Phascolosoma esculenta is an intertidal organism that has recently attracted attention because of its ability to survive at relatively low temperatures.However,the gene regulation in P esculenta in relation to its response to low temperatures is unclear.To explore the low temperature adaptability of P.esculenta,this study analyzed the changes in the morphology and hsp70 and hsp90 gene expression of P.esculenta exposed to a low temperature gradient.At 5 ℃,P.esculenta stretched and softened,and some individuals moved apart from the group.Histological analysis revealed cuticle breaches,myofiber scattering,disruption of the body wall,and epithelial layer dispersion and muscle fiber rupturing in the nephridium.Furthermore,the mRNA expression levels of hsp70 and hsp90 increased under acute low temperature stress,suggesting that these genes function in low temperature tolerance.Overall,low temperature stress causes morphological changes and histological damage in P esculenta,and hsp70 and hsp90 potentially function in the low temperature adaptability of P.esculenta.Our results provide new insights into the adaptive strategies of P.esculenta under low temperature environments.