A NEW N.E. ATLANTIC POLYCHAETE 



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 60 





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45 



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40 



£ 





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35 







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30 



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25 





20 





15 





10 



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PAP/53201 



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PAP 



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TAP 



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EOS 



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MAP 



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PAP/53205 



-i 1 1 — I 1 r - 



4 6 8 



Total Length (mm) 



10 



12 



Fig. 4 Graph showing the relationship between size and number of 

 chaetigers. Individuals from different sample sites are identified. PAP- 

 Porcupine Abyssal Plain, MAP - Madeira Abyssal Plain. TAP - Tagus 

 Abyssal Plain, EOS - Cap Verde Abyssal Plain. 



Parapodia biramous; anterior parapodia laterally orientated, be- 

 coming more dorsal in median and posterior chaetigers. A row of 

 cushion-like papillae extending across dorsal surface between 

 notopodia on each chaetiger. 



Notopodia pointed, with straight, blunt-tipped internal aciculae. 

 Dorsal cirri of chaetiger 1 long, thin and tapering; nearly equal in 

 length to median antenna; subsequent dorsal cirri initially shorter 

 with wider bases, but in posterior chaetigers becoming more slender 

 longer and projecting dorsally. Large hooks emergent on chaetiger 3 

 (Fig. lb, 2, 3b) until one or two chaetigers from pygidium; in 

 posterior chaetigers hooks meeting in midline. Short, delicate capil- 

 laries projecting from most notopodia, just one in anterior chaetigers 

 (Fig. lb, 3a), usually becoming two in posterior segments. 



Neuropodial lobes pointed, with blunt-tipped, straight aciculae 

 (Fig 3a); initially orientated laterally but become more vertical and 

 dorsal in posterior chaetigers. Ventral cirri absent on chaetiger 2; on 



12 



10 



u> 8 



■g 



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■6 6 



c 



o 



O 4 



4 6 8 



Total Length (mm) 



10 



12 



Fig. 5 Histogram showing the range of sizes of S.magnuncus collected in 

 the NE Atlantic. 



other chaetigers thin and tapering, equal to or shorter than neuro- 

 podia, equal to or slightly longer than dorsal cirri. Neurochaetae 

 simple capillaries, slightly expanded at the base just free of the 

 podia, tips quickly taper into a prolonged point (Fig. 3 c,d). 



Pygidium with two tapering cirri. Anus dorsal. 



Distribution. S. magnuncus has been recorded from the abyssal 

 plains of the NE Atlantic at depths from 4000 m to 5085 m. 



Etymology. The name of this species derives from the large 

 conspicuous hooks on the notopodia (Latin magnus - large uncus - 

 hook). 



DISCUSSION 



Taxonomic Affinities 



Licher & Westheide ( 1994) suggested that the Pilargidae was not a 

 separate family and that species in the family belonged in the 

 Hesionidae. This hypothesis has been rejected by Pleijel (1998) and 

 Pleijel and Dahlgren (1998) on the basis that Licher & Westheide's 

 (1994) original study was not rooted in an appropriate outgroup. 

 Subsequent analysis by Pleijel and Dahlgren (1998) indicated that 

 the Pilargidae and Hesionidae were different and non-overlapping 

 groups. We. therefore, retain the family Pilargidae. 



Including S. magnuncus, there are 17 described species of 

 Sigambra (Licher and Westheide, 1997). Based on examination of 

 Sigambra material in the NHM and the revision of Licher & 

 Westheide (1997), S. magnuncus shares certain features with S. 

 ocellata (Hartmann-Schroder, 1959), S. bidentata Britaev & 

 Saphronova. 1981 and S. qingdaoensis Licher & Westheide, 1997, 

 namely the ventral cirrus is missing on chaetiger 2 and there are 

 eight papillae in the pharynx (Licher & Westheide, 1997). The 

 relative proportions of the dorsal and ventral cirri suggest similari- 

 ties with S. ocellata, however, in S. magnuncus the notopodial hooks 

 start on chaetiger 3 rather than chaetiger 6 as in S. ocellata. In 

 5. bidentata and S. qingdaoensis the notopodial hooks can start from 

 chaetigers 3, similar to S. magnuncus, but in addition to differences 

 in cirral length, S. magnuncus differs from 5. bidentata in not having 

 bidentate neurochaetae. S. magnuncus differs from S. qingdaoensis 

 in having one capillary notochaeta in anterior chaetigers, becoming 

 two in posterior chaetigers. whereas in S. qingdaoensis there are 

 always two notopodial capillaries. Finally, the notopodial hooks in 

 S. magnuncus are much larger than in comparable sized individuals 

 of the other species. 



Growth and abundance 



S. magnuncus was most common in samples from the Porcupine and 

 Tagus abyssal plains with densities of 4 to 32 individuals per m 2 , 

 while lower numbers were found in the Madeira and Cap Verde 

 samples. This was partly due to lower overall densities of polychaetes 

 at these latter sites (Paterson et at. 1998), but their distribution 

 suggests that this species is more common in northern abyssal areas. 

 Also analysis of the distribution within the sediment suggests that 

 this species is found within the sediment rather than on the surface. 



There is a good range of sizes within the collection, allowing 

 allometric changes to be noted. Notopodial hooks in smaller speci- 

 mens appear to be extremely large, but in larger specimens these 

 hooks are proportionately smaller. This suggests that hooks are 

 produced at a set size, not affected by growth. The hooks always 

 occur first on chaetiger 3. 



Size of specimens ranges from 0.5 to 10.5 mm, although most 



