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Square Starfish Care | 10 Astonishing Facts About Them |

According to the rules of nature, starfish is like a star. Could this be different? If there are different ones, can they survive? So, the square starfish is the best example of this exciting topic. Let’s explore the square starfish deeply. 

Square Starfish

Quick overview

Common nameSquare starfish, Square biscuit starfish
Care levelModerate 
Reef CompatibleReef safe 
Native toSouth Australia, Western Australia, Sydney, Victoria, and Tasmania
Color Bright orange color 
Tank size50- 100 gallons tank 
Preferred temperature72 to 82 Fahrenheit
Other water parameters pH level- 8.1-8.4Hardness level – 8-12 dKH 
Preferred salinity1.023 to 1.025
SizeGrow up to about 35 cm 
Temperament Peaceful 
Recommended tank matesNon-aggressive corals and saltwater fish 
Preferred foodSponges, sea squirts, bryozoans, and algae
Feeding frequency2 or 3 times per day 
Propagation bySexually and asexually 

Description Of Square Starfish 

When you hear the name Square starfish, you are definitely wondering. Generally, starfish has five arms like a star. But is there any possibility of having a square-shaped starfish live in the ocean? That’s a little wired, isn’t it? When we go to examine their appearance, of course, Square starfish has a square shape skeleton. However, researchers and scientists also explore details about starfish and how they deviated to this unique shape. 

But, till now, there is limited information about them. But one fact is proved by the scientist. That is, these starfish exist in the ocean. However, Dr Michael Sweet, an award-winning researcher and lecture professor in Molecular Ecology, said that some starfish could be born in square shape due to a genetic abnormality. But some people do not believe it as it is. Their opinion is, Square starfish is not a result of genetic abnormality.

Moreover, these researchers introduced one of the rare starfish varieties, namely, square biscuit starfish. But, whether square starfish or square biscuit starfish is a mutation of evaluation or not, it is a wonderful creation of nature by removing one of its five limbs and making a square shape. When we examine the appearance square biscuit starfish, it has a distinctively bright orange.

If you carefully observe them, you can notice that there are small interlocking plates on their body. Also, their upper surface is covered with these beautiful plates. Further, a square biscuit starfish’s color and pattern are similar to a large biscuit. Further, you can discover that the six to eight plates along the edge of each short arm. However, they are one secret that camouflages with the seabed. 

What Are The Habitats Of Square Starfish?

Actually, there is little information discovered about them. But we can conclude if square starfish is a variety or genetic abnormality of biscuit starfish, they can be found from the places where biscuit starfish live. So, generally, biscuit starfish can be found in South Australia, Western Australia, Sydney, Victoria, and Tasmania. Also, their habitats are coastal waters and intertidal rocky shores depth of 40m in the ocean. 

However, their square shape skeleton makes us wonder if this starfish can walk or move. But their shape is not a problem to move. Because generally, starfish do not use their main limbs to move. Further, starfish have hundreds of small feet at the bottom of their body. So, these feet help them to move. So, square biscuit starfish also use these feet to walk. The truth is, square biscuit starfish lack arms, but I think they can live a normal life as other starfish. So, what do you think about it? 

Tank Requirements

They are also members of the starfish family. So, you can go with the requirement of biscuit starfish. Generally, biscuit starfish is easy to rear in the aquarium. So, you can add square starfish to your marine collection. But you should provide a proper environment to live them. So, let us see how we create a proper place for your square starfish. 

Size Of The Tank

Actually, the size of the aquarium depends on the size of the square starfish that you have. Generally, if you have a square starfish, you should go with a 50 to 100 gallons tank. But if your square starfish is not large, you can go with another small tank too. However, the important thing is to remember that starfish requires a fair amount of space to move around and scavenge foods.

Also, starfish need more floor space than wall space. So, always try to go with a long tank than tall ones. Moreover, if you wish to rear multiple square biscuit starfish, you should highly consider the size of the tank. If it is not enough, definitely you should go for another large tank. 

Water Quality

This marine creature is susceptible to water conditions. So, if you want to keep your square starfish without any worries, the one thing that should be considered is the water conditions. So, you should keep below conditions at the ideal level in your square starfish tank. 

  • Water temperature: You have to maintain the temperature between 72 to 82 Fahrenheit
  • pH level: The ideal pH level is ranging 8.1 to 8.4 
  • Water hardness: It is better to keep the water hardness in between dKH 8 to 12
  • Salinity level:  This reef-safe marine creature lives happily in sg 1.023- 1.025

Flow Rate

It is better to provide a moderate to high flow rate for your square starfish. 


Starfish need full-spectrum lighting. So, you can concern the lighting condition of your square biscuit starfish aquarium. 

How To Place Them In A Tank

The following steps will guide you to place your new square starfish in your tank.      

Step 1: First, you should ensure that your marine aquarium is ready to welcome the square starfish by setting up preferable water conditions

Also, you should add the starfish into a well-established tank, not a new aquarium. 

Step 2: Before placing your square starfish in the tank, you should follow the acclimation process

Additionally, you can acclimate your starfish with many acclimating methods like the drip method and cup method. 

Step 3: After finishing the acclimating process, you can place your square starfish in your aquarium

Here, do not expose the square starfish into the air much. Thus they are very sensitive. Therefore, when this transferring process, you should transfer starfish as soon as and place them on a rock. Simply your goal should be to limit the time that starfish expose to the air. Then check whether the starfish move around the rock or not. But this takes a few times. 

How To Breed Starfish 

Starfish is an excellent marine creature that can reproduce in more than one way. It means starfish can breed both sexually and asexually. But the asexual reproduction is not the ideal way to promote genetic diversity. Because through this way, the new starfish is formed by the dismemberment of the same DNA. However, the natural reproduction way is a sexual method, and it is better. So, let’s see how starfish are reproducing by spawning. 

  • Each starfish has gonads or sexual organs in the arm. 
  • Male starfish’s sexual organs fill with sperms, while female starfish’s sexual organs fill with eggs during the breeding time. 
  • When starting the spawning process, both male and female starfish release their sex cells into the water.
  •  Also, they do this as a group. It increases the possibility of eggs and sperm finding each other. 
  • At once, female starfish releases millions of eggs into the water while male releases sperms in great numbers. 
  • After fertilizing the eggs, they hatch and release larvae into the water after a few days. 

What Do Square Starfish Eat

Generally, square starfish are omnivores, and they accept both plant and animal matters. So, square starfish eats sponges, sea squirts, bryozoans, and algae. On the other hand, you can feed them on frozen shrimps and prawns. 

How To Feed Square Starfish 

Generally, you can use a tweezer to give the foods to your square starfish. Simply hold the food close to the limb of the starfish until they gradually catch the food. 

Feeding Frequency

It is better to feed them 2 or 3 times per day. However, you can notice whether your starfish is hungry or not by a simple activity. Put a food species besides the starfish. If your starfish is hungry, they will quickly eat it. 

After Feeding

After finishing your square starfish eat, you should remove the uneaten foods quickly because those extra foods can affect your water conditions badly. Consequently, it causes the health of all marine animals. 

Predators Of Square Starfish 

Many different animals can be identified as predators. For instance, various fish, crabs, snails, birds, otters, and sea turtles eat starfish. The top predators of starfish are included in the below list. 

  • Sharks 
  • Manta Ray 
  • Red king crab 
  • Sea turtle 
  • Bony fish 
  • Sea snails 
  • Shrimps
  • Other some starfish 

Is Square Starfish Good Or Bad For Your Aquarium

Actually, the answer to this question depends on your preference. Square starfish is a great collection for marine aquariums, and it increases the uniqueness of the aquarium. If you show your aquarium with the square starfish, the word wow will inevitably come out from friends’ mouths. 

Why Are Starfish Dying?

Many reasons can be caused to die your starfish. Let us see one by one. 

Poor water conditions 

Starfish is highly sensitive to water parameters. If your tank water condition is not have enough quality, It can be killed your starfish. The polluted water has acidic condition. Also, square starfish are made with calcium carbonate skeleton. So, when water becomes acidic, their outer skeleton tends to dissolve. It may lead to killing starfish. Furthermore, uneaten foods mostly create poor water conditions. On the other hand, you can maintain the water quality by performing water changes regularly. 

Unpreferable water temperature 

Unpreferable water temperature can kill your starfish. So, you should highly consider the water temperature if you want to keep your starfish healthy. 

Stressful environment 

If your marine aquarium is overcrowded, automatically, starfish do not have enough space to live peacefully. Consequently, the starfish will stress. So, this stress leads to gradually kills your starfish. In addition to that, if you keep your starfish with their predators, it will stress your starfish. This stress also affects starfish badly. On the other hand, predators also hunt and kill your starfish. 


Many diseases can kill your starfish. Most probably, poor water conditions promote many diseases. Therefore, always try to keep ideal water conditions in your aquarium. 

What Is The Rarest Starfish?

Prickly sea star or Paulia horrida is the rarest starfish that can find the deep sea. Paulia horrida belongs to Asterodiscididae family of Asterodiscid sea stars. They can find in Mexican waters in the Pacific Ocean. Further, they live on corals and rocks, depths up to 123 cm or 400 feet. This brilliant red color starfish has large spines. These spines help them to protect themselves from predators. Also, it has a wide central disc with five tapering arms. The special character is numerous, sharp, conical spines covering their aboral or dorsal surface, the marginal surface of the disc, and arms. 

Are Sea Stars Poisonous?

The starfish is not poisonous at all. But many people think all starfish are dangerous because starfish have spikes. Spikes of starfish can not hurt you unless it pierces the skin. However, there are some exceptions. Some types of starfish’s spikes like urchins, a crown of thorns, and a few species of sun starfish have venomous.

These starfish can hurt and be poisonous. So, the best thing is, do not touch starfish without knowing them well. Someone can have a question, can starfish hurt me? Yes, they can hurt you when you step on the starfish. But do not misunderstand. Starfish is peaceful creature, and they do not attack or bite humans. 

What Is The Prettiest Starfish?

Panamic Cushion Star is the prettiest starfish of all. It is also known as Pentaceraster cumingi, Cortez starfish, or Knobby star. Panamic Cushion Stars have inflated and thick discs with moderately short arms. The color of their aboral surface is ranging grey to brown color. The beautiful thing is, numerous orange or red color conical spines cover their surface, and these spines connect with a brown reticulate pattern. This pattern, like a net, enhances their beauty and uniqueness. Also, this starfish can reach up to 17.5cm in diameter. 

Credit to : LMLive

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About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.