본 연구는 종밋 Arcuatula senhousia의 생식생태학적 기초자료와 생물자원의 관리를 위한 정보를 제공하기 위해 수행하였다. 시료는 벌교읍 여자만에서 2019년 6월부터 2020년 5월까지 채집하여 분석하였다. 생식소는 다수의 생식소형성소낭으로 구성되었다. 성비 (암:수)는 1:1.1 (n=128:140, 암컷 46.4%)였으며, 각장이 증가함에 따라 수컷의 비율이 높아지는 경향을 보였다. 생식소지수는 암, 수 모두 5월에 연중 최고값을 보인 후 급격히 감소하여 11월부터 이듬해 1월까지 1.0 이하의 낮은 값을 보였다. 육중량비는 생식소지수와 유사한 경향을 보였다. 월별 생식소발달단계의 변화는 비활성기 (1-2월), 초기활성기 (3-4월), 후기활성기 (4-5월), 완숙기 (5-6월), 방출기 (6-8월), 퇴화기 (9-1월)였다. 종밋의 생식소 활성은 암컷과 수컷 모두 하계에 높고, 동계에 낮은 뚜렷한 계절적 변화를 보였으며, 주 산란기는 6-8월로 분석되었다. 종밋 개체군의 암컷과 수컷 모두 최소 72.7% 이상이 각장 10.1 mm 이상에서 성숙하였으며, 50% 군성숙 크기는 각장 약 10.0 mm로 분석되었다.

This study aimed to reconfirm the sex change scale and pattern of Tegillarca granosa. Although the sex ratio (female : male, female proportion) of T. granosa was 1:2.32 (30.2%) at the initial stage (2011) of the study, it was 1:0.94 (51.5%) after one year (2012) in the same population. The increase of the female proportion was greater in the 2+ year class (23.0%) when compared to the 1+ year class (19.2%). Overall, sex change ratio of 37.6% was observed in this population of T. granosa. The sex change ratio of the 2+ year class (39.3%) was higher than that of the 1+ year class (35.3%). And sex change ratio in the males (42.2%) was higher than that in the females (26.9%). The female proportion was the opposite of the result from 2006~2007, and one of the causes was presumed to be the difference in cumulative water temperature during the gonadal inactive stage (winter).

Environmental changes exert harmful effects on organisms inhabiting coastal regions. These changes are also associated with reduced production in aquaculture farms. In this study, we investigated internal and external responses of two Bivalvia species (Crassostrea gigas and Mytilus galloprovincialis) in Gamak Bay under stressful environmental conditions in aquaculture farms. We investigated external responses such as weight, size, and environment exposure time, and analyzed the expression of the HSP70 gene. C. gigas HSP70 gene expression level was significantly high in the C3 aquaculture farm site, but the weight and size of C. gigas were high in the C2 aquaculture farm site. The response of C. gigas HSP70 mRNA was associated with the environmental exposure time in each aquaculture farm. Expression of M. galloprovincialis HSP70 gene was found to be significantly higher in the M2 aquaculture farm site than in the M1 site, whereas the weight of M. galloprovincialis was observed to be higher in the M1 site. The size and environmental exposure time of M. galloprovincialis were similar between M1 and M2 sites. In addition, HSP70 sequences of C. gigas and M. galloprovincialis showed high similarity with that of another marine species. According to our results, there were differences in internal responses following environmental stress in aquaculture farms, with respect to HSP70 gene expression. The results suggest that the HSP70 gene is a useful molecular indicator for monitoring stress responses in Bivalvia species in the field.

본 조사에서는 양식업 및 수산업에 있어서 중요한 부분을 차지하고 있는 가막만을 대상으로 수질환경 변화에 대한 이매패류의 군집구조 및 연간변동을 파악하고 물리적 화학적 환경이 이매패류 군집에 미치는 영향을 분석하고자 하였다. 가막만 해역의 12개 정점을 설정하고 2001년부터 2006년까지 4월, 7월, 9월, 11월 계절별로 조사한 결과 이매패류 총 28종이 출현하였으며, 평균 서식밀도는 226.72±196.20 ind. m-2의 변동범

한국산 살조개 (Protothaca jedoensis)의 새로운 산업화 양식품종으로 개발하기 위한 기초자료를 얻기 위하여 1998년 9월부터 1999년 8월까지 주로 조직학적 방법에 의해 생식소의 발달과정과 생식주기를 조사하였다. 살조개는 자웅이체로서, 생식소는 해부학적으로 소화맹낭과 족부근육 사이에 위치하였다. 난소와 정소는 각각 난자형성소낭과 정자형성소낭으로 구성되어 있었다. 비만도는 2월에 20.6로 가장 높았으며 8월에 최소값 (9.6)을 보였다

The sex of bivalves is classified into gonochorism and hermaphroditism, and hermaphroditism is further divided into simultaneous, and sequential. Simultaneous hermaphroditism is the simultaneous release of eggs and sperm by one organism during the same season. Sequential hermaphrodites are either male or female for one or several annual cycles (Heller, 1993; Gosling 2004; Collin, 2013). T. granosa is a sequential hermaphroditic bivalve undergoing sex change (Lee et al., 2014). However, definitive conclusion on whether the scale and pattern of sex change of T. granosa is always consistent could not be made. Therefore, the objective of this study was to reconfirm sex change in T. granosa and consider the scale and pattern of sex change compared to the results of Lee et al. (2014). The total number of T. granosa used for sex change identification was 777 with a shell length (SL) between 25.1-35.0 (30.9±2.13) mm. For Tegillarca granosa, the scale of sex change during 2006-2007 was reported to be 15.1% (Lee et al., 2014). In this study, the overall scale of sex change in T. granosa was 37.6% during 2011-2012, which was approximately 2.5 times higher than that reported by Lee et al. (2014). In addition, the difference between the sex change ratio from females to males and that from males to females was 15.3% during the period of 2011-2012, which was similar to the finding of 15.0% during 2006-2007 (Lee et al., 2014). The sex change ratio of female→male : male→female was 1 : 3.42 during 2006-2007 reported by Lee et al. (2014). It was 1 : 1.57 during 2011-2012 in this study.

Ultrastructural studies of oocyte degeneration in the oocyte, and the functions of follicle cells during oocyte degeneration are described to clarify the reproductive mechanism on oocyte degeneration of Mactra chinensis using cytological methods. Commonly, the follicle cells are attached to the oocyte. Follicle cells play an important role in oocyte degeneration. In particular, the functions of follicle cells during oocyte degeneration are associated with phagocytosis and the intracellular digestion of products. In this study, morphologically similar degenerated phagosomes (various lysosomes), which were observed in the degenerated oocytes, appeared in the follicle cells. After the spawning of the oocytes, the follicle cells were involved in oocyte degeneration through phagocytosis by phagolysosomes. Therefore, it can be assumed that follicle cells reabsorb phagosomes from degenerated oocytes. In this study, the presence of lipid granules, which occurred from degenerating yolk granules, gradually increased in degenerating oocytes. The function of follicle cells can accumulate reserves of lipid granules and glycogen in the cytoplasm, which can be employed by the vitellogenic oocyte. Based on observations of follicle cells attached to degenerating oocytes after spawning, the follicle cells of this species are involved in the lysosomal induction of oocyte degeneration for the reabsorption of phagosomes (phagolysosomes) in the cytoplasm for nutrient storage, as seen in other bivalves.

This study attempts to propose the possibility of the sex reversal in Sinonovacula constricta and Gomphina veneriformis by confirming the changes in the sex ratio with the shell length in the same population level. For analysis of sex ratio, 100 individuals of S. constricta (SL 26.5-95.0 mm) and 2385 individuals of G. veneriformis (SL 15.1-60.1 mm) were used. Sex was analyzed histologically. Both species displayed the tendency of increase in the female proportion with increase in shell length. In this study, changes in the sex ratio in accordance with the growth of S. constricta and G. veneriformis are determined to be indirect evidence that signifies their sex reversal.

The sex ratio (F:M) in the same population of oyster, Crassostrea gigas at the commencement of the study (2007) was 1:1.0, but changed to 1:2.8 by the end of the study (2008). The sex reversal rate in two-year-old oysters was 40.2%. Specifically, female to male sex reversal rate was 66.1%, which is higher than the male to female sex reversal rate of 21.1%. The sex reversal pattern of C. gigas appears to go from male female male, and as such is determined to be rhythmical hermaphroditism.

The ovarian cycle, the biological minimum size, and artificial spawning frequency by artificial spawning induction of the female hard clam, Meretrix petechialis, were investigated by histological observations and morphometric data. The ovarian cycle of this species can be classified into five successive stages: early active stage, late active stage, ripe stage, partially spawned stage, and spent/inactive stage. The spawning period was from June to September, and the main spawning occurred between July and August when the seawater temperature exceeds over . The biological minimum size (shell length at 50% of first sexual maturity) in females were 40.39 mm in shell length (considered to be two years of age), and all clams over 50.1 mm in shell length sexually matured. In this study, the mean number of the spawned eggs by spawning induction increased with the increase of size (shell length) classes. In case of artificial spawning induction for the clams > 40.39 mm, the number of spawned eggs from the clams of a sized class was gradually decreased with the increase of the number of the spawning frequencies (the first, second, and third spawning). In the experiments of artificial spawning induction during the spawning season, the interval of each spawning of this species was estimated to be 15-18 days (approximately 17 days).

This study attempts to propose the possibility of the sex reversal in Tegillarca granosa and Ruditapes philippinarum by confirming the changes in the sex ratio with the shell length (SL) in the same population level. For analysis of sex ratio with SL, 1500 individuals of T. granosa (SL 10.1-45.0 mm) and 712 individuals of R. philippinarum (SL 15.1-70.0 mm) were used. Sex was analyzed histologically. The average sex ratios (F:M) of T. granosa and R. philippinarum were 1:1.22 and 1:0.96, respectively. However, sex ratio was found to differ when the clams were divided into groups according to SL in 5.0 mm intervals. Both species displayed the tendency of increase in the proportion of female with increase in SL. In this study, changes in the sex ratio in accordance with the growth of T. granosa and R. philippinarum are determined to be indirect evidence that signifies their sex reversal.

The ultrastructural characteristics of germ cell differentiations during spermatogenesis and mature sperm morphology in male () were evaluated via transmission electron microscopic observation. The accessory cells, which contained a large quantity of glycogen particles and lipid droplets in the cytoplasm, are assumed to be involved in nutrient supply for germ cell development. Morphologically, the sperm nucleus and acrosome of this species are ovoid and conical in shape, respectively. The acrosomal vesicle, which is formed by two kinds of electron-dense or lucent materials, appears from the base to the tip: a thick and slender elliptical line, which is composed of electron-dense opaque material, appears along the outer part (region) of the acrosomal vesicle from the base to the tip, whereas the inner part (region) of the acrosomal vesicle is composed of electron-lucent material in the acrosomal vesicle. Two special characteristics, which are found in the acrosomal vesicle of A. () in Pinnidae (subclass Pteriomorphia), can be employed for phylogenetic and taxonomic analyses as a taxonomic key or a significant tool. The spermatozoa were approximately in length, including a sperm nucleus (about in length), an acrosome (about in length), and a tail flagellum (about ). The axoneme of the sperm tail evidences a 9+2 structure.

Spermatogenesis and taxonomic values of mature sperm morphology of in male Septifer (Mytilisepta) virgatus were investigated by transmission electron microscope observations. The morphologies of the sperm nucleus and the acrosome of this species are the cylinder shape and cone shape, respectively. Spermatozoa are approximately 45-50 in length including a sperm nucleus (about 1.26 long), an acrosome (about 0.99 long), and tail flagellum (about 45-47 ). Several electron-dense proacrosomal vesicles become later the definitive acrosomal vesicle by the fusion of several Golgi-derived vesicles. The acrosome of this species has two regions of differing electron density: there is a thin, outer electron-dense opaque region (part) at the anterior end, behind which is a thicker, more electron-lucent region (part). In genus Septifer in Mytilidae, an axial rod does not find and also a mid-central line hole does not appear in the sperm nucleus. However, in genus Mytilus in Mytilidae, in subclass Pteriomorphia, an axial rod and a mid-central line hole appeared in the sperm nucleus. These morphological differences of the acrosome and sperm nucleus between the genuses Septifer and Mytilus can be used for phylogenetic and taxonomic analyses as a taxonomic key or a significant tool. The number of mitochondria in the midpiece of the sperm of this species are five, as seen in subclass Pteriomorphia.

The reproductive life-history of molluscs can be divided into gonochorism and hermaphroditism, while hermaphroditism is further classified into simultaneous (synchronous or functional) and sequential (asynchronous) (Heller 1993 Gosling 2004). Approximately 40% of the 5600 mollusc genera are either simultaneous or sequential hermaphrodites. Hermaphroditism occurs in 100% of the Solenogastres, 99% of the Opisthobranchia, 100% of the Pulmonata, 3% of the Prosobranchia and 9% of the Bivalvia. Simultaneous hermaphroditism is the simultaneous release of eggs and sperm by one organism during the same season. Sequential hermaphroditism is the function of an organism first as one sex, then as another (Heller 1993). This study investigated the sex of Manila clam, Ruditapes philippinarum by verifying changes in sex ratio (F:M) with size and sex reversal stages. Adult one-year-old (11 months; SL 36.75±3.0 mm) R. philippinarum were used for sex reversal identification. Each individual was tagged on its shell prior to being reared in the wild for reproductive analysis, and sex was confirmed using the germ cell aspiration (GCA) method. Sex ratio (F:M) at the commencement of the study (June 2009) was 1:1.23, but changed to 1:0.87 by the end (July 2010). Overall sex reversal rate was 19.0%. Specifically, male to female sex reversal ratio was 21.05%, which was higher than the female to male sex reversal ratio of 12.9%. Based on our results, R. philippinarum has been confirmed to possess a sequentially hermaphroditic life-history.

Some characteristics of the formations of acrosomal vesicles during the late stage of spermatids during spermiogenesis and taxonomical charateristics of sperm morphology in male two species (Saxidomus purpurata and Meretrix petechialis) in the family Veneridae were investigated by electron microscope observations. In two species, the morphologies of the spermatozoa have the primitive type and are similar to those of other bivalves in that it contains a short midpiece with five mitochondria surrounding the centrioles. The morphologies of the sperm nuclear types of S. purpurata and M. petechialis in Veneridae have the curved cylindrical and cylinderical type, respectively. And the acrosome shapes of two species are the same cap-shape type. In particular, the axial filament is not found in the lumen of the acrosome of two species, however, subacrosomal material are observed in the subacrosomal spaces between the anterior nuclear fossa and the acrosomal vesicle of two species. The axoneme of the sperm tail flagellum shows a 9+2 structure. In particular, taxonomically important some charateristics of sperm morphologies of two species in the family Veneridae are acrosomal morphology of the sperm, The axial filament is not found in the acrosome as seen in a few species of the family Veneridae in the subclass Heterodonta. The acrosomal vesicle is composed of right, left basal rings and the apex part of the acrosomal vesicle. These charateristics belong to the subclass Heterodonta, unlikely a characteristic of the subclass Pteriomorphia showing all part of the acrosome being composed of electron opaque part (region). Therefore, it is easy to distinguish the families or the subclasses by the acrosomal structures. The number of mitochondria in the midpiece of the sperm of S. purpurata and M. petechialis in Veneridae are five. However, the number of mitochondria in the midpiece of the sperm in most species of Veneridae in the subclass Heterodonta are four. Therefore, the number of mitochondria of the sperm midpiece of two species are exceptionally 5, and it is only exceptional case in the species in Veneridae in the subclass Heterodonta. Except these cases, the number of mitochondria in the sperm midpiece in all families in the subclass Heterodontaare are 4, and now widely used in taxonomic analyses.

본 연구는 수컷 살조개 Protothaca (Notochione) yessoensis의 정자 형성 과정 중 생식세포들의 분화와 성숙정자의 미세구조 특징에 관한 몇 가지 특징을 투과전자현미경 관찰에 의해 조사하였다. 본 종의 정자형태는 원시형(primitive type)으로, 이매패강, 이치아강(Heterodonta)에 속하는 다른 종들과 유사하다. 생식세포에 인접하여 연결되어 있는 보조세포들은 생식세포들의 발달을 위해 영양공급에 관여한다. 본 종의 정자의 핵형은 긴 원통형이며 첨체의 형태는 모자모양이다. 정자는 길이가 대략 46～50 ㎛이며, 길다란 정핵(길이 약 2.44 ㎛)과, 첨체(길이 0.45 ㎛), 그리고 미부 편모(약 42～46 ㎛)로 이루어져 있다. 미부 편모의 악소님(axoneme)은 9+2 구조를 나타낸다. 첨체소포의 특징으로써 basal ring의 기저부 위에서 측면부위는 전자밀도가 불투명한 부위를 나타내나, 첨체소포의 앞쪽 정단부위는 전자밀도가 비교적 투명한 부위로 나타나는 특징을 보인다. 이것이 이치아강에 속하는 백합과와 또 다른 여러 과들에 속하는 종들의 정자들이 갖는 첨체소포의 공통특징이다. 따라서 이치아강이 갖는 이들 첨체소포가 갖는 공통특징은 분류의 key 또는 중요한 도구로써 계통․분류를 위해 사용될 수 있다. 정자 중편에 있는 미토콘드리아 수는 4개로 이치아강 내에서 백합과의 3종을 제외한 모든 종들과 다른 과들의 종들에서 공통으로 나타나고 있는데, 예외로, 개조개, 백합, 가무락조개 만은 중편의 미토콘드리아가 5개로 이루어져 있다. 미토콘드리아 수는 과나 또는 상과 수준에서 종들의 분류학적 분석을 할 경우, 분류 key 또는 중요한 도구로 사용될 수 있다.