Ilyphagus gebruki n. sp., an abyssal flabelligerid from the Eastern Pacific (Annelida: Sedentaria: Flabelligeridae)

Ilyphagus gebruki n. sp., un flabeligérido abisal del Pacífico oriental (Annelida: Sedentaria: Flabelligeridae)

Resumen

The study of abyssal polychaetes is always problematic, because, besides the need for a high level of sophisticated equipment such as vessels and collecting machines, abyssal annelids are often delicate, and easily damaged during sampling, sorting or identification.

Ilyphagus Chamberlin, 1919 and Bradabyssa Hartman, 1967 include most abyssal flabelligerid species (Salazar-Vallejo, 2012, 2017, 2019). Ilyphagus comprises only 4 known species, all with fragile, thin body walls, and all recorded from abyssal depths. During the study of all specimens available for a revision of Ilyphagus, I came across an undescribed species from the Eastern Pacific; a similar specimen from the Northern Pacific was also detected, but the specimen was in suboptimal conditions. Consequently, I decided to postpone the description of the species, in order to have the chance to study some additional specimens in Russian collections. Unfortunately, none were available, despite the fact that Russian scientists have undertaken an impressive series of collecting expeditions all over the world (Mikhailov et al., 2002), especially the vessels belonging to the Shirshov Institute of Oceanology, including the Akademik Kurchatov (Neiman et al., 2017). More recently, German-Russian expeditions in the German R/V Sonne in the Northwestern Pacific have focused on the Kurile Kamchatka Trench (Brandt & Malyutina, 2012), and in the Okhotsk Sea (Malyutina et al., 2018). This delayed description is herein provided, aiming to encourage the study of abyssal flabelligerids, along with an updated key to species.

Material and methods

Twenty specimens were carefully cleaned of excessive sediment particles by gently brushing the body, and they were often immersed during a few seconds in a 1:1 white vinegar-70% ethanol solution to facilitate the removal of adsorbed materials. Chaetae were carefully removed, cleaned, and mounted in temporal glass slides for observing patterns of articulation. In one specimen, the anterior end was dissected to observe the anterior end and count the branchial filaments. Digital photos were compressed by using HeliconFocus. The material is deposited in the collections of El Colegio de la Frontera Sur, Chetumal, México (ECOSUR), the Museum of Natural History of Los Angeles County, Allan Hancock Foundation Polychaete Collection, Los Angeles, California, U.S.A. (LACM-AHF), and the Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow (SIORAS). The description is based mostly on the holotype with some comments on variation of the other specimens.

Results

Class Polychaeta Grube, 1850

Family Flabelligeridae de Saint-Joseph, 1894

Ilyphagus Chamberlin, 1919

Ilyphagus gebruki n. sp.

Figure 1

http://zoobank.org/urn:lsid:zoobank.org:act:B766A586-
663C-4FFE-B460-65F040996501 

Diagnosis. Ilyphagus with body arenicoliform, more than 5 times longer than wide. Body papillae long. Branchial plate with 8 branchial filaments. Notochaetae with articles progressively longer; neurochaetae smooth.

Description. Holotype (SIORAS AK 294) without posterior end, whitish, some chaetae broken (Fig. 1A). Body arenicoliform, elongate, anteriorly rounded, tapered posteriorly (Fig. 1C); 52 mm long, 5 mm wide, cephalic cage broken (remaining chaetae 4 mm long), 30 chaetigers. Body papillae very dense; papillae filiform, cylindrical, slightly capitate, with abundant fine sediment particles adherent on its basal and medial regions.

Anterior end not exposed in holotype; observed in a non-type specimen (LACM Sta. 69) (Fig. 1D). Cephalic hood short, margin smooth, longer dorsally. Prostomium distorted, without eyes. Caruncle not seen. Palps massive, contracted, longitudinally cleft, longer than branchiae; palp lobes reduced. 

Branchiae cirriform, sessile on branchial plate, slightly projected, with 4 thick filaments per side, arranged in an irregular marginal row. Nephridal lobes not seen.

Cephalic cage chaetae mostly broken; complete size relationships with body length or width unknown. Chaetiger 1 involved in the cephalic cage; notochaetae of chaetiger 2 as long as body width. Chaetiger 1 with an unknown number of chaetae in dorsal bundle series; neurochaetae in short curved series, only 1-3 chaetae remaining. 

Anterior dorsal margin of first chaetiger papillated, depressed in relation to nearby enlarged, projected notopodia; anterior chaetigers without especially long papillae. Chaetigers 1-3 of about the same length. Chaetal transition from cephalic cage to body chaetae abrupt; neurospines from chaetiger 4; chaetigers 1-3 with some transitional neurochaetae with long articles distally, articulated region progressively reduced from first to third chaetiger. Gonopodial lobes in chaetigers 5-6, as long as 1/3 segment length, short rounded, covered by thin integument, once removed dark brown (Fig. 1B). Parapodia lateral, low, long transverse lobes; median neuropodia ventrolateral. Noto- and neuropodia close to each other.

Median notochaetae arranged in short transverse rows; all multiarticulated capillaries, articles short basally, progressively longer in medial and distal regions (Fig. 1E); 1-2 per ramus, as long as 2/3 body width. Neurochaetal spines from chaetiger 4, arranged in transverse series, 7-8 per ramus; each with very short anchylosed articles basally and medially, distally hyaline, tapered, smooth (Fig. 1F). 

Posterior end missing in holotype; another complete specimen (SIORAS Vitjaz 6085) tapered posteriorly, pygidium with anus terminal, without anal cirri.

Variation. Complete specimens have 22-37 chaetigers; gonopodial papillae in chaetiger 5, or in chaetigers 5 and 6.

Taxonomic summary

Type locality. Off Trujillo, Peru, in 6,200-6,240 m.

Type material: Eastern Pacific Ocean. Holotype (SIORAS AK 294) and paratypes (SIORAS AK 294b and ECOSUR 000), R/V Akademik Kurchatov, Sta. 294 (08°23’ S, 81°00’ W), off Trujillo, Peru, 6,200-6,240 m, Sigsbee trawl, 31 Oct.-1 Nov. 1968 (paratypes 2 anterior fragments, damaged, 25/32 mm long, 4/4 mm wide, cephalic cage broken, remaining chaetae 3/3 mm long, 14/18 chaetigers; gonopodial lobes in chaetigers 5-6).

Additional material: Eastern Pacific Ocean. One specimen (LACM-AHF unnumb.), complete, Peru Chile Trench Expedition, R/V Anton Bruun, Cruise II, Sta. 36 (05°43’ S, 82°01’ W), 5,047 m, Menzies trawl, 5 Oct. 1965 (47 mm long, 14 mm wide, cephalic cage broken, 23 chaetigers). Eight specimens (LACM-AHF unnumb.), one without pygidium, another one regenerating the posterior end, others without posterior end, Peru Chile Trench Expedition, R/V Anton Bruun, Cruise II, Sta. 69 (06°19’ S, 81°49’ W), 5,750 m, Beam trawl, 9 Oct. 1965 (w/o pygidium 44 mm long, 3 mm wide, cephalic cage broken, 37 chaetigers, gonopodial papillae in chaetigers 5 and 6, black, digitate, visible after brushing sediment; regen. posterior end 27 mm long, 3.5 mm wide, cephalic cage broken, 28 chaetigers, gonopodial papillae in chaetiger 5). Three specimens (LACM-AHF unnumb.), one complete, others broken off, Peru Chile Trench Expedition, R/V Anton Bruun, Cruise II, Sta. 72 (08°25’ S, 81°05’ W), 6,220-6,052 m, Menzies trawl and beam trawl in tandem, 12 Oct. 1965 [(34 mm long, 4 mm wide, cephalic cage broken, 23 chaetigers). One specimen (LACM-AHF unnumb.), complete, Peru Chile Trench Expedition, R/V Anton Bruun, Cruise II, Sta. 113 (08°44’ S, 80°45’ W), 5,986-6,134 m, Menzies trawl and Beam trawl in tandem, 19 Oct. 1965 (23 mm long, 5 mm wide, cephalic cage broken, 23 chaetigers). Three specimens (LACM-AHF unnumb.), one complete, others broken off, Peru Chile Trench Expedition, R/V Anton Bruun, Cruise II, Sta. 38 (05°46’ S, 82°00’ W), 5,379 m, Beam trawl, 6 Oct. 1965 (complete 62 mm long, 8 mm wide, cephalic cage broken, 22 chaetigers). North Pacific Ocean. One complete specimen and an anterior fragment (SIORAS V-6085), heavily eroded, R/V Vitjaz, Sta. 6085 (50°48.6’ N, 173°29.0’ W), south of Andreanof Islands, Aleutian Islands, 6,965-7,000 m, Sigsbee trawl, 1 May 1969 (complete/anterior fragment 33/36 mm long, 8/7 mm wide, cephalic cage chaetae 3.5/1.0 mm long [most broken], 29/20 chaetigers; both with gonopodial lobes in chaetigers 5-6).

Etymology. This species is named after Dr. Andrey Gebruk, head of the Benthic Ecology group of the Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, in recognition of his publications on deep-sea ecology, especially dealing with holothurians, and to thank his generous support to study the rich SIORAS collections. The epithet is a noun in the genitive case.

Remarks

Ilyphagus gebruki n. sp. is a member Ilyphagus Chamberlin, 1919 because of its body shape, abundant papillae and chaetae. It resembles I. coronatus Monro, 1939 from the Indian Ocean and redescribed elsewhere (Salazar-Vallejo, 2012), because both have an elongate body with abundant thin papillae; they differ, however, in branchial and chaetal features. In I. gebruki there are 8 branchial filaments in a single series, notochaetae have articles progressively longer medially and distally, and neurochaetae have well-defined anchylosed articles with smooth tips. On the contrary, in I. coronatus there are 14 branchial filaments in 3 successive series, notochaetae have small to medium-sized articles medially and distally, and neurochaetae have poorly defined anchylosed articles with hirsute tips.

On the other hand, I. gebruki differs from I. bythincola Chamberlin, 1919, the other Eastern Pacific species in body shape, and in fine details of chaetae. In I. gebruki the body is elongate, arenicoliform, markedly longer than wide, notochaetal distal articles are 10 times or more longer than wide, and neurochaetal anchylosed articles are 1/5 as long as wide. On the contrary, in I. bythincola, the body is short, ovoid, longer than wide, notochaetal distal articles are 3 times longer than wide, and neurochaetal anchylosed articles are 1/10 as long as wide. 

One specimen from the North Pacific (SIORAS V-6085) is almost without body papillae, but chaetal articles resemble those present in I. gebruki. However, because the collecting sites are far away, and there are some differences in the relative body shape (northern specimen having a wider posterior region and with some lobate regions along body) and body wall pigmentation (darker in the type series, paler the northern one), this northern specimen is herein included with some hesitation, pending the study of better-preserved specimens.

Distribution. In sediments in 5,047-6,400 m depth off Peru, along the Peru-Chile Trench, and off the Aleutian Islands (6,965-7,000 m).

Key to species of Ilyphagus Chamberlin, 1919 (modified from Salazar-Vallejo 2012).

1 Body short, about 3 times longer than wide…………………………………………………………………………………… 2

– Body cigar-shaped or arenicoliform, more than 5 times longer than wide…………………………………………………………………………………… 3

2(1) Neurochaetae markedly hirsute subdistally (oblique fibers exposed); chaetiger 1 with 3-4 neurochaetae per side…………………………………………………………………………………… I. hirsutus Monro, 1937 Indian Ocean

– Neurochaetae barely hirsute or smooth subdistally; chaetiger 1 with about 8 neurochaetae per side…………………………………………………………………………………… I. bythincola Chamberlin, 1919 partim Eastern Pacific

3(1) Body velvety (papillae short); most neurochaetae smooth or barely hirsute…………………………………………………………………………………… 4

– Body pilose (papillae long); neurochaetae smooth and hirsute (by fracture), or smooth…………………………………………………………………………………… 5

4(3) Chaetiger 1 with about 8 neurochaetae per side; about 40 branchial filaments…………………………………………………………………………………… I. bythincola Chamberlin, 1919 partim Eastern Pacific

– Chaetiger 1 with 10-12 neurochaetae per side; about 16 branchial filaments…………………………………………………………………………………… I. wyvillei (M’Intosh, 1885) Antarctic

5(3) Notochaetae with articles progressively smaller; neurochaetae smooth and hirsute; up to 14 branchial filaments…………………………………………………………………………………… I. coronatus Monro, 1939 Indian sector, Antarctic (1200-3500 m water depth)

– Notochaetae with articles progressively longer; neurochaetae smooth; 8 branchial filaments…………………………………………………………………………………… Ilyphagus gebruki n. sp. Eastern Pacific (5,000-7,000 m water depth)

Acknowledgments

The generous support by Andrey Gebruk and Natasha Budaeva (SIORAS), as well as Anna Zhadan (Lomonosov State University, Moscow) was very helpful with paperwork for the visa and finding some housing facilities in Moscow. Leslie Harris and David Ocker were very supportive during my long visits to their home, and I have enjoyed their warm hospitality and friendship. Luis F. Carrera-Parra processed the ECOSUR paratypes. The careful reading and useful recommendations by Drs Emanule Mancini and Naoto Jimi resulted in a much improved contribution. María Antonieta Arizmendi helped greatly with editorial issues.

References

Brandt, A., & Malyutina, M. (2012). The German-Russian deep-sea expedition KuramBio (Kurile Kamchatka Biodiversity Study) to the Kurile Kamchatka Trench and abyssal plain on board of the R/V Sonne. 223^rd Expedition, July 21^th – September 7^th. https://doi.org/10.13140/RG.2.1.2473.6401 

Chamberlin, R. V. (1919). The Annelida Polychaeta of the Albatross Tropical Pacific Expedition, 1891-1905. Memoirs of the Museum of Comparative Zoology, Harvard, 48. 

de Saint-Joseph, A. (1894). Les annélides polychètes des côtes de Dinard, troisième partie (Nephtydiens – Serpuliens). Annales des Sciences Naturelles, Zoologie, 7ème Série, 17, 1–395.

Grube, A. E. (1850). Die Familien der Anneliden. Archiv für Naturgeschichte, Berlin, 16.

Malyutina, M. V., Chernyshev, A. V., & Brandt, A. (Eds.). (2018). The Russian-German deep-sea expedition SokhoBio (Sea of Okhotsk Biodiversity Studies). Deep Sea Research, Part II, 154, 1–382 https://doi.org/10.1016/j.dsr2.2018.08.012

M’Intosh, W. C. (1885). Report on the Annelida Polychaeta collected by H.M.S. Challenger during the years 1873-76. Challenger Reports, 12, 1–554.

Mikhailov, N. N., Vyazilov, E. D., Lomonov, V. I., Studyonov, N. S., & Shaimardanov, M. Z. (2002). Russian marine expeditionary investigations of the World ocean. NOAA Atlas NESDIS, 56, 1–180. ftp://ftp.nodc.noaa.gov/pub/data.nodc/woa/PUBLICATIONS/atlas56.pdf

Monro, C. C. A. (1937). Polychaeta. Scientific reports of the John Murray expedition 1933-34, 4, 243–321.

Monro, C. C. A. (1939). Polychaeta. Reports of the British Antarctic Research Expedition 1929–1931, series B, 4, 87–156.

Neiman, V. G., Sokov, A. V., & Filyushkin. (2017). Fifty years since the first voyage of the R/V Akademik Kurchatov. Oceanology, 57, 899–900. https://doi.org/10.1134/S000143
7017060108

Pettibone, M. H. (1982). Annelida. In S. P. Parker (Ed.), Synopsis and classification of living organisms (pp. 1–43). New York: McGraw Hill.

Salazar-Vallejo, S. I. (2012). Revision of Ilyphagus Chamberlin, 1919 (Polychaeta, Flabelligeridae). Zookeys, 190, 1–19. https://doi.org/10.3897/zookeys.190.3059 

Salazar-Vallejo, S. I. (2017). Revision of Brada Stimpson, 1853, and Bradabyssa Hartman, 1967 (Annelida, Flabelligeridae). Zootaxa, 4343, 1–98. https://doi.org/10.11646/ZOOTAXA.
4343.1.1 

Salazar-Vallejo, S. I. (2019). Flabelligeridae Saint-Joseph, 1894. In G. Purschke, M. Böggemann, & W. Westheide (Eds.), Handbook of Zoology: Annelida, 1. Annelida basal groups and Pleistoannelida, Sedentaria (pp. 398–421). Berlin: DeGruyter.