7-11 Profile of Crab Origin and Characteristics

Crab (Carpilius maculatus)

The 7-11 crab gets its name from the seven spots on top of its shell and the four spots on the bottom (although it has more than that). It should be termed a 7-4 crab based on the most apparent spots, but 7-11 sounded better and the crab's distinctive spots equaled 11, thus the name persisted. This crab adjusts to aquarium life rapidly. However, because of its destructive propensity, it is not recommended for home aquariums, despite its adorable and appealing appearance when young.


Scientific Name

Carpilius maculatus


Carpiliuss maculatus, Cancer maculatus

Common Names

7-11 crabs, brachyura crabs, reef crabs, round crabs, true crabs, blood-spotted crabs, blood-spotted round crabs, dark-finger coral crabs, large-spotted crabs, redspot rock crabs, red-spotted crabs, round reef crabs, spotback coral crabs, spotted crabs, clown crabs, alakuma crabs (Hawaiian)

Family Carpiliidae
Origin Indo-Pacific oceans
Adult Size 7 inches (18 centimeters)
Social Aggressive
Lifespan 6 to 8 years
20 gallon
Diet Omnivore
Breeding Egg-scatterer
Care Intermediate
pH 8.1 to 8.4
Hardness 8 to 12 dGH
72 to 78 F

Origin and Distribution

The Indian Ocean, the South Pacific, the Hawaiian Islands, Australia, the Red Sea, and South Africa are all home to these crabs, as well as places south of mid-Honshu in Japan. The majority may be found on coral and rocky reefs, gently traveling through sandy bottoms.

Colors and Markings

It features an oval body with a smooth and convex surface and an orangish-light red tint. On its back are seven huge dark reddish-maroon colored markings. These dots might sometimes appear to be a dark brownish tint. It has a thick, hefty shell that is devoid of spines.

According to Hawaiian folklore, this crab got its spots after a sea deity tried to catch and consume it, but the crab drew blood. The sea god's bleeding fingers continued trying to capture the crab, which is why he has so many red-brownish blotches.

Although most people assume this crab only has 11 spots, the most visible ones, it actually has 18 spots. On the dorsal surface of its carapace or shell, it bears nine big violet-to-maroon patches, three on the middle area, two on the posterior region, two on the anterolateral region, and two surrounding its eyes. One claw develops larger than the other, as it does in most crabs.


The pinchers on this crab are quite powerful. It's tough to force it to let go or open the pincers once it's clamped on to something. It will assault and consume other crustaceans and invertebrates, as well as sleeping fish if given the opportunity. Males frequently compete for females, with the larger male typically coming out on top. Keeping this crustacean with other animals is not advised.

Habitat and Care

The 7-11 crab's great strength and strong armor make it a destructive animal in an aquarium. Its hard shell allows it to act like a bulldozer moving rockscapes and corals around in an aquarium.


This crab eats sea snails in the wild. The 7-11, like other crabs, is a scavenger who will eat almost anything. This crab has been seen carrying sea urchins and cowrie shells in the wild, indicating a likely diet. It only comes out to eat at night and hides throughout the day.

Sexual Differences

The 7-11 crab is gonochoric, which means it only has one sex, unlike other marine species that can switch sex because to a shortage of viable mating mates. Most crabs have an abdominal flap on the bottom that may be used to determine whether they are male or female. A male crab's abdominal flap is tiny and triangular, while a female crab's flap is large and oval-shaped.


This crab does have a mating courtship ritual in which it employs olfactory (pheromone) and tactile signals to woo the object of its affection. The male normally waits until the female molts before approaching her. The male may detect the female's impending molt by smelling her pheromones. He then keeps her in a deep hug known as amplexus, which literally means "embrace" in Latin, until she molts, ensuring that he will be the mating partner.

This pre-molting hug, with each crab sternum to sternum, can endure up to a week until the female molts. The female flips right-side-up during the final phases of the amplexus, which is preceded by her squeezing the male's eyestalks to loosen his grip. Regardless of how much eye pinching occurs, the male never entirely releases the female throughout her molt. The mating couple returns to a sternum-to-sternum posture approximately an hour and a half after the female molts, when the new exoskeleton has firmed up a bit and the mating pair is back in a sternum-to-sternum position.

When a male and female crab copulate, the female crab receives a bundle of male sperm, which she stores in her abdominal cavity until her eggs are ready to be discharged. The stored sperm runs over the eggs as they are released, fertilizing them. The fertilized eggs are held in a large spongy mass between the female crab's abdominal flap and the body. The "berried" look is achieved by cementing the eggs to the pleopods, which are little legs. The mother crab uses her pleopods to constantly "wave" water over the eggs to keep them healthy.

When the eggs hatch into zoea larvae, they float away as plankton in the ocean currents. The crab goes through a series of molts as it develops in size, culminating in transformation. Its form and function vary with each larval stage. At each molt, the clawed limbs replace the feathered limbs, and additional segments are added to the end (posterior). It most nearly resembles an adult crab when it is a megalops, the final stage before transformation and before becoming a juvenile crab.

More Pet Fish Breeds and Further Research

If you like the 7-11 crab and want to have a saltwater aquarium, you should look into other saltwater species. These fish are excellent for saltwater aquariums, but not for living with a 7-11 crab:

For more information on different or fish, look up further fish breed profiles.