings & Peart 2002), that are much shorter in BIOICE specimens (Fig. 6D).

On the other hand, the uncini of A. auricoma have been described as having 1–2 vertical rows of main teeth (cf. Hartmann-Schröder 1971: fig. 157b, and later works: Holthe 1986: fig. 4e; Hartman-Schröder 1996: fig. 234b). However, SEM micrographs of BIOICE material shows a well-defined rostrum, surrounded in all its length by long teeth forming, in turn, a subrostral process (Fig. 6 A–B); the rostrum is surmounted by a capitium constituted by many large teeth not arranged in vertical lines (as described in the original description) but with a typical avicular arrangement (Figs 5 E–F, 6A–B). Anyway, these uncini may resemble in lateral view (Fig. 6C) the typical ones of A. auricoma and this may have led previous authors to confusion.

In addition, uncinal denticulation shows dorsoventral variation within chaetigers depending on body size. Thus, in large specimens (Fig. 3A) uncini seem avicular along the whole torus (Fig. 5 E–F); in smaller ones, the avicular uncini are only found in the dorsal part of the torus (Fig. 7A, C) while in the ventral side all capitium teeth are similar in size and covering most of the rostrum (only showing the pointed distal end; Fig. 7B, D). This pattern is even more evident in the last unciniger, where the capitium teeth seem mixed with those of the subrostral process and leaving a small opening through which the tip of the rostrum is visible (Fig. 7E).

Finally, we have found two longitudinal rows of ciliated tufts/patches along the whole ventral body surface (Fig. 5B) that have not been mentioned in the literature to the best of our knowledge, and those tufts may be related to water irrigation within the tube.