Although they have a velvet-like appearance just like some mites, they are apparently most closely related to a group of web-less armored arachnids that went extinct 290 million years ago. The ricinulids share just one specific character with their extinct cousins: a complex locking mechanism between the head and abdomen, that has to be unlocked during mating and egg-laying.
And yes you are correct, they have no eyes! The critters have some light-sensitive areas on the sides of their heads, but they bear no real function. They do have a pair of appendages called pedipalps, like most known spiders. The clawed palps, often folded against the underside of the body, are very sensitive and can be used to feel around and therefore navigate.
Although obscure, there is something mighty interesting going on in the evolution of the Ricinulei. Living members of the group can only be found on Western Africa and North and South America, with a largely tropical distribution. Taking this into account, It is believed that the spider-like arachnids were here during the splitting of continents. In the past, North and South America were attached to Africa — forming a supercontinent called Gondwana — which broke up around 150 million years ago. The African continent took one of the three distinct groups of Ricinulei with it, which previously shared the same habitats as groups now found in South America.
Not a lot has been done in the wonderful field of Ricinulei research, but two recent articles shed some light on the anatomy (Talarico et al, 2011) and evolutionary relationship (Fernández & Giribet, 2017) of this group. The last article highlights the current taxonomic status of this group and quotes Savory, a famous arachnologist (spider expert): “The discovery of each new specimen is still something of a zoological triumph!”
The low amount of species and limited knowledge might indicate a “forgotten” group, but knowing that studies are still being conducted on this group, we might hear more from the prehistoric ricinulids in the future.
References
Giovanni Talarico, Elisabeth Lipke and Gerd Alberti. 2011. Gross Morphology, Histology, and Ultrastructure of the Alimentary System of Ricinulei (Arachnida) With Emphasis on Functional and Phylogenetic Implications. Journal of Morphology.
Rosa Fernández and Gonzalo Giribet. 2015. Unnoticed in the tropics: phylogenomic resolution of the poorly known arachnid order Ricinulei (Arachnida). Royal
Society Open Science 2 (6): 150065.
Theodore Savory. 1964. Arachnida. Academic Press London and New York.
Image Credit:
The President and Fellows of Harvard College
Werner
de Gier
Guest Writer
