Triops: A Three-Eyed Prehistoric Wonder - Animalassic

Triops, also known as Triassic triops, shield shrimp, or tadpole shrimp, are a genus of crustaceans that have existed for around 220 million years. One of the most striking features of these creatures is their three eyes, which make them unique and intriguing creatures to study. Triops fish belong to the order Notostraca, which includes about a dozen species. These creatures are found in temporary freshwater pools, ponds,vernal pools and streams around the world. Triops fish are considered to be "living fossils" because they have remained virtually unchanged for millions of years and are one of the oldest surviving species on the planet, with fossils dating back to the Triassic period, over 200 million years ago

 

Triops

T. longicaudatus by Steve Jurvetson  via Flickr

    

Scientific classification
Kingdom	Animalia
Phylum:	Arthopoda
Class:	Branchiopoda
Order:	Notostraca
Family:	Triopsidae
Genus:	Triops Schrank,1803
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Triops, also known as Triassic triops, shield shrimp, or tadpole shrimp, are a genus of crustaceans that have existed for around 220 million years. One of the most striking features of these creatures is their three eyes, which make them unique and intriguing creatures to study.

Triops fish belong to the order Notostraca, which includes about a dozen species. These creatures are found in temporary freshwater pools, ponds,vernal pools and streams around the world. Triops fish are considered to be "living fossils" because they have remained virtually unchanged for millions of years and are one of the oldest surviving species on the planet, with fossils dating back to the Triassic period, over 200 million years ago. 

 

According to molecular clock

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Molecular Clock

The molecular clock is a method that uses the mutation rate of biomolecules to estimate the time when different species diverged in prehistory. It was first proposed in 1962 by Emile Zuckerkandl and Linus Pauling, and later supported by Motoo Kimura's neutral theory of molecular evolution. The molecular clock technique uses molecular data to estimate divergence times, which can be calibrated using node and tip calibration. Bayesian methods are commonly used, but there are challenges such as variation in mutation rates and species-specific differences. The technique has been useful in molecular systematics, macroevolution, and phylogenetic comparative methods, but is based on statistical inference and faces challenges at short and long timescales.

estimates, it is inferred that Triops and Lepidurus diverged from each other in the Triassic or Jurassic period, approximately 152.3-233.5 million years ago. The regions where the earliest distinct Triops lineages exist today are located within the territoriesthat were once part of the ancient supercontinent Gondwana. This observation implies that Triops likely originated within Gondwana.

Third - Eye

Triops Closeup by Karsten Grabow  via Wikimedia Commons

One of the most striking features of Triops is their eyes. Thier name Triops has been coined from the Greek τρία (tría) meaning "three" and ὤψ  (ops) meaning "eye".

They have two large compound eyes, which are located on either side of their head, and a third, smaller eye in the center called Naupliar ocellus

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Naupliar Ocellus

The Naupliar ocellus, also known as the "third eye," is an anatomical feature found in the larval stage of certain crustaceans, specifically copepods. This stage is characterized by three head segments covered by a single carapace, with an unsegmented posterior body. The presence of a simple, unpaired eye, referred to as the naupliar eye, is located within the head region and is responsible for perceiving light. The naupliar ocellus plays a vital role in the nauplius larvae's survival and behavior, helping them respond to light stimuli, aiding in their orientation and navigation within their aquatic environment. However, not all crustacean groups possess this larval type, such as isopods, which lack the naupliar ocellus. The absence of this stage suggests that isopods have evolved alternative strategies for larval development and survival.

. The compound eyes are the main visual organs and are made up of thousands of individual lenses, which allow the Triops fish to see a wide range of colors and movements. The third eye, or median eye, is much smaller and less complex, but it is still a valuable tool for these creatures.

The third eye of Triops fish is located on the top of their head, and it is believed to be used for navigation and sensing light levels. This eye is unique because it is not a true eye in the traditional sense, but rather a group of photoreceptor cells that are sensitive to light. This allows the Triops fish to detect changes in light levels and adjust their behavior accordingly, such as swimming to deeper waters to avoid bright sunlight. 

Life - Cycle

Triops longicaudatus by Micha L. Rieser  via Wikimedia Commons

Another fascinating aspect of Triops is their life cycle. These creatures have a brief lifespan, typically lasting for only a few months. However, they are incredibly resilient and can survive in harsh environments with low oxygen levels and high temperatures. Triops fish lay their eggs in the mud or sand at the bottom of ephemeral pools, where they can remain dormant for years until the conditions are right for hatching. The Triops larvae grow swiftly when the eggs hatch, reaching adulthood in just a few weeks.

Dried eggs of various triops species are sold in kits for raising as aquarium pets, marketed as "aquasaurs", "trigons", or "triops". 

Triops can reproduce through both sexual and asexual means, allowing for the development of populations from different types of eggs. Most triops can produce viable eggs without the need for fertilization through parthenogenesis

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Parthenogenesis

Parthenogenesis is a natural form of asexual reproduction in which growth and development of embryos occur in a gamete (egg or sperm) without combining with another gamete. It occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea and parasitic wasps) and a few vertebrates (such as fish, amphibians, reptiles, and birds). Normal egg cells form in the process of meiosis and are haploid, with half as many chromosomes as their mother's body cells. Parthenogenetic offspring usually have the diploid chromosome number and may have anywhere between all and half of the mother's alleles. In species that use either the XY or the X0 sex-determination system, they have two X chromosomes and are female.

In species that use the ZW sex-determination system, they have either two Z chromosomes (male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female). Parthenogenesis does not apply to isogamous species.

. Additionally, some triops are hermaphrodites, which means that an individual has both male and female reproductive organs, implying that an entire population can develop from just one egg.

Diet

Captive T. longicaudatus feeding on carrot by John Alan Elson  

Triops primarily feed on small organisms such as zooplankton, insects, and other small aquatic animals. They are also known to scavenge on dead organic matter, including decaying plants and animals, and will sometimes eat algae and other plant material as well.

In captivity, Triops can be fed a variety of different foods, including commercially available fish food pellets, algae wafers, and even small pieces of vegetables or fruits.

Distribution

Map data  via Google, INEJI

Triops can be found all around the world, especially in temporary pools and wetlands. They are known to inhabit a variety of environments including ponds, streams, marshes, and even temporary pools that may dry up during the summer months.They have been observed to inhabit a variety of habitats, such as ponds, streams, marshes, and even transient pools that can dry up in the summer. These depending on the particular type of Triops, different Triops species have different distributions. Triops cancriformis, for instance, is native to Europe and some regions of Asia, but Triops longicaudatus is native to North America but has also been brought to other continents. 

Overall, Triops are found in a wide range of geographical regions including North and South America, Europe, Asia, Africa, and Australia.However, due to habitat loss, pollution, or other conditions that impede their capacity to survive and reproduce, their existence may be more restricted in some locations.

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References

• Triops (Genus Triops). (n.d.). iNaturalist United Kingdom. Retrieved May 17, 2023, from  https://uk.inaturalist.org/taxa/60400-Triops.
 
• Wagner, P., Haug, J. T., Sell, J., & Haug, C. (2017, August 18). Ontogenetic Sequence Comparison of Extant and Fossil Tadpole Shrimps: No Support for the “Living Fossil” Concept - PalZ. SpringerLink. Retrieved May 17, 2023, from
https://link.springer.com/article/10.1007/s12542-017-0370-8.

• MyTriops - Introduction. (2010, August 5). MyTriops - Introduction.Retrieved May 17, 2023, from
https://web.archive.org/web/20100805092533/http://mytriops.com/articles/triops_intro.stm.

• Hannum. (2020, July 3). Triops Eggs: Millions of Years of Evolution - My Triops. My Triops. Retrieved May 17, 2023, from
https://mytriops.com/a-recipe-for-hundreds-of-millions-of-years-of-success. 

• Bell. (1892). The Masterpiece of Nature : The Evolution and Genetics of Sexuality. In Google Books (pp. 1–514). Cambridge University Press.
https://books.google.com/books/about/The_Masterpiece_of_Nature.html?id=q5g9AAAAIAAJ.