The type material of the species Carybdea murrayana Haeckel, 1880 was rediscovered in the Cubozoa collection of the Natural History Museum in London. A comparison of C. murrayana with Carybdea marsupialis (Linnaeus, 1758) and with Carybdea branchi Gershwin & Gibbons, 2009 was performed because the validity of the species has been doubted for over a century and because C. murrayana had been declared a synonym of C. marsupialis by authors like Mayer, Bigelow and Kramp, due to an apparent overlapping distribution range. The results demonstrate that C. murrayana is different from C. marsupialis but identical to C. branchi. Therefore, C. branchi is declared a junior synonym of the valid species C. murrayana Haeckel, 1880 according to the International Code of Zoological Nomenclature.
Additionally, the line drawings and/or descriptions of the carybdeid species Procharagma prototypus Haeckel, 1880 and Procharybdis cuboides Haeckel, 1880 were translated, diagnosed, compared to well-known carybdeid species and revised.
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.
Neomysis awatschensis is an important prey item for various fishes in Lake Kasumigaura, Japan. There is, however, a contradiction concerning the major food sources of this mysid species: whether “bottom mud”, “particulate organic matter (POM) including phytoplankton”, or “mesozooplankton” is the main diet, and this uncertainty may be due to differences in the methodology used to determine the prey items in previous studies. This study examined the main food sources of N. awatschensis by combining three methods to eliminate methodological biases: DNA metabarcoding, microscopy and stable isotope analysis. Planktonic diatoms and green algae sequences were the main taxa detected by DNA metabarcoding and microscopy on the fecal pellets. The δ15N values of the mysids were similar to those of phytoplankton feeders rather than carnivorous planktonic crustaceans. These results suggest that diatoms and green algae were the major food sources for N. awatschensis in Lake Kasumigaura during the investigation period, and that its trophic level is as low as that of herbivores. However, the partial contribution of other “POM” (e.g., benthic diatoms) is also implied, considering the dispersion in δ13C values. Mesozooplankton prey, such as copepods, were detected both using DNA metabarcoding and microscopy, but they could not be a major food source due to the low nitrogen stable isotopic signature of the mysids. The opportunistic feeding habits of N. awatschensis possibly explain the consistent dominance of this species in the lake, where the ecosystem structure was substantially changed because of successive desalination.
A record of the occurrence of Lucensosergia lucens is hereby added to the literature due to the present finding off Cape Nomo and off the Goto Islands, Nagasaki, western Japan. The sampling areas are connected to the presumptive paleo-East China Sea Gulf area in which the species has evolved. The species occurs in the western Pacific only; from Suruga Bay, Japan to off Tung-kang, south-western Taiwan, and presumably off Borneo, off the Philippines, and off New Guinea. Distribution at the latter three areas by the “Dana” records is needed to be reconfirmed by sampling.
Corbicula leana and C. fluminea are hermaphroditic and ovoviviparous freshwater clams. Although they are considered to reproduce using self-fertilization, the possibility of outcrossing was suggested due to lineage discordance between mitochondrial and genomic DNA. In these species, outcrossing means “egg parasitism” by the spermatozoa from one or more other clams, because they reproduce by androgenesis in which only the nucleus of spermatozoa is transmitted to the progeny. Moreover, the presence of males in these species was reported in the previous study, and they were estimated to reproduce by egg parasitism of hermaphrodites. In this study, we investigated the paternity of juveniles in the brood pouches of six hermaphrodites by comparing the genotypes of the brooded juveniles, brooding clams, and neighboring adult clams using two microsatellite DNA markers. Brooded juveniles showed either identical genotypes to the parental clam or different genotypes from their parent in one clam with brooding. The genotypes of brooded juveniles were identical to those of neighboring hermaphrodites and males. These results indicate that androgenetic Corbicula reproduce not only by self-fertilization but also by egg parasitism, with outcrossing among hermaphrodites and from males to hermaphrodites.
A total of 40 robust tonguefish (Cynoglossus robustus) larvae [2.1–10.2 mm body length (BL)] collected from Osaka Bay, eastern Seto Inland Sea were investigated. Those larvae that were smaller than 4 mm BL possessed a single filament-like elongate fin ray emitting from the most anterior dorsal fin. In larvae of between 4 and 5 mm BL we subsequently observed a second short fin ray, next to the first one. At the preflexion stage, 6.5–7 mm BL, the longer of the elongated fin rays extended to about 60% of BL and the shorter one extended to approximately 30–40% of the length of the longer one. These specimens did not develop transverse bands of melanophores laterally on their tails. These characteristics are the same as those presented in hatchery-reared larvae of the same tonguefish. Osaka Bay is also home to larvae from C. interruptus and C. joyneri, both with double elongated dorsal fin rays. These larvae can be easily distinguished from larval C. robustus by counting the myomeres, dorsal and anal fin rays, and by observing the pigmentation pattern on the tail.
In 2011, a tropical holothurian was found off the temperate coast of Kagoshima, Kyushu, Japan. This holothurian was identified as Stichopus naso Semper, 1867, which was first described in the Philippines, and is known to be distributed within the tropical Indo-West Pacific region. Herein, we examined its morphological characteristics and compared it with pre-described examples and discuss its origin from the perspective of climate change and artificial transfer. We considered that both perspectives are plausible because sea water temperature has recently risen around Japan, creating the possibility of eggs and larval transfer from southern regions and the consequent establishment of adult S. naso populations. Accidental introduction via ballast water from vessels and other pathways may not be implausible. In any case, ocean warming caused by global climate change is considered as a key factor in the survival and settlement of adult S. naso populations.