Manayunkia Leidy, 1859

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 : 9-12

Manayunkia Leidy, 1859

Dybowscella Nusbaum, 1901 , subjective synonymy

Fabricia (Manayunkia) Southern, 1921 , superseded original combination

Garjaiewella Dybowski, 1929 , subjective synonymy

Haplobranchus Bourne, 1883 , objective synonymy

Trichosobranchella Dybowski, 1929 , subjective synonymy

Type species: Manayunkia speciosa Leidy, 1859 , by monotypy.

Diagnosis (after Bick et al. 2024, emended). Eight thoracic and three abdominal chaetigers. Three pairs of pectinated radioles present, i.e., radioles asymmetrically branched, only in the largest species arise 2 or more branches from a common base, so that the branches appear to be arranged in two rows; radiolar lobes completely separated from one another; acellular supporting tissue of radioles (=radiolar skeleton) consists of a thin layer of an extracellular matrix. Unbranched vascularized ventral filamentous appendages present. Dorsal lips erect, broadly rounded or tapered. Ventral lips or lip-like processes absent. Between base of branchial lobes and base of dorsal lips, ciliated food groove forms as a continuation of the ciliated epithelial cells of the radioles, which extends ventrally to the mouth opening; mouth opening bounded ventrally by the anterior peristomial ring lobe. Branchial heart dorsally in the peristomium. Anterior margin of anterior peristomial ring developed as a membranous collar with rectangular or rounded ventral lobe, narrowly separated mid-dorsally; ciliated band between anterior and posterior peristomial ring ventrally. Inferior thoracic notochaetae short, narrowly hooded or pseudo-spatulate. Thoracic uncini with rows of equal-sized or progressively smaller teeth above main fang; sexual dimorphism present: transitional chaetae or transitional uncini in chaetigers 6–8 present in females. Brood chamber usually present in females. Dentate region of abdominal uncini with multiple rows of equal-sized teeth; manubrium distinctly longer than dentate region. Peristomial eyes present, pygidial eyes absent. Spermiogenesis in chaetigers 6–8. Pigmented spermathecae in females at the base of the radiolar crown.

Remarks. The number of radioles in Manayunkia is a recurring point of discussion. According to Bick (2020), all Fabriciidae , including Manayunkia , always have three pairs of radioles. However, it was also discussed whether Manayunkia could only have 2 pairs of radioles, but additionally a pair of slender, filiform appendages without branching in the dorsalmost position of the radiolar crown (e.g., Fitzhugh 1989). These appendages have also been referred to as ‘Dorsallippenauswüchse’ ( Zenkevitsch 1925), ‘mediodorsal tentacles’ ( Pettibone 1953) or ‘displaced pinnules’ ( Fitzhugh 1992). Bick (2020) also discussed the type of branching of the radiolar crown in the Fabriciidae . In Manayunkia , the branching of the radioles is pectinate. This pattern has also been demonstrated in Monroika ( Bick & Armendáriz 2021) . In M. baicalensis and M. godlewskii , by far the two largest valid species of this genus, a two-row arrangement of the branching of the radiolar crown has been described (e.g. Sitnikova et al. 1997; Zenkevitsch 1925). This interpretation did not take into account that two or more branches actually originate from a common base. A more detailed presentation of the different interpretations of the radiolar crown can be found in the Discussion at the end of this paper.

Species of Fabriciinae subfam. nov. have an acellular radiolar skeleton (see above, and also Bick 2020; Randel & Bick 2012; Tilic et al. 2021) and a ciliated patch ventrally on the anterior peristomial ring ( Fig. 4D ). Manayunkiinae subfam. nov., i.e. Manayunkia and Monroika and maybe also Echinofabricia Huang, Fitzhugh & Rouse, 2011 , lack this ‘supporting tissue’ (= radiolar skeleton). The extracellular matrix, which usually forms the supporting tissue of the radioles in Fabriciinae subfam. nov., is only poorly developed ( Bick 2020, see Description of M. aestuarina ( Fig. 7 ) and Discussion). Manayunkia and Monroika also have a ciliated band ventrally at the posterior margin on the anterior peristomial ring instead of a ciliated patch ( Bick 2004, 2020; Bick & Armendáriz 2021). Darkly pigmented, sac-like spermathecae at the base of the radiolar crown in females have been described for several species ( Bick et al. 2024; Rouse, 1995, 1996; Zenkevitsch 1925).

In most or even all species, so-called transitional chaetae or transitional uncini ( Bick 2020) may occur in the neuropodia of chaetigers 6 to 8 in females ( Atkinson et al. 2020; Bick 2020; Bick et al. 2024; Sitnikova et al. 1997). Transitional chaetae represent an intermediate form of narrowly bended hooded chaetae and thoracic uncini that usually occur in this position. Transitional uncini are similar to normal thoracic uncini. However, the dentate region is elongated, a distinct main fang is absent and the entire upper surface is covered with a multitude of small, equally sized teeth. It is not yet known whether there is a character for the beginning of the reproductive period, i.e., whether they are only developed when females reach sexual maturity. It is assumed here that these chaetae or uncini do not occur in males. But this type of chaetae is also found in Monroika and Brandtika asiatica Jones, 1974 (now Monroika asiatica ( Jones, 1974) n. comb.). This character is explained in more detail in the Discussion.

A brood chamber in females has so far only been described in Manayunkia species. This brood chamber exists as at least two types. It is formed by wing-like protrusions of the integument of the brood chamber chaetigers, i.e. chaetigers 6–8, or by bulge-like protrusions on chaetigers 6 and 8 (see descriptions of various species).

Figures

FIGURE 4. Fabriciinae subfam. nov.; A–E Fabricia stellaris (Müller, 1774) from the Baltic Sea. A. Total view of a living individual. B. Radiolar crown of a living specimen. C. SEM micrograph of radiolar crown, dorsal view. D. Anterior end, ventral view (arrow points to ciliated patch of the anterior peristomial ring lobe). E. TEM micrograph of a branch of a radiole. Scale bars. A–B 200 µm, C 100 µm, D 50 µm, E 3 µm µm (abbr: bh branchial hearts, ecm extracellular matrix, pre peristomial eyes, pye pygidial eyes, sp spermatheca).

FIGURE 7. Manayunkia aestuarina (Bourne, 1883), TEM micrographs.A. B Cross-section of a branch of a radiole at the base. C. Extracellular matrix between both epithelia. D. Cross-section of a branch of a radioles near the tip. E. Cross-section of a branch of a radiole at the tip. F. Aboral section of a branch of a radiole. Scale bars. A, B 10 µm, C 0.2 µm, D 5 µm, E 2 µm, F 1 µm. (ab aboral, ad adoral, adc adoral cilia, c coelom, cp cytoplasmic projections, cu cuticle, ecm extracellular matrix, fc, frontal cilia of the food groove, gly glycogen, lfc latero-frontal cilia of the food groove, m mitochondria, mv microvilli, myo myoepithel cell, n nucleus, vac vacuole).