Family: Triopsidae, Order: Notostraca, Class: Branchiopoda, Subphylum: Curstacea, Phylum: Arthropoda, Kingdom: Animalia.
In simpler terms, they are crustaceans. They look almost like small horseshoe crabs but with three eyes. They are sometimes called tadpole shrimp or more formally, notostracans. One of the most interesting facts about this order of animals is that their external morphology has not changed in roughly 200 million years. This means the Triops you see today are the same creatures the dinosaurs in the Triassic period observed. Some scientists believe they are actually the oldest living animal species on Earth.
Another interesting fact: Triops don't have antennae like many crustaceans. What may look like antennae are actually their first pair of legs. These do act as sensory organs however, and have evolved to serve a similar purpose.
Every thoracic segment from the thirteenth back will have 4-6 pairs of legs. That's right, this creature can have as many as 70 legs total. No other crustacean comes close to this.
How do you tell male from female Triops? The only exact way would be to look at their eleventh pair of legs. In the females, this pair has evolved into a round egg capsule to carry their eggs. In the males... nothing. Just a regular leg.
Having three eyes, one might think that Triops have an excellent sense of sight. This is only partially true. They don't use their eyes to find food, but their eyes do help orient them toward or away from the light in their environment. An interesting experiment to demonstrate this would be to observe them in their tank in a normally lighted room, then turn the lights off and use a flashlight to light the bottom of the tank. The crustaceans will then reorient themselves thinking the bottom of the tank is the top.
Life Cycle
The most interesting study these creatures offer is their life cycle. In any Triop pool, there are relatively few males. In the northern hemisphere, the ratio is often less than one in 100 Triops being male. For this reason, most of the females' eggs are unfertilized; however this makes little difference in their hatching rate.
The eggs are enclosed in a strong thick shell and can withstand some very harsh conditions. The eggs can withstand temperatures from below freezing to about 180 degrees Fahrenheit (80C). They can be eaten by a frog or fish, digested, expelled and still hatch. They can exist in a diapause state for many years, some scientists think for decades. The hardiness and longevity of these eggs have contributed to the widespread regions in which Triops can be found.
Some of the eggs will ultimately wind up in a pool with suitable conditions for hatching, and the larva will hatch about a year later. Within about two weeks, the creature will have molted about 12-14 times and will thus be an adult. The Triop will molt about 40 times before it reaches sexual maturity.
The life span of Triops in the lab (or your aquarium) and in the wild are about the same. Most will live between 50 and 90 days.
There are several sources of information on Triops available. Wikipedia has a great page as well as a Scottish site called www.mytriops.com. Check out our special Triops promotion to see how you can get free eggs.
