De novo transcriptome analysis of the sandworm (Sipunculus nudus) and identification of differentially expressed genes associated with body size

The sandworm (Sipunculus nudus) is an aquatic species of economic importance because of its high nutritional and medicinal value. Under the same culture conditions, substantial individual growth variation is often found in populations of sandworms. However, the genetic mechanisms of individual growth variation are poorly understood. In this study, the transcriptome of the body wall muscle of the sandworm at different growth rates was analyzed by Illumina sequencing and bioinformatics analysis. A total of 185 181 unigenes were obtained after processing raw reads and about 96,824 (47.72%) of them were annotated. Among the annotated transcripts, 418 differentially expressed genes were identified, of which 207 were upregulated and 211 were downregulated in large worms relative to small worms. We identified several genes that had a possible association with individual growth variation. These results will provide insight into the growth mechanism of sandworm, and will further assist in the selective breeding of improved strains of this species.