The pygmy sea horse is an inch-long fish that lives on corals in the Pacific. The corals, fan-shaped and knobby, are venomous, yet the sea horse can safely wrap its tail around a branch to feed on tiny animals passing by.
Some species of pygmy sea horse are pink, others are yellow, each a perfect match to the species of coral on which it lives. The sea horse also has knobs on its body to match the size and spacing of the knobs on its corals. Instead of the typical sea horse snout, the pygmy sea horse has a face like a pug; its snout resembles yet another coral knob.
By mimicking coral so well, the pygmy sea horse can hide from predators. And because it is also immune to the corals’ venom, it gains a kind of protective shield by living among them. (Each knob of coral houses a tiny animal called a polyp that kills prey by firing poisonous harpoons.)
If that wasn’t remarkable enough, pygmy sea horses flip the typical roles of the sexes. After a pair of pygmy sea horses mate, the female inserts the fertilized eggs into the male’s body, and the males, not the females, carry the embryos.
Male pregnancy occurs in all sea horses, but pygmy sea horses take it to the extreme. A typical male sea horse carries its eggs in a kangaroolike pouch on its tail. In male pygmy sea horses, the brood pouch is more like a uterus, growing deep inside his body cavity near his kidneys and intestines. The male nurtures his young with a special organ in the pouch that functions like a mammalian placenta. Once the baby sea horses hatch, they exit their father’s body through a tiny slit and swim away.
How did so extraordinary a creature evolve? To better understand, a team of Chinese and German scientists have sequenced the genome of a pygmy sea horse for the first time.
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