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Sperm morphology provides an abundant source of potentially informative characters for gastropod taxonomy. In the present study, this character was used to offer additional information concerning the genus Babylonia (Mollusca, Gastropoda), the most promising economic marine gastropods of the present century. Light and transmission electron microscopy was used to study the ultrastructure of spermatozoa in five groups of Babylonia, including B. areolata populations from Hainan, China, from Thailand, and the reciprocal hybrid offspring of these two populations and B. lutosa. Principal component analysis was conducted to examine morphological differences of spermatozoa. The results showed that morphology can contribute to the classification of the two species B. areolata and B. lutosa. The reciprocal hybrid offspring of the two B. areolata varieties exhibited ultrastructure of spermatozoa similar to that of their male parents, and each showed greater similarity to the male parent in the fine structural details. This study aimed to compare the ultrastructure of sperm in five groups of Babylonia and to compare the differences between the parents and the hybrids to provide basic information for genetic studies of Babylonia. [ABSTRACT FROM AUTHOR]

Disease outbreaks among cultured ivory shells (Babylonia areolata) have occurred frequently in recent years, causing mass mortality and seriously hindering the development of the B. areolata industry. Hybridization is an effective way of improving germplasm in aquaculture, as it often generates desirable traits in the hybrids, including increased disease resistance. This study analyzed the dynamic changes in several immune indexes, including the survival rate, total hemocyte count (THC), hemocyte mortality, reactive oxygen species (ROS) level, and hemolymphatic pathogenic bacteria content, in two parental populations, Thailand B. areolata (TT) and Hainan B. areolata (HH), and their reciprocal hybrids, Thailand B. areolata ♀ × Hainan B. areolata ♂ (TH) and Hainan B. areolata ♀ × Thailand B. areolata ♂ (HT), challenged with Vibrio harveyi , the main pathogenic bacterial species affecting B. areolata. The results showed that the median lethal concentrations (LC 50) of the four populations were in the order HH-LC 50 > TT-LC 50 and TH-LC 50 , and HT-LC 50 > TT-LC 50 at 48 and 72 h post challenge. The changes in non-specific immune parameters showed that under control conditions, HT had a higher THC than the other three populations and that it maintained this level throughout the infection process, while HH and HT showed significantly lower hemocyte mortality rates and higher ROS levels than TT and TH. In addition, the pathogenic Vibrio (V. harveyi) count in the hemolymph of the four populations increased sharply to a peak value and then slowly decreased after infection. Compared with the control groups, the change rates of the cumulative total pathogen content in the hemolymph were in the order TT > TH > HH > HT at 72 h after infection, indicating that HT suppressed and eliminated pathogenic microorganisms most effectively. HT may have inherited the more efficient non-specific immune function from HH. Overall, the results suggest that TT may be more susceptible to V. harveyi infection than HH, and hybridization could be a useful way to improve the disease resistance of the ivory shell, thereby benefiting the aquaculture industry. • The disease resistance of two populations of ivory shell and their hybrids was compared. • The Thailand ivory shell population was more susceptible than the Hainan ivory shell population to pathogenic Vibrio infection. • Hybridization increased the disease resistance of hybrids, especially the HT, which showed a higher ROS level, more efficient pathogen removal ability and lower hemocyte mortality under Vibrio harveyi challenge. [ABSTRACT FROM AUTHOR]