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DIFFERENCE BETWEEN TRACHEAL GILLS AND TERGALII
Primary tracheation of tracheal gills and secondary tracheation of tergalii.
A – abdominal segment of larva of
Protochauliodes sp. (Eumegaloptera) with left tracheal gill
6, 7, 8 – abdominal segments; br – branchia (gill); ter – tergalius; to – tracheal ostium (primary spiracle).
Pre-spiracular tracheal gill.
Paired abdominal appendage, whose trachea arises either directly from spiracular
trachea of the same abdominal segment, or from the nearest point of tracheae
branching (Fig. A). Such tracheal gills appeared independently in aquatic larvae
of various insect taxa: some Odonata (e.g. Euphaeidae), some Plecoptera (e.g. Archiperlaria),
all Meganeuroptera (Fig. A), some Coleoptera (e.g. Gyrinidae, Psephenidae), some
Birostrata (e.g. Sisyridae), many Trichoptera, some Lepidoptera, some Diptera.
In course of evolution, tracheal gill appeared as respiratory organ substituting
the primary spiracle and tracheated from the primary spiracular trachea.
Terrestrial larvae of Diptera have secondary spiracles of the same origin.
Tracheal gills are analogous, but not homologous organs, because they appeared independently in non-related taxa to serve for the same function.
Tergalius. Paired abdominal appendage of peculiar structure, known only in larvae of Ephemeroptera. Tergalii have constant place of attachment on posterior-lateral corner of abdominal tergum, always moved by the special tergalial muscles having constant position in abdomen, have homologous morphological features and the same developmental features (Kluge 2004). In contrast to tracheal gills, tracheation of tergalii is secondary: tergalial trachea arises not from the spiracular trachea, but from the longitudinal tracheal trunk; point on the trunk, from which tergalial trachea arises, belongs not to the abdominal segment bearing this tergalius, but to the next abdominal segment (Fig. B) (Landa 1949). Tergalii of various pairs in various mayfly taxa have various functions or are non-functional; sometimes they serve for respiration, and in this case could be called "tracheal gills" (if use the term "tracheal gill" for other respiratory appendages of known origin, e.g. maxillary palps of Arthroplea). Probably, abdominal tergalii of mayfly larvae are serial homologs of meso- and metathoracic wings and are inherited by Ephemeroptera from the common ancestor of Pterygota (Kluge 1989).
Tergalii are homologous, but not analogous organs, because they have the same origin and different functions.
[Kluge N.J.] Клюге Н.Ю. 1989. Вопрос о гомологии трахейных жабр и паранотальных выростов личинок поденок и крыльев насекомых в связи с систематикой и филогенией отряда поденок (Ephemeroptera) [The problem of the homology of the tracheal gills and paranotal processi of the mayfly larvae and wings of the insects with reference to the taxonomy and phylogeny of the order Ephemeroptera]. // Чтения памяти Холодковского: доклады на 41-м ежегодном чтении памяти Н.А. Холодковского 1 апреля 1988 г., Ленинград, "Наука". ["Chteniya pamyati N.A. Kholodkovskogo", Leningrad, "Nauka"] 41: 48–77.
Kluge N. 2004. The phylogenetic system of Ephemeroptera. // Kluwer Academic Publishers. p. i-xiii + 1-442
Landa V. 1949. Svlékáni tracheálního systému larev a nymf jepic. [Moulting of the tracheal system of ephemerids larvae and nymphs.] // Casopis Ceské spolecnosti Entomologické (= Acta Societatis Entomologicae Cechosloveniae) 46(1–2): 1–10.