Flattop Crab

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This was a tiny, but super cool find while tidepooling on the California coast. A member of the Porcelain Crab Family, it shares the general body plan of a squat lobster, but their bodies are more compact and flattened – an adaptation for living and hiding under rocks.

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These are quite fragile animals and often shed their limbs to escape predators, hence the family name “Porcelain Crab.” What struck me the most about this creature was its oversized claws which it uses to defend its territory.

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Flattop Crabs are an example of carcinisation, whereby a noncrab-like animal (in this case a relative of a squat lobster) evolves into an animal that resembles a true crab. They can be distinguished from true crabs by the apparent number of walking legs (three instead of four pairs) and the long antennae located on the front outside of the eyestalks.

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These crustaceans feed by combing plankton and other organic particles from the water using long bristle-like structures on their mouthparts. At a a shell size of less than one inch across, its prey is quite small, mainly consisting of diatoms.

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The Flattop Crab can be found in the lower intertidal of sheltered waters. Its range extends from southeastern Alaska to southern California. It prefers areas with strong currents and can be found under rocks, especially those embedded in gravel or sand under seaweed and mussel beds in both exposed and sheltered shores.

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This was an awesome find on my Golden State adventure.

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Marsh Crab

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While staying at North Beach, Maryland, I would often see these crustaceans in rock piles that bordered the brackish water shorelines. They were shy and would quickly retreat into their rock hideout if they felt they were being watched or approached.

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The Marsh Crabs live communally within interconnected burrows in the mud. The tunnels may be 2 to 3 feet deep and often filled with water. Males are known for making “rapping” sounds when defending their burrows by striking two of their legs together.

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Though I saw them in the daytime, they are mainly nocturnal. These invertebrates eat the outermost leaves of marsh plants, especially cordgrass.

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Sometimes known as Squareback Marsh Crabs, these creatures live in a marine environment, but do not require seawater to survive, making them true terrestrial crabs.

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Red Rock Crab

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As its name implies, this crustacean is often found in and around rocky places and features reddish-purple coloration.

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It can grow to more than 10 inches across, but 4 to 6 inches is more common. Its large claws are tipped in black and they have a wide, fan-shaped body.

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This cool creature crushes barnacles with its large pincers and eats them. It also eats smaller crabs, sea cucumbers, and many other intertidal invertebrates, as well as dead fish.

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While searching tidepools, I saw this “shell” move. It didn’t take long to realize that it was not a shell at all, but rather a juvenile Red Rock Crab, which can be white with a pattern of dark lines.

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I enjoy finding these hard-shelled creatures, whose other common names include Red Crab, Cancer Crab and Red Cancer Crab.

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Asian Shore Crab

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While visiting New York last week, I flipped a few rocks along the East Coast and encountered quite a few of these small crustaceans; they were often found in dense aggregations.

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Adults are small, measuring about an inch and a half in shell width. They have a squarish shell and light and dark bands on their legs.

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Though native to the western Pacific Ocean from Russia to Hong Japan, it is likely that Asian Shore Crabs were discharged at harbors in the United States as larvae from the ballast water of a cargo ship.

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This creature is not a picky eater, and feeds on a wide range of plants and animals. It can tolerate a wide range of environmental conditions. These characteristics help to make it successful in areas where it is not native.

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Although undeniably cute, Asian Shore Crabs have displaced both large and small native crabs along the East Coast.

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Tadpole Shrimp


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While hiking in Valley of Fire State Park one morning, I decided to investigate several pools on the desert floor, some no bigger than large puddles.

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In the water there were tiny, interesting crustaceans. Tadpole Shrimp are considered “living fossils,” since they have not changed significantly in outward form since the Triassic.

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Their broad protective shell at the front end, and a long, slender abdomen gives them a similar overall shape to a tadpole, from which their common name derives.

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To complete their lives, these creatures depend on the changing nature of the temporary pools of water that they inhabit. During the dry season (Summer and Fall), their offspring stay inside the eggs and the pools are devoid of water.

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As pools fills with rainwater during the Winter and Spring, the eggs hatch and feed on tiny invertebrates as well as algae and other organic debris.

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Not only was it cool to encounter this “mini horseshoe crab,” but Tadpole Shrimp is also considered a human ally against the West Nile virus, since they eat mosquito larvae.

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Freshwater crayfish are a wonderfully diverse group of organisms with over 605 described species of freshwater crayfish distributed throughout North America, Australia, southern South America, Asia, Europe, Madagascar and New Zealand.


They come in a variety of sizes, from the members of the dwarf crayfish, which reach less than an inch as adults, to the world’s largest freshwater invertebrate, the endangered Tasmanian Giant Freshwater Crayfish, which reaches lengths over 15 inches and weights of over 11 pounds.


These beautiful creatures come in many colors, including red, blue, orange, green, brown, and even white. There are crayfish with spots, stripes, and various patterns. They also have a degree of ecological variation, inhabiting four main habitat types: fast flowing streams (like where this one was caught), mud burrows, slow water species (ponds and lakes) and cave species.


Like their relatives, lobsters and crabs, Crayfish are crustaceans. They are omnivores and will eat almost anything, plant or animal, live or dead. They belong to the order Decapoda, meaning 10 feet – 4 pairs of legs and 2 pincers. They are not afraid to use those pinchers to defend themselves or to start fights with other Crayfish.


Crayfish have long been used in research to determine the role of vitamin A in vision. They are also a food source for people as well as bait for fishermen. Crayfish have an extraordinary sense of smell. It is estimated that 40% of their brain is devoted to the sense of smell, as opposed to less than 1% of a human’s.


Some people keep Crayfish as pets – including me. Whenever I walk near my the tank, my Crayfish will come running out of its hiding place with its claws above its head, anticipating that I will feed it. Let’s face it: Crayfish may be smarter than we think.

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European Sowbug

Even in the Winter if it is not too cold out, by heading out into the woods and turning a few logs, you can find European Sowbugs. Though the high temperatures have only been in the 30s for the last few days, there were plenty of these interesting creatures to be found.

Despite the “bug” in its name, the sowbug is actually a terrestrial crustacean and is more closely related to lobsters, shrimp and crayfish than insects. This is not a native species, although it is found throughout much of North America; it was introduced from Europe.

Sowbugs love dark, damp places and are commonly found in yards under wood or rocks. Compost heaps are another great retreat for this animal. They also often crawl through spaces in the foundation or through gaps around basement windows and end up in the basement where they can survive quite well if the basement is unfinished.

They feed primarily on dead plant and animal matter, including rotting wood. Sowbugs are considered beneficial because they are effective decomposers.

The European Sowbug has a smooth texture and has a wide, flat, oval-like shape. When disturbed it tends to freeze before moving off. They cannot “roll up” like their relative, the Pillbug.

Like a kangaroo, female sowbugs have a pouch called a marsupium, in which the eggs are incubated until they hatch. The young leave the pouch and typically molt soon after. It may take a number of months to mature and the mother sowbug will often stay close to her young until they are adults.

In some parts of the world, it is believed that eating sowbugs can help ease an upset stomach. Although not proven, this might be true, because sowbug shells are high in calcium carbonate. Sowbugs have the amazing ability to store very high concentrations of metals in the pancreas. This trait has been used by scientists to study metal contamination of various environments.

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