Would a sexual dimorphism like monkfish be useful for bigger or terrestrial animals? Would it bring an advantage or would be more harmful?

Question

In the monkfish, the females are the larger sex, while the males are very small: in comparison males measure only one tenth of the female, for example a female can measure up to 20 centimeters long but male only 2.

While the females grow, males are born just to survive till sexual maturity and then start searching a female to mate. When they do, they cling to the female through a bite and practically from that moment on they become part of the female's body, as they begin to lose their organs until their circulatory and nervous systems merge completely, at which time they are practically an appendix for the female, releasing the required gametes when the female needs it. Also, a female can have multiple males.

This is a type of polyandry thing that multiple species do, but I can't think of another mating method like the monkfish. So I want to know what impediments are there for the development of this type of mating and breeding in terrestrial species (or just aquatic bigger animals; probably is related with the capacity to carry more mass, but I'm not sure about this)?

But removing that fact are some species that I thought could develop it, from arthropods, amphibians to reptiles. My best current example: I knew that some snake species have notable differences in the size of males and females, some species (I don't remember the exact name) in which males search out females and then wrap themselves around the female to achieve intercourse and can last for several days that way. The "why" leads to how, so, why would this adaptation be useful for other animals?

But the method of reproduction being like a monkfish could be more problematic than benefit, because could reduce the movements (it's a cool idea but fictional and even ridiculous thought that the new "appendix males" can be a functional limb). So, I don't have more ideas for utilities to this type of mating at terrestrial animals, maybe if they don't lose all their senses and in this way can be used as new sensory organs.

Now, this characteristic seems harder to apply to mammals and birds -- in which males are usually bigger than females -- so if you want to apply this to these animals it's fine, but another doubt is how could the opposite exist: polyginy, carrying multiple females. I don't know if something like that exist, but I vaguely remember reading about something like that (and still quite different), a creature in which the larger male wraps up the smaller female for protection, basically becoming a biologic armor with a perpetual sexual exchange. I'm not sure if it's real; if I'm wrong let me know. Do these mechanisms already exist in real animals?

(Probably the last two ideas could be for other questions, but I want to know if mating mechanisms like those already exist, so do not explain too much in these cases just let me know if they already exist and if they have a formal name).

From this I will ask myself a new question (since in order not to extend so much it should be in another post) about, from ecosystems to societies based on these kinds of mating.

Answer 1

Only in "Abyssal" Environments.

The female anglerfish:

1. Is much larger than most other animals
2. Produces millions of eggs at a time (like most fish)
3. Is very rare.

This is the evolutionary reason for the males being small. The female benefits from being huge, but that means they must be very rare since food is scarce. It is easier for males to find a mate if there are many small males and harder if there are a few big males.

So you need to recreate this scenario. You need the females to be so big and eat so much that the environment cannot support many at once. The first option is just make them massive. This is the most interesting option: The females are 1 mile long and eat forests. There are only 10 on the planet, one per continent. By the time they make a full 100-year circle of the continent the forest has grown back and they eat it again.

The males are small winged creatures than hatch and immediately fly to the far side of the planet and attach to something other than their mother. It also opens up the hydra possibility.

Of course in reality being huge poses loads of secondary problems though, in particular a massive creature takes a very long time to mature.

The second option is to restrict food supply. For example the females are 1 foot long but live in the desert where food is scarce and everything else is much smaller than 1 foot. This is pretty much the same scenario as the deep water angler fish except the type of abyss is different.