Melinnopsis Angolensis (Annelida: Polychaeta: Ampharetidae), a New Species from the Angola Basin Brigitte Hilbig

ARTICLE IN PRESS

Organisms, Diversity & Evolution 5 (2005) 215–220 www.elsevier.de/ode RESULTS OFTHE DIVA-1 EXPEDITION OFRV ‘‘METEOR’’ (CRUISE M48/1) Melinnopsis angolensis (Annelida: Polychaeta: Ampharetidae), a new species from the Angola Basin Brigitte Hilbig

Lehrstuhl fu¨r Spezielle Zoologie, Ruhr-Universita¨t Bochum, Germany

Abstract

A new species of ampharetid polychaetes, Melinnopsis angolensis sp. nov. is described. It was collected with an Agassiz trawl at seven stations in the Angola Basin in depths between 5385 and 5448 m. The new species differs from the few other species described in this genus by the number of thoracic setigers, the number of enlarged tentacles, presence of reduced notosetae in the anterior thorax, and morphological details of the gills and postbranchial membrane. A brief overview of the other species of the genus is given, and the synonymization of Amelinna and Melinnopsides with Melinnopsis is discussed. r 2004 Elsevier GmbH. All rights reserved.

Keywords: Polychaeta; Ampharetidae; Deep sea; Melinnopsis; Southeast Atlantic

Introduction Material and methods

During the expedition DIVA 1 with the RV ‘‘Meteor’’ The stations at which specimens of Melinnopsis to the Angola Basin in July 2000, six areas with several angolensis sp. nov. were collected are listed in Table 1, stations each for different types of gear were defined the whole transect is depicted in Fig. 1. along a 700-km transect through the length of the basin. The animals were fixed in 4% formalin and preserved In each of these areas, a modified Agassiz trawl in 70% ethanol. For examination, they were carefully (Kro¨ ncke and Tu¨ rkay 2003) was employed, among extracted from their tubes, measured (length excluding other gear, to collect samples of the large benthic epi- tentacles, width in thorax region), and drawn with the and infaunal organisms. These samples were to be used help of a dissection microscope. Details of the setae were to help answer basic questions about the species richness examined with a Zeiss Axioskop. The type material is in the deep oceans of the world on the one hand and a lodged at the Zoological Museum Hamburg (ZMH) possible gradient in infaunal diversity from the equator (holotype) and the Senckenberg Museum Frankfurt to the poles on the other, although the latter question (SMF) (2 paratypes), additional specimens are harbored was addressed mainly with the quantitative analysis of at the ZMH (ZMH P-24672 through ZMH P-24675) box core samples. Much of the benthic infauna in and the SMF(SMF13827, SMF13828). general and the polychaete material in particular turned out to belong to undescribed species. Among those, a yet unknown ampharetid was found which is described in this paper. Description

Material examined: Expedition DIVA-1, RV ‘‘Me- E-mail address: [email protected] (B. Hilbig). teor’’, Area 5, Sta. 343, holotype (ZMH P-24671) and 2

Table 1. Areas and stations where M. angolensis was collected with an Agassiz trawl

Area Station Position at Beginning Position at End Depth (m) Specimens

2 327 19159.20S, 3100.90E20107.50S, 3107.90E 5448–5439 1 3 333 19112.90S, 3148.00E19117.40S, 3152.20E 5424–5426 7 3 334 19112.50S, 3149.00E19119.80S, 3155.60E 5425–5426 5 4 337 18103.30S, 4137.90E18124.60S, 4145.10E 5393 11 4 339 18105.60S, 4134.90E18125.30S, 4144.00E 5389–5406 15 5 343 17107.50S, 4142.90E17111.60S, 4145.90E 5415 3 6 351 16125.20S, 5127.10e16133.20S, 5127.30E 5385–5387 2

Fig. 1. Transect of areas sampled with a modified Agassiz trawl during expedition DIVA 1. paratypes (SMF13826). Additional specimens: Area 2, Sta. 327 (1 incomplete), Area 3, Sta. 333 (3 complete or nearly complete, 4 incomplete), Sta. 334 (2 complete, 3 incomplete), Area 4, Sta. 337 (4 complete, 7 incomplete), Sta. 339 (4 complete, 11 incomplete) Area 6, Sta 351 (1 complete, 1 incomplete). Holotype (Figs. 2 and 3) 22 mm long, 3 mm wide for 52 setigers. Length of other complete specimens 21–50 mm (n ¼ 14; including some that were obviously Fig. 2. M. angolensis sp. nov. (a) holotype (ZMH P-24671), lacking only a few prepygidial segments and/or the habitus, ventrolateral view; and (b) prostomium, schematic pygidium), width 3–4 mm, setigers 17 thoracic +25–38 dorsal view. Scale bar: 2 mm. abdominal. Body arched and inflated through anterior six segments (Figs. 2a and 3a), wide and somewhat flattened through remainder of thorax, abdomen con- Setigers 1 and 2 with needle-like neurosetae only, siderably narrower, gradually tapering toward pygi- somewhat flattened, covered with fine surficial spines dium. Segments generally short and crowded, (Fig. 4), setigers 3 and 4 also with small notosetae; lengthening in posterior part of abdomen. Several remaining thoracic setigers with stiff regular notosetae specimens ovigerous or filled with sperm; ripe females armed with surficial spines (Fig. 5) and about 70–90 greenish, ripe males pink; color fading quickly in neuropodial uncini per fascicle, bearing four teeth in a alcohol. Some tubes filled with yellowish eggs or white row (Fig. 3d); abdominal uncini similar, somewhat sperm packets. smaller, apical teeth paired and arranged side-by-side Prostomium scoop-shaped, with crescentic nuchal (Fig. 3e), about 20–25 per fascicle. organs (Fig. 2b). Buccal tentacles grooved, in two rows Branchiae four pairs, fused at bases, arising from on tentacular membrane; anterior (ventralmost) row short membrane, arranged with three pairs in a front consisting of about six short ones, easily breaking off; row and the fourth slightly behind; somewhat flattened posterior (dorsalmost) row consisting of 4–6 long ones, but not distinctly foliaceous, innermost one of each exceeding the others considerably in length and width. group longer than others or all branchiae subequal, ARTICLE IN PRESS B. Hilbig / Organisms, Diversity & Evolution 5 (2005) 215–220 217

Fig. 4. M. angolensis sp. nov., regular notosetae, SEM micrographs. (a) Middle region, surficial spines; and (b) Fig. 3. M. angolensis sp. nov. (a) anterior end, ventrolateral subdistal region from the ‘‘backside’’. view; (b) last thoracic and first abdominal segments, lateral view; (c) posterior end, ventral view; (d) thoracic uncinus; (e) abdominal uncinus. (a–c) holotype, (d–e) additional specimen. Scale bars: (a–c) 1 mm. gently tapering to filiform tips; roughly half as long as longest tentacles. Postbranchial dorsal membrane long and narrow, distinct when not damaged, serrated, with about 10–15 teeth, rarely up to 21. Setiger 1 with deep ventral pocket at anterior margin, edge scalloped, concealing thick yellowish glandular area of lower lip. Neuropodial tori in thorax about twice as long as in abdomen. First four abdominal segments with globular lobe above neuropodial torus, may be notopodial rudiments; lacking in following segments (Fig. 3b). Last few preanal segments lengthening and softening, followed by large, longitudinally ridged pygidium (Fig. 3c). Anus terminal, wide, surrounded with circlet of about 20 small papillae representing ends of ridges. Tubes thick-walled, about 2–3 times as long as animals, muddy with fine inner mucus lining. Etymology: The species name refers to the type Fig. 5. M. angolensis sp. nov., modified neurosetae of locality in the Angola Basin. anteriormost setigers, SEM micrographs. (a) surficial spines, Distribution: Angola Basin, southeast Atlantic ocean, middle region; (b) part of fascicle; (c) subdistal region, in depths greater than 5000 m. ‘‘frontal’’ view; and (d) same, ‘‘lateral’’ view. ARTICLE IN PRESS 218 B. Hilbig / Organisms, Diversity & Evolution 5 (2005) 215–220

Table 2. Valid genera of the ampharetid subfamily Melinninae (according to Holthe 1986 and Jirkov 1989) and some of the main discriminating characters

Genus (# species) Pairs branchiae Notosetae Neuropodia Nuchal Dorsal crest Tentacles Thoracic from with spines hooks (segment 6) uncinigers

Isolda (5) 1 or 2 smooth 5 or 7 ? 1 pair Present ? 12 or 13 Mu¨ ller, 1858 2 pennate Melinantipoda (1) 4 smooth 5 and 6 (fine) 3–6 Absent Present Similar 16 Hartman, 1967 Melinna (26) 4 smooth 5 or 6 (fine), 3–5 or 6 Present Present Similar 14 Malmgren, 1866 7 (limbate) Melinnopsides (1) 3 smooth 5 ? Absent Absent Similar 10 Day, 1964 (illustration) Melinnopsis (12) 3–4 smooth 5 (fine), 3 or 4–6 Absent Present or 1 or more long, 10–14 McIntosh, 1885 7 (limbate) absent many short Moyanus (1) 4 smooth ? ? 2 pairs on Present ? 12 Chamberlin, 1919 4 and 5

Remarks: The genera of the subfamily Melinninae are Among the characters for species discrimination there closely related and sometimes not very well separated are some that are unusually variable compared to the (Table 2). The only character common to all genera other Melinninae, namely the number of thoracic described to date is the presence of minute neuropodial uncinigers and the presence or absence of the postbran- spines in a few segments anterior to the first notosetae chial dorsal membrane (Table 3). which in turn may be much finer in the first one or two Of the 12 species of Melinnopsis, only two known setigers than in the following ones. All other characters species have a thoracic region with 13 regular uncinigers. typical for the name-giving genus Melinna, such as the One of these species, M. moorei (Hartman, 1960) from presence of large dorsal (‘‘nuchal’’) hooks anterior to the off California, differs markedly from M. angolensis sp. branchiae and a postbranchial dorsal crest or mem- nov. in the morphology of the branchiae, which are very brane, are variable among the other genera of the broad and foliaceous and abruptly taper toward the subfamily. Melinnopsis lacks nuchal hooks (although filiform tips, whereas the branchiae of the new species tubercles in the same place are reported for M. somovi are only somewhat flattened and taper gently. Addi- (Ushakov 1957)) and differs from most other Melinni- tionally, M. moorei has reduced notosetae only on the nae by the tentacles which include one or a few that are last segment with needlelike neurosetae (segment 6), considerably larger than the others. However, a yet whereas M. angolensis n. sp. has these notosetae on the undescribed species of Melinna from the US continental two last segments with needlelike neurosetae (segments 5 slope and rise has very inconspicuous nuchal hooks and and 6). M. armipotens (Moore, 1923) co-occurs with M. a median tentacle that is much larger than the others moorei even though it has a much wider depth range (Ruff, pers. comm.). This species may eventually prove than the latter. This species apparently has only two the genus Melinnopsis invalid and a synonym of very large tentacles aside from several regular-sized Melinna. For the time being, however, until the Atlantic ones, the postbranchial membrane is absent according species has been formally described, the genus Melin- to the text (although a structure is illustrated by Moore nopsis McItosh, 1885 is accepted as defined by Holthe indicating at least the presence of a dorsal ridge across (1986). One other genus, Amelinna Hartman, 1969, also segment 6), and needlelike neurosetae are present on has tentacles of two different sizes. The genus was segments 4–6 rather than 3–6. synonymized with Melinnopsis by Jirkov (1989), and the M. angolensis resembles M. dubita (Hoagland 1920) synonymy is followed here. The genus Melinnopsides from the Philippine Islands in the arrangement of the Day, 1964, however, is regarded as valid contrary to buccal tentacles; the two may be closely related, but this Jirkov’s opinion as he did not consider the palps as a cannot be confirmed as the number of thoracic setigers generic diagnostic character. Although Day (1967) does is not defined due to the incompleteness of the type not refer to the palps in the text, his illustration clearly specimen of M. dubita. shows palps of only one size, which is in contradiction to M. angolensis is the first record of the genus from the Melinnopsis (Table 2). south Atlantic and only the second one from the ARTICLE IN PRESS B. Hilbig / Organisms, Diversity & Evolution 5 (2005) 215–220 219

Table 3. Comparison of all known species of Melinnopsis McIntosh, 1885; sensu Day, 1964, after Holthe 1986 (includes Melinnexis Annenkova, 1931 and Melinnides Wesenberg-Lund, 1950) and Jirkov (1989) in part (includes Amelinna Hartman, 1969 but not Melinnopsides Day, 1964)

Species Neurop. Fine Dorsal Branchiae Thoracic Distribution spines in notosetae in membrane in uncinigers setigers setigers setiger 6

M. abyssalis (Hartman, 3–6 5–6 (nearly Absent 4 pairs, anterior 12 NE Pacific, 1900 m 1969)asAmelinna normal) much the largest M. annenkovae 3–6 5–6 Glandular 4 pairs, median 12 Arctic, Pacific, (Ushakov, 1952)as ridge much the largest 4000 m Melinnexis M. atlantica McIntosh, Not Not Absent 4 pairs ?14 NW Atlantic, 3000 m 1885 mentioned mentioned M. arctica (Annenkova, 3–5 (6) 5–6 Absent or 3 or 4 pairs, 12 Arctic, E Greenland, 1931)asMelinnexis indistinct anterior (inner) Barents Sea, thickest 200–1200 m M. armipotens (Moore, 4–6 Not ?Indistinct 4 pairs, anterior 13 NE Pacific, 4100 m 1923)asSosanopsis mentioned (illustration) largest M. collaris (Hartman, 3–6 5–6 absent 4 pairs 12 Antarctica, 1967)asMelinnexis 4000–4800 m M. dubita (Hoagland, 3–6 5–6 (6 nearly Indistinct 4 pairs ?12 Philippines, 1000 m 1920)asMelinna normal) ridge M. moorei (Hartman, 3–6 6 Present 4 pairs, 13 NE Pacific, 1960)asMelinnexis foliaceous 500–4000 m M. monocera (Augener, 3–6 6 Indistinct 4 pairs 12 Caribbean, 1906)asMelinna 200–300 m M. rostrata 3–6 5(6), nearly Present 4 pairs 12 Arctic, 3200 m (Wesenberg-Lund, normal in 6 1950)asMelinnides M. tentacula Not Not Not 4 pairs, outer Not Hawaii, 500–1400 m (Treadwell, 1903)as mentioned mentioned mentioned largest mentioned Terebellides M. tetradentata 3–6 5 Present 4 pairs 13 Japan, 400–800 m (Imajima, 2001)as Melinnexis M. angolensis sp. nov. 3–6 5–6 Present 4 pairs, inner 13 SE Atlantic, Angola largest Basin, 5200 m

southern hemisphere. The species of the genus seem to The sample analysis was funded by the DFG, grant FI have their main distribution in deep waters of the Arctic 433/5-1. and the northeast Paciﬁc.

Acknowledgements References

Thanks are due to the crew of R/V ‘‘Meteor’’ for Annenkova, K., 1931. Zur Polychaetenfauna von Franz- their help during sampling, to Andreas Allspach for Joseph-Land (Melinnexis gen. nov. arctica sp. n.). Zool. sorting of the trawl samples, and to Claudia Brefeld Anz. 95, 269–272. for their help with the literature. Dieter Fiege is thanked Augener, H., 1906. Reports on the results of dredging, under the supervision of Alexander Agassiz, in the Gulf of Mexico for helpful discussion and support. I am also grateful and the Caribbean Sea, and on the east coast of the United to Christian Schmidt for translation of two Russian States, 1877–1880, by the USS. Coast Survey Steamer species descriptions and to R. Eugene Ruff for his help Blake. Westindische Polychaeten. Bull. Mus. Comp. Zool. with two publications by Jirkov. Gabriele Striesow is Harvard 43, 91–196. thanked for her assistance with the SEM micrographs, Day, J.H., 1964. A review of the family Ampharetidae and an anonymous reviewer for helpful comments. (Polychaeta). Ann. S. Afr. Mus. 48, 97–120. ARTICLE IN PRESS 220 B. Hilbig / Organisms, Diversity & Evolution 5 (2005) 215–220

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