Paecilaemula smaragdula Mello-Leitão, 1941, from Brazil. Photo copyright Tiago N. Bernabé.
Cosmetidae, with around 700 species, is the second most diverse family of the Suborder Laniatores. They are Gonyleptoidea distributed from Argentina to southern USA, most diverse in northern South America, Central America and Mexico. This Nearctic-Neotropical family comprises Opiliones with elaborate white/yellow/green/orange/red stripes and spots on the dorsal scutum and peculiar pedipalps strongly compressed and applied on the chelicerae. The family currently contains (see below) 2 subfamilies, Cosmetinae and Discosomaticinae.
Historical taxonomic backgroundEdit
From Opilionomicon (Kury 2009) 
The first described cosmetids appeared in the book by Maximilian Perty on the Brazilian arthropods collected by Spix & von Martius in the early 19th century (Perty, 1833). There we can find description of species such as Cosmetus andreae, C. bipunctatus, C. conspersus, C. lagenarius, C. pictus, C. U-flavum, C. varius and Discosoma cinctum, which mostly later became types of different genera. The first reference to the cosmetids as a group was made by Koch (1839) using the expression “Breittasterige Kanker” as well as “Cosmetides”. The family was readily accepted by subsequent authors (e.g. Simon, 1879; Karsch, 1880; Sørensen, 1884; Banks, 1893), so that it was well established by the end of 19th century. Pickard-Cambridge (1905) created the family Palpinidae, which was later rejected as being based on juvenile cosmetids, which have unusual pedipalpal morphology. Roewer (1912) did the first revision, dividing the family, by presence/absence of pectinate claws III-IV, in two unsupported subfamilies (Ringuelet, 1959). This author over the years created dozens of monotypic genera unsupported in the real world, to the point where Goodnight & Goodnight (1953a) made an extensive synonymy in the Mexican genera of Cosmetinae, leaving only three genera out of 64. Goodnight´s proposal considered the uselessness of the number of articles on tarsi II-IV and armature of dorsal scute due to intraspecific variation and distinguished the genera only by number of articles on tarsi I, the only character considered least variable within the species, which they therefore considered (by unclear reasons) to be suitable for defining genera. Although those authors had recognized and emphasized the intraspecific variation (Goodnight & Goodnight 1953a; 1953b), their proposal was mindless and, fortunately, none of subsequent researchers followed it. Other authors who contributed large numbers of species were Mello-Leitão (e.g. 1933) and Sørensen (1932). The only author more or less actively publishing on this family until recently was González-Sponga (deceased 2009), who produced a monographic work (1992), describing new species, although without giving any revisionary treatment.
- Eye mound is very low, saddle shaped, placed on middle of cephalothorax, each ocular globe bears a crest of small pointed tubercles or is smooth. Ozopores slit-like, one opening partially covered by tubercle of coxa II. Scutal areas are often indistinct; sometimes the sulci can be distinguished by color pattern or absence of tubercles; scutum and tergites are typically weakly armed.
- Genitalia. Penis are standard gonyleptoid and very conservative, with rectangular ventral plate, puffed sac-glans, well-developed thumb-like dorsal process.
See more details in Kury & Pinto-da-Rocha (2007).
The Cosmetidae are endemic of the New World. The peak of their diversity is in northern South America, Central America, and Mexico, where maybe one third to half of species of Opiliones are represented by this single family; they are numerous in Amazonian and Andean realms and also in the Caribbean. They are absent in Chile. They also reach southwards as far as Argentina and even southern Brazil (genus Metalibitia). There are a few species in the Brazilian Atlantic Forest, mostly belonging to the genus Metavononoides. A few species now in Vonones reach far northwards into the USA, were they occur in many of the southern states.
The family Cosmetidae is currently divided into 2 subfamilies, Cosmetinae with smooth claws on tarsi III–IV, and Discosomaticinae with pectinate claws on tarsi III–IV. As of 2006, there are 125 genera and 712 species described. Most species belong to Cynorta (153 spp), Paecilaema (102 spp), Flirtea and Erginulus (30 spp each). However, there is no reason to believe most of genera of cosmetids are natural groups, except for a few like Metavononoides (Kury, 2003). Attempts to organize the family in supra-specific units are hindered by the poorly resolved basic taxonomy.
Cosmetidae and its sister-group Metasarcidae compose the sister-group of the Greater Gonyleptidae (GG, that is, Cranaidae, Gonyleptidae, Manaosbiidae). All these together form the unranked group Microsetata (Kury 2014).
- ↑ Kury, AB (2009) Family Cosmetidae. In: Kury AB (Ed.), Project Opilionomicon. Museu Nacional, UFRJ, Rio de Janeiro. Online at: http://www.museunacional.ufrj.br/mndi/Aracnologia/Opilionomicon/Family%20Cosmetidae.htm
- ↑ González-Sponga, M.A. (1992) Aracnidos de Venezuela. Opiliones Laniatores II. Familia Cosmetidae. Acad. Cienc. Fisicas, Matematicas y Naturales, Caracas, 432 pp.
- ↑ Kury, A.B. & Pinto-da-Rocha, R. (2007). Cosmetidae Koch, 1839. Pp 182-185. In: Pinto-da-Rocha, R., G. Machado & G. Giribet (eds.). Harvestmen: the biology of the Opiliones. Harvard University Press, Cambridge and London. x + 597 pages.
- ↑ Kury, A.B., Villarreal-M., Osvaldo & Costa, Cristiano S. (2007) Redescription of the type species of Cynorta Koch, 1839 (Arachnida, Opiliones, Cosmetidae)The Journal of Arachnology, South El Monte, 35(2): 325–333.
- ↑ Kury, A.B. (2003). Annotated catalogue of the Laniatores of the New World (Arachnida, Opiliones). Revista Ibérica de Aracnología, vol. especial monográfico, 1: 1-337.
- ↑ Kury, A.B. (2014) Why does the Tricommatinae position bounce so much within Laniatores? A cladistic analysis, with description of a new family of Gonyleptoidea (Opiliones, Laniatores). Zoological Journal of the Linnean Society, 172, 1–48.