Aricidea (Strelzovia) parabelgicae Sikorski, 2017, n. sp.

Aricidea (Strelzovia) parabelgicae n. sp.

(Figs 1, 2)

Material examined. 3940 Askeladd Beta SA –4; 71.4781°N – 20.4501°E (Finnmark); 270 m; 26.06.2007; holotype (ZMBN 116012) and five paratypes (ZMBN 116013). 3940 Askeladd Beta SA –2; 71.4751°N – 20.4476°E; 278 m (Finmmark); 26.06.2007; two paratypes (ZMBN 116014). 3940 Askeladd Beta SA–1; 71.4762°N–20.4454°E; 275 m; 26.06.2007; one specimen. 4664 Hasselmus HT1–05; 64.3988°N–7.7123°E; 252 m; 10.06.2009; two specimens. 5796 Linnorm ON–09; 64.4164°N–6.9609°E; 300 m; 09.06.2012; seven specimens.

Description. Holotype longest specimen, complete, 10.0 mm long for 105 chaetigers, 0.3 wide at tenth chaetiger level. Branchial region very slightly inflated and flattened, composed of segments twice wider than long; postbranchial region cylindrical, segments as long as wide. Preserved specimens whitish, without any colour marking. Prostomium rounded, slightly wider than long; antenna or insertion scar totally absent; apical sensory organ as a minute rounded pitch located on anterior margin of prostomium (Figs 1A, 2A, B); eyes absent. Mouth anteriorly oriented; anterior lip as a double ridge extending inward mouth, posterior lip extending through first chaetiger only. Nuchal organs straight and oblique, joining to posterior end of prostomium; secondary ciliary organs appreciable, extending obliquely from near posterior end of nuchal organs to anterior end of corresponding lateral lip (Figs 1A, 2C). Branchiae from chaetiger 5 (Figs 1A, 2A, B), reaching chaetiger 12; all similar in length, nearly reaching mid-dorsal line except the last two pairs, which are slightly shorter; tips of branchiae tapering (Figs 1A, B, 2D). Notopodial postchaetal lobe short and subulate on prebranchial chaetiger 1, digitiform and twice as long on prebranchial chaetigers 3 and 4 (Figs 1A, 2B, C); progressively increasing in length through branchial region, becoming nearly as long as corresponding branchia (Figs 1B, 2D); on most of post-branchial region similar in shape to posterior thoracic ones but half sized (Fig. 1C); long again in the last 14 chaetigers (Fig. 1D). Neuropodial postchaetal lobe as low ridge, of even height on prebranchial and branchial chaetigers; with a subpodial flange on postbranchial chaetigers; interramal process not observed. Chaetae of pre- and branchial segments in dense fascicles, arranged in two rows in both noto- and neuropodia, those of posterior row at least twice longer; notochaetae thin and slightly curved, numbering 5 on chaetiger 1, 15 on chaetiger 7, and 25 on chaetiger 12; neurochaetae thicker than notochaetae, narrowly limbate, and slightly geniculate, numbering 14 on chaetiger 1, 40 on chaetiger 7, and decreasing to 30 on chaetiger 12. Chaetae of postbranchial segments as straight capillaries, clearly thicker in neuropodia (Fig. 1 C, D); far less numerous than on branchial segments (seven notochaetae and 15 neurochaetae on chaetiger 58); modified neurochaetae from chaetiger 72, gradually tapering, with a terminal mucro as continuation of tip (Fig. 1D). Pygidium rounded, bearing two pairs of triangular pygidial cirri, ventral pair one and a half as long as dorsal one and similar in length to last chaetiger.

Remarks. The new species is very similar to Aricidea (S.) belgicae (Fauvel, 1936), from Antarctic waters (Fauvel 1936). The two species have virtually identical prostomia regarding both the disposition of sensory organs and the lack of antenna (Hartley 1984; López 2008). However, A. (S.) parabelgicae n. sp. has four instead of three prebranchial chaetigers, an infrequent condition in Aricidea species (Strelzov 1973; Aguirrezabalaga & Gil 2009) that is not shared with A. (S.) belgicae (López, 2008). Clear differences in the branchiae can also be observed, since the new species bears distinctly fewer branchiae (up to seven pairs instead of 13 pairs) that are shorter and do not surpass mid–body level as in A. (S.) belgicae (López, 2008). Additionally, the notopodial postchaetal lobes are all similarly shaped and bear a subdistal swelling from chaetiger 1 in A. (S.) belgicae (López 2008), whereas in the new species those of chaetiger 1 are very short and subulate and the remainder are very long and digitiform. López (2008) assessed the taxonomic status of the Aricidea species lacking antenna and the systematic significance of this character, and considered other features, such as the presence of secondary ciliary organs or the nuchal organs contacting the posterior end of prostomium, as more significant in order to characterize species of the genus.

Within the genus, A. (S.) mediterranea (Laubier & Ramos, 1974), from deep Mediterranean waters, and A. (S.) sardai Aguirrezabalaga & Gil, 2009, from Bay of Biscay, resemble the new species in having four prebranchial chaetigers followed by less than 10 pairs of branchiae. However, these two species bear antennae (bifurcate in A. (S.) mediterranea and club shaped in A. (S.) sardai) and their modified chaetae have a pubescent area near the beginning of the mucro (Laubier & Ramos 1974; Aguirrezabalaga & Gil 2009). Furthermore, A. (S.) mediterranea have digitiform notopodial postchaetal lobes from chaetiger 2, instead of beginning on chaetiger 3 as in A. (S.) parabelgicae n. sp. Aricidea (S.) facilis Strelzov, 1973 from deep waters of the central Pacific Ocean is likewise similar, as it has three or four prebranchial chaetigers and nine to 15 pairs of branchiae (Strelzov 1973). However, besides having a short antenna and modified chaetae with a subdistal pubescent area, it differs from A. (S.) parabelgicae n. sp. in the ventral lip, which indents at the second chaetiger, and in the notopodial postchaetal lobes, which are digitiform from chaetiger 1 and shorten strongly on the posterior-most branchial chaetigers, becoming five times shorter than the preceding ones (Strelzov 1973) and disappearing after chaetiger 15 (Aguirrezabalaga & Gil 2009).

Etymology. The specific name of the taxon refers to its resemblance to Aricidea (S.) belgicae (Fauvel, 1936).