Amphitritides namibiensis, Bick & Zettler, 2024

Bick, Andreas & Zettler, Michael L., 2024, Description of three new species of Amphitritides Augener, 1922 (Terebellida, Annelida) from the coast of Namibia (South West Africa), Zootaxa 5446 (1), pp. 42-64 : 48-55

Amphitritides namibiensis sp. nov.

( Figs 3–7 , 11A–E, P )

Material examined. Holotype. Off Namibia: 20.013°S 12.984°E, depth 44 m, 30.08.2011, complete specimen ( ZSRO-P2675 ) . Paratypes. Off Namibia : 20.013°S 12.984°E, depth 44 m, 30.08.2011, 47 specimens ( ZSROP2676 ) ; 20.010°S 13.004°E, depth 33 m, 27.08.2011, about 80 specimens ( ZSRP-P2677 ) ; 20.022°S 12.969°E, depth 56 m, 30.08.2011, 4 specimens ( SMF 329075 ) ; 19.998°S 13.010°E, depth 30 m, 27.08.2011, 10 specimens ( SMF 32976 ) ; 20.003°S 12.971°E, depth 41 m, 04.11.2016, 15 specimens ( ZSRO-P2678 ) ; 20.000°S 12.999°E, depth 33 m; 10.05.2019, 5 specimens ( ZSRO-P2679 ) . Additional material. Off Namibia: 20.013°S 12.984°E, depth 44 m, 30.08.2011, about 50 specimens ( ZSRO-P2680 ) ; 20.010°S 13.004°E, depth 33 m, 27.08.2011, 4 specimens ( ZSROP2681 ) ; 19.998°S 13.010°E, depth 30 m; 27.08.2011, 5 specimens ( ZSRO-P2682 ) ; 20.013°S 12.984°E, depth 44 m, 30.08.2011, 5 specimens ( ZSRO-P2683 ) ; 17.267°S 11.724°E, depth 31.5 m, 04.03.2008, 1 specimen ( ZSROP2684 ) ; 17.2671°S 11.7241°E, depth 33 m, 31.08.2019, 1 specimen ( ZSRO-P2685 ) ; 19.0000°S 12.4483°E, depth 26 m, 23.01.2022, 1 specimen ( ZSRO-P2686 ) .

Diagnosis. Two pairs of stalked arborescent branchiae; first pair distinctly longer than second pair, often longer than body width. Without distinct lateral lobes on anterior segments, but midventral lobe on segment 1 present. Twenty-four thoracic segments. One pair of nephridial papillae on segment 3, inserted laterally and close to branchial stalk. Three pairs of genital papillae on segments 6 to 8, located anteriorly to base of the corresponding notopodia and aligned with them. Notochaetae with bulbous wings in the middle of longer chaetae or basally, distally serrated. Neuropodia from segment 5, double rows of uncini only on thoracic segments, beginning on segment 11. Anterior abdominal segments with papillae-like structures situated dorsally above the neuropodia. Pygidium with crenulated margin.

Description. Large species, complete holotype 63 mm long, 4.1 mm wide for about 105 segments. Paratypes 25–110 mm long, and 1.8–6.4 mm wide, maximum 100–110 segments, but most specimens incomplete. Anterior body not distinctly swollen.

Body surface of the dorsal and ventral side very different from each other, especially on thorax. Ventral side glandular, and well stained with methylene blue, with well-developed ventral shields, i.e., clearly separated from the lateral sides by furrows, on segments 5 to segment 12–14 usually, last ventral shields narrower and shorter; mid-ventral groove usually beginning after few transitional segments, without clearly marked ventral shields. Dorsal side papillose throughout, papillae in more or less distinct rows, up to about segments 4–6 in 2 rows, 3 rows until segment 11, and, from segment 12 onwards 4 rows of papillae; segments secondarily annulated as a result ( Figs 3B, C, E ; 4A ; 5A–F ).

Prostomium at base of upper lip; basal part without eyespots; distal part forming shelf-like tentacular membrane from which numerous filiform and deeply grooved, ciliated buccal tentacles originate ( Figs 3A–C ; 4A–C, F ).

Peristomium well developed, with conspicuous hood-like upper lip, trilobate, with corrugated anterior margin, directed anteriorly or upwards curved; lower lip narrow and swollen, often with transverse groove separating the lower lip from the pharyngeal organ, visible posteriorly ( Figs 3A, C ; 4A–C ; 5C ).

Segment 1 dorsally narrow, conspicuous developed ventrally, forming mid-ventral lobe below lower lip, anterior margin concave and crenulated ( Figs 3A, C, E ; 4A, C ). Segments 2 and 3 without any lobes but with small rounded dorsal projections ( Figs 3A, E ; 4A, C ; 5C ).

Two pairs of large arborescent branchiae on segments 2 and 3, with wide medial gap; first pair distinctly longer than second pair, usually about twice as long as second pair, often longer than body width; first pair about 6–9 mm (exceptionally 18–20 mm) long; second pair about 2–5 mm (exceptionally 10–12 mm) long, usually shorter than body width; thick main stem, with irregular dichotomous branching; branches end in short branchial filaments ( Figs 3A, B, D, E, G ; 4A, D ).

Notopodia starting from segment 4, usually extending for 21 segments, until segment 24 (n= 24 specimens); rarely also for 16 (until segment 19; n=1), 17 (until segment 20; n=1), 18 (until segment 21; n=3) and 19 (until segment 22; n=1) segments; first pair of notopodia same size as following pairs; notopodia short, rectangular to conical; all laterally aligned; notopodia and neuropodia clearly separated ( Figs 3A, E ; 4A, C ; 5A ; 6B–D ). Notochaetae arranged indistinctly in two or more rows, chaetae of first row shorter; chaetae of each row with symmetrical limbation, bulbous wings in the middle of longer chaetae or basally; longer and shorter chaetae with serrated tips; no difference observed between notochaetae of anterior and posterior thoracic segments ( Figs 5A ; 6B–D, F ; 7A–C ; 11A–C, P ). First abdominal segments with papillae-like structures dorsally above neuropodia, visible on first 12–18 (10–25 among paratypes) abdominal segments ( Fig. 6B, E ).

Neuropodia beginning from segment 5; thoracic and abdominal neuropodia as long lateral ridges, distinctly raised from body surface, almost reaching ventral shields on thorax, and reaching ventral groove on abdomen ( Figs 3A ; 4A, C ; 5A ; 6A ); neuropodia of posterior thoracic and anterior abdominal segments slightly thickened at upper margin ( Fig. 6B, E ). Uncini arranged in double rows, in face-to-face arrangement, from segment 11 until end of thoracic region (usually up to segment 24); rows completely separated from each other ( Figs 5A ; 6A–E ). Avicular uncini, 36–46 µm wide and 28–35 µm high; short triangular or rounded heel, rounded prow, to a great extent upwards directed, short dorsal button inserted closer to prow than to base of main fang, convex base; uncini with 3 more or less distinct rows of apical teeth above main fang, first row with about 2–3 teeth, 2–4 on second row, and 6–10 on third row; dental formula MF: 2–3: 2–4: 6–10; thoracic and abdominal uncini all similar, the latter slightly narrower ( Figs 7D, E ; 11D, E ).

One pair of nephridial papillae on segment 3, inserted laterally and close to branchial stalk. Three pairs of tubular genital papillae on segments 6–8, present anterior to base of corresponding notopodia and aligned with them; all genital papillae of same size, and much longer than corresponding notopodia ( Figs 3A, E ; 4A, C, E ).

Pygidium terminal, margin crenulated ( Fig. 3F ).

Live individuals purple in colour, with red-orange branchiae; pale after preservation ( Fig. 3A–C, E–G ).

No specimen with gametes observed.

Remarks. Amphitritides namibiensis sp. nov. differs from the seven already known Amphitritides species ( Read & Fauchald 2024a) and the two species described in this paper (see Table 1 ) by the combination of the following characters: number of thoracic segments, complete absence of uncini in double rows on abdominal segments and number of genital papillae (see Arvanitidis & Koukouras 1995; Nogueira & Hutchings 2007). There is only one other species within this genus that lacks double rows of uncini on abdominal segments, A. pectinobranchiata Hartmann-Schröder, 1965 , which Arvanitidis & Koukouras (1995) suggested should be transferred to Paramphitrite . All species of Paramphitrite have lateral lobes on the first anterior segments, particularly on segment 2, segment 1 is reduced dorsally, and the branchiae are much shorter than body width, mainly due to the lack of a distinct stem ( Day 1963, Holthe 1976, Hutchings et al. 2021b, Jirkov 2020, Lavesque et al. 2021). Apart from a small midventral lobe on segment 1, A. namibiensis sp. nov. has no lobes on the anterior segments, segment 1 is not reduced dorsally, and the branchiae are rather long, with a well-developed stem. Amphitritides namibiensis sp. nov. also differs from A. pectinobranchiata in the number of thoracic segments ( A. namibiensis sp. nov. with usually 24 and A. pectinobranchiata with 20 segments), the number of pairs of notopodia with notochaetae ( A. namibiensis sp. nov. with usually 21 and A. pectinobranchiata with 13 pairs) and in the size of sexually mature individuals ( A. namibiensis sp. nov. 110 mm long and A. pectinobranchiata 33 mm long). In these three characters A. namibiensis sp. nov. also differs clearly from all three accepted Paramphitrite species (see Day 1963, Holthe 1976, Jirkov 2020, Lavesque et al. 2021). There are also no other species in the genus Amphitrite to which the above characters apply (see Jirkov 2020).

Moreover, within the genera mentioned above, there is no species that has papillae-like structures situated dorsally above the neuropodia of the first abdominal segments. These papillae could represent reduced notopodia.

There are only minor differences between large (width 5–6 mm) and small (width 2 mm) individuals. The uncini in small immature specimens are smaller in general (18–22 µm high, 28–30 µm wide), especially shorter than those in larger mature individuals. In contrast, the genital papillae are clearly visible even in the smallest immature individuals.

Etymology. The specific epithet namibiensis is named after the type locality off Namibia.

Distribution. Only known from the northern part of Namibia (Kunene region) between 17° and 20°S in water depths between 26 and 56 m.

Habitat. The salinity was marine (35.1–35.7 psu). Depending on the season, the bottom water temperature fluctuated between 12.4 and 17.8 °C, and the oxygen content of the bottom water was very low to low and varied between 3.74 and 174 µmol/l. The mean grain size of the sediments was between 35 and 103 µm, while the organic content was between 1 and 10 %. The tube consists of very fine silty sediment grains, with relatively thick wall, which inner inside is lined with a thin parchment-like organic membrane.

Figures

FIGURE 3. Amphitritides namibiensis sp. nov. A. Anterior end, lateral view. B. Anterior end, dorsal view. C. Anterior end, ventral view. D. First and second branchiae, methyl blue staining. E. Anterior end, lateral view (note: nephridial and genital papillae). F. Posterior end, methyl blue staining (note: crenulated pygidium). G. Living individuals. Scale bars. A–E 1 mm, F 500 µm G 20 mm. Abbreviations: br1 branchia of first pair, br2 branchia of second pair, bt buccal tentacles, gp genital papillae, ll lower lip, ne abdominal neuropodia, np nephridial papilla, ul upper lip, numbers refer to segments.

FIGURE 4. Amphitritides namibiensis sp. nov. SEM micrographs. A. Anterior end, lateral view. B. Anterior end of a small specimen, frontal view. C. Anterior end, lateral view. D. Second branchia of a small specimen (note: short stalk and short filaments). E. Segment 3 (note: nephridial papilla). F. Buccal tentacles. Scale bars. A 1 mm, B, C 500 µm, D 200 µm, E 100 µm, F 50 µm. Abbreviations: br branchia, br1 branchia of first pair, br2 branchia of second pair, bt buccal tentacles, ch1 chaetiger 1 (=segment 4), ci ciliated groove, gp genital papillae, ll lower lip, np nephridial papilla, ul upper lip, numbers refer to segments.

FIGURE 5. Amphitritides namibiensis sp. nov. SEM micrographs. A. Segments 7–14, lateral view (arrows: start of secondary annulation on segment 13 or 14). B. Segments 12–14, dorsolateral view (arrows: start of secondary annulation on segment 13 or 14). C. Anterior end, ventral view. D. Pore openings on the ventral shield of segment 2. E. Abdomen, dorsal view. F. Abdomen, ventral view (note: mid-ventral groove). Scale bars. A, B, F 500 µm, C, E 200 µm, D,10 µm, F 50 µm. Abbreviations: ll lower lip, numbers refer to segments.

FIGURE 6. Amphitritides namibiensis sp. nov. SEM micrographs. A. Neuropodia of segments 9–12, lateral view (arrow: start of double row of thoracic uncini on segment 11). B. Transition from thorax to abdomen (arrows point to papillae-like structures on abdominal neuropodia). C. Segments 6–8, lateral view (arrows point to genital papillae; note: neuropodia with single rows of uncini). D. Posterior thoracic parapodia (note: double rows of uncini). E. Abdomen, dorsal view (note: papillae-like structure dorsally above neuropodia, anterior end is on the right). F. Serrated thoracic notochaetae. Scale bars. A–E 200 µm, F 50 µm.

FIGURE 7. Amphitritides namibiensis sp. nov. SEM micrographs. A–C. Serrated notochaetae of anterior thoracic segments, different views. D. Thoracic uncini. E. Abdominal uncini. Scale bars. A–E 10 µm.

FIGURE 11. Notopodial chaetae, thoracic and abdominal uncini of the new species of Amphitritides described herein. A–E. A. namibiensis sp. nov. A. Notopodial chaetae, segment 19. B–C. Notopodial chaetae, segment 10. D. Thoracic uncini, segment 10. E. Abdominal uncini, segment 31. F–J. A. jirkovi sp. nov. F. Notopodial chaetae, segment 10. G. Notopodial chaeta, segment 21. H. Thoracic uncini, segment 20. I. Abdominal uncini, segment 50. J. Thoracic uncinus, segment 20. K–O. A. skeletonensis sp. nov. K. Longer notopodial chaetae, segment 11. L–M. Shorter notopodial chaetae, segment 11. N. Abdominal uncini, segment 34. O. Abdominal uncini, segment 40. P. A. namibiensis sp. nov. thoracic chaetae with bulbous wings, segment 10 (arrows). R. A. jirkovi sp. nov. thoracic chaetae with bulbous wings, segment 8 (arrows), S. A. skeletonensis sp. nov. thoracic chaetae with indistinct bulbous wings, segment 15 (arrows). Scale bars. A, C–G, J–N, O, R, S 20 µm, B, H, I, O, P 50 µm.