This Animal Has No Heart

The impossible claim

This animal has no heart, no blood, and no brain — and it can regrow its whole body from a single arm.

Sea stars (“starfish” — though they’re not fish) are echinoderms, cousins of sea urchins, and they break almost every rule we associate with animals:

No heart, no blood — seawater is pumped through their water vascular system instead, and that hydraulic pressure is what powers the hundreds of tiny tube feet they walk with
No brain — just a nerve ring around the mouth and radial nerves running down each arm
They eat with their stomach outside their body — a sea star pulls a mussel’s shells slightly apart, everts its cardiac stomach through the tiny gap, and digests the prey externally before sucking the soup back in
Regeneration: lose an arm, it regrows — weeks to months. Some species (Linckia) can rebuild an entire body from a single detached arm plus part of the central disc; full regrowth can take up to a year
Most have five arms, but the sunflower sea star can carry up to 24

🎬 See the Short on YouTube — This Animal Has No Heart

Hyman, L. (1955). The Invertebrates: Volume IV — Echinodermata. McGraw-Hill.
Feder, H. B. (1955). The Feeding Mechanism of Asteroids. Biological Bulletin.
San Miguel-Ruiz, J. E., Maldonado-Soto, A. C. & García-Arrarás, J. E. (2011). Whole-body regeneration in echinoderms. Echinoderm Research.
NOAA (2022). Endangered Species Act Status Review Report: Sunflower Sea Star, Pycnopodia helianthoides.
Hidrobiológica (2016). Regeneration of the sea star Phataria unifascialis: asexual reproduction and morphallaxis, vol. 26(1).

Part of Impossible Creatures — every fact verified, every creature real. Watch the Shorts at https://www.youtube.com/shorts/f0TVbJ3lFwI.