The Indo-Pacific nassariids (genus Nassarius) possesses the highest diversity within the family Nassariidae. However, the previous shell or radula-based classification of Nassarius is quite confusing due to the homoplasy of certain morphological characteristics. The toxin accumulators Nassarius glans and Nassarius siquijorensis are widely distributed in the subtidal regions of the Indo-Pacific Ocean. In spite of their biological significance, the phylogenetic positions of N. glans and N. siquijorensis are still undetermined. In the present study, the complete mitochondrial genomes of N. glans and N. siquijorensis were sequenced. The present mitochondrial genomes were 15,296 and 15,337 bp in length, respectively, showing negative AT skews and positive GC skews as well as a bias of AT rich on the heavy strand. They contained 13 protein coding genes, 22 transfer RNA genes, two ribosomal RNA genes, and several noncoding regions, and their gene order was identical to most caenogastropods. Based on the nucleotide sequences combining 13 protein coding genes and two rRNA genes, a well-supported phylogeny of Nassarius was reconstructed, and several morphological synapomorphies were observed corresponding to the phylogenetic framework. In addition, the sister group relationship between N. variciferus and the remaining toxin-accumulated nassariids was determined, suggesting that the phylogeny might be related to their diet. The divergence time estimation analysis revealed a correlation between speciation events of nassariids and glacial cycles during the Pliocene-Pleistocene epoch.

In this study, an eight-week feeding trial was performed to investigate the effects of different taurine supplementation levels (0.0% as control, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%) on the growth performance, lipid composition, and antioxidant ability in juvenile ivory shells Babylonia areolata. The results showed that taurine supplementation significantly improved the specific growth rates (SGRs) and survival rates of ivory shell (except the survival rate in the 3.0% taurine diet group) (p < 0.05). The SGRs showed an increasing and then decreasing tendency with increasing dietary taurine supplementation, and the highest value was observed in the 2.0% taurine diet (2.60%/d). The taurine content in the muscle of ivory shells fed taurine-supplemented diets significantly increased when compared to the control group (p < 0.05). The profiles of C22:2n6 in the muscle of ivory shells fed taurine-supplemented diets were significantly higher than in the control group (p < 0.05), and the highest values were observed in the 2.0% taurine supplementation group. The high-density lipoprotein cholesterol (HDL-C) content in the hepatopancreas showed an increasing and then decreasing tendency with increasing dietary taurine supplementation, while the low-density lipoprotein cholesterol (LDL-C) concentration showed a decreasing tendency. Furthermore, the activities of pepsin and lipase in both the intestine and hepatopancreas significantly increased at moderate taurine supplementation levels compared to the control group (p < 0.05). Accordingly, obvious increases in the histological parameters in the intestine of ivory shells fed taurine-supplemented diets were also found. As for the antioxidant ability, the activities of the total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) showed an increasing and then decreasing tendency with increasing dietary taurine supplementation, and the highest values were observed in the 1.0% and 1.0–2.0% taurine supplementation groups, respectively; the malondialdehyde (MDA) contents significantly decreased with increasing dietary taurine supplementation (p < 0.05). The taurine intake affected the expression of four appetite-related genes in the hepatopancreas, in which orexin and NPY showed an increasing and then decreasing tendency, while leptin and cholecyatoklnin decreased with increasing dietary taurine supplementation. In conclusion, moderate taurine supplementation in an artificial diet (about 1.5–2.0%) could improve the growth performance and antioxidant ability and change the lipid composition of juvenile ivory shells.