Field of Science

Gonyleptids are Just So Cool

I was recently sent the following photos by Gabriel Whiting asking if I was able to supply an ID:

He had photographed this animal at Itatiaia in the province of Rio de Janeiro in Brazil. The photos don't give a direct indication of its size but Gabriel told me that it was quite big (at least for a bug) and you can see a couple of other insects in the wider photo for comparison.

It's obviously a harvestman of the South American family Gonyleptidae. A photo of a similar individual in Kury & Pinto-da-Rocha (2007) led me to identify Gabriel's mystery opilionid as Acutisoma unicolor (a paper currently in press will apparently shift its genus allocation to Goniosoma). According to Kury (2003), Itatiaia happens to be the type and (so far) only recorded locality for this species and information specifically relating to this species seems to be thin on the ground.

Casting the net wider, Acutisoma unicolor belongs to the subfamily Goniosomatinae which is endemic to the Brazilian coastal region (Kury & Pinto-da-Rocha, 2007). As large, readily visible animals, goniosomatines have been subject to a reasonable amount of study, particularly in regard to reproduction. Males of at least some goniosomatines may maintain territories in which they may guard harems of up to five females. Fights over territory may be long and fierce with the main appendages used being the long filiform legs II and the powerfully armed legs IV (Machado & Macías-Ordóñez, 2007). Most goniosomatines observed to date lay their batches on eggs in gaps between rocks or on the walls of caves. The eggs are generally looked after by the females though males have been recorded watching over eggs laid in their territory whose mother has temporarily gone elsewhere (Buzatto & Machado, 2009). Newly hatched juveniles may also remain clustered around the female.


Buzatto, B., & G. Machado. 2009. Amphisexual care in Acutisoma proximum (Arachnida, Opiliones), a neotropical harvestman with exclusive maternal care. Insectes Sociaux 56 (1): 106-108.

Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachida, Opiliones). Revista Ibérica de Aracnología, special monographic volume 1: 1-337.

Kury, A. B., & R. Pinto-da-Rocha. 2007. Gonyleptidae Sundevall, 1833. In Harvestmen: The Biology of Opiliones (R. Pinto-da-Rocha, G. Machado & G. Giribet, eds) pp. 196-203. Harvard University Press: Cambridge (Massachusetts) and London.

Machado, G., & R. Macías-Ordóñez. 2007. Reproduction. In Harvestmen: The Biology of Opiliones (R. Pinto-da-Rocha, G. Machado & G. Giribet, eds) pp. 414-454. Harvard University Press: Cambridge (Massachusetts) and London.


  1. Obviously you arachnologists use the word "obviously" in exactly the same way that we mathematicians use it.

  2. For such a pretty creature, purple-wrapped,
    The unicolor epithet's inapt.

    Legs IV with coxal spines and bent-thighed might
    Mean "male" in a gonyleptid, right?

  3. It's not uncommon for colours in preserved specimens to change or bleach from live coloration - probably that's what happened with the type of this species. And yep, this individual's a male.

  4. EVIL. It is EVIL. It longs to spill the blood of babes, sir!

  5. Awesome! What a beautiful Opilione!

  6. By constitutional determination regarding the educational system, the aforementioned legislation still applies as long as it does not go against the Constitution. This ambiguity is a consequence of the absence of a new Bases and Guidelines Law and characterizes a transition phase until the new law is finally elaborated and enacted. The bill has already been submitted to congress.



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