The sea monster that is mating is permanently attached

Of the 160 Anglefish species, up to 25 species have bizarre mating behavior with tiny males using their thorns to plug into their offspring and transmit sperm and suck blood to the end of life.

The female Linophryne brevibarbata has the male plugged in under the abdomen

And this is the female Chaenophryne quasiramifera

Female Caulophryne pelagica

Bufoceratias shaoi female

Photocorynus spiniceps females have males plugged in at the top

The female Thaumatichthys binghami

Haplophryne mollis female

Female Melanocetus eustales

Female Himantolophus appelii

Female Lasiognathus amphirhamphus