Checklist of the Collembola: Some notes on the Ultrastructure of the Cuticula. Corneula

http://www.collembola.org/publicat/integum/corneula.htm Last updated on 2019.09.26 by Frans Janssens

Checklist of the Collembola: Some notes on the Ultrastructure of the Cuticula. Corneula

Frans Janssens, Department of Biology, University of Antwerp, Antwerp, B-2020, Belgium
Jean-Auguste Barra, Laboratoire de Zoologie, Université Louis Pasteur, Strasbourg, 67000, France

This page is under construction.

Differentiation of the corneular epicuticula

Barra, 1971:322-353 describes four different types of corneular ultrastructure:

corneula without a surface ultrastructure (with a smooth surface);
corneula with a surface ultrastructure of microtubercles identical but smaller to the epicutilar ultrastructure of the surrounding integument;
corneula with a surface ultrastructure of parallel ridges;
corneula with a surface ultrastructure of nipples.

Corneula with smooth surface

Fig.2a. Corneula with smooth surface of *Hypogastrura purpurescens*
After Barra, J.-A. 1971 Fig.1.B

The corneula has a smooth surface and lacks a microtubercular ultrastructure (Fig.2a after Barra, 1971:Fig.1.B; x 6000). This type of corneula is found with species of the genus Hypogastrura, more in particular with Hypogastrura tullbergi and Hypogastrura purpurescens (Barra, 1971:327).

Fig.2b. Corneula with smooth surface of *Gomphiocephalus hodgsoni*
After Meyer-Rochow, V.B. & al. 2005 Fig.9

Fig.2c. Corneula with smooth surface of *Gomphiocephalus hodgsoni*
After Meyer-Rochow, V.B. & al. 2005 Fig.6

In Gomphiocephalus hodgsoni from Antarctica, the hexagonal tesselation is completely lacking on the surface of the ocelli (Meyer-Rochow & al. 2005:Fig.9) (fig.2b & 2c) (C = cornea, Nret = retinula cell nucleus, * = rhabdom). Note that, contrary to what Meyer-Rochow & al. claims (Meyer-Rochow & al. 2005:Fig.11), a biconvex corneal lens is absent. The cornea is formed by a parallel cuticular layer (C) as in Hypogastrura.
In Pseudachorutini, an intermediate arrangement is found: the microtubercular tesselation is present only at a basal ocellar border (Barra, 1971:Fig.2.A). This intermediate arrangement is also found with Neanura muscorum (Barra, 1971:329).

In Isotoma aff. saltans, the hexagonal tesselation is also completely lacking on the surface of the ocelli (Eisenbeis & Wichard, 1985:227(Tafel 103 fig.e)).

Corneula with microtubercular ultrastructure

Fig.1. Corneula with microtubercular ultrastructure of *Tomocerus problematicus*
After Barra, J.-A. 1971 Fig.1.A

The corneula has a surface ultrastructure identical to the epicutilar ultrastructure of the surrounding integument (Fig.1 after Barra, 1971:Fig.1.A; x 6000). The size of the microtubercular tesselation on the corneula is smaller than that of the integument. This type of corneula is found with Lepidocyrtus curvicollis, Pseudosinella duodecimoculata, Tomocerus minor and Tomocerus problematicus (Barra, 1971:327).

Corneula with parallel ridges

Fig.3a. Epicuticular ultrastructure of ocellus of
*Pogonognathellus flavescens*
After Eisenbeis, G. & Wichard, W. 1985 Taf.92 Fig.b

Fig.3b. Differentiation in the epicuticular ultrastructure of the corneula of the ocellus of *Pogonognathellus flavescens*
After Eisenbeis, G. & Wichard, W. 1985 Taf.92 Fig.c

In Pogonognathellus flavescens, a differentiation of the surface structure of the ocelli is observed (Fig.o,p): at the base of the ocellus the typical microtubercular pattern is found but it does not occur at the centre of the corneula (Eisenbeis & Wichard, 1985:205(Tafel 92 fig.b & fig.c)). Note also the size gradient of the hexagons on the ocellus compared to those on the integument of the head.

Fig.3c. Corneula with parallel ridges of
Pogonognathellus longicornis
After Barra, J.-A. 1971 Fig.1.C

Fresnell effects? To be completed.

Corneula with nipples

Fig.4. Corneula with nipples of
*Dicyrtoma atra*
After Barra, J.-A. 1971 Fig.4.A

To be completed.

Corneular ultrastructure phylogeny

Fig.5. Corneular ultrastructue phylogeny
Janssens, F. © 2019.09.26

In the protoCollembola (pC), the plesiomorph condition of the ultrastructure of the cornula is the microtubercular ultrastructure of the epicuticula. In the Poduromorpha (P) the microtubercles of the corneular epicuticula reduced to a smooth surface. In the Neanuridae (P:N) partly reduced, in the rest of the Poduromorpha (P:*) completely reduced. In the Neocollembola, the corneular microtubercles evolved to nipples in the Symphypleona (S). In the Entomobryomorpha (E) the microtubercles remained mostly present (E:*). But they differentiated in Pogonognathellus into parallel ridges at the center of the ocellus (E:T:P). And in Isotomidae the microtubercles reduced to a smooth surface (E:I).