Let me be clear that this is my opinion which has arisen from looking at several publications at different levels of specificity, where for me, there is not enough detail (compared to what I'm seeing on my specimen) or very precise representations (again, my opinion).
I'm working on the description of the mouthparts of one species of Globulosis (Hydrophilidae: Acidocerinae) and today I'm feeling a little bit frustrated (probably accumulated frustration is finally escaping), and several reasons come to mind, specifically regarding publications and available information. I've checked general publications for Coleoptera, for insect morphology as well as specific publications on Hydrophilids (and relatives),
Australian Beetles (2013) by Lawrence and Slipinski do a very good job at listing thoroughly and describing general structures of the adult morphology. They include many neat images, but then, there are no labels for specific structures in some of the plates (I realize this might sound picky, but labels reduce ambiguity), and fair enough, if you are into beetle morphology you are supposed to know which sclerite corresponds to which structure, or at least you for sure know Snodgrass (1993).
Snodgrass (1993) is a more general publication in taxonomic scope, but far much detailed on the morphological treatment. It includes for example names for the areas of a mandible, details on the musculature and somehow an evolutionary perspective on what is the ancestral condition and what are some of the particular variations on some orders. It also includes very detailed and fully labeled illustrations. Extremely helpful, but then, as it includes variation among orders (and not within, which is completely fine for this kind of work), it results complicated for me to figure out what is it that I'm looking at, specifically with the whole epipharynx, cibarium, hypopharynx, also because in the specimen I'm looking at, there are several other sclerites and membranous areas that I'm not sure how to name.
There is another nice (but very general) publication on mouthparts of Coleoptera from Williams (1938), with labeled illustrations, but it only includes the maxilla and the ventral side of the labium.
So I turned to publications on Hydrophilids and relatives... for one thing, most of the descriptions and revisions only refer to what you see externally, which is kind of straightforward and it is completely fine (until you become obsessed with morphological features and variation as I think I am) . A few works, compared to the amount of descriptions/revisions out there that I have seen so far, nicely illustrate dissected mouthparts, for example Hansen (1991) for Hydrophiloidea, Anton & Beutel (2004) for Helophorus, Komarek (2004) for Anacaena, Fikáček & Vondráček (2014) for Pseudorygmodus. My problem with these has more to do with the descriptive part rather than with the illustrations (don't get too excited, I also have issues with some illustrations), as some authors are more thorough than others, and then there is no consistency among publications that allow comparison.
There is an additional attempt to describe mouthparts of an hydrophilid by Shukla & Upadhyý (1978), but I have mixed opinions on that one, so no further comments in here.
In addition, there are some very impressive works by Arens (1989, 1994) on mouthparts of aquatic invertebrates as cases of convergence.
My whole point with all this complaining is that when I look at the mouthparts of this tiny brown creature, there is so so much amazement... so many details, so much perfection and craziness at the same time, that I can't help but think why they don't even look at this structures??? they are not boring at all!! would they be too complicated for people to dissect and describe? In my experience with weevils, mouthparts might not be very informative at species level, but they certainly are at genus level and higher, so why just avoid/ignore them? is it because it takes longer to prepare, dissect and describe mouthparts than simply squeeze molecular sequences out of the specimens?
Here is the tiny and mind-blowing mentum of Globulosis in lateral view... the one I haven't finished figuring out.
There are many reasons for me to be fascinated by mouthparts, one of those is what they say "you are what you eat". Wouldn't it be awesome to learn what and how are this things eating? I would love to have the Ant-Man suit and go live on a stream or a seepage to see what this guys are up to at dinner time!
And then a sense of envy comes to me from two main sources:
- The Hymenoptera Anatomy Ontology Portal, where lucky hymenopterists have an awesome resource to reach when they get lost in morphology and terminology usage, including references and images that point exactly what they are referring to. I know that a few years ago there was (?) an initiative to build the Coleoptera Anatomy Ontology, but there is not available information on that.
- There are several works on comparative morphology of mouthparts in Staphylinidae, Chrysomelidae and Curculionidae. Even Diptera people have looked at this things!
I'm aware that I might be asking for too much detail in publications, but there are works out there, just not what I want and need to see. Perhaps (and hopefully?) it is my duty to fill in this gap on the knowledge of Hydrophilids... let's see.
References
Anton, E., & Beutel, R. G. (2004). On the head morphology and systematic position of Helophorus (Coleoptera: Hydrophiloidea: Helophoridae). Zoologischer Anzeiger-A Journal of Comparative Zoology, 242(4), 313-346.
Arens, W. (1989). Comparative functional morphology of the mouthparts of stream animals feeding on epilithic algae. Archiv für Hydrobiologie. Supplementband. Monographische Beiträge, 83(3), 253-354.
Arens, W. (1994). Striking convergence in the mouthpart evolution of stream‐living algae grazers. Journal of Zoological Systematics and Evolutionary Research, 32(4), 319-343.
Fikáček, M., & Vondráček, D. (2014). A review of Pseudorygmodus (Coleoptera: Hydrophilidae), with notes on the classification of the Anacaenini and on distribution of genera endemic to southern South America. Acta Entomologica Musei Nationalis Pragae, 54(2), 479-514.
Hansen, M. (1991). The hydrophiloid beetles. Phylogeny, classification and a revision of the genera (Coleoptera: Hydrophilidae). Biologiske Skrifter, 40, 1–367.
Komarek, A. (2004) Taxonomic revision of Anacaena Thomson, 1859 I. Afrotropical species. Koleopterologische Rundschau, 74, 303-349.
Lawrence, J., & Slipinski, A. (2013). Australian Beetles Volume 1: Morphology, Classification and Keys (Vol. 1). CSIRO PUBLISHING.
Shukla, G. S., & Upadhyý, V. B. (1978). Studies on the morphology of mouth parts of Dactylosternum hydrophilioides (Coleoptera, Hydrophilidae). Deutsche Entomologische Zeitschrift, 25(1‐3), 63-69.
Snodgrass, R. E. (1993). Principles of Insect Morphology, with a new foreword by George C. Eickwort. (Cornell University Press: Ithaca, NY.) 667 pp.
Williams, I. W. (1938). The comparative morphology of the mouthparts of the order Coleoptera treated from the stand-point of phylogeny. Journal of the New York Entomological Society, 46(3), 245-289.
