Quick Take
- Square-shaped starfish are usually cushion starfish, whose rounded, inflated bodies can appear angular in rare cases.
- Unusual starfish shapes can also result from injury or genetic mutations that affect how their arms grow back.
- While striking in appearance, perfectly square starfish are extremely rare and often misunderstood natural variations.
A square starfish may seem like a contradiction, but such creatures do exist. While it may sound unreal, these strangely shaped starfish are rare but do exist in the ocean. There are a few reasons why square starfish occur, including genetic mutations or the presence of cushion starfish, which naturally have unusual shapes. This Instagram post by @oceanandcoastals shows a picture of a perfectly square starfish. Read on to learn more about these sea life anomalies.
Cushion starfish can look like squares if their bodies grow large enough.
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What Causes a Square Starfish?
A square starfish is a shocking sight. Given their iconic form, it’s hard to imagine them having any other shape. However, there are a few reasons for this strange appearance. The first, and most likely reason, is that it is a cushion starfish. Cushion starfish are a species of sea star with short, thick arms instead of the long, slender arms seen in other species. Their arms are fused to the body, creating a puffy appearance that often changes their shape into a pentagon or even a sphere. While most sea stars of this species look rounded, in rare cases, they can appear somewhat square. Other indicators of a cushion starfish include overall symmetry and the absence of distinct arms. The puffy appearance often reduces the arms to the point where they are no longer visible. Like classic sea stars, cushion starfish are symmetrical, retaining five-point symmetry, although it is less distinct.
Another reason a starfish might appear square is due to a genetic mutation or deformity. Starfish that have been injured or have undergone a mutation may have missing or uneven arms, resulting in asymmetrical growth. After an injury, a starfish’s arms may regrow irregularly, resulting in unusual shapes. While this could result in a square shape, it is less likely to occur. It is practically impossible for a starfish to grow in a way that results in a perfectly square shape. For this reason, the starfish in the post above is most likely a cushion starfish. The inflated, puffy body, symmetrical shape, and indistinct arms all support this conclusion. While cushion starfish are not necessarily rare—they are common in tropical waters like the Great Barrier Reef—they are still amazing to see.
