Transcriptome Analysis of the Digestive Tract of Tachypleus tridentatus and Carcinoscorpius rotundicauda

Transcriptome assemblies for the stomach, midgut, and fecal mucosa of Tachypleus tridentatus and Carcinoscorpius rotundicauda are reported for the first time in this study. Genome assembly resulted in 373069 unigenes with an N50 of 1314, while transcriptome assembly resulted in 736378 unigenes and an N50 of 2121. The annotated unigenes showed the highest similarity to fishes, amphibians, and reptiles, with most unigenes closely related to metabolism, translation, biogenesis, signal transduction, energy production, immune response, and secretion. Unigenes (4768) were mapped to KEGG pathways, and the most enriched pathways were involved in translation, environmental information signal processing, metabolism, endocrine system, immune system, nervous system, and varying metabolism. Totally 65889, 2001, and 7162 differentially expressed genes (DEGs) were identified in the stomach, midgut, and fecal mucosa between the two horseshoe crab species, respectively. Compared with C. rotundicauda , 99.95% of the DEGs in the T. tridentatus stomach were down-regulated, while 99.97% of the DEGs of T. tridentatus fecal mucosa and 55.42% of the DEGs of the T. tridentatus midgut were up-regulated. Most midgut DEGs were involved in hydrolase activity, protein metabolism, and cell cytoplasm, while most stomach and fecal mucosa DEGs were involved in catalytic activity and primary metabolic processes. Most stomach DEGs were assigned to the cellular component in cellular macromolecular complexes, while most fecal mucosa DEGs were assigned to the cellular component in cell and cell parts. These results will benefit the investigation of the molecular mechanisms of the digestive tract related to the feeding habits and environmental traces of horseshoe crabs.