Catenulida

Catenulida is an order of flatworms in the classical classification, or a class of flatworms in a phylogenetic approach.[2] They are relatively small free-living flatworms, inhabiting freshwater and marine environments. There are about 100 species described worldwide, but the simple anatomy makes species distinction problematic.[2]

Catenulida
Catenula lemnae
Scientific classification
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Catenulida
Meixner, 1924[1]
Families
Synonyms

Notandropora Reisinger, 1924

Description

The anatomy of catenulids is simple and lacks hard parts. The mouth is located anteriorly and connects to a simple pharynx and a simple intestine that forms a ciliated sac. They possess two pairs of nerve cords and often a statocyst, as well as a single protonephridium.[2]

The gonads are unpaired. Unusually, the male gonopore opens on the dorsal surface of the animal, above the pharynx, while the female reproductive system lacks any of the usual ducts and related structures found in other flatworms. The sperm is nonmobile and lacks flagella or cilia.[2] Asexual reproduction by paratomy is common, and it usually leads to a chain of organisms (zooids), hence the name, from Latin catenula, small chain.[2]

Members of the symbiotic genus Paracatenula lack a digestive tract, and instead harbor intracellular chemoautotrophic bacterial symbionts that are assumed to provide their nutrition.[3][4]

Ecology

All catenulids are aquatic, benthic animals. Most of them live in freshwater, being usually very abundant in mires, ponds, streams and moist terrestrial habitats. A small number of species are known to live in the sea.[5]

The diet of most catenulids consists of small invertebrates and algae that they capture from the water column.[6] Others, such as those of the genus Paracatenula use chemoautotrophic bacterial symbionts that live inside their cells as a food source.[3]

Phylogeny

The monophyly of Catenulida is supported by molecular studies and by at least 3 synapomorphies: the unpaired protonephridium, the unpaired and anterodorsally located testis and the nonmobile sperm.[7]

Although there are no known synapomorphies connecting Catenulida to other flatworms (Rhabditophora), molecular studies indicate that they are sister-groups. All characters common to both clades, such as the internal fertilization and the simple gut with a single opening, are found in other groups as well.[2]

gollark: There is apparently work on accursed optics things for the displays, and batteries... are harder, but maybe minimising power use with more efficient hardware can be done.
gollark: Enough minor conveniences stacked together gives a useful product. And you can fit smartphone SoCs into slightly bulky glasses - there are already AR devkits doing this. The main limitation is that the displays aren't very good and it is hard to fit sufficient batteries.
gollark: Also, you could sort of gain extra senses of some possible value by mapping things like LIDAR output (AR glasses will probably have something like that for object recognition) and the local wireless environment onto the display.
gollark: Oh, and there's the obvious probably-leading-to-terrible-consequences thing of being able to conveniently see the social media profiles of anyone you meet.
gollark: Some uses: if you are going shopping in a real-world shop you could get reviews displayed on the items you look at; it could be a more convenient interface for navigation apps; you could have an instructional video open while learning to do something (which is already doable on a phone, yes, but then you have to either hold or or stand it up somewhere, which is somewhat less convenient), and with some extra design work it could interactively highlight the things you're using; you could implement a real-world adblocker if there's some way to dim/opacify/draw attention away from certain bits of the display.

References
  1. Artois, T.; Tyler, S. (2015). Catenulida. In: Tyler, S., Artois, T.; Schilling, S.; Hooge, M.; Bush, L.F. (eds) (2006-2017). World list of Platyhelminthes. Accessed through: World Register of Marine Species at on 2017-02-14
  2. Larsson, K.; Jondelius, U. (2008). "Phylogeny of the Catenulida and support for Platyhelminthes". Organisms Diversity & Evolution. 8 (5): 378–387. doi:10.1016/j.ode.2008.09.002.
  3. Leisch, N.; Dirks, U.; Gruber-Vodicka, H. R.; Schmid, M.; Sterrer, W.; Ott, J. A. (2011). "Microanatomy of the trophosome region of Paracatenula cf. polyhymnia (Catenulida, Platyhelminthes) and its intracellular symbionts". Zoomorphology. 130 (4): 261–271. doi:10.1007/s00435-011-0135-y. PMC 3213344. PMID 22131640.
  4. Gruber-Vodicka, H. R.; Dirks, U.; Leisch, N.; Baranyi, C.; Stoecker, K.; Bulgheresi, S.; Heindl, N. R.; Horn, M.; Lott, C.; Loy, A.; Wagner, M.; Ott, J. (27 June 2011). "Paracatenula, an ancient symbiosis between thiotrophic Alphaproteobacteria and catenulid flatworms". Proceedings of the National Academy of Sciences. 108 (29): 12078–12083. doi:10.1073/pnas.1105347108. PMC 3141929. PMID 21709249.
  5. Larsson, K.; Ahmadzadeh, A.; Jondelius, U. (2008). "DNA taxonomy of Swedish Catenulida (Platyhelminthes) and a phylogenetic framework for catenulid classification". Organisms Diversity & Evolution. 8 (5): 399–412. doi:10.1016/j.ode.2008.09.003. ISSN 1439-6092.
  6. Núñez-Ortiz, Alma R.; Nandini, Sarma; Nandini, S.S.S. (2016). "Demography and feeding behavior of Stenostomum leucops (Dugés, 1828)". Journal of Limnology. 75 (s1): 48–55. doi:10.4081/jlimnol.2016.1369. ISSN 1723-8633.
  7. Boll, Piter Kehoma; Rossi, Ilana; Amaral, Silvana Vargas do; Oliveira, Simone Machado de; Müller, Eliara Solange; Lemos, Virginia Silva; Leal-Zanchet, Ana Maria (2013). "Platyhelminthes ou apenas semelhantes a Platyhelminthes? Relações filogenéticas dos principais grupos de turbelários". Neotropical Biology and Conservation (in Portuguese). 8 (1). doi:10.4013/nbc.2013.81.06. ISSN 2236-3777.
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