SCATOLOGICAL STUDIES OF THE BlVALVIA ( iMOLLTTSCA)
405
Thus in Nuculn and ChZam,ys the number and position of the surface
sculpturing are so constant within a species that it, is easy to distinguish
between species. The best way to observe these sculpturings is to make
cross-sections (Figs. 3, 4 and 8). However, the texture of'the waste or
undigested matter in some cases, e.g. in the Mactridae and the
Mytilidae, is often so coarse that it fails to take some of the minor
striations usually impressed on the pellet surface.
Size
The size is variable depending, as it does, on the stage of growth
even in the same species (Table 11, p. 370), but in the ovoid pellets with
little specific character, such as those of the Tellinidae, the ratio of
length to breadth of the pellets may be of some value in identification of
different genera and species (Table 11).
Colour
As a rule, the colour varies depending on the food taken in by the
animal. On the effect of food on the nature of pellets of Mytilus
edulis, Dodgson states: '' The colour, being determined by that of the
suspended matter ingested, varies considerably, but is usually dark
chocolate brown, or more rarely slate. Such white faeces have been
noted almost every spring in the tanks, for a period of a few days to a
week. It has been found due to the ingestion of a certain flagellate
protophyte, . . ." But colour may at times serve as a criterion for
identification when taken in combination with other criteria.
Texture
This is fairly constant for many species because the size of food
particles sorted by the ctenidia and the labial palps is approximately
constant in any species. Internal texture is also an important criterion.
Kornicker (1962) points out that the constituents of the sediment in
sculptured faeces are segregated in different regions whereas the composition of unsculptured, shapeless and oval pellets is uniform.
The conclusion is that, though faecal characteristics in the Bivalvia
are not so significant for the identification of genera and species as suggested by some former workers, yet there is a remarkable uniformity of
pellet types within a family and this can be of great value in clarifying
the relationships and the systematic status among larger taxonomic
divisions as will be discussed in the next section.
VI. EVOLUTIONARY TRENDS OF FAECAL PELLETS
There are indications that the structure and form of faecal pellets
may be of phylogenetic significance and therefore provide evidence for
A.M.R.-S
14
405
Thus in Nuculn and ChZam,ys the number and position of the surface
sculpturing are so constant within a species that it, is easy to distinguish
between species. The best way to observe these sculpturings is to make
cross-sections (Figs. 3, 4 and 8). However, the texture of'the waste or
undigested matter in some cases, e.g. in the Mactridae and the
Mytilidae, is often so coarse that it fails to take some of the minor
striations usually impressed on the pellet surface.
Size
The size is variable depending, as it does, on the stage of growth
even in the same species (Table 11, p. 370), but in the ovoid pellets with
little specific character, such as those of the Tellinidae, the ratio of
length to breadth of the pellets may be of some value in identification of
different genera and species (Table 11).
Colour
As a rule, the colour varies depending on the food taken in by the
animal. On the effect of food on the nature of pellets of Mytilus
edulis, Dodgson states: '' The colour, being determined by that of the
suspended matter ingested, varies considerably, but is usually dark
chocolate brown, or more rarely slate. Such white faeces have been
noted almost every spring in the tanks, for a period of a few days to a
week. It has been found due to the ingestion of a certain flagellate
protophyte, . . ." But colour may at times serve as a criterion for
identification when taken in combination with other criteria.
Texture
This is fairly constant for many species because the size of food
particles sorted by the ctenidia and the labial palps is approximately
constant in any species. Internal texture is also an important criterion.
Kornicker (1962) points out that the constituents of the sediment in
sculptured faeces are segregated in different regions whereas the composition of unsculptured, shapeless and oval pellets is uniform.
The conclusion is that, though faecal characteristics in the Bivalvia
are not so significant for the identification of genera and species as suggested by some former workers, yet there is a remarkable uniformity of
pellet types within a family and this can be of great value in clarifying
the relationships and the systematic status among larger taxonomic
divisions as will be discussed in the next section.
VI. EVOLUTIONARY TRENDS OF FAECAL PELLETS
There are indications that the structure and form of faecal pellets
may be of phylogenetic significance and therefore provide evidence for
A.M.R.-S
14