Amphitritides jirkovi, 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 : 46-48

Amphitritides jirkovi sp. nov.

( Figs 2 , 11F–J, R )

Material examined. Holotype. Off Namibia: 17.3158°S 11.7232°E, depth 26 m, 05.03.2008, complete specimen ( ZSRO-P2674 ).

Diagnosis. Distal part of prostomium as shelf-like tentacular membrane with distinct lateral lobes. Two pairs of arborescent branchiae with short stem; first and second pairs of branchiae about same length, slightly more than half the body width. Prostomium with lateral lobes, Without lateral lobes on anterior segments, but midventral lobe on segment 1 present. 25–26 thoracic segments. One pair of nephridial papillae on segment 3, inserted laterally and close to branchial stalk. Ten pairs of genital papillae on segments 6–15, originating from anteriorly bases of corresponding notopodia and aligned to them. Notochaetae with bulbous wings in the middle of longer chaetae, distally serrated. Neuropodia from segment 5, double rows of uncini from segment 11 almost to end of body. Pygidium with crenulated margin.

Description of holotype. Large species, complete specimen 60 mm long, 5 mm wide, for about 120 segments. Anterior part of body not distinctly swollen.

Body surface of dorsal and ventral sides throughout different from each other. Ventral side with glandular structure, well stained with methylene blue; true ventral shields, i.e. clearly separated from the lateral sides by furrows, from segments 3 or 4–14; last ventral shields are slightly longer (anterior-posterior axis), but narrower; mid-ventral groove begins after segments with ventral shields, initially shallow ( Fig. 2C ). Dorsal side papillose; papillae arranged in more or less distinct rows, in single row up to about segments 4–5, 2 rows on segments 6–7, 3 rows on segments 8–13, and 4–5 rows thereafter; rows of papillae continuing through abdomen, segments appearing secondarily annulated as a result ( Fig. 2A, B, D ).

Prostomium at base of upper lip; basal part without eyespots; distal part forming shelf-like tentacular membrane with lateral lobes and numerous filiform and deeply grooved, ciliated buccal tentacles ( Fig. 2A–C ).

Peristomium well developed, with conspicuous hood-like upper lip, with corrugated anterior margin, upwards curved; lower lip swollen, pharyngeal organ visible ( Fig. 2C ).

Segment 1 dorsally narrow, conspicuous developed ventrally, forming a mid-ventral lobe, with swollen flanges ventrolaterally, anterior margin concave and corrugated. Segments 2 and 3 without any lobes ( Fig. 2B–C ).

Two pairs of arborescent branchiae on segments 2 and 3 with short stem and wide medial gap; first and second pairs of branchiae about same length, slightly more than half body width; branchiae about 3–4 mm long; main stem thick, with irregular dichotomous branching; branches start shortly above the base and terminate by short filaments ( Fig. 2A–C ).

Notopodia starting from segment 4 and extending for 22 (left body side) and 23 (right body side) segments, i.e. up to segments 25 and 26; first pair same size as following ones, but more dorsally arranged; from second pair of notopodia, all laterally aligned; notopodia short, rectangular to conical; notopodia and neuropodia clearly separated ( Fig. 2B ). Notochaetae indistinctly arranged in two or more rows, chaetae of first row shorter; limbation indistinctly or absent basally; bulbous wings in the middle of longer chaetae present; tips serrated, base of serrated tip distinctly wider; no difference observed between notochaetae of anterior and posterior thoracic segments ( Fig. 11F–G, R )

Neuropodia beginning from segment 5; thoracic and abdominal neuropodia as long lateral ridges distinctly raised from body surface, almost reaching the ventral shields on thorax, reaching the ventral groove on the abdomen ( Fig. 2B–D ). Uncini arranged in double rows, in face-to-face arrangement, from segment 11 almost to end of body, only last 12 segments with single rows; rows completely separated from each other. Fully developed avicular uncini, 37–45 µm wide and 48–56 µm high; short triangular or rounded heel, distally pointed prow downwardly directed; barely visible dorsal button inserted halfway between base of main fang and tip of prow, dorsal button sometimes absent; convex base; uncini with 3–4 more or less distinct rows of apical teeth above main fang, with about 2–3 on first, 3–6 on second and more than 10 teeth on rows 3 and 4; dental formula MF: 2–3: 3–6:>10 (>10); thoracic and abdominal uncini similar ( Fig. 11H–J ).

One pair of nephridial papillae on segment 3, inserted laterally and close to branchial stalk. Ten pairs of tubular genital papillae on segments 6–15, originating anterior to base of the notopodia and aligned with them; genital papillae distinctly shorter than corresponding notopodial lobe, last 2–3 papillae shorter than previous ones ( Fig. 2E–F ).

Pygidium terminal, margin crenulated ( Fig. 2D ).

Remarks. Amphitritides jirkovi sp. nov. differs from A. namibiensis sp. nov. and A. skeletonensis sp. nov. (see below) by the presence of distinctly shorter branchiae, the larger number of genital papillae (10 pairs vs 3 pairs), and double rows of uncini on most abdominal segments, which are completely absent on abdominal segments in A. namibiensis sp. nov. and which are present only on the first 6–7 abdominal segments in A. skeletonensis sp. nov. The number of thoracic segments also differs in these 3 species (see Table 1 ).

Amphitritides jirkovi sp. nov. 60 mm in length,is among the seven largest Amphitritides species known worldwide, including A. namibiensis sp. nov. and A. skeletonensis sp. nov. described in this paper. The three remaining species are about 20 mm long. These larger species include A. bruneocomata ( Ehlers, 1887) (84 mm long), A. carawa Nogueira & Hutchings, 2007 (41 mm long), A. gracilis ( Grube, 1860) (120 mm long) and A. kuehlmanni Arvanitidis & Koukouras, 1995 (50 mm long). Of these larger species A. bruneocomata has more pairs of notopodia than A. jirkovi sp. nov. (27 vs. 22 or 23) and also significantly more genital papillae (15 vs. 10); in addition, the bases of notochaetae are narrow and not swollen, and the uncini in the double rows are partially intercalating. Amphitritides carawa is distinctly smaller, and has also more genital papillae (14 pairs); in addition, the first pair of branchiae is twice as long as the second pair. Amphitritides gracilis is twice as long as A. jirkovi sp. nov. but has fewer pairs of notopodia (17–21 pairs) and genital papillae (8 pairs); genital papillae are located between parapodial lobes, instead of being at the anterior base of notopodia as found in A. jirkovi sp. nov. Amphitritides kuehlmanni is somewhat smaller, but has considerably more segments (177 segments); this species also has 12 pairs of genital papillae, and the first pair of branchia is also larger than the second.

There are also no species in the genus Amphitrite and Paramphitrite to which the characters of A. jirkovi sp. nov. apply, i.e. the number of branchiae and genital papillae, as well as segments with notopodia and uncini in double rows (see Jirkov 2020).

Since only one specimen was available, no SEM-photos could be made.

Etymology. This species is dedicated to Igor A. Jirkov, for his great contribution to polychaete taxonomy especially the Terebellidae .

Distribution. Only known from the type locality. We found this specimen at a shallow water station (26 m depth) in front of the mouth of the Kunene River.

Habitat. The salinity of the bottom water was 35.7 psu and the oxygen content was 54 µmol/l. Bottom water temperature was 17.8 °C. No information is available on the sediment conditions and the tube shape.

Figures

FIGURE 2. Amphitritides jirkovi sp. nov. A. Anterior end, dorsal view. B. Anterior end, lateral view. C. Anterior end, ventral view. D. Posterior end, dorsolateral view. E. Segments 3 to 10, lateral view, ShirlastainA staining (note: nephridial and genital papillae). F. Genital papillae on segments 8 to 10, ShirlastainA staining. Scale bars. A–D 1 mm, E, F 500 µm.Abbreviations: gp genital papillae, ll lower lip, np nephridial papilla, po pharyngeal organ, ul upper lip, numbers refer to segments.

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.

Tables

TABLE 1. Diagnostic characters of three newly described Amphitritides species off Namibia, SW Africa.

	A. jirkovi sp. nov.	A. namibiensis sp. nov.	A. skeletonensis sp. nov.
Length of first branchiae	more than half the body width	longer than body width	longer than body width
Number of thoracic chaetigers	22 – 23	usually 21 (16 – 21)	25 – 27 (rarely 28)
Number of thoracic segments	25 – 26	usually 24 (19 – 24)	28 – 30 (rarely 31)
Position of genital papillae	segments 6 – 15	segments 6 – 8	segments 6 – 8
Double row of uncini	almost up to end of abdomen	up to end of thorax	up to 6. or 7. (rarely 4. or 5.) abdominal segment
Anterior abdominal segments with papillae-like structure above neuropodia	absent	present	absent