The aim of this study is to investigate the role of ecdysteroids in the regulation of protein turnover (i.e. IGF/mTOR signalling genes) and ion homeostasis over the moult cycle and in response to temperature of juvenile Metacarcinus magister. Moulting crabs were held at 10°C, 15°C or 20°C. After 14 d haemolymph and hepatopancreas (HP) were collected. Ion composition of the haemolymph significantly varied with moult stage, and there was a small, but significant temperature effect. Concentrations of Na+ and Cl- decreased, while those of Ca2+, Mg2+ and SO42- increased in premoult. Preliminary results suggest that Na+/K+-ATPase activity increases in premoult along with total protein in the HP of crabs at ambient temperature. This suggests that the HP contributes to ion homeostasis over the moult cycle. It is also the major site of reserve accumulation and recycling. To be able to determine changes in gene expression by qPCR, we generated (Illumina sequencing, assembly using Trinity, cd-hit-est clustering and annotation) and queried a M. magister reference transcriptome of the moulting gland for genes of interest. We identified genes involved in ecdysteroid production and signalling (Neverland, Spook, Phantom, Disembodied, Shadow, Shed, EcR, RXR, E75, E78, HR3, HR38, FTZ-F1, Broad complex), protein turnover (IGFBP, IGFR, AKT, AMPK, Rheb, TSC1/2, mTOR, S6K), and ion homeostasis (Na+/K+-ATPase, Mg2+-ATPase, PMCA, NCX, NHE3, NCKX, CA).