EPOW - Ecology Picture of the Week

Harvestmen of the Night Forests

Harvestman (cf. Megalopsalis sp.), Family Monoscutidae
North Island, New Zealand

Explanation:  It is night in the the darkened native woods of Pureora Forest Park in North Island, New Zealand.  Perched on this fern frond is a most unusual spider ... a harvestman.  But this is no typical harvestman.  This belongs to the arachnid family Monoscutidae and, more precisely, to the tongue-twisting subfamily Megalopsalidinae.  

Maybe.  Read on.

This subfamily of spiders have enormously enlarged chelicerae, which are the spider's appendages that grow from between the mouth and the eyes and are used to seize and subdue its prey -- shown above as the large leg-like extensions in the front, bent back under the body.  Chelicerae are equipped with poison-tipped claws that serve as fangs.  

Also shown above are the spider's pedipalps which appear here as tiny white legs bent backward.  Pedipalps are appendages that extend from the sides of the mouth and that are used to mash the prey.  In males, the tips of the pedipalps also contain the reproductive organs.  

Notice the prey that has been seized by this harvestman in the above photo.  It is likely a species of forest cockroach, as I also found and photographed another specimen of that species nearby, apparently unaware of the fate of its friend ... 

So how many species of this harvestman genus are there, and what is its true relationship to other spiders?  Until recently, some 11 species (or 13 species) have been described for genus Megalopsalis.  Take your pick.  Further, recent research based on morphological phylogenetics (body form as compared with spiders in other families and regions), has now merged its family Monoscutidae and subfamily Megalopsalidinae with the South American family Neopilionidae and subfamily Enantiobuninae.   

Wait, it gets worse.  The same fine study also changes these New Zealand harvestmen from genus Megalopsalis to new genus Forsteropsalis.  And seven new species of the original genus have been even more recently described.  

Confused yet?

Further along this night forest trail, my entomologist colleague Dr. Steve Pawson spies another harvestman, but this one is different, likely of genus Pantopsalis ... of the same original family and subfamily as the one above, but with classification headaches of its own ... 
  

Note again, in this harvestman of genus Pantopsalis, the large chelicerae extending vertically upward from the cephalothorax (the main body part) ... and also the small, white pedipalps extruding from the sides of the mouth. 

The genus Pantopsalis and its species have been revised from recent research.  In a most interesting finding, apparently in many species of this genus, the males can appear quite diverse, with chelicerae being long and slender in some male, and short and stout in other males.  Previously, such differences were attributed to different species, not to variations among males within species.  

What else remains to be learned of these fascinating life forms?

(This specimen:  Pantopsalis cf. listeri.)

Caught by my camera flash at night, with its immense but spindly
legs, this Pantopsalis species could easily escape detection
among the mosses and shadows of the forest floor. 

Information:
     Taylor, C.K.  2011.  Revision of the genus Megalopsalis (Arachnida: Opiliones: Phalangioidea) in Australia and New Zealand and implications for phalangioid classification.  Zootaxa 2773:1065.  
     Taylor, C.K.  2004.  New Zealand harvestmen of the subfamily Megalopsalidinae (Opliones: Monoscutidae) - the genus Pantopsalis.  Tuhinga 15:53-76.
     Taylor, C.K.  2013.  Further revision of the genus Megalopsalis (Opiliones, Neopilionidae), with the description of seven new species.  Zookeys 2013 Sep 3(328):59-117.