Species Diversity 25: 11–24 Published online 1 January 2020 DOI: 10.12782/specdiv.25.11 Two New Species of Composetia (Annelida: Nereididae) from Small Estuaries in the Ryukyu Islands, Southern Japan, with a List of All Species Currently Belonging to Composetia Masanori Sato Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890-0065, Japan E-mail: [email protected] (Received 2 May 2018; Accepted 18 November 2019) http://zoobank.org/1E0F263F-FDA3-4AB8-B93E-DD534C3B1CD0 Two new species Composetia kumensis and C. tokashikiensis (Nereididae) are described based on specimens collect- ed from subtropical small estuaries in the Kume-jima and Tokashiki-jima islands in the middle Ryukyu Islands, southern Japan, respectively. Both species have the following diagnostic characteristics of Composetia Hartmann-Schröder, 1985: (1) having conical paragnaths in the maxillary ring of the proboscis and lacking paragnaths or papillae in the oral ring, (2) pro- stomium with entire anterior margin, (3) the absence of falcigers among notochaetae, and (4) the absence of simple chaetae among upper neurochaetae. These new species share the following diagnostic characters: (1) presence of notoacicula on chaetigers 1 and 2, (2) absence of notopodial prechaetal lobe throughout body, (3) presence of neuropodial postchaetal lobe only in anterior body, (4) neuropodial falcigers all heterogomph, and (5) oral ring greatly enlarged in full-everted proboscis. However, C. tokashikiensis sp. nov. is distinguishable from C. kumensis sp. nov. by the presence of heterogomph spinigers among the upper neurochaetae around chaetiger 5. A list of all of 34 species currently belonging to Composetia and a key to Japanese species of Composetia are also provided. Key Words: East Asia, non-marine species, notoacicula, polychaete, subtropical estuaries, taxonomy. islands of the middle of Ryukyu Islands, southern Japan: Introduction an estuary consisting in a small creek in the upper inter- tidal zone of the uplifted coral reef on Kume-jima island in Most polychaetes are marine species and only a limited 1999–2013, and the another one in the Tokashiki-gawa river number of species known as non-marine species occur in on Tokashiki-jima island in 1991. Specimens were found in freshwater or brackish-water habitats (about 200 species, sediment samples, which were obtained by shoveling from about 2% of the estimated 9000–12000 species worldwide); intertidal sandy bottoms. The specimens were fixed in 10% the family Nereididae includes the most abundant non-ma- formalin or in 80 or 99% ethanol, and transferred to 80 or rine species (61 species) (Glasby et al. 2009). However, taxo- 99% ethanol for preservation. Photographs of live specimens nomical surveys of non-marine species seem to be insuffi- were taken with a digital camera (Konica-Minolta Alpha-7). cient in tropical and subtropical Asia, which is an area with Water temperature and salinity were measured with a SCT the greatest diversity of coastal marine species in the world meter (Model 30, Yellow Springs Instrument, Co.). (e.g., Tittensor et al. 2010). For the preserved specimens, body length (BL) from the During a survey on nereidid fauna in subtropical small anterior end of the prostomium to the posterior end of the estuaries surrounded by coral reefs in the middle Ryukyu Is- pygidium excluding anal cirri, and anterior maximum body lands in southern Japan, two morphologically similar unde- width (BW) excluding parapodia were measured. Photo- scribed species of Composetia Hartmann-Schröder, 1985 [as graphs of the specimens were taken with a digital camera Ceratonereis (Composetia) in Sato (2012); see Sato and Sak- (Nikon COOLPIX) on a stereoscopic microscope. Drawings aguchi 2016; Sato 2017] were found from a unique habitat were prepared with a camera lucida. exposing to usually fresh water, but sometimes full-strength Terminology of paragnath groups on proboscis, and that sea water. Here, the two species are described as new species of parapodial and chaetal morphology are according to Bak- of Composetia. Additionally, a key to species of Composetia ken and Wilson (2005). recorded from Japan is also provided based on this study Type specimens are deposited in the polychaete collection and previous references. of the National Museum of Nature and Science, Tsukuba, Japan (NSMT). Materials and Methods Specimens were collected from two small estuaries on © 2020 The Japanese Society of Systematic Zoology 12 Masanori Sato Horst, 1924, which was described based on only epitokous Taxonomic Account specimens and classified as “insufficiently known species” by Hartmann-Schröder (1985), to Composetia. Thereafter, one Family Nereididae de Blainville, 1818 more species of Composetia, C. bundaiensis Hsueh, 2018, Genus Composetia Hartmann-Schröder, 1985 was described (Hsueh 2018), summarizing a total of 31 spe- cies have been assigned to Composetia up to date (Table 1). Ceratonereis (Composetia) Hartmann-Schröder, 1985: 49. However, the following eight species should be reexam- Composetia: Khlebovich 1996: 122; Bakken and Wilson ined in future, because it seems uncertain whether they 2005: 520–521; Bakken et al. 2018: 25. belong to Composetia or not: three species, C. beringiana (Levenstein, 1961), C. gorbunovi (Uschakov, 1950) and C. Diagnosis. Prostomium with entire anterior mar- paucidentata (Moore, 1903), have several paragnaths on gin, one pair of antennae, one pair of palps, and two pairs oral ring according to their original descriptions, deviating of eyes. Eversible proboscis with conical paragnaths only from the generic diagnosis; three species, C. dunckeri (Au- on maxillary ring, without any paragnath and papilla (or gener, 1925), C. monronis (Westheide, 1977) and C. tunica- soft cushion) on oral ring. Four pairs of tentacular cirri. tae (Hartman, 1936), have notopodial homogomph falcigers Parapodia of first two chaetigers sub-biramous, all follow- in posterior chaetigers, deviating from the generic diagno- ing parapodia biramous. Sub-biramous parapodia with or sis; two species, C. dubia (Rullier, 1972) and C. pietschmanni without notoacicula. Notopodial prechaetal lobe present or (Holly, 1935) were described based on only epitokous speci- absent. Notochaetae all homogomph spinigers. Neurochae- mens, without any more additional description of atokes. tae all compound with homogomph, sesquigomph or het- Though C. marmorata also lacks information of atokous erogomph articulations, simple chaetae absent. morphology in both the original description and the rede- Gender. Feminine. scription by Pamungkas and Glasby (2015), its assignment Type Species. Nereis costae Grube, 1840, fixed by origi- to Composetia is supported by the description of atokous nal designation. specimens from China by Wu et al. (1985; as Ceratonereis Remarks. Formerly, the nereidids that have the pro- marmorata), who described that all chaetae (homogomph boscis with conical paragnaths on the maxillary ring only spinigers and hererogomph falcigers) compound, lacking were all identified as the genus Ceratonereis Kinberg, 1865 simple chaeta, and notopodial falcigers absent. (Fauchald 1977). Later, Hartmann-Schröder (1985) divided Ceratonereis tripartita Horst, 1918 was also originally de- this genus into three subgenera: Ceratonereis (Ceratonereis) scribed based on only epitokous specimens (type locality: characterized by the prostomium with an indented ante- Malay Archipelago) and classified as “insufficiently known rior margin, the presence of soft cushions or papillae on species” by Hartmann-Schröder (1985). However, Fauvel the areas VI in the oral ring, and all the chaetae compound (1932, 1953) described that an atokous specimen of this with both hemigomph (sesquigomph) and heterogomph ar- species collected from the Andaman Islands had only com- ticulations; Ceratonereis (Composetia) characterized by the pound chaetae (homogomph and hererogomph spinigers, prostomium with an entire anterior margin, the absence of and hererogomph falcigers) and lacked neuropodial simple soft cushions or papillae on the area VI, and all the chaetae chaetae and notopodial falcigers, well supporting that his compound with both homogomph and heterogomph articu- specimen belongs to the genus Composetia. Therefore, this lations; and Ceratonereis (Simplisetia) Hartmann-Schröder, species is newly assigned to Composetia in the present study, 1985 characterized by the prostomium with an entire ante- though it is not enough evidenced whether the atokous rior margin, the absence of soft cushions or papillae on the specimen of Fauvel (1932, 1953) really belongs to the same area VI, and the presence of simple chaetae in middle and species as the epitokous type specimens. posterior neuropodia in addition to both compound ho- Furthermore, two new species are described as members mogomph and heterogomph chaetae. Khlebovich (1996) of this genus in the present study (see below). Thus, a total elevated each of the three subgenera to the rank of genus, of 34 species currently belong to Composetia (Table 1). and he noticed that Ceratonereis is also distinguishable Composetia was redefined by Bakken and Wilson (2005), from Simplisetia and Composetia in the presence of notopo- who provided the generic diagnosis based on the descrip- dial sesquigomph falcigers in contrast to the absence of the tions of the non-type species, C. irritabilis (Webster, 1879) same in the latter two genera, highlighting that Hartmann- and C. scotiae (Berkeley and Berkeley, 1956), owing to