Monstrilloida Sars, 1903 ( Copepoda )     ( Classification and Phylogeny )
Syn.: Monstrilloidea genuina Sars,1921 (p.7); Sewell, 1949 (p.131)
Ref.: Sars,1901 a (1903) (p.2); Wilson, 1932 a (p.393); Rose, 1933 a (p.337); Davis, 1947 (p.390); Isaac, 1975 (n°144/145, p.2); Kabata, 1979 (p.49); Razouls, 1982 (p.746); Bowman & Abele, 1982 (p.13); Marcotte, 1982 (p.189, 193); 1986 (p.187); Gardner & Szabo, 1982 (p.81); Boxshall, 1986 (p.204); Huys & Boxshall, 1991 (p.153, 154, 405, 414, 418, 422, Rem.); Zheng Zhong & al., 1984 (1989) (p.271, Rem.); Grygier, 1994 (p.235, 240); Chihara & Murano, 1997 (p.1002); Vives & Shmeleva, 2010 (p.393, Rem.); Suarez-Morales & al., 2006 (p.105: Rem.; 2011 (PLoS ONE 6(8).
Rem.: 1 Fam: Monstrillidae Dana, 1849.

For Suarez-Morales & al. (2006, p.105), the ancestral set of characters were defined by Huys & Boxshall (1991, p.153), such as the number of A1 segments in the male (5) and female (4), uniform in the cluster. Different patterns of fusions, presumedly derived states are found in the genera. In female Cymbasoma when fusion is present, the segment fused (with weak or no signs of intersegmental division) are only the 3-4 couplet; in Monstrilla, the range is wider, there are 3-4 and 2-4 fusions. Apparently, the A1 segments (particularly 3-4) are always clearly separated in the known species of Monstrillopsis. This character is excluded from the generic diagnosis until more data are obtained.
Some other characters can be traced in terms of their primitive or derived condition:
The urosome segmentation; the reduction of 1 somite in Cymbasoma is apomorphic (character derived from, and differing from an ancestral condition) state within the cluster; Monstrillopsis and Monstrilla retain the primitive segmentation pattern of 2 postgenital somites.
In the female P5, the presence of an inner lobe armed with 2 setae is the most primitive condition in the Monstrilloida; the most derived character state is present in Cymbasoma with a reduced or absent lobe; Monstrillopsis represents an intermediate reduction, with an inner lobe reduced, but never absent. The male P5 of the most primitive genus Monstrilla is represented by a small lobe armed with 1 seta; this character is lost in both Cymbasoma and Monstrillopsis.
The ancestral set of 7 caudal setae is retained almost completely in Monstrilla (6 setae); hence, the reduction of caudal setae shown by Mobnnstrillopsis (4) and Cymbasoma (3 seerm to be important apomorphies in the Monstrilloida. Following Huys & Boxshall (1991) nomenclature of the caudal setae, differences among these genera appear to be more clear: in Monstrilla, setae VI and/or VII are present besides the set II-V. In Monstrillopsis setae VI and VII are always absent, only II-V are present. Cymbasoma shows the loss of one additional seta (V), retaining only setae II-IV. The three setae of Cymbasoma (II-IV) are, therefore, homologous to three of the four (II-IV) found in Monstrillopsis. Between the latter two genera the additional setae is simplesiomorphic (common possession of an ancestral character) to Monstrillopsis, thus likely to become a paraphyletic taxon relative to Cymbasoma when considering this character alone.
The male A1 in the Monstrilloida are always 5-segmented, with a single segment distal to the geniculation. According to Huys & Boxshall (1991) , the lack of modifications in this segment is related to most Monstrilla and Cymbasoma; it is here considered to be the plesiomorphic state. An apomorphic condition is present in Monstrillopsis, with a proxcimal hyaline process on this segment and/or a curved terminal spiniform seta, the latter homologous to elements 61-2 in Monstrilla. This character would be a synapomorphy of Monstrillopsis; the elements provided by Monstrillopsis chilensis Suarez-Morales, Bello-Smith & Palma (2006) seem justify, tentatively, the retention of Monstrillopsis as a separate genus; it is clear that the entire group should be revised emphasing the evaluation of characters.
Monstrilloidea Sars, 1921 ( cyclopimorpha )
Ref.: Sars, 1921 (p.4); Sewell, 1949 (p.127); Rose, 1933 a (p.338); Razouls, 1982 (p.747); Huys & Boxshall, 1991 (p.154, 467)
Rem.: 1 Fam: Thespesiopsyllidae. Huys & Boxshall (1991) transfer this family to the order of the Cyclopoida, which is contested by J-S. Ho (1994, p.1295). Ho, Dojiri, Hendler & Deets (2003, p.593) create the order of the Thaumatopsylloida.
Monstrillidae Dana, 1849

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Razouls C., Desreumaux N., Kouwenberg J. and de Bovée F., 2005-2021. - Biodiversity of Marine Planktonic Copepods (morphology, geographical distribution and biological data). Sorbonne University, CNRS. Available at http://copepodes.obs-banyuls.fr/en [Accessed January 19, 2021]

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