Heterospio longissima Ehlers, 1874 sensu Hartman 1965

Heterospio longissima Ehlers, 1874 sensu Hartman (1965)

(Figures 1–4, 5B, 7A, 8)

Five incomplete specimens were collected in three BIOICE samples (Table 1). BIOICE sample 2414 (1 spec. in SEM stub, IINH27830); BIOICE sample 2474 (1 spec. in SEM stub, IINH27830); BIOICE sample 3500 (3 spec., IINH27831).

Most complete specimen 9 mm long, 0.4 mm wide, with 14 chaetigers. Prostomium conical, anteriorly rounded, slightly flattened dorsoventrally (Figure 2A, B). Eyes absent. Nuchal organs as deep grooves posterolateral to prostomium. Peristomial palps and palp scars not observed. Pharynx sac-like, eversible and unarmed. Anterior body region slightly flattened dorsoventrally, with eight short chaetigers (CH) (Figures 2A, B, 5B). CH 1–8 short, somewhat more than twice as wide as long. Chaetigers progressively longer from CH 9 onwards. CH 9 first elongated segment, longer than wide; length (as distance from chaetal bundle to chaetal cincture of CH 10) about three times longer than CH 8. Branchiae lacking in all specimens but eight pairs of branchial scars present from CH 2 to CH 9 (Figures 2A, B, 5B). CH 1 abranchiate (no scars). The remaining chaetigers strongly elongated and cylindrical in cross-section; length increasing backwards; CH 10 about four times longer than CH 9, CH 11 about 2.5 times longer than CH 10. CH 1–9 with biramous parapodia; with notopodial and neuropodial chaetal fascicles well separated. From CH 10 onwards parapodia as elongated ridges forming a nearly closed flange-like cincture near anterior margin of segment (Figures 2A, B, 3, 5B). Chaetae of CH 1–9 simple capillaries, in fan-shaped fascicles (Figure 2C). No neuropodial hooks in any anterior chaetiger. From CH 10 onwards chaetae arranged in two rows (Figures 2D, 4A,B): anterior row of thick subuluncini (Figure 4D–H) and posterior row of simple fine capillaries (Figure 4C). Aristate or acicular spines not observed.

In Iceland H. longissima sensu Hartman (1965) is restricted to the slope bottoms of the southwestern coast, south Reykjanes Peninsula (Figure 7A). Depth range: 784– 834 m; temperature range: 5.36–5.82°C (Table 1).

Heterospio longissima was described by Ehlers (1874) based on an incomplete specimen from the northeast Atlantic. Hartman (1965) reported the species from the western Atlantic. However, Laubier et al. (1972 –73) pointed out that Hartman’ s material was different from that of Ehlers, but further comparisons to test whether the latter corresponded to a different species were not possible because the holotype was apparently missing (Borowski 1994, p.130). Therefore, Laubier et al. (1972 –73) cautiously considered the existence of two forms of this species: the nominal species and H. longissima sensu Hartman (1965). Since then, most subsequent reports of longosomatids were assigned to either form of H. longissima (e.g. Imajima 1974; Intès and Le Loeuff 1977; Kirkegaard 1980; Amoureux 1982; Rosenfeldt 1989; see Figure 8), but the character combinations of these specimens did not always match those of the two forms (cf. Hartman 1974; Uebelacker 1984). In view of the aforementioned worldwide reports attributed to the species, it is likely that several different species are still waiting to be described, particularly all those reported outside the North Atlantic Ocean (e.g., Hartman 1974; Imajima 1974; Intes and Le Loeuff 1977; Rosenfeldt 1989).

Both Heterospio longissima sensu Hartman (1965) and the nominal species have in common that the first elongated segment is CH 9, but the degree of elongation is different. In H. longissima sensu Hartman CH 9 is about three times longer than previous chaetigers, whereas in H. longissima sensu Ehlers CH 9 is about as long as all the anterior segments together (see Laubier et al. 1972 –73, fig. 3; Borowski 1994, notes 2 and 3 in table 2 on pp.140–143; Bochert and Zettler 2009, key on p.737). Additionally, H.longissima sensu Hartman has chaetae forming cinctures from CH 10 onwards provided with thick subuluncini and fine capillaries, whereas in H. longissima sensu Ehlers all body chaetigers are provided with biramous parapodia with only simple capillaries (see Laubier et al. 1972 –73, p. 250) (Figure 5A– B). Heterospio longissima sensu Hartman most closely resembles Heterospio sinica Wu and Chen, 1966 from the China Sea, Heterospio catalinensis (Hartman, 1944) from off California and Heterospio peruana Borowski, 1994 from off Peru, because all share having CH 9 as the first elongated chaetiger, although clearly shorter than all previous segments as a whole (Figures 5B–D, 6C). Heterospio catalinensis differs from the others by having acicular chaetae in the neuropodium of CH 1. Heterospio sinica and H.peruana are clearly distinguishable from Hartman’ s form of H. longissima by the presence of aristate chaetae on elongate segments. Moreover, while H. sinica also has eight pairs of branchiae in the thorax (Figure 5D), H. peruana has only four pairs (Figure 6C).

Although aristate chaetae as illustrated by Bochert and Zettler (2009) were not observed, the shaft of the subuluncini seems to be articulated with the blade (Figure 4C–H) in a similar manner to that illustrated by Wu and Chen (1966); Borowski (1994) and Wilson (2000a) (see Discussion).