Laonice bahusiensis Soderstrom 1920

Laonice bahusiensis Söderström, 1920

(Figs 2, 3, 4, 5A, 18A, 19A, Table 3)

Laonice bahusiensis Söderström, 1920: 4–7, 81–83, 93, 98, 99, 110, 114, 128, 134, 195, 223, figs 78–82. Maciolek 2000: 534- 535, table 1. Jelsing 2003: 244, figs 1H, 3E, F. Sikorski 2003 (Part.): 320–325, figs 3A–I, 4A, B, 5A, B, 6F. Jelsing & Eibye-Jacobsen 2010: 376–377, figs 1–4.

Type locality. SWEDEN, Skagerrak, Gullmarfjord, Bohuslän, approximately 58.25°N, 11.00°E, Zool. Stn. 1893.

Type material. SMNH 4637 (lectotype), 4636, 4638 (11 paralectotypes); ZMMU Pl 973 (2 paralectotypes); UUZM 153 c, d, f, g (70 paralectotypes).

Adult morphology. Up to 60 mm long, 1.2 mm wide for 120 chaetigers. Lectotype complete specimen in three fragments, totally 41 mm long, 1.0 mm wide for 107 chaetigers. Pigmentation on body and palps absent.

Prostomium triangular, anteriorly wide, usually broadly rounded, occasionally truncate to slightly concave, fused with fronto-lateral margin of peristomium (Fig. 2A, G), posteriorly extending over 32 chaetigers (to end of chaetiger 26 in lectotype) as a low narrow caruncle, shorter in small individuals (Fig. 4A). Nuchal organs U-shaped ciliary bands on sides of caruncle (Fig. 2A). Length of nuchal organs was strongly correlated with individual number of branchiate chaetigers (Fig. 4C, r 2 = 0.7247, n = 76). Well-developed occipital antenna present in the lectotype (Fig. 3B) and in some specimens (21 of the 69 paralectotypes deposited at the UUZM), but may often be small or even greatly reduced (Fig. 3A). Two pairs of red eyes (appearing very dark red, almost black, in large formalin-fixed specimens) arranged trapezoidally, comprising one pair of large median eyes and one pair of small lateral eyes situated anteriorly and set wider apart; lateral eyes well separated from median pair but often deeply embedded inside epithelium and hardly discernible, especially in large individuals. Palps as long as 5–15 chaetigers, with deep frontal longitudinal groove lined with cilia.

Chaetiger 1 with well-developed capillary chaetae and small postchaetal lamellae in both rami; notopodial lamellae triangular; neuropodial lamellae rounded. All notopodia with capillary chaetae only. Low prechaetal lamellae present in noto- and neuropodia on anterior chaetigers after chaetiger 1. Notopodial postchaetal lamellae large, leaf-like on branchiate chaetigers, greatly diminishing in size on posterior abranchiate chaetigers; lamellae on anterior branchiate chaetigers with upper tips pointed (Fig. 2C–E). Neuropodial postchaetal lamellae ear-like on branchiate chaetigers, greatly diminishing in size on posterior abranchiate chaetigers.

Branchiae from chaetiger 2, up to 35 pairs (on chaetigers 2–32 in lectotype); first pair shorter or similar in length to notopodial postchaetal lamellae of chaetiger 2; from chaetigers 5–6 branchiae up to twice as long as notopodial postchaetal lamellae (Figs 2E, 3A, B), gradually diminishing in size on succeeding chaetigers, posteriorly present on 0–10 chaetigers after end of nuchal organs (Figs 4A, C, 19A). Branchiae free from lamellae, slightly flattened, with surfaces oriented perpendicular to body axis, with ciliation along inner and outer edges. Afferent and efferent branchial blood vessels forming a loop and interconnected by numerous circular capillaries giving branchiae annulate appearance. Individual number of branchiae was strongly correlated with length of nuchal organs (Fig. 4C).

Dorsal transverse crests connecting notopodial postchaetal lamellae present, one per chaetiger, beginning on a chaetiger posterior to caruncle and continuing up to the 21 succeeding chaetigers (Fig. 2B) (on chaetigers 27–47 in lectotype).

Lateral interneuropodial pouches from chaetigers 8–25 (from chaetiger 17 in lectotype) to end of the body. Anterior start of pouches was weakly correlated with individual number of branchiate chaetiger (Fig. 18A, r 2 = 0.3928, n = 77).

Sabre chaetae in neuropodia from chaetigers 10–20 (from chaetiger 19 in lectotype), from more anterior chaetigers in small individuals (Fig. 4B), 1–3 in a tuft; chaetae with weak granulation on shaft. First appearance of sabre chaetae in neuropodia was weakly correlated with individual number of branchiae (Fig. 4D, r 2 = 0. 2879, n = 76).

Hooded hooks in neuropodia from chaetigers 18–32 (from chaetiger 29 in lectotype), from more anterior chaetigers in small individuals (Fig. 4B), up to 14 in a series. Hooks tridentate or quinquedentate, with one or two pairs of upper teeth and a very small median superior tooth above main fang (Fig. 3D). Start of hooks in neuropodia was moderately correlated with the individual number of branchiae (Fig. 4D, r 2 = 0.6559, n = 76).

Pygidium with up to seven pairs of cirri arranged around terminal anus, comprising one pair of ventral cirri and up to six pairs of thinner and longer dorsal cirri (Fig. 3C); fewer cirri in small individuals.

Digestive tract without gizzard-like structure.

Reproduction. Laonice bahusiensis is dioecious. The lectotype is a female with small (apparently not yet fully developed) oocytes.

Methylene green staining. Tips of notopodial postchaetal lamellae from chaetigers 4–5 to chaetigers 6–12 usually well stained (Fig. 2G). Narrow bands of light staining present dorsally along anterior edge of prostomium and peristomium (Fig. 2G) and ventrally around mouth (Fig. 2F).

Remarks. Most species of Laonice typically have one occipital antenna on the prostomium, inserted between the palp bases. In the L. bahusiensis examined in our study, the length of the occipital antennae varied a great deal, with more than half of the type specimens having neither occipital antenna nor scars to suggest that they were broken. In other type and non-type specimens possessing all the other characteristics of the species, a well-developed antenna was not always present between the palps.

Distribution. Norwegian Sea, from Kolvereidvågen (64.9°N) south to Kattegat, Västra, Sweden and off Frederikshavn, Denmark (Fig. 5A). At 14–373 m depth.