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Euplokamis is a genus of ctenophores, or comb jellies, belonging to the monotypic family Euplokamididae. Despite living for hundreds of millions of years, there is minimal research regarding Euplokamis, due to their body structure. These organisms have been found in fossil records from the Cambrian period, part of the Paleozoic Era, and it is estimated that some may have evolved prior to this period.[1] Originally, cnidarians and ctenophores were classified under the same phyla, Coelenterata. Ctenophore bodies are made up of a gelatin substance, similar to cnidarians, but the multiple rows of combs present in fossil records are unique to ctenophores.[2] Research on the evolution of the basic body structures of diploblastic metazoans revealed that there are four major phyla, including ctenophores and cnidarians.[1] Although the morphology of Euplokamis, and other related groups, often resemble the Medusa stage of cnidarians, their distinct features, such as the eight rows of combs, led to the official classification of ctenophores.[3] In 1880, Chun expanded the family Euplokamidae after the the discovery of a new species, Euplokamis dunlapae.[4] This research indicated that Euplokamis should be identified from Mertensiidae due to the rows of plates, or combs, and some compression.[5] They may also be distinguished from the genus Pleurobrachia due to their more elongated shape.[5] Other characteristics, including a defined mesoderm, lack of stinging cells, developmental differences, and symmetry all supported the reclassification of these organisms.[6]

Figure 1. Pelagic ctenophores: (a) Beroe ovata, (b) Euplokamis sp., (c) Nepheloctena sp., (d) Bathocyroe fosteri, (e) Mnemiopsis leidyi, and (f) Ocyropsis sp.

Distribution, Behaviors, Adaptations

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Distribution/Habitat

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Euplokamis sp. are distributed widely around the world, and are most commonly found in warm coastal waters.[7] For example, they have been found in the, Mediterranean Sea, the north Pacific, and the Gulf of Maine.[8] However, since this genus was originally grouped in the family Pleurobrachiidae, there is limited information regarding their actual distribution and habitat. They are free swimmers, meaning they lack they float freely in the water column and are primarily found in marine environments.

Figure 2. Structure of Ctenophora: Order Cypiddia

Feeding Behavior

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According to research, Euplokamis sp. are carnivorous, like all other known species of Ctenophores.[9] They are known to feed primarily on rotifers and other small crustaceans: including copepods, amphipods, and euphausiids), and some planktonic larvae.[9] They have long tentacles with branches that are used for feeding. These branches are known as tentilla and are held tightly in coils, forming droplet shapes.[10] To catch prey, they will extend the tentilla and wrap them around copepods.[11] The tentilla are covered in sticky colloblasts, which keeps the prey stuck in place.[12] Not only can the tentilla be released at high velocities to quickly capture prey, but they also can be released in a slow and controlled manner, likely to attract prey.[12] Additionally, the cilia that make up the comb plate move by making a stroke in a certain direction. After capturing their prey, they can reverse the stroke, or beat, in the other direction on two rows, while the other rows continue to beat in the normal direction.[13] They are then able to push the prey to their mouth in a sweeping motion, and the ciliary reversal causes the organism to rotate, which tangles the prey further into its mouth.[13]

Bioluminescence

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Another adaptation that many ctenophores have developed is bioluminescence, or the ability to produce their own light. For example, Euplokamis dunlapae were found to produce light off the coast of Washington when exposed to stimuli.[8] After physical stimulation, they produced bright flashes of light, consistent with bioluminescence. According to research, bioluminescence in Euplokamis sp. is both intrinsic and extrinsic, because light can appears in the comb rows or as bursts of light in the water. [14] Additionally, off the coast of Maine, Euplokamis sp. was found to be one of the two brightest species to have bioluminescence.[15] Research suggests that bioluminescence in Euplokamis sp. may function as a defense mechanism.[15] Euplokamis sp. release bursts of luminescent particles into the water.[16] The light was only seen directly in response to a disturbance or stimulation, which indicates it is used to distract or blind predators when they are sensed. Additionally, some produce light as a warning signal, or to expose nearby predators. The various strategies may impact predator-prey relationships or other the population dynamics in an area. [15]

Figure 3. Bioluminescent Euplokamis sp.

Nervous System

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Additionally, despite their simple exterior, research on the nervous system of Euplokamis indicates the use of more complex systems, including axons. The use of these axons have allowed some species of Euplokamis to swim backwards rapidly. The direction of the cilia come plate may be reversed causing them to move backwards.[8] Therefore, they are unique due to giant axons in their combs that allow for a rapid escape response.[17] Euplokamis sp. have a aboral sensory organ, which is by passed to produce this escape response.[18]

Anatomy and Morphology

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Ctenophores are divided into two classes based on either the presence (Tentaculata or the lack (Nuda) of tentacles.[7] Within each class, there are multiple orders to further distinguish their structures and characteristics. The class Tentaculata contains the following orders: Cydippida, Lobata, and Cestida.[19] The genus Euplokamis sp. is part of the class tentaculate, meaning tentacles are present and are part of the order Cydippida—distinguished by their tentacles and their round body shape.[6] These tentacles are long, may display branching, are have a sheath allowing them to be retractile.[7] The branching of tentacles is known as tentilla, which are held tightly in coils.[10] Further, the widely spaced tentillia droplets allow for organisms to be classified to the genus level, and are one of the only examples of striated muscle found in ctenophores.[13]

Additionally, these organisms have biradial symmetry with a mouth on their front end and a statocyst, or sense organ, at the other end.[6] The sides of their stomachs are lined with distinct bulbs, shaped like tadpoles,[10] and unlike other well known jellyfish, Euplokamis sp. do not have any nematocytes, known as stinging cells. The mouth is connected to the digestive tract via the pharynx. The digestive system, or gastrovascular cavity, is made up of intricate canals that allow for both digestion and circulation to occur.[6] They also lack an anus, but are able to excrete some waste through pores on the adoral end. Typically, Euplokamis sp. are small, only growing up to approximately 20 millimeters (mm) in length.[10]

Another distinct feature of this genus is the eight rows of combs present. While they are known as comb plates, they are actually made up of large cilia, which are hair like structures.[13] These plates are unique, because they consist of some of the largest known cilia found on any organism.[13] Additionally, the combs primarily function in movement, allowing some species to move forwards and backwards.[3] Since their bodies are made up the mesoglea--a translucent, gelatin-like substance--the 8 comb rows can be easily identified. These combs function in movement, due to their large ciliary structures.[13]

Taxonomy[19]

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References

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  1. ^ a b Giribet, Gonzalo (2002-09-01). "Current advances in the phylogenetic reconstruction of metazoan evolution. A new paradigm for the Cambrian explosion?". Molecular Phylogenetics and Evolution. 24 (3): 345–357. doi:10.1016/S1055-7903(02)00206-3. ISSN 1055-7903.
  2. ^ Parry, Luke A.; Lerosey-Aubril, Rudy; Weaver, James C.; Ortega-Hernández, Javier (2021-09-24). "Cambrian comb jellies from Utah illuminate the early evolution of nervous and sensory systems in ctenophores". iScience. 24 (9). doi:10.1016/j.isci.2021.102943. ISSN 2589-0042. PMC 8426560. PMID 34522849.{{cite journal}}: CS1 maint: PMC format (link)
  3. ^ a b Minni, M. (2021). "Phylum Ctenophora – Characteristics, Classification & Examples". Embibe Exams.
  4. ^ Mills, Claudia E. (2011-02-14). "Revised classification of the genus Euplokamis Chun, 1880 (Ctenophora: Cydippida: Euplokamidae n. fam.) with a description of the new species Euplokamis dunlapae". Canadian Journal of Zoology. doi:10.1139/z87-404.
  5. ^ a b RITTER, WILLIAM (1906). Zoology: Volume II. Berkley the University Press: University of California Publications. p. 46. ISBN 048477736X.
  6. ^ a b c d Britannica, T. (2013). "Ctenophore: Marine invertebrate". www.britannica.com. Encyclopedia Britannica.
  7. ^ a b c Shah, R (2016). "Phylum Ctenophora: Features, Characters and Other Details". Biology Discussion.
  8. ^ a b c Haddock, Steven H. D.; Case, James F. (1995). "Not All Ctenophores Are Bioluminescent: Pleurobrachia". Biological Bulletin. 189 (3): 356–362. doi:10.2307/1542153. ISSN 0006-3185.
  9. ^ a b Wright, Jeremy. "Ctenophora (comb jellies)". Animal Diversity Web. Retrieved 2022-04-10.
  10. ^ a b c d Gershwin, L; Lewis, M; Gowlett-Holmes, K; Kloser, R (2014). The Ctenophores. In: Pelagic Invertebrates of South-Eastern Australia: A field reference guide. CSIRO Marine and Atmospheric Research: Hobart. pp. 5–6.
  11. ^ Haddock, Steven H. D. (2007). "Comparative Feeding Behavior of Planktonic Ctenophores". Integrative and Comparative Biology. 47 (6): 847–853. ISSN 1540-7063.
  12. ^ a b Mackie, G. O.; Mills, C. E.; Singla, C. L. (1988). "Structure and function of the prehensile tentilla of Euplokamis (Ctenophora, Cydippida)". Zoomorphology. 107 (6): 319–337. doi:10.1007/bf00312216. ISSN 0720-213X.
  13. ^ a b c d e f Tamm, Sidney L. (2014). "Cilia and the life of ctenophores". Invertebrate Biology. 133 (1): 1–46. ISSN 1077-8306.
  14. ^ Widder, Edith (2002-01). "Bioluminescence and the Pelagic Visual Environment". Marine and Freshwater Behaviour and Physiology. 35 (1–2): 1–26. doi:10.1080/10236240290025581. ISSN 1023-6244. {{cite journal}}: Check date values in: |date= (help)
  15. ^ a b c Widder, E.A.; Greene, C.H.; Youngbluth, M.J. (1992). "Bioluminescence of sound-scattering layers in the Gulf of Maine". Journal of Plankton Research. 14 (11): 1607–1624. doi:10.1093/plankt/14.11.1607. ISSN 0142-7873.
  16. ^ Dybas, Cheryl (2013). "RIPPLE MARKS—The Story Behind the Story". Oceanography. 26 (2). doi:10.5670/oceanog.2013.23. ISSN 1042-8275.
  17. ^ Mackie, G. O.; Mills, C. E.; Singla, C. L. (1992). "Giant Axons and Escape Swimming in Euplokamis dunlapae (Ctenophora: Cydippida)". The Biological Bulletin. 182 (2): 248–256. doi:10.2307/1542118. ISSN 0006-3185.
  18. ^ Norekian, Tigran P.; Moroz, Leonid L. (2019). "Comparative neuroanatomy of ctenophores: Neural and muscular systems in Euplokamis dunlapae and related species". Journal of Comparative Neurology. 528 (3): 481–501. doi:10.1002/cne.24770. ISSN 0021-9967. {{cite journal}}: line feed character in |title= at position 72 (help)
  19. ^ a b World Register of Marine Species, WoRMS (2022). "WoRMS taxon details: Euplokamis". www.marinespecies.org.
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