Nitric oxide synthase (NOS) in the cyprid of Amphibalanus amphitrite (Cirripedia, Crustacea)

• Nitric oxide synthase (NOS) was localized in the cyprid of Amphibalanus amphitrite.
• NOS ir was present in: muscles, gut, eye, mantel, cement gland and oil cells.
• NADPH diaphorase activity was localized in muscles, gut and oil cells.
• NO role in settlement as from literature is linked to its anatomical distribution.
• Antifouling strategies directed against the nitrergic system should be tested.

The Amphibalanus amphitrite barnacle is a sessile marine crustacean and a major constituent of benthic as well as intertidal communities. A. amphitrite is also an important component of biofouling on artificial substrates. The role of nitric oxide (NO) was recently observed in the settlement of this species. In this work, we used immunohistochemical and histoenzymatic methods to investigate, for the first time, the presence and distribution of NO synthetic enzymes (NOS) in the competent-for-settlement cyprid of A. amphitrite. NOS-like immunoreactivity was observed in various regions of the cyprid: gut mucosa, mantel epithelium, thoracic muscle, and abductor muscles. Intense immunoreactivity was also present in the cement gland and oil cells, while widespread immunoreactivity was observed in the compound eye. NADPH-diaphorase method was used to provide further data and understand NOS-distribution. The results show that NOS is likely to be present in structures – such as muscles and cement gland – which are key for settlement.