Polar Biol (1995) 15:307-317 �9 Springer-Verlag 1995

J.I. 5i.aiz Salinas

Sipuncula of the southeastern Weddell Sea (Antarctica)

Received: 8 July 1994/Accepted: 30 September 1994

Abstract Sipunculans collected during the EPOS ("European PoIarstern Study") leg 3 cruise (13.1.89-10.3.89) to the Weddell Sea shelf area from dept as ranging from 186 to 2037 m are recorded. Seven species in three genera are recognized; Nephasoma capiIleforme and Phascolion convestitum have not been recorded hitherto in Antarctica. Significant mor- phological characters as shown by light (LM) and elec- tron (SEM) photographs are described and illustrated. Antarctic distribution maps of the species collected and a chezklist of the sipunculan species south of the Ant- arctic Convergence with depths and bibliographic ref- erences are included.

Introd.ction

The current knowledge of South Polar Sea sipunculans is based on the results of several cruises, mainly to the Anta:ctic Peninsula, around the Scotia Arc, Ross Sea and to other locations close to the eastern part of the Antarctic coast. The credit for the first published de- scripl[on of a sipunculan from the Southern Ocean should perhaps go to the French naturalist Lesson (18301, who named Sipunculus Iumbrisciformis from So- ledad, the eastern Falkland Island. Baird (1868) re- ported Phascolosoma capsiforme from the same group of Islands. Apparently, the first sipunculan collections from localities south of the Antarctic Convergence were taken by the German "Deutsche Polarkommission", which wintered at South Georgia during the years 1882--1883, the sipunculans being described by Michz,~elsen (1889). Next, the "Swedish Antarctic Ex- pedition" of 1901-1903 made important collections. The sipunculans were described by Th6el (1911), who

J.I. Sai:_~ Sa l inas Univer:ddad del Pals Vasco, E-4808~1 Bilbao, Apdo. 644, Spain

also discussed the phenomenon of bipolarity. Although a few more species were collected by several further expeditions, the most extensive collections prior to leg 3 EPOS were made mainly during the cruises of several British and Russian research vessels (Dell 1972). To date, 12 species, plus 2 additional subspecies of sipun- culans organized in 3 genera, have been recognised from Antarctic seas. An updated list of all sipunculans found south of the Antarctic Convergence with depths and bibliographic references is given in Table 1. The most recent and comprehensive review of this fauna covering sub-Antarctic and Antarctic waters is that of Edmonds (1969).

Until recently (cf. Voss 1988), nothing was known about the composition, abundance, diversity and distri- bution of sipunculans in the Weddell Sea. The pack-ice cover prevents sampling throughout most of the year. Water temperatures are relatively constant (below - I ~ on the shelf, whereas some variations (rising

above 0.4~ have been recorded in the deeper bottom waters (Arntz et al. 1992). The "European Polarstern Study" (EPOS) expedition to the Weddell Sea col- lected, in January-March 1989, a large number of macrobenthic samples, which were later distributed for identification among international taxonomists (Arntz et al. 1990). The aims of the present work are: (1) to document the systematics of the collection of sipun- culans, and (2) to compare the results with other in- formation about their distribution south of the Antarc- tic Convergence.

Materials and methods

The EPOS leg 3 research programme was carried out from the RV "Polarsrern" in three areas of the southeastern Weddell Sea: Kapp Norvegia, Vestkapp and Halley Bay. Samples were taken both quantitatively with a ninefold simultaneous sediment sampler or multibox corer (MG) and non-quantitatively with three types of trawls (AGT, Agassiz trawl; GSN, bottomtrawl; and BPN,

308

Table 1 Checklist of sipunculans beyond the Antarctic Convergence together with their known depth ranges. Each record is composed of two letters plus two or three numbers indicating respectively the author name (first two letters) and year of publication in the literature. An asterisk * indicates the species collected in the present work

Phylum SIPUNCULA Sedgwick 1898 Class S IPUNCULIDEA Cutler and Gibbs 1985 Order GOLFINGI IFORMES Cutler and Gibbs 1985 Family GOLFINGIIDAE Stephen and Edmonds 1972 Genus Golfingia Lankester 1885 Subgenus Golfingia (Golfingia) Lankester 1885 1. G. (GoIfingia) anderssoni Th6ek 1911"

depth range: 75-2037 m

2. G. (Golfingia) elongata Keferstein 1863 depth range: 40 m

3. G. (Golfingia) margaritacea margaritacea Sars 1851" depth range: 8-3030 m

G. ( Go!fingia) margaritacea ohlini Th6el 1911" depth range: 4-1900 m

4. G. (Golfingia) muricaudata Southern 1913" depth range: 186-2037 m

Genus Nephasoma Pergament 1946 5. N. abyssorum benharni Stephen 1948

depth range: 540-640 m 6. N. capilleforme Murina 1973"

depth range: 1948-2037 m 7. N. co~fusurn Sluiter 1902

depth range: 650 4556 m 8. N. diaphanes diaphanes Gerould 1913"

depth range: 443-6150 m N. diaphanes corrugaturn Cutler and Cutler 1986

depth range: 1779-1879 m 9. N. eremita Sars 1851'

depth range: 300-920 m (2012 ?m)

Family PHASCOLIDAE Cutler and Gibbs 1985 Genus Phascolion Th6el 1875 Subgenus Phascolion (PhascoIion)

10. Phascolion ( Phascolion) strombus Montagu 1804 depth range: 100 (28?)-400 m

Subgenus Phascolion (Isomya) Cutler and Cutler 1985 11. Ph. (Isomya) hedraeum Selenka et al. 1883

depth range: 698 m 12. Ph. (Isomya) convestitum Sluiter 1902"

depth range: 483-705 m Subgenus Phascolion (Montuga) Gibbs 1985 13. Ph. (Montuga) lutense Selenka 1885

depth range: 1820-6150 m

14. Ph. (Montuga) pacificum Murina 1957 depth range: 296-6070 m

Ed65 Mu 57a Mu 72 Mu 74 Si 90 St 41 St 48 Th 11

He 06 He 07a He 07b

Be 22 Cu 80 Ed 65 Fi 895 Fi 20 Fi 28 He 06 He 07a He 07b La 08 Mi 889 Mu 57a Mu 64 Mu 72 Mu 78 Sh 02 Si 90 St 41 St 48 Th 11

Ar 74 Be 22 Cu 80 Ed 65 Ed 72 Fi 20 Mu 57a Mu 72 Mu 74 Mu 93 Si 90 St 41 St 48 Th 11

Fi 22

Fi 28 St 48

Mu 57a Mu 72 Mu 74

Mu 57a Mu 72 Mu 74

Mu 74

Be 22 Mu 72 Mu 93

Mu 78

Mu 72 Fi 28 Si 90 St 41 Th 11 St 48?

Cu 80

Mu 57b Mu 61 Mu 72 Mu 74 Mu 78 Se 885

Mu 72 Mu 74 Mu 78

benthopelagic trawl). For further details reference should be made to the expedition report by Arntz et al. (1990).

The preserved benthic material was sorted into groups at CENTOB (French Sorting Centre, IFREMER, Brest) and later distributed to taxonomists in Europe. A total of 383 specimens of sipunculan worms, collected from 28 trawls and 56 cores, was received by the author for study. In the laboratory, the specimens

were sorted under a Carl Zeiss Jena Citoval dissecting microscope, and parts of the integument mounted for examination using No- marski interference microscopy (Nikon Labophot) and scanning electron microscopy (Jeol JSM-T 220 A).

Identifications were based mainly on the works of Stephen and Edmonds (1972), Murina (1977), and Cutler (1995) and the generic revisions of Cutler and Cutler (1985, 1986, 1987a). The classification

309

Tab;e 2 Data summary of sipunculan fauna from the southeastern Weddell Sea (Arntz et al. 1990). Each station number is preceded by letters indicating the type of gear used: AGT, Agassiz trawl; GSN, bot tom trawl; BPN, semipelagic (benthopelagic, 1088) trawl; MG, mul~ibox corer (between parentheses is indicated the box

number). Species names are abridged as follows: G and, Golfingia anderssoni ; G mar, Golfingia margaritacea ; G tour, Golfingia muricaudata ; N cap, Nephasoma capilleforme; N dia, Nephasoma diaphanes ; N ere, Nephasoma eremita ; N sp, Nephasoma species; P con, Phascolion (Isomya) convestitum

GEA R ST. H A U L D E P T H L O N G S LAT W TAXA

GS)~ 217 3 237 60~ ' 46~ , 4 G mar GSN 224 4 186 71~ ' 13~ ' 1 G a n d 2 G m a r 1 G m u r M G 224 02 (1) 193 71~ ' 12059 ' 2 G mar M G 224 02(2) 193 71~ ' 12059 ' 1 G m a r M G 224 02 (3) 193 71~ , 12059 ' 2 G mar M G 224 02 (3)? 193 71~ 12~ ' 4 G mar M G 224 02 (4) 193 71~ ' 12~ ' 3 G mar M G 224 02(5) 193 71~ ' t2~ ` 1 G m a r AGT 226 1 593 75 ~ 17' 25~ 1 G and GSI~? 226 5 574 75 ~ 15' 25 ~ 2 G and 8 G mar M G 226 03 (8) 577 75~ ' 25~ ' 1 G mar M G 226 03 (9) 577 75~ 25~ ' 1 G and 2 G mar AGT 229 4 498 75~ ` 26~ ` 2 G m a r M G 229 04(t) 506 75~ ' 26~ ` 2 G m a r M G 229 04(3) 506 75~ ' 26~ ' 1 G a n d M G 229 04 (4) 506 75 ~ 14' 26013 ' 2 G mar 1 G mar? M G 229 04 (5) 506 75 ~ 14' 26 ~ 13' 2 G mar M G 229 04 (6) 506 75~ ' 26~ ' 1 G mar M G 229 04(7) 506 75~ ' 26~ 2 G m a r M G 229 04 (9) 506 75 ~ 14' 26~ ' 1 G mar A G 2 230 5 270 75~ ' 26~ ' 1 G mar GSN 235 7 407 75~ ' 27034 ` 2 G and 18 G mar AGT 235 7 404 75~ ` 27~ , 3 G mar M G 235 06 (3) 399 75~ ' 27~ ' 1 G mar M G 235 06 (4) 399 75 ~ 27~ ' 1 G mar M G 235 06(7) 399 75~ ' 27~ ` 5 G m a r M G 235 06 (8) 399 75 ~ 27~ ' 1 G mar AGT 241 8 462 75~ ' 27~ ' 1 G and 3 G mar G S N 241 8 451 75~ ' 28~ , 1 G mar M G 241 07 (1) 462 75~ ` 28~ , 1 G and M G 241 07(4) 462 75~ ' 28~ ' 1G and 1 G mar AGT 245 9 483 74~ ' 29~ , 1 G a n d 2 G m a r 1 N d i a G S N 245 9 516 74039 ' 29~ ` 3 G mar M G 245 08 (2) 500 74~ ' 29~ ' 1 G mar M G 245 08 (3) 500 74~ ' 29~ ' 1 G mar 1 N dia M G 245 08 (5) 500 74~ ` 29o40 ' 1 G mar M G 245 08 (6) 500 74~ ` 29~ ' 2 G mar M G 245 08 (7) 500 74~ , 29~ , 2 G mar G S N 248 10 602 74039 ' 29~ , 4 G a n d 3 G m a r 1 P c o n M G 248 09 (1) 610 74038 ' 29~ ` 1 G mar 1 N dia M G 248 09(4) 610 74~ ' 29~ ' 1 G m a r 1 N d i a M G 248 09 (6) 610 74~ ' 29~ ' 1 N dia 1 P con M G 248 09 (9) 610 74~ ` 29~ ' 1 P con M G 249 10 (2) 705 74~ ' 29o40 ̀ 1 N dia M G 249 10 (3) 705 74~ ' 29~ ` 1 P con M G 250 11 (2) 820 74~ ' 29~ ` 1 G mar M G 250 12 (2) 839 74~ ' 29~ ' 1 G mar M G 250 12 (3) 839 74~ , 29~ ` 1 G mar A G T 252 12 1153 74028 ̀ 29~ ' 11 N d i a M G 252 13 (3) 1185 74~ ` 29~ ' 1 N dia M G 252 13 (5) 1185 74032 ' 29~ ` 1 G m a r M G 252 13(9) 1185 74~ ' 29 ~ 18' 1 G mar AGT 253 13 2012 74009 ̀ 29041 ` 1 5 2 G m u r 2 N d i a 1 N e r e ? M G 253 14 (6) 1948 74~ ' 30~ ' 1 N cap BPN 258 3 484 74040 ̀ 29036 ' 1 G mar AGT 270 14 294 73021 ' 20045 ` 1 G mar A G T 272 16 409 73~ ' 21~ 1 G mar AGT 273 17 197 73~ ` 21~ ' 1 G m a r AGT 274 18 196 71~ , 12~ , 1 G m a r 3 G m u r M G 274 15 (1) 211 71~ ' 12o10 , 1 N? sp

1 P con

310

Table 2 (continued)

GEAR ST. H A U L D E P T H L O N G S LAT W TAXA

M G 274 15(2) 211 71~ , 12~ ' 1 2 G m a r M G 274 15 (3) 211 71~ ' 12~ ' 1 G mar M G 274 15(4) 211 71~ ' 12o10 ' 3 G m a r M G 274 15 (6) 211 71~ ' 12~ ' 1 G mar M G 274 15 (7) 211 71~ 12 ~ 3 G mar AGT 275 19 301 71~ ` 12~ ' 3 G m a r M G 277 17 (3) 405 71~ ` 12~ ' 2 G mar M G 277 17(5) 405 71039 , 12034 ' 1 G m a r M G 277 17 (9) 405 71~ ' 12o34 ' 2 G mar M G 278 20(3) 537 71~ ' 12o32 ' 3 G m a r M G 278 20 (5) 537 71~ ' 12~ ` 3 G mar AGT 281 21 402 71~ ` 12~ , 1 G mar AGT 282 22 609 71~ ' 12027 ' 3 G m a r G S N 284 13 402 71 ~ 12' 13 ~ 14' 7 G mar AGT 289 23 672 71 ~ 13o27 ' 6 G mar G S N 291 14 499 71~ ' 12%3' 1 G and M G 292 21 (1) 561 71o03 ' 12~ ' 1 N dia? M G 292 21 (2) 561 71~ ` 12~ ' 1 N dia M G 292 21 (3) 561 71~ , 12~ ' 1 G m a r M G 292 21 (4) 561 71~ ' 12042 ' 1 G m a r GSN 293 15 771 71o06 ' 12~ ' 1 Nere AGT 295 26 2037 71~ 13~ ' 1 G and M G 295 24 (4) 2037 71~ 13~ ` 1 G mar M G 295 24 (7) 2037 71~ 13~ , 1 G mar

8 G mar 1 N dia 2 P con

1 N dia

1 N ? s p 4 G m u r 1 N cap

and terminology of Cutler have been used and all supra- specific categories have been taken from this work. The material examined is now in the collection at the Mus6um National d'His- toire Naturelle in Paris.

pendage 1-12 mm long. Large bladder-like papillae up to 1 mm in diameter at the posterior end. Introvert without hooks. Four retractor muscles, the ventrals attached in the middle of the trunk.

Systematic results

The collection was found to contain 7 species of Si- puncula: 168 specimens were identified as Golfingia margaritacea (Sars 1851), 160 specimens as Golfingia muricaudata (Southern 1913), 24 specimens as Nephasoma diaphanes (Gerould 1913), 18 specimens as Golfingia anderssoni (Thbel 1911), 7 specimens as Phascolion (Isomya) convestitum (Sluiter 1902), 2 spe- cimens as Nephasoma capilleforme (Murina, 1973); 2 specimens as Nephasoma eremita (Sars 1851), 2 other specimens were assigned tentatively to Nephasoma. Table 2 lists the stations sampled with depths, locations and gears used. Detailed descriptions and synonyms of the taxa have been omitted, but where necessary a cita- tion for a reliable description, preferably recent, is given.

Golfingia anderssoni (Th6el, 1911)

Description

Trunk 5-110 mm long, mostly 29-110 ram; introvert slightly longer or shorter than the trunk. Caudal ap-

Remarks

The presence of both large posterior papillae and a caudal appendage is diagnostic for this species (Cutler and Cutler 1987a). Externally, G. muricaudata re- sembles G. anderssoni (Cutler and Cutler 1987b), from which it can be separated mainly by the absence of bladder-like papillae at the posterior end of the trunk. Some small specimens from stations 224, 291 and 295 with small swollen papillae were difficult to identify with complete confidence, since they also fit the de- scription of G. muricaudata. A problem arose concern- ing differences in these bladder-like papillae as the size of the animal changes. The material that I had showed intermediate stages with relatively small swollen papil- lae on a 5-mm specimen from station 291 (Fig. 1A) or inconspicuous papillae on two of the four specimens coming from stations 224 and 295. The specimens that under the binocular microscope showed any trace of papillae at the posterior end of the trunk were inter- preted as G. muricaudata, in spite of the fact that they appeared simultaneously with G. anderssoni. Whether these structures are affected by environmental influen- ces, or whether the bladder-like papillae are the final

311

Fig. 1A-F Photographs (LM: E,F, others SEM) of Antarctic sipun- culans. A Small swollen papillae on a 5-mm specimen of Golfingia anderssoni, B,C Presence (arrows in B) and absence of hooks on two small specimens of G. margaritacea, D Caudal appendage of G.

muricaudara, E Small scattered hooks of Nephasoma capilleforme, F Weakly swollen anterior part of the trunk of the same species. Scale bars: E 30 gm; F 100 ~m

stage of development of a unique species, remains to be demonstrated.

G. anderssoni has been collected from almost all Antarctic waters except the Bellingshausen and Amund-

sen Seas (Fig. 2A). The distribution of the species is mainly restricted to the southern hemisphere at depths of 75 1880 m (Cutler 1995), although some other iso- lated records exist.

Fig. 2A-D Distribution maps of Antarctic sipuncula.ns. A Golfingia anderssoni, B G. margaritacea, C G. muricaudata (with crosses) and Nephasoma erernita (with rhombs), D N. diaphanes

(A)

50~ S ~

(C) (D)

'~

312

Golfingia margaritacea (Sars, 1851)

Description

Trunk 1.3-110 mm in length and 0.71-28 mm in width. Some specimens show a distinctive pointed posterior end, but others are clearly rounded. Introvert usually shorter than the trunk. Hooks deciduous, small speci- mens ( < 24 mm) usually bear scattered small hooks, 24-60 gm high, whereas larger specimens lack these. Conspicuous papillae at the posterior end of the trunk. Four retractor muscles, the ventrals attached in the middle third of the trunk. Nephridia open above the anus .

Remarks

Recently Cutler and Cutler (1987a) reviewed the complex nomenclatural history of what they called a golfingiid 'superspecies', since many of the characters used by previous authors were considered variations

within one biological species. Only the name Phas- colosoma ohlini, proposed by Th6eI (1911), escaped complete demotion, since it was ranked at a sub- specific level within the broad margaritacea complex. The two alleged differences in comparison with the nominal form are: (i) the presence of hooks, and (ii) the presence of a pointed posterior end of the trunk. However the identification of this subspecific popula- tion is troublesome, since the nominal form has been also recognised from Antarctic seas by several authors (Table 1), in many cases as a variety or subspecies that is now merely a junior synonym of the nominal form. The question, then, is whether the aforemen- tioned characters are sufficiently basic and constant to be utilized in separating these common Antarctic subspecies. According to Cutler and Cutler (1987a, Fig. 2), the putative differences become highly variable, since smaller specimens within one population may bear hooks and possess rounded to pointed posterior ends. Accordingly the retention of a subspecific rank cannot be upheld. Therefore my specimens have been identified only as far as the specific level.

313

Although experimental evidence is lacking, G. mar?aritacea is known to be influenced by environ- mel~ ml factors in many of its characters, particularly the external ones, as has been summarized by Cutler and Cutler (1987a). Besides the variations in size fronl gigantic to dwarf specimens, with some of the smaller specimens (less than 7 mm long from stations. 217, 274, 284, 289 and 291) having ova in the coelom, my material showed variability of hooks, some being deciduous in the small specimens (Fig. 1B-C), and posterior trunk ends. This again reinforces the diffi- cult2~ in justifying taxonomic differences within such a plastic species on morphological grounds. If the vari;.bility of G. margaritacea in Antarctic waters encompasses the striking ability to alternate between r-strategies and K-strategies depending on environ- menial variables, this would explain the attainment of n:aturity at different sizes, but it remains to be demonstrated.

G. margaritacea is the commonest Antarctic sipun- cula:a (see Fig. 2B). It has been recorded in all Antarc- tic ~vaters except for the Lazarev, Riiser-Larsen, Amundsen and Bellingshausen Seas. According to Cutb.~r (1995), the species is widely distributed through- out :he oceans of the world, especially in shallow wate:*s.

Golfi:'~gia muricaudata (Southern, 1913)

Description

Tru•k 4-55 mm long; introvert shorter than the trunk. Caudal appendage 0.5-7 mm long (Fig. 1D). Introvert without hooks. Four retractor muscles, the ventrals attaclaed in the first fifth of the trunk.

Remcrks

The ;~resence of a caudal appendage and the absence of both hooks and bladder-like papillae at the base of the caudal appendage are diagnostics for this species. G. m~ricaudata and G. anderssoni are similar exter- nally except that in the latter bladder-like papillae are present at the base of the caudal appendage. Conse- quently, in this report all specimens without papillae, or traces of them, have been identified as G. muric~udata. Antarctic records of the species are rare, however (Fig. 2C); the only one, from Bouvet Island, is that of Fischer (1922). The finding of these speci- mens from the southeastern Weddell Sea extends both the known latitudinal and vertical range of the species in Antarctica, the latter to bathyal depths. Ac- cording to Cutler (1995), the species is known mainly from deep waters of the Atlantic and southeastern Indian Oceans, but some records come also from Paci- fic waters.

Nephasoma capilleforme (Murina, 1973)

Description

Slender 5.5-mm-long trunk that is 0.36mm wide. Trunk length to width ratio about 15:1. Introvert shorter than the trunk. Scattered hooks, 30-36 gm in height (Fig. 1E). Anterior part of the trunk weakly swollen and gold coloured (Fig. 1F). Posterior part of the trunk with thick cuticle bearing ovoid skin bodies. Two retractors are attached in the middle third of the trunk. Intestine well coiled.

Remarks

In Nephasoma capilleforme the trunk is thread-like and lacks papillae and the introvert hooks are small (Murina 1973). Cutler and Cutler (1986) refered to additional specimens with introverts longer than the trunk and an intestine with loosely wound coils, characters that are now diagnostic in their key to Nephasoma species. However Murina (1973) also reported shorter introverts in some specimens and figured a well-coiled intestine for the type material. While this species is alleged to have small hooks (20-25 gm), my material had larger ones (30-36 gm), making me uncertain about this identifica- tion. Since my specimens varied somewhat from the Murina (1973) and Cutler and Cutler (1986) descrip- tions, positive assignment to Nephasoma capilleforme becomes doubtful. The presence of a slender trunk with a golden-coloured anterior swelling has helped me with an identification.

Nephasoma capilleforme has not been recorded pre- viously in Antarctica. Some published records of N. glacialis were considered later to be N. capilleforme as stated by Cutler and Cutler (1987b); N. capilleforme is known from two deep-water localities close to the Falkland Islands (Murina 1974). Its distribution is now located in some areas of the southern and northern Atlantic and southern Pacific Oceans at depths of 82-5840 m (usually over 2000 m).

Nephasoma diaphanes (Gerould, 1913)

Description

Trunk 2-5 mm long; introvert shorter than the trunk. Ratio of trunk length to width is 2.3:10. Skin smooth and translucent. Posterior part of trunk with thick cuticle bearing ovoid skin bodies. Scattered hooks (Fig. 3A), 24 48 gm in height. Two retractors are attached to the trunk in the middle third of the trunk. Some mature specimens with ova are recorded.

314

Fig. 3A-E Photographs (LM: C, F, others SEM) of Antarctic sipun- culans. A-C Hooks of N. diaphanes showing pyramidal edges (arrow in B) and circular bases (arrow in C), D Papillae on anterior part of

trunk in Phascolion convestitum, E Holdfast papillae of the same species, F Recurved and broad-based hooks of this species. Scale bars: C, 10 gm; F, 30 btm.

Remarks

As outlined by Saiz Salinas (1993) N. diaphanes serves as an 'omnium gatherum' for all the small Nephasoma species. Because the introverts of my specimens were contracted, it was impossible to determine whether the

tentacles had been reduced to lobes, a character de- scribed for the species. The remaining characters ap- pear to justify assignment to this taxon, based on their small size, cylindrical appearance of the trunk covered by ovoid skin bodies, and the lateral view of the hook shorter on its concave side. While the hooks from

315

station 248 have circular bases (Fig. 3B), those from stations 245, 249, 252, 253, and 292 are pyramidal (Fig. 3C). In this respect they resemble, respectively, N. lilljeborgi (Gibbs 1982) or small-sized specimens of hi. abyssorum (Saiz Salinas 1990). In view of the variability of the hook shape shown by my material, it seems advisable to regard them as N. diaphanes since a wide range of variation in cuticular structures has beer previously recognised for this species (Cutler 19720.

With the generic revision of Cutler and Cutler (1985), the names Golfinoia minura and Golfingia schfit- tei [which Murina (1972, 1974) used to identify some Antarctic material] were abandoned as the organism were: classed as two subspecies of Nephasoma diapha- nes, namely the nominal form and Nephasoma diapha- nes corrugatum, both of which had previously been colle,zted from bathyal depths in different areas of the Antarctic Ocean (Table 1, Fig. 2D). Nephasoma diaphanes is a cosmopolitan, deep-water species (Cutler 1995~.

Nep,"asoma eremita (Sars, 1851)

Desc~qption

Trur;k 5-55 mm long; introvert a little longer. Papillae distributed over the entire trunk, larger and crowded aroulad the posterior end. Hooks absent. Two retractor muscles originate in the middle third of the trunk.

Rem,:r

The lack of hooks and the presence of numerous papil- lae over most of the trunk distinguish this species from othe; Nephasoma. The only specimen from station 253 was placed here with reservations, since its introvert tip was Jamaged. Some of the external features of N. eremita, however, must be variable, since Phascolosoma eremita austraIis Benham, established on differences in the dJ stribution and size of its papillae, was recorded as a syr onym for N. eremita by Cutler and Cutler (1986). Therffore the species is already known from bathyal bottoms of Antarctic seas (Table 1, Fig. 2C). Cutler and Cutler (1980) characterized N. eremita as a bipolar, bath)al species.

Phascolion (Isomya) convestitum (Sluiter, 1902)

Description

Trunk 1.5-10mm long; introvert slightly longer or shorter than the trunk. Skin smooth and opaque. Digi- tate papillae 120-170 gm tall (Fig. 3D) on the anterior part of the trunk. Granular holdfast papillae (Fig. 3E) 150-200 gm tall, interspersed in middle trunk region. At the posterior end of the trunk digitate papillae about 70 ~tm high. Scattered, broad-based, recurred and well- cuticularized hooks (Fig. 3F), 20-130 gm in height. Two retractors of equal width, originate at the end of the trunk.

Remarks

The presence of two retractors of approximately equal size, a weak cuticularized border on holdfast papillae and broad-based recurred hooks are diagnostic for this species. The hooks are distinctive and identify this species as P. convestitum, rather than the closely related P. hedraeum Selenka et al. 1883-84, the latter already known from Antarctic seas. The new taxonomical con- cept of Phascolion convestitum, proposed by Cutler and Cutler (1985), has synonymized two junior names, giv- ing as a result the picture of a shallow-water species found at isolated localities in the Indian Ocean and Mediterranean Sea. It is a little disturbing to broaden the distribution of this species to include Antarctic shallow water; my record is the first for Antarctic seas. However, I suspect that some of the previous records of Phascolion species from Antarctic seas could well fit my material. For instance, Th6el (1911) with some hesita- tion referred several Antarctic specimens to Phascolion strombus, since they presented slightly larger hooks and more irregular holdfast papillae. His careful analysis and excellent drawing of the internal anatomy (Th6e!, 1911) are even more disconcerting, because they show the presence of two almost equal-sized retractors even with the introvert fully everted. Finding these speci- mens from the Weddell Sea extends both the known latitudinal and vertical ranges of P. convestitum, the latter to bathyal depths.

Discussion

Nepk~soma sp.

Remarks

Despite the presence of two retractors, by reason of their small size, missing introverts or bad preservation, my specimens could not be referred to any existing speci~::s of this genus.

The survey of the sipunculan fauna was carried out as a part of a study of the benthos of three areas of the southeastern Weddell Sea. About 22,000 free-living in- vertebrates coming from the non-quantitative gears were sorted on board, of which 278 were received as sipunculans for identification purposes, i.e. 1.26% of the macrobiota, which is quite low. The greater part of the continental shelf and slope in the southeastern

316

Weddell Sea consists of soft bottoms inhabited by a sipunculan population composed almost entirely of Golfingia margaritacea. Specimens collected from multibox corers (MG) gave a maximum density of 500 individuals per square metre. However, the mean den- sity is much lower, with 62 individuals per square metre, whereas the remaining species of sipunculans showed mean densities below 5 individuals per square meter. Despite these low figures, sipunculans were not rare in the sampling, being present in 28 trawls and 56 cores, which represents about 57% of the total samples. This overall pattern was also corroborated by updating the results of the semi-quantitative study of macroben- thic assemblages (Gal~ron et al. 1992), in which sipun- culans were present in 70% of the trawls, whereas they were only common in 8% of them. One trawl (station 253 at 2012 m depth) was exceptionally productive, since it yielded 152 individuals of G. muricaudata from a single haul.

Gigantism for Golfingia anderssoni and G. mar- garitacea specimens has already been recognized by Arnaud (1974), G. anderssoni with a maximal individual weight of 35 g (Edmonds 1969). Taking into account the specimens collected from multibox corers (MG), sipunculans attained a mean biomass value of 3.5 g (wet weight) per m 2 (CENTOB, personal communi- cation), which is quite low when compared with the mean overall density of the benthos biota, which reached values of 0.12-1644 g wet wt. m -2 (Gerdes et al. 1992). The evidence for a high variability at nearly all stations was readily apparent, with a large biomass standard deviation of 583.6, which confirmed the out- lined strategy (Arntz et al. 1992) of high biomass patches in the soft bottom distribution of echiurans and sipunculans from the Weddell Sea.

In relation to their bathymetric range, the EPOS sipunculans can be divided roughly into two major groups. The first group contains members of Golfingia margaritacea, G. anderssoni and PhascoIion convestitum which in about 95% of cases prefer the depth range 186-610m, although occasional specimens can be found at greater depths. A second group of deeper- water inhabitants comprises G. muricaudata and N. capilleforme, and these species are found mostly below 1948 m. N. diaphanes, however, seems not to show bathymetric preferences, being the most eurybathic species.

There are some faunal characteristics and affinities that deserve to be pointed out. The number of sipun- culan species obtained in this study is higher than that previously reported from Antarctic waters, and is com- parable with that compiled by Murina (1972) from widely separated locations off Antarctica. Almost all species have been reported by former expeditions, except for N. capilleforme and P. convestitum. The close external resemblance of the latter to P. strombus has probably prevented the recognition of P. convestitum in the area for so long. The seven species identified from

the EPOS leg 3 expedition testify once more to the relative poverty of sipunculan species as a component of Antarctic benthos. This fauna now includes 14 spe- cies-group taxa organized into only three genera. No endemism is recorded. The majority of the representa- tives of the Antarctic fauna are either widespread and eurytopic species, or cold deep-water members that have penetrated the deep bottoms of this marine eco- system. Their affinity with the far southern hemisphere sipunculan fauna is tenuous, since the latter comprises 11 genera and 32 species, as seen from the updated detailed distribution maps of Edmonds (1969). The indication for a latitudinal diversity gradient of sipun- culans, corresponding to a similar pattern known for some other invertebrate groups, e.g. decapods and fishes (cf Clarke and Crame 1989), is given by the fact that the cold waters around Antarctica appear to be unsuitable for 8 genera and 19 species, especially for those belonging to the class Phascolosomatidea, which show a higher thermophilic distribution.

The main feature of the distribution of sipunculans in the Southern Oceans is the progressive loss of species richness along a polar gradient from locations above the Antarctic Convergence to the high latitudinal Antarctic regions. While unobserved factors may be of importance in the explanation of this loss of biodiversity, the effects of extremely cold temperatures appear to be the main struc- turing factor. In conclusion, the Antarctic sipunculan fauna can be described as a depauperate outlying element of the far Southern hemisphere fauna.

Acknowledgements The European Polarstern Study (EPOS) was sponsored by the European Science Foundation and the Alfred Wegener Institute for Polar and Marine Research. This work was carried out under the auspices of two Spanish Council of Scientific and Technical Research (CICYT) Antarctic Programmes (no. ANT 93-0996 and no. ANT 94 1161-E). I thank G. Franc6s for working on a part of the collection and Dr. S.J. Edmonds for helpful com- ments on the manuscript.

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