1. Epithelium: The outermost layer of the gills is composed of thin, squamous epithelial cells. These cells help protect the gills from damage and facilitate the exchange of oxygen and carbon dioxide.
2. Basement membrane: Beneath the epithelium lies the basement membrane, a thin layer of connective tissue that provides support and anchors the epithelial cells to the underlying tissue.
3. Capillary network: The capillaries are the smallest blood vessels in the body and form an extensive network within the gills. The capillaries are responsible for transporting oxygen-rich blood to the gill filaments and removing oxygen-depleted blood from the gills.
4. Spiracles: Located on the underside of the gills, the spiracles are small openings that allow water to flow out of the gill chambers. The spiracles help to regulate the flow of water over the gills and facilitate the exchange of oxygen and carbon dioxide.