Ancient harvestman had four eyes

A study of a 305 milion year old fossil harvestman from France has revealed that this specimen had four eyes. This is rather special, because all currently living harvestmen, as well as other fossilised harvestmen that have been studied, only have two eyes. The finding is important for understanding the evolutionary development of the harvestmen and related groups, and for studying how morphological characteristics are acquired and lost during evolution.

Hastocularis_argus

3D scan of the extinct fossil harvestman Hastocularis argus. Screen shot taken from a video made by Garwood et al. 2014 (see text).

The researchers made two 3D images of the fossil harvestman Hastocularis argus using microCT-scans at the Natural History Museum in London (they placed a very nice video online in which you can see the harvestman from all sides, to see it click the link and download movie S1). Apart from one pair of eyes on the top of the head, that almost all present-day harvestmen have, this specimen also had a pair of eyes at the side of its head, just above the first pair of legs. Interestingly, modern-day harvestmen still have genes that code for these lateral eyes, but the extra eyes are lost during embryonic development.

There are not many findings of fossilised harvestmen, because their exoskeleton is relatively fragile and doesn’t preserve well. According to researcher Garwood, the fossil of H. argus is unique because was preserved in three dimensions. That enabled the researchers to examine the details of its morphology more closely than scientists have been able to do in the past. According to the researchers, H. argus is closely related to Eophalangium sheari, which is the oldest harvestman fossil ever found and believed to be one of the earliest terrestial animals.

R.J. Garwood, P.P. Sharma, J.A. Dunlop, G.Giribet (2014). A paleozoic stem group to mite harvestmen revealed through integration of phylogenetics and development. Current Biology.

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3 species in one

Mitopus morio is one of the most widespread species of harvestman in the world (see also my post about harvestmen on Iceland). Now researchers have figured out that this species is actually at least 3 different ones.

It was already known that Mitopus morio has both short- and long-legged individuals. After someone observed a short- and a long-legged individual refusing to mate with each other in the field, researchers decided to study whether these two forms were in reality different species. They collected hundreds of individuals from two areas in Austria and carried out mating trials, measured nineteen different body parts and analysed DNA from multiple areas of the genome.

Mitopus morio male

In the end, they found out that there were not two, but three different species. Interestingly, these turned out to be ‘cryptic species’: indistinguishable for the human eye. The length of the legs that the study started out with did not differ among the species, each one having both long-, intermediate- and short-legged forms. But the mating trials and genetic differences were in line with each other, pointing out the existence of three distinct groups.

Using morphology for identification appeared to be possible, but only when taking into account several morpholocgical characters at the same time. To make it even more complicated, the characters are quite difficult to measure and the sets of characters to be used are different for females and males. For females you can for example look at the length of tibia of pedipalpus, the number of medial bristles on the tarsus of the pedipalpus and the number of spines on tibia II (still hanging in there?).The combination of these three characters gives almost 100% certainty on the identity of a specimen. For males a good set of characters is the interocular distance, the length of femur of pedipalpus and the number of distal bristles on the tarsus of pedipalpus. Of course this is based on Austrian specimens only – it is unknown how many ‘Mitopus morio-species’ exist in other parts of the world, let alone how to identify them.

So, I guess that for us opiliophiles there is not much that will change, unless we take along a portable lab into the field from now on. Anyway it’s fascinating to think how many more species might exist that we just don’t recognize, don’t you think? To read the full story, take a look here. There’s a video of two specimens of Mitopus morio mating during the trials available too. The scientific publication can be found here.

W. Arthofer, H. rauch, B. Thaler-Knoflach, K. Moder, C. Muster, B.C. Schlick-Steiner, F.M. Steiner. How diverse is Mitopus morio? Integrative taxonomy detects cryptic species in a small-scale sample of a widespread harvestman. Molecular Ecology 22, p. 3850-3863.

Giant harvestman found in Laos

This month a giant harvestman has been found in a cave in Laos by Dr. Peter Jäger of the Senckenberg institute. They have not yet been able to identify it to the species level, but it probably is a member of the genus Gagrella in the Sclerosomatidae family.

Giant Harvestman Laos

(c) Senckenberg

Giant Harvestman Laos

(c) Senckenberg

While the body of this harvestman is not even 1 cm in length, the legs have a span of 33 cm. That means there is only one harvestman ever found that is larger: a species from Brazil with a span of 34 cm. (Unfortunately I can’t find out which species. Do you know? Please leave me a message!)

The interesting thing is that also other invertebrates reach giant dimensions in those caves in Laos, for example the Laotian huntsman spider Heteropoda maxima (span 30 cm), the whip scorpion Typopeltis magnificus (span 26 cm) and the predatory centipede Thereuopoda longicornis (40 cm). The reason why ‘giantism’ has developed there is still unclear. It is expected however that the invertebrates cannot become much larger than this. Either the oxygen supply would become a problem, or, in the case of harvestmen, the legs would become too long for fast movement.