Anobothrus konstantini Säring & Bick, 2022

Säring, Friederike, Bick, Andreas & Link, Heike, 2022, A new species of Anobothrus (Polychaeta, Ampharetidae) from the Weddell Sea (Antarctica), with notes on habitat characteristics and an updated key to the genus, European Journal of Taxonomy 789, pp. 130-152 : 136-143

Anobothrus konstantini Säring & Bick sp. nov.

urn:lsid:zoobank.org:act:6E3CCF0F-C510-4BA2-813A-CF43BDB4B744

Figs 3–6

Diagnosis

Four pairs of branchiae; three pairs in anterior transverse row with a small gap, and fourth pair posteriorly shifted, directly between innermost and middle branchiae of anterior row. Segment 6 (thoracic chaetiger 5, thoracic unciniger 1) with circular glandular band. Segment 12 (thoracic chaetiger 11, thoracic unciniger 7) with elongated ridge between notopodia; modified notochaetae present. Segment 2 (thoracic chaetiger 1) with long and thin paleae, about 12–14 on each side. Sixteen thoracic segments (15 thoracic chaetigers, 11 thoracic uncinigers); 2 intermediate and 10 abdominal segments.

Etymology

This species is dedicated to the brother of the first author (FS), Konstantin Zülske, who will be always a special part of her life.

Type Material

Holotype SOUTH-EASTERN WEDDELL SEA • body length 9.3 mm; North Filchner Trough, PS96 exp., station 017-3; 75°00.85′ S, 32°52.51′ W; depth 608.2 m; 4 Jan. 2016; H. Link and G. Veit-Köhler leg.; multicorer; ZSRO-P2655 .

Paratypes SOUTH-EASTERN WEDDELL SEA • 1 spec.; South Filchner Trough, PS96 exp., station 061-5 ; 76°05.93′ S, 30°18.23′ W; depth 467.6 m; 21 Jan. 2016; same collector and sampling as for holotype; ZSRO-P2660 • 1 spec.; South Filchner Trough, PS96 exp., station 072-9 ; 75°51.37′ S, 32°17.44′ W; depth 755.1 m; 24 Jan. 2016; same collector and sampling as for preceding; used for SEM; ZSRO-P2661 • 3 specs; North Filchner Trough, PS96 exp., station 017-3 ; 75°00.85′ S, 32°52.51′ W; depth 608.2 m; 4 Jan. 2016; same collector and sampling as for preceding; ZSRO-P2662 • 1 spec.; North Filchner Trough, PS96 exp., station 026-8 ; 75°15.10′ S, 37°54.85′ W; depth 481.9 m; 8 Jan. 2016; same collector and sampling as for preceding; used for SEM; ZSRO-P2663 .

Additional Material

ANTARCTIC PENINSULA • 1 spec.; Drake Passage , PS81 exp. , station 235-2 ; 62°6.60′ S, 60°36.50’ W; depth 355m; 7 Mar. 2013; H. Link leg; multicorer; ZSRO-P2656 • 1 spec.; Drake Passage , PS81 exp. , station 241-5 ; 62°6.60′ S, 60°36.50′ W; depth 403 m; 9 Mar. 2013; same collector and sampling as for preceding; ZSRO-P2657 • 2 specs; Bransfield Strait , PS 81 exp. , station 217-5 ; 62°53.25′ S, 58°14.13′ W; depth 532 m; 2 Mar. 2013; same collector and sampling as for preceding; one specimen used for micro-CT; ZSRO-P2658 • 1 spec.; Bransfield Strait , PS81 exp. , station 225-2 ; 62°56.08′ S, 58°40.76′ W; depth 543 m; 4 Mar. 2013; same collector and sampling as for preceding; ZSRO-P2659 .

Description

Complete specimens 7–13 mm long (holotype 9.3 mm), and 0.5–0.8 mm wide (holotype 0.5 mm) on thorax ( Fig. 3D , compare Fig. 3A ).

16 thoracic segments (15 thoracic chaetigers, 11 thoracic uncinigers) ( Fig. 1 ). Thorax wider and longer than abdomen, abdomen tapering posteriorly (compare Figs 3A , 4A ). Continuous ventral shields on segments 2–12 (thoracic chaetigers 1–11). Median ventral groove from segment 13 (thoracic chaetiger 12) to pygidium.

Prostomium trilobed, anteriorly rounded, Ampharete- type ( Jirkov 2009), without eye spots (compare Fig. 5B–C ). Nuchal organs not observed. Buccal tentacles apparently smooth, observed for one specimen (ZSRO-P2662: paratype).

Four pairs of branchiophores; between two groups a small gap half as wide as branchiophores. Branchiae were lost on almost all specimens (11), one specimen with one outer gradually tapering papillose branchia (compare Figs 3A , 4A ). First three pairs of branchiophores arranged in anterior transversal row (inner, middle and outer pairs), forming a high fold, originating from segments 2–4 (thoracic chaetigers 1–3), fourth pair of branchiae posteriorly shifted between innermost and middle branchiae of anterior row ( Fig. 4F , compare Fig. 5A–B ). Anterior end of branchiophores apparently fused together ( Fig. 3D , compare Fig. 5A ). Origin of branchiae not visible; nephridial papillae not visible.

Segment 2 (thoracic chaetiger 1) with 12–14 long, thin and slender paleae on each side, gradually tapering (holotype: left, 12 paleae plus a single small palea; right, 12 paleae plus a single small palea). Paleae protruding clearly beyond the prostomium ( Fig. 3F , compare Fig. 4A ), semicircularly arranged, with a small thin palea at the dorsal outer margin (compare Fig. 5B ).

Notopodia from segment 3 (thoracic chaetiger 2), well developed with a simple elongated lobe, and with some capillary chaetae; first notopodium smaller than subsequent notopodia and slightly shifted dorsally ( Figs 4F , 6A ); notopodia without cirri or papillae. Eleven thoracic uncinigers, from segment 6 (thoracic chaetiger 5) to segment 16 (thoracic chaetiger 15) ( Fig. 1 , compare Fig. 4A ).

Segment 6 (thoracic chaetiger 5, thoracic unciniger 1) with circular glandular band ( Figs 3D , 4F , 6A–B ). Notopodia of segment 12 (thoracic chaetiger 11, thoracic unciniger 7) elevated and connected by a pronounced dorsal ridge ( Figs 3G , 6A , compare Fig. 4K ), with ciliated band ( Fig. 6C ).

Two intermediate segments; notopodia absent but neuropodia of thoracic type present ( Figs 4L , 6E ). Abdomen with 10 segments (10 uncinigers); notopodia and -chaetae absent. Abdominal neuropodia as elongated pinnules without dorsal cirri ( Fig. 6D ).

Thoracic notochaetae bilimbate capillaries, tapering to slender tips ( Figs 3B , 6F–H , compare Fig. 4B– C ); segment 3 (thoracic chaetiger 2) with 3–4 short notochaetae in a tuft; notochaetae of subsequent chaetigers arranged in two rows ( Fig. 6F ), anterior row with 3 shorter (compare Fig. 4C ) and posterior row with 4 longer chaetae (compare Fig. 4B ). Notochaetae of modified segment 12 (thoracic chaetiger 11, thoracic unciniger 7) tapered more abruptly toward the tip than regular notochaetae ( Figs 3C , 6I , compare Fig 4D–E ). Thoracic neuropodia with 17–21 uncini (holotype: thoracic segment 5 with 20 uncini, thoracic segments 10 and 16 with 17 uncini each) in one row. Thoracic uncini about 16 µm long, pectinated, with 6–7 teeth in lateral view, above rostral tooth 3–4 teeth in a row, and about 6 teeth in apical row (compare Fig. 4G–H ). Neuropodia of intermediate segments with 15–22 uncini (holotype: intermediate segment 2 with 16 uncini), and abdominal neuropodia with 16–19 uncini (holotype: abdominal segments 1, 3 and 5 with 16 uncini each) in marginal position of pinnules. Abdominal uncini about 8 µm long, pectinated, with 5–6 teeth in lateral view, above rostral tooth 7–8 teeth in a row, about 2 teeth in apical row ( Fig. 6J–K , compare Fig. 4I–J ). Number of uncini declines towards pygidium.

Pygidium with terminal anus, without cirri but papillose folds present ( Fig. 6D ).

METHYL BLUE STAINING PATTERN. Intensive staining of bases of noto- and neuropodia. Body uniformly spotted blue, without distinct pattern, but a circular glandular band on segment 6 (thoracic chaetiger 5, thoracic unciniger 1) becomes visible.

SHIRLASTAINA STAINING PATTERN. Staining pattern similar to methyl blue staining pattern ( Fig. 3B–G , compare Fig. 3A ), but additional structures are visible: the circular glandular band on segment 6 (thoracic chaetiger 5, thoracic unciniger 1) ( Fig. 3D ) and an elevated dorsal ridge on segment 12 (thoracic chaetiger 11, thoracic unciniger 7) ( Fig. 3G ).

Biology

Male gametes, about 9–10 µm in diameter, were observed in segments 4–11 (thoracic chaetigers 3–10) in one specimen, collected in January in the North Filchner Trough.

Remarks

The branchiae were lost in almost all specimens, branchiophores are apparently fused together and are not separated (compare Fig. 5B–D ). Due to poor conservation, the segmental origin of branchiae could not be described in more detail. We suggest the following arrangement of branchiae of the anterior row: segment 2, branchiae in the middle position, segment 3, branchiae of outermost position, segment 4, innermost position, segment 5, branchiae in posterior position between innermost and middle branchiae of anterior transverse row.

The holotype and paratypes from the South-Eastern Weddell Sea did not show any significant differences in diagnostic characteristics. Specimens of the additional material showed only minor differences to the diagnosis of the holotype and paratypes. Therefore, the additional material was used for the light microscopy ( Fig. 3A ), drawing ( Fig. 4A–E, G–K ) and the micro-CT ( Fig. 5 ). However, we found one modification of one specimen from the additional material (ZSRO-P2658) when analysing the images from the micro-CT: one pair of small and fine paleae next to the regular large and thin paleae ( Fig. 5B, D ). The small paleae are placed where newly formed chaetae are expected and may be a growing state ( Tilic et al. 2015). However, the shape and form is different compared to the other paleae. The purpose of these paleae was not clearly clarified.

The presence of a reduced neuropodium on segment 5 (thoracic chaetiger 4) was presumed on one specimen using ShirlastainA because at the position of the thoracic neuropodia and of the same size as these, the same staining pattern was visible on this segment ( Fig. 3E ). However, uncini were not observed.

Uncini of the thoracic and intermediate neuropodia are about twice the size of uncini of the abdomen. A variation in size or shape of uncini along their row on a single neuropodium was not found.

Due to the fixation in 4 % formaldehyde solution and the subsequent preservation in a 70% ethanol solution, no statement can be made about the pigmentation of fresh material.

Anobothrus konstantini Säring & Bick sp. nov., A. bimaculatus Fauchald, 1972 and A. mancus Fauchald, 1972 differ from the other Anobothrus species with four pairs of branchiae and the presence of paleae, A. amourouxi Bonifácio, Lavesque, Bachelet & Parapar, 2015 , A. anatarctica Monro 1939 , A. glandularis ( Hartmann-Schröder, 1965) , A. gracilis ( Malmgren, 1866) , A. mironovi Jirkov, 2009 , A. paleatus Hilbig, 2000 , A. paleaodiscus Schüller & Jirkov, 2013 , A. patagonicus ( Kinberg, 1867) , A. patersoni Jirkov, 2009 , A. pseudoampharete Schüller, 2008 , A. rubropaleatus Schüller & Jirkov, 2013 and A. wilhelmi Schüller & Jirkov, 2013 , in having 11 instead of 12 thoracic uncinigers. Within this group, only A. paleatus has a glandular band with an elevated ridge on the fourth-to-last thoracic segment (thoracic segment 14, thoracic unciniger 9) the remaining eleven Anobothrus species, as well as A. konstantini Säring & Bick sp. nov., show a modification of the fifth-to-last thoracic segment. However, due to the difference in the number of segments (12 thoracic uncinigers vs. 11 thoracic uncinigers), A. konstantini Säring & Bick sp. nov. posseses this character on segment 12, whereas it is present on segment 13 in the previously mentioned species. In addition, the first transverse band on the anterior part of the thorax is not mentioned for A. pseudoampharete .

Anobothrus amourouxi , A. anatarctica , A. glandularis , A. gracilis , A. mironovi , A. paleatus , A. paleaodiscus and A. patersoni have a transversal band on segment 8, while A. rubropaleatus and A. wilhelmi have it on segment 7. Only one species, A. patagonicus , possesses a transversal band on segment 6, as described for A. konstantini Säring & Bick sp. nov. However, A. patagonicus differs from A. konstantini Säring & Bick sp. nov. by the larger body length of about 19 mm and up to 30 uncini on neuropodia of segment 6, while the body length A. konstantini Säring & Bick sp. nov. ranges between 7 and 13 mm, with about 16–19 thoracic uncini on the neuropodia of segment 6.

The only two species with paleae on segment 2, four pairs of branchiae and 11 thoracic uncinigers are A. bimaculatus and A. mancus . However, A. bimaculatus is significantly larger (65 mm), has eyespots and has modified notopodia on segment 11, instead of on segment 12 as in Anobothrus konstantini Säring & Bick sp. nov. Anobothrus mancus is the only species with modified notopodia on segment 12, but segments 3 and 4 are fused, and notopodia are absent on segment 3. Furthermore, A. mancus is missing the circular glandular band on segment 6.

Distribution

The holotype and paratypes of Anobothrus konstantini Säring & Bick sp. nov. were found in shelf regions in the South-Eastern Weddell Sea (North Filchner Trough and South Filchner Trough). The additional material was sampled from shelf regions of the Antarctic Peninsula, in the Drake Passage and Bransfield Strait ( Fig. 2 , Table 1 ).

Ecology

The type material of Anobothrus konstantini Säring & Bick sp. nov. (1 holotype, 6 paratypes) was collected from soft sediments at water depths between 415 and 755 m from the South-Eastern Weddell Sea. This region is characterized by a high to constant ice cover and low bottom T (around -1.9°C, Säring et al. submitted: table 2; Schröder et al. 2016). The highest abundance was detected at one sampling site in the North Filchner Trough region (4 individuals per station), with low organic (TOC 0.2% ± 0.0) and the least fresh (Chl a = 0.06 µg g-1 ± 0.01) material on the seafloor. This sampling site is described by a low amount of silt & clay (43.4%) compared to the higher amount of sand (49.1%). The remaining material (3 paratypes) was found at sites with higher silt & clay (> 63.2%) and lower sand (<33.7%) content, and low Chl a concentrations (<0.19 µg g-1). Anobothrus konstantini Säring & Bick sp. nov. occurs in a high variety of sediments, from fine mud to coarser sandy substrates in regions with low amount of fresh material on the seafloor.

The localities for the additional material sampled adjacent to the Antarctic Peninsula, Drake Passage (2 specimens) and Bransfield Strait (3 specimens), are known for no or a variable ice-cover and bottom T up to 0.5°C (Säring et al. submitted: table 2; Schröder et al. 2013). Nevertheless, these localities for the additional material show similar environmental conditions as the sampling sites of the type material: low Chl a concentrations (<0.31 µg g-1) and TOC content (<0.7%), and highly variable sediment substrates ( Table 1 ).

Following the classification of functional traits by Jumars et al. (2015), A. konstantini Säring & Bick sp. nov. is a hemi-sessile, tube-dwelling, subsurface deposit feeder.

Figures

Fig. 3. Anobothrus konstantini Säring & Bick sp. nov. Micrographs of ShirlastainA staining pattern. A. Complete specimen, lateral view with one outermost branchia, additional material (ZSRO-P2657). B. Notochaetae on segment 11 (TC 10), paratype (ZSRO-P2662). C. Modified notochaetae on segment 12 (TC 11, TC 7), paratype (ZSRO-P2660). D. Dorsal view of anterior end, arrow: glandular circular band on segment 6 (TC 5, TU 1), paratype (ZSRO-P2662).E. Lateral view, arrow: reduced neuropodium on segment 5 (TC 4), without uncini, paratype (ZSRO-P2662). F. Lateral view of anterior end, paratype (ZSRO-P2662). G. Lateral view of three thoracic segments, arrow: modified notopodium with dorsal ridge on segment 12 (TC 11, TU 7), paratype (ZSRO-P2662). Scale bars: A = 500 µm; B = 50 µm, C = 20 µm; D–E = 100 µm; F–G = 200 µm.

Fig. 4. Anobothrus konstantini Säring & Bick sp. nov. A. Complete specimen with one outermost branchia, lateral view, arrow: dorsal ridge on segment 12 (TC 11, TU 7), additional material (ZSRO-P2657). B. Long thoracic notochaeta, additional material (ZSRO-P2658). C. Short thoracic notochaeta, additional material (ZSRO-P2658). D. Long notochaeta of the modified segment 12 (TC 11, TU 7), additional material (ZSRO-P2658). E. Short notochaeta of the modified segment 12 (TC 11, TU 7), additional material (ZSRO-P2658). F. Dorsal view of the anterior end, paratype (ZSRO-P2662). G. Lateral view of thoracic uncinus, additional material (ZSRO-P2658). H. Frontal view of thoracic uncinus, additional material (ZSRO-P2658). I. Lateral view of abdominal uncinus, additional material (ZSRO-P2658). J. Frontal view of abdominal uncinus, additional material (ZSRO-P2658). K. Lateral view of three thoracic segments, arrow: dorsal ridge on segment 12 (TC 11, TU 7) with slightly elevated notopodia, additional material (ZSRO-P2656). L. Lateral view of last thoracic, two intermediate and first abdominal segments, paratype (ZSRO-P2663). Scale bars: A = 500 µm; B–E = 100 µm; F, K = 200 µm; G–H = 10 µm; I–J = 5 µm; L = 50 µm.

Fig. 5. Anobothrus konstantini Säring & Bick sp. nov., additional material (ZSRO-P2658). Micro-CT graphs, additional material.A. Anterior end with arrangement of branchiae, dorsal view. B. Anterior end with arrangement of branchiae, frontal view (note semicircular arrangement of paleae; arrows: small paleae on each side). C. Frontal view of anterior end, without branchiae or paleae (note: Ampharete-type prostomium). D. Anterior end, transverse section of branchiae, paleae and prostomium (note arrows: small paleae on each side). Scale bars: A–D = 100 µm.

Fig. 6. Anobothrus konstantini Säring & Bick sp. nov. SEM micrographs. A. Anterior end and thorax, dorsal view, arrows: segment 6 (thoracic chaetiger 5, thoracic unciniger 1) and segment 12 (TC 11, TU 7), paratype (ZSRO-P2661). B. Pores in glandular band on segment 6 (TC 5, TU 1), dorsal view, paratype (ZSRO-P2661).C. Elevated ridge with cilia on segment 12 (TC 11, TU 7), dorsal view, paratype (ZSRO-P2661). D. Posterior end with papillose pygidium, lateral view, paratype (ZSRO-P2663). E. Last thoracic, two intermediate and first abdominal segments, lateral view, paratype (ZSRO-P2663). F. 4 longer and 3 shorter notochaetae of notopodium on segment 15 (TC 14, TU 10), paratype (ZSRO-P2661). G. Margin of short notochaetae on segment 15 (TC 14, TU 10), paratype (ZSRO-P2661). H. Margin of long notochaetae on segment 15 (TC 14, TU 10), paratype (ZSRO-P2661). I. Modified notochaetae on segment 12 (TC 11, TU 7), paratype (ZSRO-P2661). J. Abdominal uncini on abdominal segment 8, frontal view, paratype (ZSRO-P2663). K. Abdominal uncinus on abdominal segment 8, lateral view, paratype (ZSRO-P2663). Scale bars: A, E = 100 µm; B, I = 2 µm; C, D = 20 µm; F, H = 10 µm; G = 3 µm, J–K = 1 µm.

Fig. 1. Schematic lateral view of Anobothrus konstantini Säring & Bick sp. nov. Abbreviations: see Material and methods. Vertical dotted line in TS6 represents circular glandular band. Vertical lines in TS12 represent elongated ridge between notopodia.

Fig. 2. Sampling stations in the vicinity of the Antarctic Peninsula during RV Polarstern expedition PS 81 (Drake Passage, Bransfield Strait, North-Western Weddell Sea, green frame) and the South-Eastern Weddell Sea during PS 96 (North Filchner Trough, South Filchner Trough, blue frame). Stations without Anobothrus konstantini Säring & Bick sp. nov. labeled with a cross. Information about sampled stations and number of individuals of A. konstantini Säring & Bick sp. nov. are given in Table 1.