Lancelet: Phylogeny, Environment, Adaptations, and Selective Pressures

Subject: Sciences
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Lancelets are fish-like organisms from the chordate family. They belong to the genus Branchiostoma and their scientific name is Branchiostoma lanceolatum. A lancelet’s most prominent feature is its notochord, an evolutionary trait that is synonymous with the chordates. Although lancelets resemble fish, they belong to the category of invertebrates. A lancelet does not have eyes, a brain, bones, or a true skeleton. However, years of evolution have “given the organism a cartilage-like material for stiffening its gill slits, mouth, and tail” (Holland 26).

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Lancelets thrive in shallow waters where they can be found lying with half of their bodies immersed in the sand (Miller and Levine 54). The organisms are residents in all oceans around the world in both warm and cool glasses of water. Nevertheless, the organism has been found to prefer habitats within the temperate regions in areas such as Florida (Branchiostoma floridae). Lancelets can also be found living near coastlines that have both sand and shells. In addition, the organisms are averse to muddy environments because it is hard to feed or breathe in such areas. Excessive dumping of organic matter creates muddy environments, which are responsible for the declining lancelet populations around the world.

Lancelets depict the evolution of vertebrates over the years. Lancelets ceased being part of the vertebrate family over five hundred million years ago (Romer and Parsons 39).

The first describable organism in the evolutionary phylogeny of lancelets is Branchiostoma lanceolatum, a molluscan slug of the Limax species.

In the early 1800s, scientists “brought the phylogenetic position of the group closer to the agnathan vertebrates (including hagfish and lampreys), including it in the new genus Branchiostoma” (Putnam 1068). The classification of the organism was mainly dependent on the organism having gills and a mouth. The organism was later categorized in the Amphioxus genus.

The lancelets’ are closely related to vertebrates, notochordata, and urochordata. Currently, lancelets indicate a close relationship with more than 30 other species.

Lancelets’ defense mechanisms include:

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  • They are fast swimmers
  • They have the ability to burrow in the sand as a form of protection.
  • The organisms live in large colonies of up to 10,000 lancelets per square meter.
  • The organisms “are suspension feeders, feeding by trapping tiny particles on mucous nets secreted across the pharyngeal slits whereby ciliary pumping creates a flow of water with suspended food particles into the mouth and gill slits” (Garcia‐Fernàndez and Benito‐Gutiérrez 667).
  • Lancelets reproduce sexually producing numerous amounts of eggs.
  • They are fast swimmers
    • To facilitate their movement in water (interaction with their surroundings)
  • They have the ability to burrow in the sand
    • A form of protection (predator-prey interactions).
  • The organisms live in large colonies of up to 10,000 lancelets per square meter
    • For safety in numbers (Predator-prey interactions).
  • The organisms are suspension feeders
  • For feeding success
  • Lancelets reproduce sexually producing numerous amounts of eggs.
  • To enhance reproductive success

The organism’s genomes still have traces of the vertebrates. For instance, lancelets’ gene composition indicates that the organisms have appropriated old genomes through new functions and have organs such as:

  • the pituitary gland
  • pineal organ
  • striated axial muscles,
  • kidneys
  • liver
  • thyroid gland
  • nerve cord
  • pancreatic islet (Gibson-Brown et al. 5)

These organs share structural and functional similarities with similar organs in more advanced vertebrates (Gibson-Brown et al. 5).