Manayunkia mizu Rouse, 1996

Bick, Andreas & Bastrop, Ralf, 2025, Revision of the genus Manayunkia Leidy, 1859, and establishment of two subfamilies within Fabriciidae (Annelida, Sabellida), Zootaxa 5661 (1), pp. 1-58 : 34-36

Manayunkia mizu Rouse, 1996

( Figure 19 )

Manayunkia mizu Rouse, 1996: 1772–1776 : fig. 27–41.

Material examined. Paratypes: South Pacific, Bismarck Sea, Papua New Guinea, Madang, near Riwo Village , 05°09’ 30’’S, 145°48’ 00’’ E, depth 1 m, coll. 30.08.1993, 7 specimens ( USNM 172109 ) .

Description (based on the description of Rouse (1996) and own observations). Total length of specimens 1.7 mm; width about 0.08–0.1 mm; length of radiolar crown about 0.15–0.21 mm; ratio between length of radiolar crown and body length, without radiolar crown, between 0.14–0.15; body slender, posteriorly slightly tapered ( Fig. 19A, B, D ).

Radiolar crown composed of three pairs of radioles and one pair of unbranched vascularized ventral filamentous appendages; dorsal radioles unbranched, median and ventral radioles with a maximum of 3 branches each; vascularized ventral filamentous appendages same length and width as branches of the radioles; dorsal lips tapered distally, about 60–70 µm long ( Fig. 19C ).

Peristomium with anterior and posterior rings, anterior ring about same length as posterior ring; anterior margin of anterior peristomial ring developed as a low membranous collar ventrally, and narrowly separated mid-dorsally; border between anterior and posterior rings clearly visible ( Fig. 19C ); one pair of black rounded peristomial eyes.

Metanephridia in peristomium and first 2 chaetigers. First chaetiger shorter than peristomium and second chaetiger ( Fig.19A, C ), chaetigers 2–7 successively longer, chaetiger 6 and 7 significantly longer than chaetiger 5, chaetiger 8 shorter than chaetiger 7; first 5 thoracic chaetigers wider than long, last 3 thoracic chaetigers distinctly longer than wide ( Fig 19A ); borders between thoracic chaetigers clearly visible; abdominal chaetigers short, borders between abdominal chaetigers indistinct; abdomen, including pygidium, distinctly shorter than chaetiger 8 ( Fig. 19D ); pygidium about same length as chaetiger 11, terminating as rounded lobe ( Fig. 19D ); pygidial eyes absent.

Thoracic notopodia superiorly with 2–3 elongate, narrowly hooded chaetae on chaetigers 1–8, inferiorly with 2–3 pseudo-spatulate chaetae on chaetigers 2–5 ( Fig. 19E ), and 1–2 short, narrowly hooded chaetae on chaetigers 1 and 6–8; neuropodia of chaetigers 2–8 with 2–4 uncini, with main fang and towards apical with about 4–5 rows of progressively smaller teeth; abdominal neuropodia with 1–2 elongate, narrowly hooded chaetae; abdominal notopodia with about 8–10 uncini; uncini with about 6 rows of equal-sized teeth, about 5–6 teeth per row.

Pygidium posteriorly tapered ( Fig. 19B, D ).

Nephridia but particularly dorsal lips darkly pigmented ( Fig. 19B, C ), radioles with orange pigmentation in living specimens. Preserved specimens colourless, with brownish pigmentation on radioles and gut in chaetigers 2–5 ( Fig. 19A–C ).

Remarks. With a length of just over 1.5 mm, M. mizu is the smallest Manayunkia species and the only marine species apart from M. brasiliensis . In the original description, it was stated that in preserved specimens, the gut in chaetigers 2–4 was green pigmented (certainly because of the food consumed). In the individuals we examined, however, the gut in chaetigers 2–5 was brownish.The very darkly pigmented dorsal lips were particularly conspicuous in the specimens we examined. We saw neither transitional chaetae nor transitional uncini in the paratypes available to us. We also could not find a brood chamber.

Geographic distribution. Known only from the type locality, Papua New Guinea, Madang province .

Biology. In females, oocytes develop in chaetigers 4 and 5, while spermatogenesis in males takes place in chaetigers 6–8. Larval development takes place in the tube of females ( Rouse 1996).

Ecology. Between green algae ( Halimeda spec. ) and seagrass in mangrove habitat. Tubes are composed of fine calcareous sediment, mangrove detritus, and mucus ( Rouse 1996).

Figures

FIGURE 19. Manayunkia mizu Rouse, 1996 light micrographs of preserved paratypes. A, B. Complete specimen. C. Anterior end with radiolar crown. D. Posterior end. E. Notopodia of chaetigers 3 to 5. Scale bars. A, B 200 µm, C, D 100 µm, E 50 µm. (abbr: dl dorsal lips, pc pseudo-spatulate chaetae).