Suture

The word suture is strongly engrained in the language we use for describing insects. Who would have thougt that we have been using it wrong for a long time. I know who, Snodgrass did! 

Back in the 60s Snodgrass talked about "sutres" in a treatise about the cephalic capsule. Then in1963 when his last contribution was published posthumously —he had written multiple essays on topics of insect anatomy with the goal to assemble an entire enyclopedia. I wish he have had the time to complete the task. But that's the thing with humans. We eventually pass away and we scientists are pretty good at leaving unfinished businesses. As Glenn Richards (who wrote the foreword of that last publication) put it: "who besides Snodgrass could write Snodgrass's Encyclopedia?"

Anyway. About the word suture Snodgrass (1960) wrote:

And he insisted in 1963:

In reality, the entire exoskeleton of insects is continuous, constituted by hardened (sclerotized) plates connected by flexible membranes (conjunctivae), and marked by points of inflection that produce those folding lines that have been traditionally called sutures. These lines were originally interpreted the same way as the sutures of the vertebrate skull, where separate bone plates meet and immovably join together. The whole nomenclatural system for insect anatomy being historically based on vertebrates causes many issues. A friend of mine who is an artist and works at the library, understood the situation completely and immediately referred to Kafka's metamorphosis. That is a good way to understand what happens. It is as if parts of Gregor Samsa's skin got hardened, with just enough flexible bits in between to allow him to move around.

Snodgrass, argued this position in 1960 and 1963. Beutel et al. (2014) in their Insect morphology and phylogeny textbook support this view (at least in the introductory morphology section of the book). The thing is that most people, at least on this side of the world, learned insect anatomy and morphology from Snodgrass himself, but from Snodgrass in 1935, when he had not yet analyzed the issue as he did when writing his encyclopedia.

And so, there I was, with the biggest chance I have had of changing tradition for accuracy. Of course, my coauthor and coeditors were not really on board. It is very difficult to change when you have used the term with that meaning for 20, 30, 40 years or more, and you feel there is no need to change that, since "everyone knows" what is meant. I climbed up on this hill, decided to hold the fort. I even consulted with my anatomy buddy, István Mikó, who is in the same boat as me for accuracy of definitions for anatomical terms. And then beetles happened.

Beetles, my friends, are such amazing creatures. Their external anatomy is so highly modified from the general structure of insects, that there are beetle structures in the same regions of the body as in other insects, in the thorax in particular, for which the nomenclature has been fairly recently modified (Beutel and Haas 2000; Friedrich et al. 2009; Lawrence et al. 2010, 2011).

In case you didn't know it yet, beetles do not have a mesosternum or a metasternum in the strict sense. Regions of these plates have extended internally to form endoskeletal elements for muscle attachment. The most famous, the metendosternite or metafurca. Crowson had two entire treatments about it (Crowson 1938, 1944), but even before I leaned about Crowson's work on this, I read Velázquez de Castro (1998), since he studied this structure for a particular group of broad-nosed weevils.

The ventral plates of the beetle mesothorax and metathorax are termed mesoventrite and metaventrite nowadays (Beutel and Haas 2000; Friedrich et al. 2009; Lawrence et al. 2010, 2011). The name of the visible badominal plates is now ventrites, as the first two true sternites are usually not externally visible.

Crazy, right? The most incredible thing, is that even if these terms were updated about 25 years ago, and a lof of people have larned and corrected their usage, many still use the traditional mesosternum, metasternum, and sternite when talking about beetle anatomy. I guess it takes an extra effort and for sure a long time for everyone to catch up.

The issue now is that beetles do have multiple parts that have actually fused or come together to be solidly fixed. For instance, the gular, notopleural, pleurosternal, and metakatepisternal, all seem to be sutures —the immovable connection between sclerites—. The "elytral suture" though, even if we have been calling it a "suture", is not it unless the elytra are actually fused together along the junction between the elytra.

I do think that the proper terminology should be adopted and used, just as people should stop using "mesosternum" for beetles. We'll see how long it takes for beetle researchers to catch up.