The completion percentages are 19% for insects, 14% for arachnids, and 10% for crustaceans. These match pretty closely to my own calculated values I made before this.. Myriapods were not enumerated separately in the recent blogpost, but according to my data, around 10% of known myriapod species have been recorded on inaturalist, which is about the same as for crustaceans.
There is something interesting things about this. Hexapods (insects and co.) have by far the highest species richness of the 4 major taxa, being over 80% of all arthropods, so you would think it might be harder to record them all. But in actuality, the progress on hexapod species is much more advanced than it is for all other arthropods. The completeness score for all non hexapod arthropods is around 11%. All 4 subphyla have similar problems of being difficult to impossible to identify to species level from photographs, requiring microscopic examination and/or dissection to observe things like antennal segment count, setae count, genital morphology, etc. But chelicerates, myriapods, and crustaceans all are chock full of species that are some combination of very tiny, very rare, or living in very cryptid or hard to reach places.
But here is the question of the day. Could myriapods, chelicerates, or crustaceans possibly close the gap with hexapods? Can their issues be overcome in a satisfactory manner? Which of the three groups has the highest potential to greatly exceed their current numbers?
Representatives of the 4 subphyla of arthropods I have seen. From the top left going clockwise, Selenops sp., Libellula needhami, Aratus pisonii, and Rhysida longipes
Look at both the top link on the comment, and at the three links on the bottom of the biography page. The latter lead to over a hundred papers she has written on this and similar topics
I’m working on it for the Crustaceans! (Not really, but I want to observe more Copepods, which I think are one of those phyla which are extremely poorly represented in iNat data due to them being very small, difficult to ID to species, and a decent chunk of them marine (planktonic + interstitial)).
On a more serious note, though, I doubt that that will happen any time soon while there are still so many unobserved species of insect to be observed as well. Plus: The average observer is more likely to take pictures of organisms in their back yard or their forest hike than a marine crustacean.
This is difficult.
Chelicerata (spiders, mainly) probably have a higher number of dedicated enthusiasts than the other two, but the sheer abundance of tiny mites makes “completing” the taxon difficult.
Myriapoda are afaik mostly relatively large (compared to mites and meiofaunal crustaceans), but out of all three, I’d say it is the least likely phylum to be encountered by an “opportunistic” naturalist apart from a handful of common species. Their diversity is probably also highest in areas where iNat useage is lowest.
Crustacea, apart from what I mentioned above, has a bunch of commonly observed species (land isopods, crabs found on beaches, etc.), but they are also far more diverse in habitats impossible to reach for the average naturalist (such as the deep sea benthos) than the other two. Additionally, our poor understanding of those habitats and the continual discovery of new species probably has a higher negative effect on completeness than for the other two.
All in all my guess would be Chelicerata, but that is a very uneducated guess.
Myriapoda also runs into the issue with microscopic features for most species, and on iNaturalist specifically there isn’t a lot of people to push back ID’s for wrong species.
Lithobiomorpha for example need microscopic structures to get to species for virtually everything, and yet L. forficatus has thousands of observations growing every day even wildly outside of their known range. It makes a weird feedback loop where, because it’s the only species being suggested, people assume it’s the only one in their area, and then they don’t work towards documenting species not currently on the site because they don’t realize there are more.
Soemthig also worth noting is that arachnids excluding mites has a completion score essentially the same as insects, at just over 19%. So documentary the spiders, scorpions, opiliones, vinegaroons, pseudoscorpions and such of the world is quite feasible, if daunting. It really mites dragging the whole group down.
That is good to know (though not really all that surprising).
I think, similarly to meiofaunal crustaceans, more obscure taxa such as mites have only a comparatively small portion of species described (due to morphological similarities, size, lack of prior research, etc.). I wouldn’t be that surprised if mite-biodiverity is a loooot higher than currently known. Worst case is, more new species get described than iNat-firsts added, and completeness will go down.
Something interesting worth noting is that the mite taxa with largest number of species level identifcations are ticks (ixodida) and gall mites (eriophyidae). Ticks are quite large for mites, and eriophyids have very distinctive galls, and both taxa are considered of high importance to study and identify.
