no, because then those gills gills would need gills and they would need gills and so on, so on. They have specialised cells instead.
Gills would be respiration
There would be much less surface area for the digestion and absorption, so digestion and absorption would be slowed by a lot.
No heat loss = maximum output. There would be no loss of energy, which is an ideal condition.
The gills of bivalves that I have seen, I would describe as looking like a piece of screening covered with cilia.
Yes, Siamese fighting fish, like all other fish, have gills. Gills are respiratory organs that allow fish to extract oxygen from water and release carbon dioxide.
a fish
Yes.
The maximum output of the sun is in the yellow which is also within the absorption range of chlorophyll. It is this emission/capture intersection that is of the most importance to the plant as that is where the maximum available energy is to be had. All other absorption/reflection aspects of the chemical are of lesser importance and are just what they are. It would be nice if the photochemical of plants was pure black and absorbed all wavelengths but the plant kingdom never evolved such a mixture.
they would be dead then
Gills to a fish are the equivalent of lungs in mammals. Without them the fish would not be able to breath in water.
Gills on a shark help it take oxygen out of the water.