Heterospio reducta Laubier, Picard and Ramos 1972

Heterospio reducta Laubier, Picard and Ramos, 1972 –73

(Figures 6B, 7B, 9, 10)

Thirty-one specimens were collected in 10 BIOICE samples (Table 1). BIOICE sample 2392 (5 spec., IINH27832 and 2 spec. in SEM stub IINH27833); BIOICE sample 2407 (1 spec., IINH27834); BIOICE sample 2414 (3 spec., MNCN 16.01 / 15211); BIOICE sample 2474 (7 spec., IINH27835); BIOICE sample 2719 (1 spec., IINH27836); BIOICE sample 2886 (1 spec., IINH27837); BIOICE sample 2893 (1 spec., IINH27838); BIOICE sample 3500 (5 spec., IINH27839); BIOICE sample 3613 (4 spec., IINH27840); BIOICE sample 3617 (1 spec., MNCN 16.01 /15212).

Most complete specimen 16 mm long, 0.3 mm wide, with 11 chaetigers. Prostomium conical, anteriorly rounded (Figure 9A–C); slightly flattened dorsoventrally. Eyes absent. Nuchal organs as deep grooves posterolateral to prostomium. Peristomial palps and palp scars not observed. Pharynx sac-like, eversible and unarmed (Figure 9C). Anterior body region slightly flattened dorsoventrally (Figure 9A). CH 1–6 short, somewhat more than twice as wide as long. CH 7 about 1.5 times longer than CH 6 (Figure 6B). CH 8 much longer than wide, about four times longer than CH 7 (Figures 6B, 9A). Branchiae lacking in all specimens but three pairs of branchial scars present from CH 2 to CH 4 (Figures 6B, 9A–C). From CH 9 chaetigers strongly elongated and cylindrical in cross-section, length increasing backwards. CH 9 about three times longer than CH 8. CH 1– CH 8 with biramous parapodia; notopodial and neuropodial chaetal fascicles well separated in all chaetigers. Chaetal cinctures near anterior margin of elongated segments not observed. Notochaetal fascicle of CH 7 and particularly CH 8 provided with longer chaetae and more dorsally located (Figures 6B, 9A, 10A). All chaetae fine simple capillaries. No neuropodial hooks in anterior chaetigers. Modified chaetae (subuluncini, aristate or acicular spines) not observed.

Heterospio reducta was found at slope bottoms of the west (Snaefellsnes Peninsula and western Fjords) and southwestern (south Reykjanes Peninsula) coast (Figure 7B). Depth range: 270–922 m; temperature range: 4.57–6.99°C (Table 1).

Originally described from off Algiers by Laubier et al. (1972 –73), the species was later reported by Amoureux (1982) from the continental slope (500–1400 m) off west Ireland.

Heterospio reducta is distinguished from most longosomatids by the smaller number of short anterior chaetigers (CH 1– CH 6), with CH 7 being the first elongated chaetiger, while in other species the latter is either CH 8, CH 9 or CH 10. Laubier et al. (1972 –73), while describing and illustrating CH 7 slightly longer than CH 6, consider CH 8 as the first posterior chaetiger; this is followed by Bochert and Zettler (2009) in their key of worldwide species of Heterospio. As no chaetal cinctures are present in this species, Laubier et al. (1972 –73) used the segment size as evidence of the beginning of the mid-body region, instead of the shape of the chaetal bundles. Hence, in H. reducta the first mid-body chaetiger would actually be CH 7 rather than CH 8 (see above description and Figure 6B). The only substantial difference between Icelandic specimens of H. reducta and those from the type locality is the presence of very long chaetae in the notopodia of CH 8, which are located more dorsally (Figures 9A, 10A).

Heterospio reducta differs from specimens of H. longissima sensu Hartman, 1965 also found in Icelandic waters in the number of short anterior chaetigers (six in H. reducta and eight in H. longissima sensu Hartman) and by having only one type of chaeta; furthermore, in the latter species the chaetae form almost complete circles on elongated chaetigers, which are not observed in H. reducta.

Heterospio reducta differs from H. mediterranea from the Mediterranean Sea and Heterospio sp. A as described by Uebelacker (1984) from the Gulf of Mexico in the number of short anterior chaetigers (seven in these species and six in H. reducta) and in the number of branchiae and chaetal composition, respectively. Hence, H. mediterranea has seven pairs of branchiae while H. reducta has only three; Heterospio sp. A has acicular hooks in the neuropodia of CH 1, whereas in H. reducta there are simple capillaries in both the notopodia and neuropodia.

The species most similar to H. reducta is Heterospio angolana Bochert and Zettler, 2009 from the southeast Atlantic Ocean (Angola). This species has the same number of pairs of branchiae (three) and short anterior chaetigers (six)–although Bochert and Zettler (2009) consider CH 9 as first elongated chaetiger– but they differ in length of CH 8, being more elongated in H. reducta than in H. angolana (Figure 6B,D) and in the very long chaetae of H. reducta on CH 8.