Corals that fertilize internally usually release planulae through the most obvious place: their gastrovascular cavity (AKA “mouth”). It’s a ready-made hole for baby corals to pop out.
But not Astroides calycularis. Researchers have documented that these Mediterranean sun corals fertilize eggs in their gastrovascular cavity but actually release their babies through the tips of their tentacles!
Giving birth through your appendages … nature is as bizarre as it is beautiful.
The Coral Reef paper describes this fascinating reproductive method:
We confirmed that planulae were released through the tentacles under natural conditions. Planulae originated from the gastrovascular cavity and were initially oval shaped at the oral region of the tentacle. The planulae elongated as they migrated inside the tentacle to the distal end, where they were ready to be released. Finally, the planulae slowly exited the polyp through the distal region of the tentacle. The duration of expulsion depended on the level of water movement. These observations suggest that planulae of A. calycularis mature in the tentacles.