Tadpole shrimps (Notostraca) is an order of very primitive crustaceans of the Branchiopoda class, also known as Triops. The name “triops” is derived from the Latin name of the genus Triops which includes the shield shrimps (Triops australiensis), the European tadpole shrimps (Triops canciformes) and the American tadpole shrimps (Triops longicaudatus) – species that are most popular in aquaria.
Triops are said to be living fossils because they have hardly changed since they appeared on Earth some 200 million years ago. They lived alongside the dinosaurs, but… unlike them, they not only managed to survive to our time, but also spread across the globe. And this is due to adaptation to life in rather extreme conditions.
Where do Triops live?
Triops live in puddles or other small bodies of intermittent water. Living in such puddles has its pros and cons. The advantage is that, in general, they have such a puddle to themselves and will not meet any fish that could eat them. The disadvantage is that after a shorter or longer time the puddle dries out. This makes the life of Triops intense, but short (about 10 weeks).
What does a Triops look like?
The first eye-catching characteristic of a tadpole shrimp is its flat carapace (head shield). It covers the head and thorax of the crustacean. If you gently tilt it, you will see that it is knit only with the head. On the carapace there is a pair of compound eyes and a simple eye (known as the naupliar eye), which faces upward. You read it right. These animals have three eyes. It’s simple, the extra eye responds to light, informing the tadpole shrimp about the position of its body relative to the bottom. From under the carapace you can see an elongated, segmented abdomen. Its last part is called telson and that’s where the anal opening is located. From the telson a pair of long appendages called furca (which means fork in Latin) grows.
If you turn the shrimp tadpole upside down, you will see dozens of appendages (thoracopods). There are 11 pairs of them on the thorax, a pair on each of the 11 segments. The first pair of thoracopods is transformed into feelers. It takes the form of three long, thread-like outgrowths and serves as a sense organ. Another pair of leaf-like appendages are used for swimming, digging, food catching and breathing. And although, compared to other crustaceans, the appendages of Triops are described as more primitive, because they are branched, they can perform so many functions simultaneously. You must admit that they look like a high-end multitools.
In females, the 11th pair of thoracopods is equipped with something like pouches, in which cysts are stored before they are buried in the substrate. The remaining pairs of appendages (about 70 pairs) are already on the abdomen. One segment can have from 6-12 pairs. There are no legs on the posterior segments of the abdomen. The rhythmic rapid movements of the legs are related to their respiratory function, as well as corralling food.
Food intake in tadpole shrimps
It may surprise you, but the Triops have a mouth opening that faces backward. It is led by a food groove that runs along the underside of the body. The appendages located on the sides of the groove move food from back to front. The strong mandible with which the mouth is equipped crushes and grinds it. And how does the tadpole shrimp get its food? It simply covers the food with its body. For this reason, it is not easy for it to hunt agile and fast prey. But weakened or sick tadpoles, crustaceans, insects or fry are less likely to escape. Triops also dig through the substrate in search of small invertebrates and detritus. They eat carrion as well.
Boy or girl – the sexual dimorphism of Triops
There are three sexes in Triops: males, females and hermaphrodites. The result is three different reproductive strategies. When a male and female are present in a population, copulation and fertilization occur. Their offspring are also males and females. Without the presence of a male, the female reproduces parthenogenetically – she lays unfertilized eggs, from which only females hatch. Hermaphrodites, on the other hand, have both female and male organs, making different configurations possible. For example, they can self-fertilize or fertilize females. This approach to reproduction is a guarantee of success when you live in a puddle. You never know how many Triops will hatch and what sex they will be. In this case, one female is enough, and the species will be extended. In aquarium breeding, males are rather rare.
Now you have a basic knowledge of these small, prehistoric crustaceans. If you find them interesting, it’s time to start keeping Triops.
Uwe Dost (2006), Przekopnica właściwa (Triops canciformes) – spotkanie z żywą skamieliną, „Aqua Forum” nr 14, 61-71.
Dominik Tomaszewski (2006), Niezwykłe zwierzęta z zamierzchłej przeszłości, czyli o przekopnicach. Część I. „Nasze Akwarium” nr 81, 43-46.
Dominik Tomaszewski (2006), Niezwykłe zwierzęta z zamierzchłej przeszłości, czyli o przekopnicach. Część II. „Nasze Akwarium” nr 82, 19-23.
Jura C. (2002), Bezkręgowce. Podstawy morfologii funkcjonalnej systematyki i filogenezy. Wydawnictwo Naukowe PWN.