The scutellum has no striae

For the describers of carabids….. 

We really need an online, cross-referenced, multilingual glossary of terms for carabids. I think that there are many cases that such a reference would help. One of these cases (a pet peeve of mine) is the term “scutellar stria” and its various forms. Scutellar stria (or striole) has been used to refer to short striae near the scutellum. Some authors use “abbreviated stria” to indicate the relative shortness of the stria.  However, all these terms are insufficiently precise and do not necessarily refer to homologous structures across all groups. I continue to see confusing use of these terms in recent papers. I hope we can discuss this and encourage a standard usage when we write and review papers. Here are my thoughts and suggestions.

 Why is this important?

It’s about homology. See the figures below (numbered 19-22) taken from a recent publication (I won’t cite the author as this is very widespread, and I don’t intend to pick on anyone particular). I have colored the homologous parts of the striae in orange (what I call the parascutellar stria) and blue (what I call the angular base of stria 1). In this paper the author refers to Fig. 19 as having the “base of the elytra without any trace of scutellar stria and pore” and Figs. 20-22 as having the “base of the elytra with well developed scutellar stria and small scutellar pore and seta” (no, the pore isn’t on the scutellum, leave that aside for now). In other papers, by other authors, I have seen the “scutellar stria” described as being “on interval 1” for a case like Fig. 20, but where the angular base of stria 1 is continuous with the rest of the stria and “on interval 2” if the parascutellar stria is continuous with the rest of the stria. Now that’s confusing. I have seen all possible combinations of presence/absence and connections (anastomosing) of these striae in carabids.  In some groups (well, pterostichines for sure) one state can be uniform across a whole clade and is likely a good synapomorphy. But it may vary and then it’s often useful for identification. But we must be sure we are talking about the same thing for either of these purposes.

What should we call these?

Obviously “scutellar stria” is inadequate as the scutellum has no striae. Use of “abbreviated” must also be abandoned as it implies the shortening of a plesiomorphic stria and there is no evidence that this ever existed. Using a single term to refer to the two different short striae is confusing.

I recommend these two terms:

The parascutellar stria (pss)= the stria that is directly adjacent to the scutellum on interval 1 and is mediad the basal setigerous puncture. It is usually, but not always, touching the basal margin of the elytron. It may or may not anastomose with stria 1. When it is joined, as is Fig. 20, it almost always (at least in pterostoichines) has a slight curve or kink where they meet, so you can tell that the pss is present. See comments below about cases when it lacks the little curve.

The angular base of stria 1 (abs1)= the portion of stria 1 that delimits the basal section of interval 1, when present. It may reach to or near the basal margin of the elytra or join stria 2. The setigerous pore may be on any one of the first three intervals (usually on 1 or 2 but on 3 in some Drimostomatini) or in stria 1 or 2. The abs1 may be continuous with apical portion of stria 1 or there may be a gap.

What if one can’t tell which of these is present because there is no kink at the join or the sculpturing obscures the striae? If you really can’t tell then just say so and define what you mean. Just don’t call it the pss if it isn’t clear that’s what it is. If you make an assumption based on the condition in related species then spell that out.

I have nothing to say about terms for these structures in languages other than English. I think I see the same problems, but don’t claim any expertise in French or German. This is why we need an online, cross-referenced, multilingual glossary of terms.

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About Kip Will

I'm an insect systematist with expertise in carabid beetles, who is always happiest in the bush.
This entry was posted in Carabids, Coleoptera, Entomology and tagged . Bookmark the permalink.

One Response to The scutellum has no striae

  1. George E. Ball says:

    Amen, Brother!

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