Time for some taxonomic fun and games again.
The Dipteran organisms known colloquially here in the UK via the term "Daddy Long Legs", are flies belonging to the InfraOrder Tipulomorpha. This clade contains the SuperFamilies Trichoceroidea and Tipuloidea. From the first of those SuperFamilies, we have the Family Trichoceridae, known as the Winter Gnats, and whose members share numerous anatomical features with the more commonly seen Crane Flies. However, there is one important difference - the Trichoceridae have three ocelli, or simple eyes, on the top of the head between the large compound eyes, which are absent in all the Tipuloidea. So if you see a small fly, resembling a Crane Fly, but on the wing in winter time, and with those ocelli present on the top of the head, you're dealing with a member of the Trichoceridae.
The second SuperFamily, the Tipuloidea, contains the Families Tipulidae (true Crane Flies), Cylindrotomidae (Long-Bodied Crane Flies), Limoniidae, and Pediciidae (Hairy Eyed Crane Flies). Consequently, the organisms collectively referred to as "Crane Flies" form what is known as a
paraphyletic assemblage - namely, a collection of organisms whose "family tree", or, more rigorously, cladogram, contains the common ancestor of all the members of the assemblage, but the resulting tree omits several of the descendants of that common ancestor. Trouble is, even including those missing descendants doesn't escape from the problem that the Family Limoniidae is itself paraphyletic, and taxonomists are working on solving the issues arising from this anomaly. Working out the topology of the tree structure to eliminate the anomaly is proving to be, let's call it "challenging" shall we?
These are pretty diverse organisms, with the SuperFamily Tipuloidea containing over 15,000 species worldwide. The Trichoceroidea is a much smaller assemblage, with just 160 species worldwide, and as a consequence of being little studied in the past compared to other insect groups, in need of a sustained research effort to fill in some significant gaps in knowledge.
As for the other organisms mentioned here, the Opiliones (Harvestmen) are known to comprise 6,650 species to date, with a possible final tally of 10,000 or more species being possible, once the requisite taxonomic work is complete. While this assemblage is monphyletic (the "family tree" or cladogram contains the common ancestor and
all descendants thereof), the position of the clade within the Class Arachnida still requires resolving. One interesting difference between the Opiliones and the spiders, is that the former lack venom glands associated with their chelicerae, and indeed, several other anatomical differences have led to some headaches determining the relative positions of the Opiliones and the spiders within the Arachnida.
Meanwhile, there's a third group of organisms known as "Daddy Long Legs", namely the Cellar Spiders (Family Pholcidae), just to add to the confusion.
Incidentally, the Opiliones boast an impressive fossil record compared to many other Arthropods, with exceptionally well preserved specimens dating back to 400 million years before present, being found in abundance in the Rhynie Chert geological strata in Scotland. Furthermore, a good number of these fossils are anatomically close, or even identical, to several modern lineages, which means that the basic body plan for these organisms was established very early on, and remained unchanged in some lineages for a very long time. Perhaps the canonical example of this is
Eophalangium sheari from the Rhynie Chert, dating to the early Devonian. Enjoy learning omre about that species
here.
