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.

Odiellus spinosus

Last week I spotted my first two harvestmen of this year, a Rilaena triangularis and a Nemastoma lugubre sitting under a piece of bark. Unfortunately I didn’t have my camera with me. But I just remembered some pictures of last year that I wanted to share, so I’ll post them instead. It’s a Odiellus spinosus female sitting on a grape plant in my garden.

Odiellus spinosus female Odiellus spinosus female Odiellus spinosus female Odiellus spinosus female Odiellus spinosus female

Male and female behaviour

In some species of harvestmen it is easy to distinguish females and males, while in other species they look more similar. But are there also differences in behaviour? One would expect some, such as that males are more involved in territorial behaviour, or that the females, who have larger bodies and need energy for the production of eggs, spend more time eating. Indeed this is confirmed by some studies.

In studies on both Neotropical harvestman Ilhaia cuspidata and the temperate species Phalangium opilio, the females spend more time feeding while the males were busier with ‘social interactions’: inspecting and attacking other males1/2. In another Neotropical species, Neosadocus maximus, females were resting more, while males spend more time exploring their surroundings, and, perhaps as a result of all that exploring, were busier cleaning themselves3.

Neosadocus maximus is an impressive-looking harvestman by the way, very different from all species that can be found in my regions. It is very large (male body length around 10 mm) and it is even reported to eat small frogs!4 Unfortunately I haven’t seen one myself; the two pictures in this post are made by João P. Burini (see his marvelous photo stream here).

Neosadocus maximus female

Neosadocus maximus female (c) Techuser / João P. Burini

There are indications that males and females also select different locations to rest during the day. In a study where a 100 m long brick wall in the Netherlands was examined on a weekly basis, the males of Opilio canestrinii on average sat higher up the wall than the females5. The author thinks that this distribution develops when males fight with each other for females during the night, thereby trying to get higher up the wall to be in a good position to attack other males from above. In this way, stronger males end up high on the wall and weaker ones on the bottom part. Females would then select the ‘higher’ males for mating, after which they leave the arena to rest on the lower parts of the wall. At dawn the males also go resting, staying at their higher positions.

Neosadocus maximus mating

Neosadocus maximus mating (c) Techuser / João P. Burini

No such micro-spatial pattern could be found however in a study with Phalangium opilioon soy bean plants: both males and females sat mainly on the bottom and middle parts of the plants, with only few visits to the top parts3. At dusk, all P. opilio became active and moved to the ground to forage and mate. Around 4 hours later, larger nymphs and females returned to the plants, while males did not return for another 3 hours, mainly spending the last hours walking.

1. Behavioral Repertory of the Neotropical Harvestman Ilhaia cuspidata (Opiliones, Gonyleptidae). W. Pereira, A. Elpino-Campos, K. Del-Claro and G. MacHado. 2004. Journal of Arachnology, 32 (1):22-30
2. Diel activity patterns and microspatial distribution of the harvestman Phalangium opilio (Opiliones, Phalangiidae) in soybeans. C.M. Allard and K.V. Yeargan. 2005. Journal of Arachnology, 33(3): 745-752.
3. Activity pattern of the Neotropical harvestman Neosadocus maximus (Opiliones, Gonyleptidae): sexual and temporal variations. F. Osses, T.M. Nazareth, G. Machado. Source: Journal of Arachnology, 36(3):518-526. 2008.
4. Harvestmen (Opiliones: Gonyleptidae) predating on treefrogs (Anura: Hylidae)
L.M. Castanho & R. Pinto da Rocha. Link to the article.
5. Hooiwagens op een Nijmeegse muur (Arachnida, Opiliones), II. H. Wijnhoven. Nieuwsbrief Spined 28: 32-35. Link to the article.

River forelands

Last weekend my husband and I set off to the IJssel river forelands to take a walk. And of course I had to look for harvestmen along the way.

IJssel river forelandI especially went looking for Astrobunus laevipes, a small harvestman (2,5 – 4 mm) with two rows of blunt spikes running over its back. It is an originally southern European species, that has been found for the first time in the Netherlands in 20031. It is expected to live along the IJssel, but the area has not been searched often so it has not (yet) been found. We turned over many small rocks, but unfortunately weren’t able to detect one.

IJssel riverThis pile of rocks however was home to a number of Phalangium opilio:

Phalangium opilio male on rockPhalangium opilio male on rockPhalangium opilio male on rockAt the end of the walk we found 3 specimens of Mitopus morio, which made me very happy as I had not seen this species before.

Mitopus morio maleOne male was carrying a parasitic mite larva on its leg:

Mitopus morio with parasitic mite larvaThe female looked a bit faded, perhaps she had to molt one more time:

Mitopus morio femaleMitopus morio femaleSo, al in all, a nice walk, harvestmen-wise and otherwise!

IJssel with wild horse1. H. Wijnhoven (2003) De hooiwagen Astrobunus laevipes nieuw voor Nederland (Opiliones: Phalangiidae). Nederlandse Faunistische Mededelingen 19: 73-78.  Link to article.

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.