August 28, 2026 this female is carrying eggs. by Ian Gardner. I have good news for you: clam shrimp exist nearby almost no matter where you live. As long as you can find at least at temporary body of water or pond, that is. Even in the southwestern US desert, there are emphemeral pools that form during the monsoon season in summer. So if there are clam shrimp even here, I can almost guarantee there are clam shrimp where you are, too. What the hell are you talking about? Clam shrimp are branchiopods, animals in the class Branchiopoda, which are a type of crustacean. Branchiopods are thought to be the oldest crustacean group with living members. These are tiny aquatic animals that include brine shrimp, fairy shrimp, water fleas, clam shrimp, and more. I might talk about this other groups later but today we will be discussing clam shrimp. clam shrimp observations in the US. they've been seen in every state, and in Canada and Mexico. observations in europe. pretty much everywhere. Clam shrimp have a bivalve carapace, which makes them superficially resemble molluscs (like clams), but they are not closely related. Their carapace is partially translucent so you can kind of see through it. They are fully aquatic and have gills. They have two pairs of bristly antennae, with one being simple and short and the other being long and branched, and they use these long antennae to swim around. Clam shrimp have a segmented thorax and a varying number of legs (up to 32 pairs). The gills are attached to the legs and move constantly to extract oxygen from the water. Overall their legs and antennae are kinda shrimp-like, so the overall effect is like a stumpy shrimp enclosed inside a transparent clam shell. When disturbed, these shrimp close up the carapace and will fall to the bottom of the water. The two sides of the 'shell' are held by strong muscular valves. The majority of the body is kept inside the carapace, with usually on the antennae and a 'tail' sticking out. They are quite small and usually less than 0.5 inches (10 mm) long. These tiny cute shrimp eat detritus or zooplankton. Clam shrimp can be found in vernal pools, which are depressions that hold water in spring and sometimes summer, but are dry for the rest of the year. They can be found anywhere where water holds, basically, in flooded fields, in road depressions, and at the edges of swamps There are many different species and some are hermaphroditic (one individual is both male and female). Their eggs are very interesting because they are so hardy, with tough shells that withstand very extreme conditions like drought or freezing. The eggs can remain dormant for a very long time, up to several years, before hatching. This is especially useful in desert conditions with variable rainfall, as they can wait until pools form before hatching. Baby clam shrimp are called nauplius larvae. The babies go through a few molts before they develop their shell. They have to mature pretty rapidly before their habitat dries up, so some of them reach adulthood in a couple of days. Their total lifespan is about 1-2 months. These shrimp are eaten by pretty much everything: fish, frogs & toads, and birds. Living fossils: Clam shrimp are extremely cool because they are an ancient group with a long evolutionary history. Fossils occur in the Silurian period (448-416 million years ago) and the Devonian period from 400 million years ago. They are also found during the Triassic, where many were found in saltwater deposits. During these time periods, clam shrimp were way more abundant and more diverse, with at least 300 different species recorded from fossils. Today, all species live in freshwater and there are about 150 species identified. They fossilize so well not only because they were very abundant and already living in muddy areas (which can create good fossils), but also because their shell is easily preserved. discover friends in your local temporary pond. by Franco Folini. Research: There is a lot of research concerning their fossils, but less work on currently living species. I would bet there are several unidentified species out there (possibly in your backyard). Because they're pretty small, they can be grown easily in a lab, so it's not too difficult to get things like basic biology - growth rate, reproduction, lifespan, etc. But there seems to not be much interest in the clam shrimp. Some people study them by collecting dried soil samples then rehydrating the dirt in an aquarium, and sometimes the eggs will hatch into clam shrimp! Eggs will hatch over about a 2 week period in the lab this way1. Most recent papers are describing new species, which are basically cases of looking for shrimp where no one has looked before and describing them, so kind of low-hanging fruit. Because clam shrimp have a variety of reproductive lifestyles - males and females, males and hermaphrodites, or just hermaphrodites - and they also have an extensive fossil record, they are a good model for understanding how these systems evolved. Apparently the shape of the carapace can indicate if there is sexual dimorphism for that species, which tells you whether there are males and females2. The phylogeny of the group (how they are related to each other on the evolutionary tree) is apparently pretty complicated. Weirdly clam shrimp have three different Orders. Endangered shrimp: Unsurprisingly, they are strongly affected by pollution and drought, which are both increasing at an unprecedented rate. Some species are listed as critically imperiled in the US. The American clam shrimp is listed as a candidate for endangered listing (meaning it's not on the list yet). Some US states have listed particular clam shrimp species, but it varies a lot. Massachusetts is on top of things and has the Agassiz's clam shrimp listed as endangered3. The species can be found at Cape Cod. The fuzzy cyst clam shrimp in New Mexico is listed as a species of greatest concern. Cysts are another name for the eggs. As pets: People keep other branchiopods as pets pretty often, like fairy shrimp, brine shrimp (aka sea monkeys), and triops. You can buy most of these commercially for your kids. Turns out people also keep clam shrimp! You can buy dried clam shrimp eggs online, and if you introduce them to an aquarium they will hatch. They must be more sensitive than other species, as they are listed as "intermediate hobbyist" difficulty. They're pretty amazing and beautiful so I'm not surprised that people would want to keep them. If I had time right now, I would probably keep some. Your part: Now that you know about clam shrimp, it is your duty to go out and document them around your neighborhood or favorite hiking trail. I want YOU to look for clam shrimp. Bring an aquarium net and/or some jars, because we're gonna need photos of those babies. Upload them to iNaturalist so scientists can figure out where they all are, and you can probably contribute to some new species identifications this way. The clam shrimp are relying on you. Find a map of your nearest clam shrimp here: iNaturalist - Diplostraca. The thing is that they probably exist just about everywhere there is temporary water, so there are many, many gaps where no one has ever documented them in a place before. sources: 1 Weeks, Stephen C., et al. "Breeding systems in the clam shrimp family Limnadiidae (Branchiopoda, Spinicaudata)." Invertebrate Biology 127.3 (2008): 336-349. 2 Astrop, T. I., Park, L. E., Brown, B., & Weeks, S. C. (2012). Sexual discrimination at work: Spinicaudatan ‘Clam Shrimp’(Crustacea: Branchiopoda) as a model organism for the study of sexual system evolution. 3 ma.gov: Aggasiz's clam shrimp