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Phascolosoma esculenta is an economically species inhabiting a soft substrate of mud in the intertidal zone, which is bad breathability, especially during the prolonged heavy rainstorms, that will bring hypoxia environment to P. esculenta. In this study, the negative impact of hypoxia on P. esculenta was firstly studied. The results showed that there were no P. esculenta died post 7 days hypoxia. However, P. esculenta surface became black after hypoxia stress and changed to brown after reoxygenation. The body cavity fluid’s total antioxidant capacity (T-AOC) showed notable increases at 48 h, 120 h, and 168 h post hypoxia stress and returned to the control level after reoxygenation. The contents of malondialdehyde (MDA) increased significantly at 24 h, 48 h, and 96 h but decreased substantially after reoxygenation. The activity of lactate dehydrogenase (LDH) increased during the hypoxia but decreased significantly after reoxygenation. Transcriptomic analysis was performed and a total of 55.26 GB of clean data were collected, 362 DEGs were obtained based on FPKM values, including 77 DEGs between control and hypoxia groups, 48 DEGs between control and reoxygenation groups, and 237 DEGs between hypoxia and reoxygenation groups. DEGs are enriched in pathways associated with immune system, carbon metabolism, apoptosis, ribosome and ion transport. These data enriched the molecular mechanism of invertebrate hypoxia tolerance and provided genetic material reference for future breeding of hypoxia-tolerant P. esculenta and other aquatic species.

Phascolosoma esculenta is an economically species inhabiting the intertidal zone and is farmed with high output. During artificial propagation, P. esculenta underwent mass death after torrential rain due to low salinity. In this paper, the effect of salinity on P. esculenta was studied for the first time. The results showed that P. esculenta died when exposed to water of 10‰ salinity, and their body lengths were about two times larger than when exposed to salinity of 25‰. The groups exposed to 10‰ salinity underwent severe necrosis. The activity of T-SOD and T-AOC in nephridial tissues increased between 3 and 12 h, but not at 9 h, T-SOD was highest in the control group and lowest in the death group, and T-AOC was highest in the death group and lowest in the survivor group. The concentration of MDA increased from 3 to 9 h and then decreased, and was highest in the death group and lowest in the control group. 35,053 unique genes, including 15,445 new genes, were acquired based on the 61.63 Gb Clean RNA-Seq Data. 27773 average alternative splicing (AS) events were found in the death group, which was 83.74% and 83.54% of that in the control and survivor group, respectively. Additionally, 1596 significantly differentially expressed genes (DEGs) were observed, which were classified into several functional categories, including genes involved in ion transporters, cation transport, RNA processing, immune response etc. The study had also found a significant number of genes involved in the pathways, including Mineral absorption, AMPK signaling pathway, Oxidative phosphorylation, and Phagosome pathways, such as Hsp70, Hsp20, Gst, solute carrier family genes, calcium channel regulatory activity genes, and pre-rRNA processing proteins. Overall, these results provide numerous candidate genes for future investigations and valuable insights into the mechanisms underlying the culture of P. esculenta in lower salinity.

The Sox family plays essential roles as transcription factors in vertebrates; however, little is known about the Sox family in Lutraria sieboldii. L. sieboldii are pleasant to eat with a short growth cycle and have become one of the best bottom-seeded enrichment species in Guang Xi. In this study, Sox2 (named LsSox2) and Sox9 (named LsSox9) from L. sieboldii were cloned, and their expression patterns were analyzed. The length of the LsSox2 gene coding sequence was 1011 bp, encoding 336 amino acids, and LsSox9 was 1449 bp, encoding 482 amino acids. LsSox2 had its highest expression levels in the ovary, which were 356 times those in testis, whereas LsSox9 presented higher expression in testis, which was 6 times more highly expressed than in the ovary. LsSox2 exhibited the highest expression during the morula stage, which was 20 times that of the D-shaped larvae or zygote. LsSox9 exhibited two expression peaks, one at the four-cell stage and the other at the trochophore stage, while the lowest expression was in the zygote. LsSox9 was 73 times more highly expressed in the four-cell stage than in the zygote stage. During gonadal development, LsSox2 presented the highest expression in the mature ovary, which was 756 times more highly expressed than in mature testis. LsSox9 presented higher expression in testis at the emission stage which was 6 times more highly expressed than in the ovary. These results indicate that LsSox2 and LsSox9 may play important roles in embryonic and gonadal development.