Known by two popular names – seed-shrimp and sea firefly the ostracod is one of the most fascinating creations of Mother Nature.

This tiny organism is aquatic by nature and displays some of the most amazing features in the entire animal kingdom. So, if you are one who loves to learn more about this fascinating world around us, this is one post that you should not miss!

Let us embark on a journey to the world of 30 interesting ostracod facts and amaze ourselves.

Interesting Ostracod Facts: 1-5

1. Ostracods are aquatic crustaceans that belong to the class Ostracoda. By small, we mean pretty small. They grow to a length of 0.3 mm to a maximum of 5 mm.

2. The characteristic feature of an ostracod is its hinged, bi-valve and hard shell that covers the non-mineralized body parts completely. This shell is known as calcitic carapace.

3. The carapace or the shell of some ostracods are very smooth and round, which is why they are often referred to as the seed-shrimps.

4. This however is not true for all ostracods. Some may feature ridges, spines, flanges, striations or pits on the carapace.

5. Inside the carapace is one hell of a complex body featuring 8 pairs of appendages. Ostracods use these appendages for several purposes like mating, feeding, crawling, swimming and sensing.

ostracod facts
By Hannes Grobe – Own work, CC BY 3.0, Link

Interesting Ostracod Facts: 6-10

6. Ostracods have 8 pairs of appendages that are extended out through the gaps when the carapace is slightly opened.

7. Many ostracods absorb oxygen directly from water through their body cuticles. Some larger ostracods have gills for respiration.

8. Most ostracods are single-eyed with the eye being located on the anterior end of the shell’s hinge. This singular eye is actually a fusion of three cups.

9. In some ostracods however, this singular eye may have two distinct halves with a middle connection producing a dumb-bell shaped view when looked at from above.

10. There are some groups of ostracods which, in addition to the single dorsal eye, also have laterally located pair of compound eyes.

Interesting Ostracod Facts: 11-15

11. Ostracods display both sexual as well as asexual reproduction. While sexual reproduction is mostly found in marine forms, asexual reproduction is usually displayed by freshwater breeds.

12. Asexual breeds usually belong to the Cyprididae family with most of the population being females capable of cloning themselves via a process that has been termed as parthenogenesis.

13. A weird thing is often observed in case of those ostracods that reproduce sexually. The males produce sperm that are often longer than themselves.

14. The longest ostracod sperm that has been recorded till date is 11.7mm, which is 3.6 times the length of the male itself. This however is usually seen in the family Cypridoidea.

15. Most of the males in the Cypridoidea family have very complex sexual apparatus. They usually have two penises, 8 testes (4 on either side) and two Zenker organs.

Interesting Ostracod Facts: 16-20

16. Zenker organs are actually muscular pumps that the males use to transfer their sperm into the females.

By Ilse Anahi Carrasco – Own work, CC BY 4.0, Link

17. In terms of aquatic environment, ostracods are kind of omnipresent. Go deep in the sea and you can find them. Come to the shore and they will greet you. Wet leaf litters, springs, groundwaters, puddles, small pools, rice fields, ponds, lakes and rivers – they are present everywhere.

18. Because their habitat is extremely diverse, in fossil records they hold the record of most abundantly preserved anthropod.

19. Because of their calcitic carapace, their fossilization potential is extremely high. The oldest known fossil dates back to 485-443 million years ago and was found in the rocks of the Ordovician period.

20. Because of their high fossilization potential and their diversity, palaeontologists successfully use ostracod fossils as palaeo-environmental and stratigraphical indicators.

Interesting Ostracod Facts: 21-25

21. As mentioned earlier, many of the habitats of ostracods are temporary. The question is, how do they manage to reach such temporary habitats? The global presence of ostracods is explained by their dispersal abilities. The eggs are very tiny and light and can be carried long distances by wind.

22. These eggs often get attached to the feet of migratory birds and even toad skin, explaining their presence in weird places.

23. The question that naturally follows is that how come the eggs survive such long transits? The answer to this question is stunning. The eggs can dry up and stay viable for years. If water becomes available again, eggs begin to hatch.

24. Some ostracods, when eaten up by small bluegill sunfish, manage to come out alive from the rear end of the fish and that too, absolutely unharmed. This is possible because they shut themselves close very tightly inside their carapace and travel through the gut, eventually to be excreted out by the fish.

25. Talking of fossils, the oldest known fossilized ostracod penis dates back to 425 million years. That’s astonishing because penis, like other soft body parts, decay very rapidly.

Interesting Ostracod Facts: 26-30

26. The credit for this preservation goes to volcanic ash that fell into the sea, preserving many marine animals and their soft body parts.

ostracod facts
Sea fireflies | By self – Own work, CC BY-SA 3.0, Link

27. We know you have been waiting for this – sea-firefly! Sea-fireflies is a common name used in Japan for describing Myodocopida ostracods. The actual Japanese name is Umi-Hotaru.

Sea Fireflies | By User:Almandine – Own work, CC BY-SA 3.0, Link

28. The bright blue light produced by the Myodocopida ostracods is a result of two different chemicals mixing together in presence of oxygen. The ostracods use the light for mating display and in order to prevent confusion between different species, the ostracods flash at different rates.

29. The Japanese made good use of the Umi-Hotaru during WWII. They caught these ostracods, dried them up and grounded them to powder. At night, they mixed water to the powder to trigger the chemical reaction, producing a faint blue light, just bright enough to read maps and orders without giving away their positions to the enemies.

30. William Ho – a Taiwanese photographer captured the images of phenomenal bioluminescent waves (pictured above) at one of the Maldives beaches. Previously it was considered that the blue light was emitted by a specific type of phytoplankton but James Morin, biology professor of Cornell clarified that the light was produced by the ostracod crustaceans. Read full report of Huffington Post here.

Sources: 1, 2

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