Microbioerosion - Trace Fossils as Indicators of Sedimentary Environments - page 216

Bangiaceae genera Porphyra and Bangia . Their complex heteromorphic life
cycle includes an endolithic Conchocelis stage that has received semiichnological
treatment in the form of Paleoconchocelis by Campbell et al. (1979; described as
body fossil but including image of cast) .
Chlorophytes first appear in the Cambrian and the oldest endolithic forms
are known from the Ordovician, as recorded by the ichnospecies Ichnoreticu-
lina elegans and Cavernula pediculata ( Vogel and Brett, 2009 ) . Fossil rhodo-
phytes and particularly the endolithic genus Bangia have been reported from
strata as old as the Proterozoic ( Butterfield et al., 1990 ), whereas the ichnolo-
gical record commences in the Ordovician ( Vogel and Brett, 2009 ).
3.3 Fungi
Endolithic marine fungi are chemoheterotrophic and reproduce by vegetative
and sexual means. They biodegrade calcareous shells in order to exploit min-
eralized organic matter such as organic lamellae, conchiolin, or chitin, as well
as other endolithic organisms ( Golubic et al., 2005; Jones and Pemberton,
1987 ). As a consequence, they are not restricted to the photic zone but are found
down to abyssal depths, except for where they engage in parasitic, saprophytic,
and symbiotic relationships, which may result in an indirect light dependency
( Golubic et al., 2005 ). This is, for instance, the case where fungi and cyanobac-
teria and/or algae consort as lichens, which show a specific zonation pattern in
the inter- and supratidal zones ( Schneider, 1976 ). Euendolithic and cryptoendo-
lithic fungi are, together with chlorophytes, often found thriving in a complex
interaction within living tropical corals ( Priess et al., 2000 ). Little is known
about the mode of penetration in marine fungi. Jones and Pemberton (1987)
found organic acids such as citric acid, and Golubic et al. (2005) suggest the
presence of specific enzymes for digestion of the organic matter facilitating
penetration of shells rich in organic matrices.
At least 16 genera among the Eumycetes (higher fungi) and Phycomycetes
(lower fungi) are known to follow an endolithic mode of life ( Zeff and Perkins,
1979 ). Important genera are Dodgella , Conchyliastrum , Ostracoblabe , Litho-
pythium, and Schizochytrium . Corresponding ichnospecies are found within
the ichnogenera Saccomorpha ( Fig. 6 A-C), Polyactina ( Fig. 6 D), Orthogonum
( Fig. 6 E), and Flagrichnus ( Fig. 6 F).
The oldest marine endolithic fungi, the Chytridiomycetes, were reported
from Cambrian shell material ( M¨ ller and L¨ffler, 1992 ) and the first ichnotaxa
Orthogonum fusiferum and Saccomorpha clava are known from the Ordovician
( Vogel and Brett, 2009 ).
3.4 Other Chemotrophs
A number of further microendoliths or their traces are commonly encountered
down to aphotic depths and are thus identified as chemotrophic in nature. The
biological identity of two very common traces, Orthogonum lineare ( Fig. 7 A)