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Observe: In some rows (Order, Family), the third column reveals a discerning physical characteristic or body type (Elongate, Slender).

What are the discerning characteristics, missing from the other rows (Superfamily, Subfamily, Genus, Species)?

Basically I want this knowledge so I can work towards being able to separate, categorize (catalogue) and/or identify new or unknown species, etc.


Imagery

Exhibit A  Collembola: Entomobrya unostrigata Entomobrya unostrigata
(aka. Cotton Springtail)


Taxonomy

Domain      | Eukaryota        | (Eukaryotes)  
Kingdom     | Animalia         | (Animals)  
Phylum      | Arthropoda       | (Arthropods)  
Subphylum   | Hexapoda         | (Hexapods)  
Class       | Collembola       | (Springtails)  
Order       | Entomobryomorpha | (Elongate)  
Superfamily | Entomobryoidea   |  
Family      | Entomobryidae    | (Slender)  
Subfamily   | Entomobryinae    |
Genus       | Entomobrya       |
Species     | Unostrigata      |

Sources: Image; photographed by myself. Text; transcribed from my own hand-written notes. Most likely (originally) gleaned and adapted from publicly available, online information. It may contain errors or inaccuracies.
Resources: Check out Bugguide.net and Collembola.org.


Reprise

Okay, the question has been put on hold, preventing answers from being posted (very irritating and obstructionist policy for those seeking answers, I might add). So I will attempt to clarify.


Exhibit B  Collembola: Orchesella cincta Orchesella cincta


Exhibit C  Collembola: Willowsia nigromaculata Willowsia nigromaculata


Exhibit D  Collembola: Entomobrya multifasciata Entomobrya multifasciata


Exhibit E  Collembola: Seira bipunctata Seira bipunctata


The diversity of these specimens; span not only multiple species, but multiple genera. Yet, despite the fact that they each exhibit relatively distinctive combinations of patterns and colours across their cuticle (epidermis, surface epithelium), setae, scales, etc. they all look pretty much identical.

This seems to be the equivalent of declaring a homo sapiens of African descent; a different species to a homo sapiens of Irish descent, on account of their superficial aesthetic differences (most notably regarding melanin; the pigments that determine the colours of a human's skin, hair[s], and iride[s] (eye[s]), and so on). Which, at first seems absurd. But for those of you who disagree, observe the differences between (for instance): Exhibit X vs Exhibit B & Exhibit Y vs Exhibit E. Similar variations between individuals of the same species are not uncommon in the least.

Thus, my question: What are the discerning taxonomical differences between various species and genera of the Arthropoda known as Collembola (aka Springtails)?


Exhibit X  Collembola: Orchesella cincta Orchesella cincta


Exhibit Y  Collembola: Seira bipunctata Seira bipunctata

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closed as too broad by fileunderwater, AliceD, kmm, WYSIWYG Jan 9 '17 at 6:04

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Don't know the answer to your question, but I have had the same problem as you; feeling like there should be a set of criteria for each and every binomial systematic group (otherwise what's separating them?). Also, I sometimes find that once you get to Order, Superfamily, Subfamily, Subfamily, they groups tend to change from resource to resource making them unreliable, there doesn't seem to be any one official resource of all the known species in all of their groups. So, yes, I agree, being a bit of a perfectionist myself I find it annoying that there isn't always a criterion for every group. $\endgroup$ – Lucas Dyson-Diaz Jan 4 '17 at 12:17
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    $\begingroup$ Is the third column supposed to contain characteristic features? At the moment, this is not really the case (its a mixture of common names of taxonomic groups and physical descriptions). I also doubt that "slender" can be used by itself as a trait to separate Entomobryidae from other families. Are you looking to construct a dichotomous Identification key of springtails, or what is the exact purpose of the question? $\endgroup$ – fileunderwater Jan 4 '17 at 12:22
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    $\begingroup$ Continued; If the purpose is a determination key, you need to decide whether your key is supposed to mimic the phylogenetic situation (which your table implies), or if it supposed to be easy to arrive at a species determination. For a key that moves along with the phylogenetic tree, you will need to find good "taxonomic characters" for all taxonomic levels, that are easy to diagnose. If you are only looking for a way to determine species, there might be better ways to structure the key (even though it is in many situations preferable that keys follow the phylogeny). $\endgroup$ – fileunderwater Jan 4 '17 at 12:36
  • $\begingroup$ The third column is just for notes, including common names, etc. But if you're really getting hung up on that, you're probably missing the point of the question. $\endgroup$ – tjt263 Jan 9 '17 at 7:19
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    $\begingroup$ @LucasDyson-Diaz is on the right track. Some kind of key or matrix would be nice, for instance; a discerning characteristic of arachnidae VS insecta, might be something like 8 legs VS 6 legs, or something of that nature. $\endgroup$ – tjt263 Jan 9 '17 at 7:26
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The third column doesn't contain distinguishing characteristics at all -- they are the first word of the vernacular (or common) names for those groups on Bug Guide. Specifically, Bug Guide lists order Entomobryomorpha as Elongate-bodied Springtails, and family Entomobryidae as Slender Springtails -- so I think you're just looking at truncated data that's misleading you!

What you're looking for a taxonomic or identification key, which gives you set of yes-or-no questions that will allow you to identify an individual to a particular taxonomic group. Know Your Insect has a taxonomic key that allows you to identify insects to order Collembola, which provides exactly the sort of distinguishing characteristics you're looking for: "This illustration shows two characteristic features of members of this order: the collophore (center), a tube-like structure used to secrete fluids; and the furculum (lower left arrow)." Note that this resource refers to this group as an order, not a class -- that's not uncommon among different taxonomic resources. Wikipedia refers to this group as subclass Collembola!

Unfortunately, it doesn't look like there's a freely available taxonomic key for species within this group, unless you buy a specialized guide like A Key to the Collembola (Springtails) of Britain and Ireland.

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  • $\begingroup$ You're wrong; elongate and slender​ are discerning physical characteristics. For example: The Poduromorpha and Entomobryomorpha have an elongated body, while the Symphypleona and Neelipleona have a more rounded, globular shaped body. But yes, the taxonomic rank of Collembola has been disputed, given the more recent genetic evidence that suggests any similarities between springtails and insects are a matter of convergent evolution. $\endgroup$ – tjt263 Jan 9 '17 at 7:40
  • $\begingroup$ Sure, but they aren't very helpful characters (how slender? Elongate how?), and the first couple of values are clearly not characters at all (What sort of characters are Arthropods? Springtails?), which is why I'm pretty certain that third column is common names, not characters. I think you're looking for are apomorphies -- characters shared by individuals within a group but not found within its close relatives, like hair in mammals or hollow bones in birds. $\endgroup$ – Gaurav Jan 9 '17 at 18:24

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