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The present study was carried out to design a simple, new and accurate method for identification of the morphologically similar four species (forms A and B of P. shikueii, P. mictodonta, and P. wilsoni) of the Perinereis nuntia species complex by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) patterns of the internal transcribed spacer (ITS). Restriction digestion analysis in the following two steps generated a specific restriction pattern for each species: (1) by the first digestion of amplified ITS fragments with AluI, we can distinguish the two forms of P. shikueii from P. mictodonta and P. wilsoni; (2) by the subsequent digestion of ITS fragments with Cfr10I, we can distinguish between the forms A and B of P. shikueii, and by that with HinfI, we can distinguish P. mictodonta from P. wilsoni. Our result indicates that this method enable easy and accurate identification of these taxa. We additionally examined the distributions of the two forms of P. shikueii in Japan, Korea and Taiwan using this new method. The form B was distributed in a wide range in western Japan and Korea, whereas the form A was distributed in few limited sites in the inner parts of the Seto Inland Sea and the Ariake Sea in Japan, the western and southern coasts of Korea, and the western coast of Taiwan. [ABSTRACT FROM AUTHOR]

Two new species Composetia kumensis and C. tokashikiensis (Nereididae) are described based on specimens collected 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) prostomium 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. [ABSTRACT FROM AUTHOR]

The recruitment process of planktic larvae of the nereidid polychaete Hediste diadroma, which has a catadromous life cycle, was examined in an estuary in Kagoshima Bay, Southern Japan. Our laboratory experiments showed that the phototaxis of the planktic larvae changed drastically from positive to negative during the 3-chaetiger nectochaeta, 3.5-4.0 days after fertilization. During this stage, the prostomial antennae, first peristomial cirri, and anal cirri appeared and the ciliary bands used for swimming were reduced; these results suggest that larvae shifted from pelagic to demersal stage at approximately 4.0 days after fertilization. Field sampling took place in the estuary, where reproductive swarming of mature adults was observed in late February to April; planktic larvae of, mainly, 5- to 8-chaetiger stages were collected in evening high tides during the spring tides of April and May 1989, 2013, and 2015. During the same period, 5- or higher chaetiger benthic juveniles were collected at low tide from intertidal flats from a wide area of the estuary where adults inhabited. The morphology of benthic juveniles of 5- and 6-chaetiger stages differed from that of planktic larvae of the same stages in the following characteristics: (1) the long larva-specific spinigers were lost; (2) the second peristomial cirri, originating from the parapodial lobes of chaetiger 1 of the planktic larvae, appeared; and (3) the anal cirri were elongated. Our results indicate that 5- to 8-chaetiger nectochaeta are critical phases for the successful settlement of planktic larvae, which come back into an estuary with rising tides. [ABSTRACT FROM AUTHOR]

Taxonomic reexamination of Japanese populations of the Perinereis nuntia species group, which constitutes a major polychaete component in intertidal benthic communities, was carried out by analyzing the mitochondrial 16S rDNA and the nuclear ribosomal ITS sequences of 80 specimens, newly collected from 27 sites in Japan, together with 18 museum-preserved specimens collected from southern neighboring countries outside Japan. The Japanese populations of the Perinereis nuntia species group could be divided into four genetically different groups, which corresponded morphologically to four nominal species (P. mictodonta, P. wilsoni, P. shikueii, and P. nuntia), with some exceptions. Perinereis nuntia and P. shikueii were recorded as new to the Japanese fauna, with their distributions restricted to southern Japan. The clade containing P. shikueii was subdivided into two sister clades (forms A and B), indicating that cryptic speciation has occurred within this clade. Our results revealed a remarkable variability in the number of bars in area VI of the proboscis in form B of P. shikueii, which appeared to be caused by breakage of the long bar into short bars during growth from a juvenile to an adult. [ABSTRACT FROM AUTHOR]

The reproductive season and life span of the common estuarine polychaete Simplisetia erythraeensis (Annelida: Nereididae) was investigated by monthly sampling during the years 2015 and 2016 in two tidal flats at two different regions in southern Japan: Shigetomi in Kagoshima Bay, Kyusyu Island, a warm-temperate region and Ichi on Amami-Oshima Island, Ryukyu Islands, a maritime subtropical region. At both sites, one or two cohorts were distinguished simultaneously using monthly body-width histograms. Recruitment of new cohorts occurred from August in Kagoshima Bay and from July on Amami-Oshima Island. Ovigerous females were observed from March to August in the former area and from April to July in the latter area, with the highest female maturity rate (number of females with oocytes/total number of adults larger than the smallest mature size) in July in both areas. The maximum value of the mean oocyte size of each female increased with increasing female maturity rates. The density of each cohort decreased from May onward because of the death of adults after reproduction, which resulted in the complete disappearance of the cohort in early October. Our results showed that the life span of S. erythraeensis was one year, and the reproductive period occurred in summer. [ABSTRACT FROM AUTHOR]