Newly hatched tadpoles soon develop gill pouches that cover the gills. Acorn worms have gill-like structures they use for breathing, similar to the gills of fish. The eggs hatch into aquatic larvae called tadpoles that have tails and internal gills. The carapace encloses two branchial chambers which enclose the gills. Giant squid breathe using two large gills inside the mantle cavity. Tadpoles feed on algae, including diatoms filtered from the water through the gills. The tadpoles initially have three pairs of external gills and several rows of labial teeth. Whale sharks have five large pairs of gills. This parasite enters fish through the gills. Jaws are thought to derive from the pharyngeal arches that support the gills in fish. This includes holding the fish in water deep enough to submerge its gills. They breathe through feather-like gills. It actively excretes salt out from the gills. The external gills seen in salamanders differs greatly from that of amphibians with internalized gills. A hymenium is a layer of microscopic spore-bearing cells that covers the surface of gills.