Commensalism is a type of symbiosis, specifically, a biological relationship in which one specie benefits from an interaction, while the host species is neither positively or negatively affected to any tangible degree. There is an explanation video available below.
Hyphae that have walls between the cells are called septate hyphae; hyphae that lack walls and cell membranes between the cells are called nonseptate or coenocytic hyphae) There is an explanation video available below.
External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. Many fish, amphibians, and other sexual aquatic animals use external fertilization (the exceptions are aquatic mammals, sharks, and some other special types of fish). There is an explanation video available below.