Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladus: Spiralia
Cladus: Platyzoa
Phylum: Platyhelminthes
Subphylum: Rhabditophora
Ordo: Polycladida
Subordines (2): Acotylea – Cotylea
Genus Insertae sedis (1): †Platydendron
Name
Polycladida Lang, 1884
References
Template:Lang, 1884
Bahia, J. & Schrödl, M. 2018. Brazilian Polycladida (Rhabditophora: Platyhelminthes): Rediscovery of Marcus’ type material and general revision. Zootaxa 4490(1): 1–121. DOI: 10.11646/zootaxa.4490.1.1 Paywall Reference page.
Holleman, J.J. 2007. Some New Zealand polyclads (Platyhelminthes, Polycladida). Zootaxa 1560: 1–17. Abstract & excerpt
Holleman, J.J. 2007. Correction to "Some New Zealand polyclads (Platyhelminthes, Polycladida)". Zootaxa 1607: 68.
Links
Polycladida in the World Register of Marine Species
Vernacular names
Ελληνικά: Πολύκλαδοι
The Polycladida[1] represents a highly diverse clade of free-living marine flatworms. They are known from the littoral to the sublittoral zone (extending to the deep hot vents), and many species are common from coral reefs. Only a few species are found in freshwater habitats.
Description
Polyclads range from 3 millimetres (0.12 in) to 10 centimetres (3.9 in) in length with a flattened, roughly oval, body shape and, in many cases, a pair of short tentacles on the head. They are distinguished from other related animals by the presence of a folded pharynx, an elongated intestine with numerous complex diverticula, and multiple ocelli.[2]
The etymology of the order name Polycladida corresponds to the two ancient Greek words πολύς (polús), meaning "numerous", and κλάδος (kládos), meaning "branch".[3][4] It refers to the ramified shape of the intestine in these flatworms.[5]
Most polyclads hide away from direct light. However, some of the brightly colored species often are active during the day. With their flamboyant coloring they advertise their potential toxicity to visual predators such as fish.
Development
Some polyclads develop through a Müller's larval stage.
Ecology
Often polyclads are associated with other invertebrates, such as bivalve mollusks, sponges, corals, or ascidians. In such associations, the worms may use the invertebrates as a source of food, or they may find protection from predators inside the structural framework of these hosts.
Systematics
The order Polycladida is divided into the two suborders, Cotylea and Acotylea, based on the character "presence/absence of a cotyl or sucker". Of the two, the Acotylea is the larger group with over 26 families worldwide. Acotyleans are major predators of sessile marine invertebrates such as all commercial bivalves species (including pearl and rock oysters), mussels, scallops and giant clams. Acotyleans are dull in coloration, and cryptic in their behavior, hiding in crevices and under coral during the day.
Cotyleans, on the other hand, with as many as 16 families, are prominent members of tropical coral reef communities and have bright, colorful bodies. Although cotylean flatworms are conspicuous predators in subtropical and tropical ecosystems, they are difficult to study. These worms are very fragile and when disturbed can break apart.
Some examples of Polycladida families are as follows:
Discocelidae
Cestoplanidae
Planoceridae
Stylochidae
Ditremageniidae
Prosthiostomidae
Opisthogeniidae
Pseudocerotidae
Phylogeny
In 2017, molecular analyses produced well-supported phylogenetic hypotheses that confirmed the monophyly of Polycladida,[6][7] as well as that of Acotylea and of Cotylea.[7]
Images
References
Lang, Arnold (1884). Die Polycladen (Seeplanarien) des Golfes von Neapel und der angrenzenden Meeresabschnitte. Eine Monographie. Fauna und Flora des Golfes von Neapel und der angrenzenden Meeresabschnitte, herausgegeben von der Zoologische Station in Neapel. Leipzig: W. Engelmann. p. 688.
Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 229. ISBN 0-03-056747-5.
Bailly, Anatole (1981-01-01). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN 2010035283. OCLC 461974285.
Bailly, Anatole. "Greek-french dictionary online". www.tabularium.be. Retrieved November 25, 2018.
Bulnes, Veronica (2010-01-01), Polycladida-Marine Flatworms, pp. 356–368, ISBN 9789563322446, retrieved 2018-11-25
Bahia, Juliana; Padula, Vinicius; Schrödl, Michael (2017-05-11). "Polycladida phylogeny and evolution: integrating evidence from 28S rDNA and morphology". Organisms Diversity & Evolution. 17 (3): 653–678. doi:10.1007/s13127-017-0327-5. ISSN 1439-6092. S2CID 34263342.
Aguado, M. T.; Noreña, C.; Alcaraz, L.; Marquina, D.; Brusa, F.; Damborenea, C.; Almon, B.; Bleidorn, C.; Grande, C. (2017). "Phylogeny of Polycladida (Platyhelminthes) based on mtDNA data". Organisms Diversity & Evolution. 17 (4): 767–778. doi:10.1007/s13127-017-0344-4. ISSN 1439-6092. S2CID 26677216.
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