Complex sentence: Mudskippers can remain out of water for considerable periods, exchanging gases through skin and mucous membranes in the mouth and pharynx, and swamp eels have similar well-vascularised mouth-linings, can remain out of water for days and even aestivate in mud.
Split into simpler sentences: Mudskippers can remain out of water for considerable periods, exchanging gases through skin and mucous membranes in the mouth and pharynx. Swamp eels have similar well-vascularised mouth-linings, and can remain out of water for days and even aestivate in mud.