Manayunkia occidentalis, Atkinson & Bartholomew & Rouse, 2020

Atkinson, Stephen D., Bartholomew, Jerri L. & Rouse, Greg W., 2020, The invertebrate host of salmonid fish parasites Ceratonova shasta and Parvicapsula minibicornis (Cnidaria: Myxozoa), is a novel fabriciid annelid, Manayunkia occidentalis sp. nov. (Sabellida: Fabriciidae), Zootaxa 4751 (2), pp. 310-320 : 313-315

Manayunkia occidentalis sp. nov.

Figures 2–4

Manayunkia speciosa: Hazel, 1966 ; Bartholomew et al. 1997; 2006; 2007; Alexander et al. 2014; Stocking and Bartholomew, 2007; Bjork & Bartholomew 2009; Willson et al. 2010; Atkinson et al., 2011; Malakauskas et al., 2013; 2015.

Holotype (in 70% ethanol, initially fixed in 10% formalin). Adult male from Klamath River mainstem near confluence with Beaver Creek, California, USA. 41.867240°N, - 122.809763°E, collected by Julie Alexander ( OSU), 25 April 2014 ( SIO-BIC A12115 )

Paratypes (in 70% ethanol, fixed in 10% formalin); One specimen, adult female, same locality, collector and date as holotype ( SIO A12116 ); One specimen, adult male, same locality, collector and date as holotype ( SIO A12117 ) .

Etymology. The specific epithet is derived from the Latin word for “west”, to contrast with M. speciosa , which occurs in eastern and central North American drainages.

Description. Holotype (SIO-BIC A12115 ) a male with eight thoracic segments and three abdominal segments. Total length (unfixed) 3.0 mm, crown 0.3 mm. Body cylindrical with tapering, dorso-ventrally flattened abdomen. Body wall translucent grey with minor brown pigmentation on peristomium and pygidium, and green pigmentation on chaetiger 6. Branchial crown ~10% of total body length. Two pairs of radioles, each with six pinnules. One ventral pinnule on radiole with 4–5 yellow-white spots in life ( Fig. 2 B–C). One pair of vascularised, unbranched ventral filamentous appendages present, extending for about two-thirds length of radiolar crown, approximately same width as pinnules ( Fig. 2 B–C). Anterior peristomial ring with membranous collar, followed by posterior peristomial ring ( Fig. 4 A–B,D). Collar margin smooth, higher ventrally, separated by a narrow dorsal gap that corresponds with ciliated faecal groove ( Fig. 4D ). Peristomial eyes, black rounded spots ( Fig. 2E ). Pygidial eyes absent. Superior thoracic notochaetae elongate, narrowly hooded; 5–7 per fascicle (chaetigers 1–5), 4–5 per fascicle (chaetigers 6–8) ( Figs 3A ; 4 A–C). Inferior thoracic notochaetae on chaetigers 1–8 short; 3–4 per fascicle except chaetiger 2, which has 6 per fascicle. Thoracic neuropodia each with 4–7 uncini in chaetigers 2–8 ( Fig. 3B ). Thoracic uncini with rows of evenly small teeth gradually decreasing in size away from main fang ( Figs 3B ; 4E ). Position of chaetae and uncini reversed in abdominal segments; number of abdominal uncini per fascicle decreasing posteriorly from 22 to 9. Abdominal uncini each with multiple rows of teeth that are uniform in size ( Figs 3C ; 4H ); manubrium at least five times longer than dentate region, with base about two thirds the width of the dentate region. Abdominal neuropodia are elongate, narrowly hooded, decreasing posteriorly from 4–6 to 2 per fascicle ( Fig. 4G ).

Variation. Paratypes are similar to the holotype. However, females have oocytes in thoracic chaetigers 4–5 ( Fig. 2C ) and a pair of pigmented spermathecae in the base of the radiolar crown. Females differ from males in having thoracic neuropodia with uncini in chaetigers 2–5 followed by 3–6 elongate hooded chaetae in neuropodia of chaetigers 6–8 ( Fig. 3E,G ).

Remarks. Manayunkia occidentalis sp. nov. is the sister group to M. speciosa based on COI sequence data with a minimum pairwise distance (simple distance) to our M. speciosa samples of 11.0%, clearly supporting that they can be regarded as a separate taxon, although phylogenetic support for this relationship was weak (bootstrap 28%). Manayunkia occidentalis sp. nov. and M. speciosa are the only species of Manayunkia , and in fact of any Fabriciidae (see Huang et al. 2011), to show sexual dimorphism with regards to thoracic chaetal complement. Males of M. occidentalis sp. nov., and M. speciosa (Rouse pers. obs.) on specimens from near the type locality (SIO-BIC A12106 ), show the typical arrangement of thoracic uncini in each of chaetigers 2–8, while females have thoracic uncini in chaetigers 2–5 only ( Fig. 3H ). The neuropodia of chaetigers 6–8 instead have elongate hooded chaetae ( Fig. 3G ). These elongate hooded chaetae were seen in all females examined. Larval development would be worth studying to see if there is a loss of thoracic uncini or if they never develop in chaetigers 6–8. It is somewhat surprising that this major difference in chaetal complement was never noted previous in observations on M. speciosa . Manayunkia occidentalis sp. nov. differs markedly from descriptions of M. speciosa by Leidy (1883) and Pettibone (1953) in that it has far fewer pinnules on the radioles. In this regard Manayunkia occidentalis sp. nov. is similar to other Manayunkia species that have relatively few pinnules (see Rouse 1996).

Figures

FIGURE 2. Gross morphological features of Manayunkia occidentalis sp. nov. resolved by light microscopy: A, multiple individuals emerged and feeding from their tubes; B, Individual annelid with prominent vascularized appendages (va) and showing refractile spots on one feeding palp on each side (arrowheads); C, female in reflected light, showing white oocytes (o) in segments 4–6; D, male in reflected light showing bright spermatogonic tissue (sp) in multiple posterior segments; E, Male in transmitted light showing parallel vascularized appendages (va) and fanned-out feeding palps anteriorly with two dark eyespots in peristomium, and granular coelom posteriorly due to presence of developing sperm.

FIGURE 3. Images showing chaetal characters of Manayunkia occidentalis sp. nov.: A, inferior and superior notochaete typical of thoracic segments 2–8; B, thoracic uncini; C, abdominal uncini; D, dorsal view of posterior thoracic segments and abdomen of male showing typical uncini in chaetigers t7 and t8 (arrowheads) and in scanning electron micrograph shown in F; E, dorsal view of posterior thoracic segments and abdomen of female showing neuropodia of thoracic chaetigers 6–8 with elongate neuropodia instead of uncini, seen also in scanning electron micrograph in G (arrowhead). H, anterior thoracic segment of female showing notochaetae and uncini (arrowhead), characteristic of thoracic segments 2–5 in both sexes.

FIGURE 4. Morphological features of Manayunkia occidentalis sp. nov. resolved by scanning electron microscopy: A, lateral view; B, dorsal view; C, ventral view; D, anterior showing membranous collar (c) of the peristomal ring (pr), margin with fecal groove (fg); mucus covers the pinnules and adheres diatoms; E, detail of typical thoracic uncini; F, abdominal segments and anus, showing ciliated fecal groove extending anteriorly and wrapping around to the ventral surface at boundary between abdominal and thoracic segments; G, lateral view of thoracic segments showing contracted uncini and prominent neuropodia; H, higher magnification view of retracted abdominal uncini.