Ceratonereis ( Composetia) Hartmann-Schröder, 1985: 49. Composetia: Khlebovich 1996: 122; Bakken and Wilson 2005: 520 –521; Bakken et al. 2018: 25.
Diagnosis. Prostomium with entire anterior margin, one pair of antennae, one pair of palps, and two pairs of eyes. Eversible proboscis with conical paragnaths only on maxillary ring, without any paragnath and papilla (or soft cushion) on oral ring. Four pairs of tentacular cirri. Parapodia of first two chaetigers sub-biramous, all following parapodia biramous. Sub-biramous parapodia with or without notoacicula. Notopodial prechaetal lobe present or absent. Notochaetae all homogomph spinigers. Neurochaetae all compound with homogomph, sesquigomph or heterogomph articulations, simple chaetae absent.
Gender. Feminine.
Type Species. Nereis costae Grube, 1840, fixed by original designation.
Remarks. Formerly, the nereidids that have the proboscis with conical paragnaths on the maxillary ring only were all identified as the genus Ceratonereis Kinberg, 1865 ( Fauchald 1977). Later, Hartmann-Schröder (1985) divided this genus into three subgenera: Ceratonereis ( Ceratonereis) characterized by the prostomium with an indented anterior margin, the presence of soft cushions or papillae on the areas VI in the oral ring, and all the chaetae compound with both hemigomph (sesquigomph) and heterogomph articulations; Ceratonereis ( Composetia) characterized by the prostomium with an entire anterior margin, the absence of soft cushions or papillae on the area VI, and all the chaetae compound with both homogomph and heterogomph articulations; and Ceratonereis ( Simplisetia) Hartmann-Schröder, 1985 characterized by the prostomium with an entire anterior margin, the absence of soft cushions or papillae on the area VI, and the presence of simple chaetae in middle and posterior neuropodia in addition to both compound homogomph and heterogomph chaetae. Khlebovich (1996) elevated each of the three subgenera to the rank of genus, and he noticed that Ceratonereis is also distinguishable from Simplisetia and Composetia in the presence of notopodial sesquigomph falcigers in contrast to the absence of the same in the latter two genera, highlighting that Hartmann- Schröder (1985) incorrectly described that all of the three subgenera have such falcigers.
After Khlebovich (1996), 29 of 30 species categorized as Ceratonereis ( Composetia) by Hartmann-Schröder (1985) and Hartmann-Schröder and Rosenfeldt (1988) have been assigned to the genus Composetia, except for Ceratonereis ( Composetia) burmensis ( Monro, 1937) that was regarded as a junior synonym of Neanthes glandicincta Southern, 1912 by Lee and Glasby (2015). Additionally, Pamungkas and Glasby (2015) transferred Nereis ( Ceratonereis) marmorata Horst, 1924, which was described based on only epitokous specimens and classified as “insufficiently known species” by Hartmann-Schröder (1985), to Composetia. Thereafter, one more species of Composetia, C. bundaiensis Hsueh, 2018, was described ( Hsueh 2018), summarizing a total of 31 species have been assigned to Composetia up to date ( Table 1).
However, the following eight species should be reexamined in future, because it seems uncertain whether they belong to Composetia or not: three species, C. beringiana ( Levenstein, 1961), C. gorbunovi (Uschakov, 1950) and C. paucidentata ( Moore, 1903), have several paragnaths on oral ring according to their original descriptions, deviating from the generic diagnosis; three species, C. dunckeri ( Augener, 1925), C. monronis ( Westheide, 1977) and C. tunicatae ( Hartman, 1936), have notopodial homogomph falcigers in posterior chaetigers, deviating from the generic diagnosis; two species, C. dubia ( Rullier, 1972) and C. pietschmanni ( Holly, 1935) were described based on only epitokous specimens, without any more additional description of atokes.
Though C. marmorata also lacks information of atokous morphology in both the original description and the redescription by Pamungkas and Glasby (2015), its assignment to Composetia is supported by the description of atokous specimens from China by Wu et al. (1985; as Ceratonereis marmorata), who described that all chaetae (homogomph spinigers and hererogomph falcigers) compound, lacking simple chaeta, and notopodial falcigers absent.
Ceratonereis tripartita Horst, 1918 was also originally described based on only epitokous specimens ( type locality: Malay Archipelago) and classified as “insufficiently known species” by Hartmann-Schröder (1985). However, Fauvel (1932, 1953) described that an atokous specimen of this species collected from the Andaman Islands had only compound chaetae (homogomph and hererogomph spinigers, and hererogomph falcigers) and lacked neuropodial simple chaetae and notopodial falcigers, well supporting that his specimen belongs to the genus Composetia. Therefore, this species is newly assigned to Composetia in the present study, though it is not enough evidenced whether the atokous specimen of Fauvel (1932, 1953) really belongs to the same species as the epitokous type specimens.
Furthermore, two new species are described as members of this genus in the present study (see below). Thus, a total of 34 species currently belong to Composetia ( Table 1).
Composetia was redefined by Bakken and Wilson (2005), who provided the generic diagnosis based on the descriptions of the non-type species, C. irritabilis (Webster, 1879) and C. scotiae (Berkeley and Berkeley, 1956), owing to their situation that the type material of the type species C. costae could not be located. In fact, however, at least 11 syntypes of C. costae have been safely preserved in the Museum of Natural History in Berlin ( Hertwich 1993; recent unpublished observation by the present author). Composetia seems not to be a monophyletic group, but to include some morphologically distinct groups, as suggested by Bakken and Wilson (2005). Revision of Composetia with the exact generic definition based on the redescription of the type material of C. costae is needed.
1 Several paragnaths present on oral ring in the three species, deviating from the generic diagnosis (see also Table 2).
2 synonymized to Nereis ( Ceratonereis) costae by Fauvel (1923).
3 synonymized to Nereis ( Ceratonereis) costae by Fauvel (1953).
4 synonymized to Ceratonereis ( Composetia) costae by Read and Fauchald (2019) in the online database, based on Hartman (1959).
5 Since the original description was based on only epitokous specimens, without any more additional description of atokes, further study is needed to confirm whether this species belongs to Composetia or not.
6 Notopodial homogomph falcigers present in posterior chaetigers, deviating from the generic diagnosis (see also Table 2).
7 Original description and redescription ( Pamungkas and Glasby 2015) was based on only epitokous specimens. Atokous morphology was described by Wu et al. (1985).
8 Original description was based on only epitokous specimens. Atokous morphology was described by Fauvel (1932, 1953).
The generic diagnosis presented above is based on not Bakken and Wilson (2005) but Hartmann-Schröder (1985) and Khlebovich (1996), partially modified here to allow for some unique characteristics of the two new species in the present study (see below).