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by Frans Janssens
Department of Biology, University of Antwerp, Antwerp, B-2020, Belgium
Laboratoire de Zoologie, Université Louis Pasteur, Strasbourg, 67000, France
This page is under construction.
Barra, 1971:322-353 describes four different types of corneular
- 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
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).
After Barra, J.-A. 1971 Fig.1.B
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
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.
After Meyer-Rochow, V.B. & al. 2005 Fig.6
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
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).
After Barra, J.-A. 1971 Fig.1.A
Corneula with parallel ridges
Fig.3a. Epicuticular ultrastructure of ocellus of
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
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.
After Eisenbeis, G. & Wichard, W. 1985 Taf.92 Fig.c
Fig.3c. Corneula with parallel ridges of
After Barra, J.-A. 1971 Fig.1.C
Fresnell effects? To be completed.
Corneula with nipples
Fig.4. Corneula with nipples of
After Barra, J.-A. 1971 Fig.4.A
To be completed.
Corneular ultrastructure phylogeny
Fig.5. Corneular ultrastructue phylogeny
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).
Janssens, F. © 2019.09.26
To be completed.