Before I take off, I wanted to highlight one more marvel of evolution: the phenomenon of sexual parasitism in anglerfish. There are many species of these deep-sea fish, who make their living as predators in the abyssal depths. Because the population density is low, when a male finds a female his best strategy (apparently) is to fuse his tissues with hers, becoming in effect a permanently parasitic sack of gonads, whose only function is to fertilize the female (no anthropomorphizing, please!). Sometimes more than one male attaches to a female. Here are some photos.
The phantom anglerfish, Haplophryne mollis, with male attached on bottom.
Photocorynus spiniceps, an anglerfish from Sumatra. This female is 46 mm long (1.8 inches). Attached to her is a 6.2 mm male (about 0.25 inches), which may be the smallest sexually mature vertebrate known. Below is an enlarged photo of the male.