Lancelets are fish-like organisms from the chordate family. A lancelet’s most prominent feature is its notochord, an evolutionary trait that is synonymous with the chordates. A lancelet is made up of fluid-filled large cells and they give form to this organism by making it flexible and rigid. The notochord is the part that is responsible for providing support to a lancelet’s body. The form of a lancelet has “a dorsal hollow nerve cord, a tail that extends beyond the anus and a dorsal supporting rod called the notochord” (Heimberg 2950). When they are in their natural habitats lancelets usually burry a half of their body in the sand thereby leaving the other half exposed for feeding purposes. 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). This report offers a biological analysis of lancelets, their adaptations, environment, and selection pressures. The organism was chosen for the report mainly because of its unique adaptations. The organism also presents peculiar traits that are not common among other invertebrates.
Evolutionary Phylogeny
Lancelets present a unique case study when investigating how vertebrates have evolved over the years. Lancelets ceased being part of the vertebrate family over five hundred million years ago (Romer and Parsons 39). Nevertheless, 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. The first describable organism in the evolutionary phylogeny of lancelets is the ‘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, notochord data, and urochordata. Currently, lancelets indicate a close relationship with more than 30 other species.
Environment
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 waters. Nevertheless, the organism has been found to prefer habitats within the temperate regions in area such as Florida. 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.
Selection Pressures and Adaptation
Lancelets’ defense mechanism includes the fact that the organisms are fast swimmers and they have the ability to burrow in the sand as a form of protection. The organisms also 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 through ‘asexual budding’ even though they have different sexes.
Works Cited
Garcia‐Fernàndez, Jordi, and Èlia Benito‐Gutiérrez. “It’s a Long Way from Amphioxus: Descendants of the Earliest Chordate.” Bioessays 31.6 (2009): 665-675. Print.
Heimberg, Alysha. “MicroRNAs and the Advent of Vertebrate Morphological Complexity.” Proceedings of the National Academy of Sciences 105.8 (2008): 2946-2950. Print.
Holland, Linda. “The Origin and Evolution of Chordate Nervous Systems.” Phil. Trans Soc. Biology 370.1684 (2015): 20-48. Print.
Miller, Kenneth, and Joseph Levine. Biology, Upper Saddle River, NJ: Prentice Hall, 2004. Print.
Putnam, Nicholas. “The Amphioxus Genome and the Evolution of the Chordate Karyotype.” Nature 453.7198 (2008): 1064-1071. Print.
Romer, Alfred, and Thomas Parsons. The Vertebrate Body, Philadelphia, PA: Holt-Saunders International, 2007. Print.