Friday Fellow: Sharp-Toothed Venus Seed-Shrimp

by Piter Kehoma Boll

We reached again one of those problematic weeks in which I have to talk about something of which I know very little. This time the problem is called Euphilomedes carcharodonta, a small crustacean of the class Ostracoda, known as ostracods or seed shrimps. I decided to adapt the name of this species as sharp-toothed Venus seed-shrimp.

Although seed shrimps form a very diverse and species-rich group of organisms, I cannot find much details on particular species, so it is a challenge to present one here, but I decided to talk a little about the sharp-toothed Venus seed-shrimp, so let’s go.

A male of the sharp-toothed Venus seed-shrimp. The dark spot is a lateral eye. Photo by Ajna Rivera.*

Measuring only a few milimeters, the sharp-toothed Venus seed-shrimp is found in the sea along the west coast of the United States. It has a typical ostracod appearance, looking like a small shrimp within a bivalvian shell.

Males and females of the sharp-toothed Venus seed-shrimp show sexual dimorphism, part of which is not only related directly to sex, but actually to the different niches that each sex occupies in the environment. Females pass most of their time buried in the sediments where light and predators are limited and, as a result, they have poorly developed eyes. The males, on the other hand, spend a lot of their time swimming in the water and are very vulnerable to predators, such as fish. Therefore, males have very well developed eyes that allow them to see fish from the distance. Experiments have shown that the eyes do not help them to identify the tiny females, but are essential to survive predation.

A female sharp-toothed Venus seed-shrimp. Notice how she does not have the lateral eye seen on the male. Photo by Ajna Rivera.*

And that’s what I got about this fellow. As I asked before while talking about other groups of organisms, such as foraminiferans, if you have good resources on more detailed knowledge about species in this group, please share them in the comments. We need to give more visibility to those tiny and neglected souls that share this planet with us.

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References:

Sajuthi, A., Carrillo-Zazuetta, B., Hu, B., Wang, A., Brodnansky, L., Mayberry, J., & Rivera, A. S. (2015). Sexually dimorphic gene expression in the lateral eyes of Euphilomedes carcharodonta (Ostracoda, Pancrustacea) EvoDevo, 6 : 10.1186/s13227-015-0026-2

Speiser, D. I., Lampe, R. I., Lovdahl, V. R., Carrillo-Zazueta, B., Rivera, A. S., & Oakley, T. H. (2013). Evasion of Predators Contributes to the Maintenance of Male Eyes in Sexually Dimorphic Euphilomedes Ostracods (Crustacea) ntegrative and Comparative Biology, 53 (1), 78-88

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Friday Fellow: Réaumur’s Desert Woodlouse

by Piter Kehoma Boll

We all know that crustaceans are mainly aquatic animals, but that some species have conquered the land, especially the woodlice. But did you know that some woodlice went as far as to find a way to live in the desert? Today’s Friday Fellow is one of those species. Actually, it is the woodlouse that lives in the driest habitat where a crustacean can be found. Its name is Hemilepistus reaumuri, which I decided to call the Réaumur’s Desert Woodlouse.

A specimen of Hemilepistus reaumuri in Tunisia. Photo by Ferenc Vilisics.*

Found in the deserts of North Africa and the Middle East, the Réaumur’s Desert Woodlouse is considerably large, reaching up to 22 mm in length. It feeds on leaves and is mainly active at dusk. Being found in great densities, this little fellow is also an important food source for some predators, especially the large-clawed scorpion Scorpio maurus.

In order to tolerate the high temperatures and the low relative humidity of the air in the desert, the Réaumur’s Desert Woodlouse constructs burrows that are at least 40 cm deep, so that it can find an environment in which the relative humidity is of at least 6%, since it cannot survive when it drops below that value. When it gets lost, it usually finds its burrow again in a few minutes by using a systematic search behavior in the environment, exploring regularly the area around the point in which it became lost until its home is located.

About to enter its burrow. Photo by Ferenc Vilisics.*

One peculiar aspect of the Réaumur’s Desert Woodlouse is that it take care of its offspring. A male and a female form a monogamous couple and construct together a burrow where they live and take care of their young. The female usually bears 50 to 100 live young and those remain in the burrow for 10 to 20 days, being fed by their parents. Members of the same social group are able to recognize each other using pheromones, and when the young leave the burrow they may be captured by adults of other groups, killed and offered as food to that adult’s offspring.

Having a lifespan of only 15 months, the Réaumur’s Desert Woodlouse produces only one brood during their life. Having a long life does not seem to be a privilege for desert crustaceans.

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References:

Hoffmann, G. (1983) The random elements in the systematic search behavior of the desert isopod Hemilepistus reaumuri. Behavioral Ecology and Sociobiology 13(2): 81-92.

Linsenmair, K. E. (1985) Individual and family recognition in subsocial arthropods, in particular in the desert isopod Hemilepistus reaumuri. Fortschritte der Zoologie 31: 411-436.

Wikipedia. Hemilepistus reaumuri. Available at < https://en.wikipedia.org/wiki/Hemilepistus_reaumuri >. Access on March 25, 2018.

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Friday Fellow: Glacial calanus

by Piter Kehoma Boll

Today’s Friday Fellow comes swimming tinily through the freezing waters in the north. It is a small crustacean, more precisely a copepod, and its name is Calanus glacialis. It lacks a common name, but I adapted it as the “glacial calanus”.

Tiny, but beautiful. Credits to University of Alaska Fairbanks*.

Found in the Arctic Ocean and the northernmost areas of the Atlantic and Pacific Oceans, the glacial calanus is one of the most abundant polar species of copepods and one of the main components of the zooplancton in this region. As a result, it is an important food source for other animals, such as fish, birds and even whales.

The life cycle of the glacial calanus varies from 1 to 3 years and depends on the temperature and food availability. Most of its development occurs in summer, when the water is warmer and there is plenty of food, which for our fellow consists mainly of algae, such as diatoms. In autumn, the glacial calanus starts to accumulate lipids and then migrates downwards to deep waters and becomes dormant to survive the long, dark and food-poor winter.

As its life cycle depends on such seasonal variations, global warming may have profound impacts on the populations of the glacial calanus and on that of other species that depend on it as food.

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References:

Kosobokova, K. N. 1999. The reproductive cycle and life history of the Arctic copepod Calanus glacialis in the White Sea. Polar Biology 22:254–263. DOI: 10.1007/s003000050418.

Søreide, J. E.; Leu, E.; Berge, J.; Graeve, M.; Falk-Petersen, S. 2010. Timing of blooms, algal food quality and Calanus glacialis reproduction and growth in a changing Arctic. Global Change Biology 16:3154–3163. DOI: 10.1111/j.1365-2486.2010.02175.x

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