A new limpet Nipponacmea habei is described based on differences from any other known members of the genus in the shell, pigmentation of soft part, jaw, radula, and buccal cartilage. It is noteworthy that this new species contains two almost discrete forms in radula teeth morphology. The assessment of variability revealed that there is no morphological differences between two radula forms in shell and soft-part characters, and thus it is concluded that they are two scarcely continuous infraspecific populations exhibiting a north-south cline. The distributions and the cline of two radula forms are considered to be governed mainly by oceanography and strictly by microlocal environmental factors.

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A new ascoglossan opisthobranch species of the genus, Mourgona Marcus and Marcus, 1970, was found from Amami-Oshima Island in southwestern Japan. This paper is the first report on the genus around the sea waters of Japan.

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Two types of the swan mussel, Anodonta woodiana, collected from 3 river systems in Kinki district were investigated at 10 protein coding loci using starch-gel electrophoresis. They were fixed for different alleles at 5 loci. No hybrid was observed in collected stations where both types appear. These results suggest that each type of the swan mussel are clearly discrete species.

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Two sympatric types of freshwater mussel, Anodonta woodiana (Lea), were distinguished by means of isozyme analysis, in a small creek in Hyogo Prefecture. They were investigated from May 1991 to April 1993. They were fixed for different alleles at 5 loci investigated at 10 protein. The average density of the number of A. woodiana per 1 m^2 was 17.8. 141 mussels divided in the ratio A : B=3.41 : 1. B-type was smaller in both shell width and shell length than A-type. A-type mussels incubated eggs and larvae from March and June. B-type mussels incubated through winter, and released the glochidia during the early spring. Genetic isolation between A-type and B-type differs remarkably from each other in breeding season.

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Chromosome analysis in the embryo of an ovoviviparous freshwater snail, Semisulcospira reiniana from Iga Basin, Mie, Japan, revealed that the diploid number (2n) was 36. The haploid number of chromosomes was found to be 18 in testis. The chromosome pairs in the complement were composed of twelve pairs of metacentrics, five pairs of metaor submetacentrics and a pair of submeta- or subterocentric.

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タイワンバイの交尾と産卵を観察した。交尾は観察期間内(1990年10月∿1991年1月)に1度見られ, 産卵はこの期間内継続した。卵嚢は梯形で透明な袋で長さ0.4∿0.48cm, 幅0.63∿0.73cmで, 最低5個, 最高101個, 1卵嚢中には平均19.8±8.8個の卵が入っている。1♀1時期産卵数は平均29.4卵嚢, 610粒である。タイワンバイの卵嚢はバイのそれに比し小さく, 1卵嚢中卵数も小さく, 孕卵数も新腹足目類の中でも少ないほうに属する。産卵期は9∿1月であるが別亜種ハベバイでは6月∿9月と異なる。

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テレビ東京「ときめきマリンII」のスタッフのご好意により, 沖縄県慶良間諸島に生息するウコンハネガイCtenoides ales (Finley, 1927)の発光をビデオテープを通じて観察することができた。発光は外套膜縁に沿って走る青白く光る筋が素早く明滅するものである。左右の外套膜縁の閃光状の発光はかならずしも同調しないので, しばしば交叉して稲妻のように見えることもある。従来, 二枚貝綱における発光はツクエガイ科のツクエガイGastrochaena cuneiformisとニオガイ科のヒカリカモメガイPholas dactylusとヒカリニオガイBarnea candidaにおける細胞外発光(発光液の分泌)しか知られていなかった。本種における発光は組織学的研究は行われていないが, 光の強さや筋状の発光部位の移動のす早い速度などからみて, 細胞内自家発光と推察される。このような形式の発光と, それが, ミノガイ科において見られるという事実はおそらく世界最初の発見と思われる。

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