Amphicteis vestis Hartman, 1965

Parapar, Julio, Helgason, Gudmundur V., Jirkov, Igor & Moreira, Juan, 2011, Taxonomy and distribution of the genus Amphicteis (Polychaeta: Ampharetidae) collected by the BIOICE project in Icelandic waters, Journal of Natural History 45 (23 - 24), pp. 1477-1499 : 1487-1493

Amphicteis vestis Hartman, 1965

( Figures 1 , 6–8 )

Amphicteis vestis: Hartman, 1965: 215–216 , fig. 46.

Material examined

BIOICE sample 2213 (two specimens); 2215 (181); 2216 (two); 2221 (23); 2222 (five); 2226 (one); 2229 (one); 2230 (three); 2233 (one); 2236 (one); 2237 (twenty-nine); 2268 (one); 2273 (six); 2282 (twelve); 2285 (one); 2303 (eight); 2308 (twenty-five); 2311 (one); 2390 (one); 2391 (four), 2392 (three); 2393 (twelve); 2398 (one); 2400 (one); 2401 (thirty-six); 2417 (two); 2418 (six); 2423 (one); 2424 (fifteen); 2434 (five); 2435 (thirty-one); 2469 (one); 2475 (five); 2484 (one); 2712 (one); 2713 (one); 2716 (one); 2717 (sixteen); 2719 (one); 2856 (one); 2859 (three); 2860 (five); 2867 (one hundred and eleven); 2868 (fifty-eight); 2869 (five); 2873 (one); 2976 (three); 2979 (eight); 2983 (43); 3067 (eleven); 3072 (one); 3164 (one); 3500 (one); 3501 (four); 3505 (one); 3510 (three); 3519 (one); 3522 (one); 3524 (one); 3528 (one); 3539 (one); 3550 (sixteen); 3565 (one); 3608 (nineteen); 3617 (sixteen).

Description

Body between 1.4 mm and 10 mm long, and 0.2 to 0.5 mm wide. Thorax and abdomen well defined; thorax about twice width and three times length of abdomen ( Figure 6 ); barely tapering towards posterior part. Prostomium pointed anteriorly with a pair of ciliated pits (nuchal organs?) located at both sides of anterior part ( Figure 7A, B ). No eyes seen. Buccal tentacles few and fairly large, with distal end expanded and ciliated on one side, but not papillated ( Figure 7C–E ). Four pairs of long and deciduous branchiae arranged in one outer row of three pairs and a fourth one in an inner position ( Figure 7F ). All branchiae of similar size; the inner one being thickest and the posteriormost of the outer row thinnest. Between 13 and 15 long and slender paleae with tapering ends. Seventeen thoracic chaetigers with notopodia with notochaetae; the posterior fourteen also with neuropodia with uncini located in a furrow distinctly off the neuropodial margin ( Figure 8A ). First abdominal segment with notopodia transformed in a double-winged expansion stretching across dorsum but with a large median notch ( Figures 6 , 8B–D ); inner margins of fans with ciliature ( Figure 8D, E ); no rows of papillae or ciliature seen in outer margins of fans. Thirteen abdominal segments; anterior ones longer than posterior ones, only with neuropodia with uncini at the very margin of the torus ( Figure 8F ). Pygidium with a pair of short lateral cirri. Notochaetae slightly flattened distally before tapering into slender tips. Thoracic and abdominal uncini slightly different in shape; thoracic uncini with three or four horizontal rows of three or four teeth above rostrum ( Figure 8A ); abdominal uncini with two horizontal rows of seven or eight teeth above rostrum ( Figure 8F ).

Colour in alcohol pale yellow. No tubes observed. Oocytes present in some specimens in the body cavity, visible through body wall.

Occurrence

In all, 730 specimens of A. vestis (40.80% of the total) were collected in 65 BIOICE samples. Amphicteis vestis is present at a wide range of depths and, to a lesser extent, of temperatures, but is more frequent in warm waters of the continental shelf and upper slope of the southwestern coast of Iceland ( Figure 1 ). Depth range: 37–2295 m; temperature range: 2.34–7.41 ◦ C. Given the small body size and fragility of this species coupled with its high quantitative presence in the finest fractions of BIOICE samples (0.5 mm), it is likely that this species has been overlooked in previous benthic studies conducted in its area of distribution (see below).

Reported distribution

Amphicteis vestis has been scarcely reported since its original description by Hartman (1965); it has, however, a wide distributional range. Originally described off New England (West Atlantic Ocean), between 200 and 2469 m depth, it was later reported by Kucheruk (1976) from deeper waters (3240–3350 m) off Alaska Bay (Aleutian Arc, Northeast Pacific) and recently by M. Schüller and B. Ebbe (ANDEEP-SYSTCO, preliminary results on line) from deep Antarctic waters below 2000 m depth. Recently, one of us (I.J.) had the opportunity to examine Antarctic specimens and tried to find Kucheruk’s material in the Shirshov Institute collections where it was supposedly deposited but with no success in the latter case.

Remarks

The presence of dorsal body features is not rare among the ampharetids. One type of these dorsal features is the so called “elevated notopodia” ( Holthe, 1986a:28), which are present in a variety of genera such as Anobothrus Levinsen, 1884 [ Anobothrella Hartman, 1967 syn. and Sosanides Hartmann-Schröder, 1965 syn., sensu Jirkov (2001)], Sosane Malmgren, 1866 [ Sosanella Hartman, 1965 syn., Sosanopsis Hessle, 1917 syn., Mugga Eliason, 1955 syn. and Mugoides Hartman, 1965 syn., sensu Jirkov (2000)] and Eclysippe Eliason, 1955 . Other types of body modification are the “dorsal ridges” present in Melinnampharete Annenkova, 1937 [ Neosamytha Hartman, 1967 syn. sensu Jirkov (2001)] and the “fan-shaped notopodia” present in Jugamphicteis Fauchald and Hancock, 1981 , Ymerana Holthe, 1986 and Zatsepinia Jirkov, 1986 . Some of these genera have previously been reported from Icelandic waters (see Wesenberg-Lund, 1951) and were also found among the ampharetid material from the BIOICE samples, which is currently being studied by the authors.

According to the key to the Ampharetidae genera provided by Reuscher et al. (2009), the presence of this special body feature in the first abdominal chaetiger in A. vestis would locate the species in the genus Jugamphicteis created by Fauchald and Hancock (1981) and later emended by Holthe (2000). This genus is, to date, composed of four species, namely J. sibogae (Caullery, 1944) , J. sargassoensis (Hartman and Fauchald, 1971) , J. paleata Fauchald and Hancock, 1981 and J. galatheae Holthe, 2000 . All Jugamphicteis species share two synapomorphies ( Holthe, 2000:60): presence of prominent nuchal ridges in the prostomium and notopodial fans in the first abdominal chaetiger. Amphicteis vestis shares with the genus Jugamphicteis the following features: number and shape of paleae and branchiae, number of thoracic and abdominal chaetigers and presence of modified notopodia in the first abdominal chaetiger. Fauchald and Hancock (1981:40) and Holthe (2000:60) pointed out, however, that this species should not be placed in Jugamphicteis because of the presence of ciliated nuchal pits in A. vestis instead of nuchal ridges and of bilobed foliose notopodia in the first abdominal chaetiger rather than a valve-like pair. The modified notopodia of A. vestis show other relevant differences to those of Jugamphicteis species. In Jugamphicteis they result from the fusion of most of the notopodial folds of the right and left chaetigers, determining a thin, non-muscular membrane at the inner dorsal sides of both folds, leaving free only the dorsalmost part of each fold which ultimately results in a “valve-like” structure sensu Fauchald and Hancock (1981:41). On the contrary, in A. vestis the pairs of notopodial fans are well-delimited from each other and from those of the other side, hence constituting a “bilobed” structure sensu Fauchald and Hancock (1981). Besides, blunt projections are present on the free margins on the dorsal outer sides of the folds in all Jugamphicteis species ; these are simple in J. paleata and J. sibogae , double in J. galatheae and probably also double in J. sargassoensis . In A. vestis , both lappets are completely free from each other and bear no projections on the lateral margins.

The ciliature observed on the inner free margins of the lateral lappets in A. vestis has never been reported in any ampharetid species. Its biological role is as yet unknown but it is possible that it helps in ventilating the tube.

The presence of fan-shaped notopodia in the thorax–abdomen transitional zone has also been reported in the ampharetid genus Ymerana Holthe, 1986 . Ymerana pteropoda was described as a new genus and species from the Norwegian and Polar seas by Holthe (1986c), who characterized this taxon by the “last pair of (thoracic) notopodia achaetous and transformed into a flattened fan with dorsal lateral wings and ridge across dorsum”. This wing-like notopodium is similar to that of A. vestis although in the latter that structure is present as two pairs instead of one. Furthermore, the genus Ymerana has three pairs of branchiae, no paleae and 14 thoracic chaetigers with notopodia, with the last pair transformed in the aforementioned way, whereas A. vestis has four pairs of branchiae, long and numerous paleae, 17 thoracic notopodia and the fan-like notopodial structure represents the first abdominal chaetiger instead of the last thoracic chaetiger.

Zatsepinia rittichae Jirkov, 1986 , collected from the northern Norwegian coasts and at both sides of the GIF Ridge, also has elevated notopodia but differs from A. vestis in having those structures in the 11th thoracic chaetiger (12 thoracic chaetigers in total), in lacking paleae and in having two pairs of branchiae.

Following the comments mentioned above and the diagnosis of the genus Amphicteis , we agree with Jirkov (2008:115) that the affinities of A. vestis with the genus Amphicteis remain highly uncertain. Hence, the shape of the prostomium, with a pair of ciliated pits (nuchal organs?) instead of the characteristic longitudinal ridges, the buccal tentacles being ciliated instead of smooth, the presence of a unique double dorsal fan in the first abdominal chaetiger and the different shape of both thoracic and abdominal uncini (with one vertical row of teeth in Amphicteis as opposed to multiple rows in A. vestis ) suggest that this species belongs neither to Amphicteis nor Jugamphicteis . Nevertheless, so as not to create more confusion in a highly diverse family with the erection of a new monotypic genus, we decided to maintain the species in Amphicteis pending a much needed revision of the genus.

Figures

Figure 1. Distribution maps of total Amphicteis material examined (A), Amphicteis vestis (B) and Amphicteis wesenbergae sp. nov. (C).

Figure 6. Dorsal view of Amphicteis vestis Hartman, 1965 (IMNH 24082).

Figure 7. Amphicteis vestis Hartman, 1965. Scanning electron micrographs from IMNH 24083. (A) Anterior end in dorsal view; (B) ciliated nuchal pit; (C) ventral view of anterior end; (D) detail of ciliated side of buccal tentacle; (E) detail of non-ciliated side of buccal tentacle; (F) basal scars of right branchiae (numbered). Abbreviations: tno, thoracic notopod.

Figure 8. Amphicteis vestis Hartman, 1965. Scanning electron micrographs from IMNH 24084. (A) Tenth thoracic neuropodia and uncini; (B) first abdominal chaetiger, dorsal view of winged expansion of notopod; (C, D) lateral and dorsal views of transitional zone between thorax and abdomen; (E) detail of ciliature present on inner edge of winged notopodia; (F) first abdominal neuropodia and uncini. Abbreviations: wn, winged notopodia of first abdominal chaetiger; tno, thoracic notopod; tne, thoracic neuropod; ane, abdominal neuropod.