Manayunkia occidentalis Atkinson, Bartholomew & Rouse, 2020

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 : 36-37

Manayunkia occidentalis Atkinson, Bartholomew & Rouse, 2020

( Figure 20 )

Manayunkia occidentalis Atkinson et al., 2020: 313–318 , fig. 1–4. – Tilic et al. (2020b): 3313 –3314, fig. 1.

Manayunkia speciosa . – Hazel 1966: 533–535, fig. 1. – Verner 1981: 182–183. – Wilson et al. 2010: 183–191, fig. 2.

Material examined. USA, California, Klamath River , 41°51'45.91"N, 122°33'53.96"W, coll. 24.07.2006, 10 specimens ( ZSRO-P2698 ) .

Description (based on the description of Atkinson et al. (2020) and own observations). Total length of specimens about 1.8–2.4 mm (unfixed 3.0– 4.5 mm); width between 0.2–0.3 mm; length of radiolar crown about 0.2–0.3 mm; ratio between length of radiolar crown and body length, without radiolar crown, about 0.12–0.18; body cylindrical, posteriorly tapered ( Fig. 20A, H ).

Radiolar crown with three pairs of radioles and one pair of unbranched vascularized ventral filamentous appendages; surface of radioles and ventral filamentous appendages wrinkled; dorsal radioles unbranched, median and ventral radioles with about 6 branches each; branches of radioles on the inner side with short median and long latero-frontal cilia ( Fig. 20B ); vascularized ventral filamentous appendages almost as long as radioles or about twothird of length of radioles, about as wide as radioles; no morphological differences in the structure of the branches of the radiolar crown, except ventral filamentous appendages.

Peristomium with anterior and posterior rings, anterior ring shorter than 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 peristomial rings visible ( Fig. 20C ); one pair of black rounded peristomial eyes.

Metanephridia located in peristomium and first 2 chaetigers. First chaetiger usually significantly shorter than peristomium and second chaetiger ( Fig. 20C ), chaetigers 2–6 successively longer, chaetiger 6 significantly longer than chaetiger 5, chaetigers 7 and 8 succesively shorter; first 5 thoracic chaetigers wider than long, last 3 thoracic chaetigers distinctly longer than wide ( Fig. 20A ); borders between thoracic chaetigers clearly visible; abdominal chaetigers short, borders between abdominal chaetigers indistinct; abdomen, including pygidium, in total about as long as chaetiger 7 ( Fig. 20A, H ); pygidium about same length as chaetiger 10, terminating as rounded lobe ( Fig. 20A, H ); pygidial eyes absent.

Thoracic notopodia superiorly with 5–7 elongate, narrowly hooded chaetae on chaetigers 1–5, 4–5 on chaetigers 6–8, inferiorly with 3–6 short, narrowly hooded chaetae ( Fig. 20D–G ); neuropodia of males with 4–6 (rarely 7) uncini on chaetigers 2–8, with main fang and apical with about 4–6 rows of progressively smaller teeth ( Fig 20I–K ); neuropodia of females with same number and shape of uncini on chaetigers 2–5, followed by 3–6 transitional chaetae on chaetigers 6–8; sometimes thoracic uncini in a slightly offset double row; abdominal neuropodia with elongate, narrowly hooded chaetae, decreasing posteriorly from 4–6 to 1–2 per fascicle ( Fig. 20H ); abdominal notopodia with about 20–22 uncini on chaetiger 9, 14–18 on chaetiger 10 and 8–12 on chaetiger 11; abdominal uncini with about 4–6 rows of equal-sized teeth; manubrium about five times longer than dentate region.

Abdomen dorso-ventrally flattened, posteriorly tapered or rounded ( Fig. 20H ).

Body wall of living specimens translucent grey with minor brown pigmentation on radiolar crown, peristomium and pygidium; one ventral radiole with 4–5 yellow-white spots in life; fixed specimens colourless, transparent, only anterior margin of peristomium, metanephridia and sometimes also radioles slightly brownish; females with pigmented spermathecae in the base of radiolar crown.

Remarks. Manayunkia occidentalis most closely resembles M. speciosa . Females of both species have transitional chaetae on chaetigers 6–8, but bulge-like protrusions on chaetigers 6 and 8 are absent. The occurrence of a brood chamber was not yet described. We also found no brood chamber when we examined specimens from Klamath River. One specimen had a longitudinal furrow on chaetigers 6 to 8, but this was located dorsally in the area of the faecal groove ( Fig. 20A ). It is therefore not very likely that this furrow actually represents a brood chamber. However, it cannot be completely excluded. Transitional chaetae are also found in the three species from Lake Baikal, but these species have bulge-like protrusions on chaetigers 6 and 8.

Manayunkia occidentalis has significantly fewer branches in the radiolar crown than M. speciosa , about 22–26 vs. about 34–42. In addition, M. occidentalis appears to be smaller than M. speciosa (fixed specimens: about 2.5 mm vs. about 4.9 mm), but still has more thoracic uncini (4–7 vs. 2–5). This is remarkable in that smaller species usually have fewer uncini.

Small (immature) females have only one transitional chaeta on each of the chaetigers 6–8. Apart from these transitional chaetae, there were no regular thoracic uncini on the neuropodia of these chaetigers.

Geographic distribution. Northwestern United States: California, Klamath and Willamette Rivers.

Biology. Manayunkia occidentalis was overlooked for a long time and confused with M. speciosa . However, only Manayunkia occidentalis is an obligate invertebrate host of the myxozoan parasites Ceratonova shasta and Parvicapsula minibicornis , which cause ceratomyxosis in salmon and trout in North America ( Bartholomew et al. 2006, Alexander et al. 2014), but not M. speciosa , which occurs in the Great Lakes region and in the eastern river systems of the USA. This is a very good example of the need for thorough taxonomic analyses. Infection with C. shasta in adult Chinook salmon causes mortality through intestinal perforations and co-occurring bacterial infections ( Bartholomew 1998). Approximately 70–100% of juvenile Chinook salmon are infected by the parasites during early summer when these fish migrate to the ocean. They can cause mortality rates of approximately 40% in Oncorhynchus spp. ( Schloesser et al. 2016). Parvicapsula minibicornis is found in the kidneys of juvenile Chinook salmon, but the effect of the infection is not yet clear because it is often present with C. shasta .

Females have oocytes in chaetigers 4–5, and males have sperm and spermatids in chaetigers 6–8. Larval development takes place in the tube of females. Adult worms with overt parasite infections often lacked gametes. The greatest number of larvae that has been found simultaneously in the tube of a female is 35; under laboratory conditions, a total of 36 larvae were recorded over the course of a season ( Wilson et al. 2010). Mechanical disturbance by large benthic species and lack of oxygen in the sediment cause the specimens to quickly leave their tube or withdraw deep into the tube. However, Wilson et al. (2010) observed that mature females with larvae in their tubes left the tubes less often than males or non-breeding females.

Ecology. Manayunkia occidentalis was found in clusters of tubes, attached to rocks or intertwined with periphyton.

Figures

FIGURE 20. Manayunkia occidentalis (Atkinson, Bartholomew & Rouse, 2020), SEM micrographs. A. Complete specimen without radiolar crown, dorsal view. B. Two branches of radiolar crown with short median and long latero-frontal cilia. C. Anterior end, lateral view. D. Notopodium of chaetiger 5 with short, and elongate, narrowly hooded chaetae. E. Thoracic chaetae of chaetiger 1. F. Notopodium of chaetiger 6 with short, and elongate, narrowly hooded chaetae. G. Short, narrowly hooded chaetae of chaetiger 6. H. Posterior end ventro-lateral view. I. Thoracic uncini of chaetiger 4. J. Thoracic uncini of chaetiger 6, frontal view. K. Thoracic uncini of chaetiger 4 frontal view. Scale bars. A 200 µm, B 10 µm, C, H 50 µm, D–F 20 µm, G, I 5 µm, J, K 2 µm.