Banggai Cardinalfish (Pterapogon kauderni)

Male cardinalfish protect their young by keeping ~25 eggs (and later the hatched fry) inside of their mouths. The dedicated dads don’t eat for a good 4-5 weeks of brooding.

(Source: 6thmoon)

Clown Triggerfish (Balistoides conspicillum)

To reproduce, these adorable fish dig a hole in the sand, lay eggs, and take turns guarding their nesting territory. Both the mom and dad will aggressively defend an inverted cone-shaped area above the eggs by chasing, biting, and generally attacking anything that swims too close.

Porous Sea Rod (Pseudoplexaura porosa)

These soft corals undergo mass spawning events about 5-6 days after each of the summer’s full moons. Both sexes (yes, they have a gender) eject gametes for about 30 minutes, allowing them to combine in the water column. Some studies have shown that their ability to reproduce is based on size, as only colonies larger than 50cm have been observed to participate in this synchronized lunar activity.

Trunkfish spawn at dusk, leaving a bunch of 2mm eggs to fend for themselves in the open ocean. The hatched larvae stay swimming around in the nekton as the plates that form their armor begin to develop into hard, protective lumps.

Moon Jelly (Aurelia aurita)

These hardy little darlings can be identified by the transparent bell and four-leaf-clover-shaped gonads. The moon jelly will metamorphose multiple times throughout its life, producing offspring both sexually and asexually. (Bonus points if you can find the 6-gonad mutant in the background of this photo!)

Ochre Sea Star (Pisaster ochraceus)

Starfish have a gender, but it’s impossible to tell which is which without identifying the content of their gonads. They reproduce when at least two opposite genders release their eggs and sperm into the water for mixing. However, every so often a male will climb right on top of a female and intertwine their arms to try and increase his baby-making chances.

(Note: It’s called pseudocopulation when an animal’s behavior looks like intercourse, but there’s no actual sexual union between the individuals.)

Image Credit: Unknown