SCATOLOGICAL STUDIES OF THE BIVALVIA (MOLLUSCA)
403
V. USE OF PAECAL PELLETS AS A SYSTEMATIC INDEX
It has been stated that the nature and form of many bivalve faeces
although so varied are yet so constant within the smaller taxonomic
divisions that they are a useful index for identification.
Moore (1931) adduced typical examples of this sort, using a number
of British marine molluscs, and since then much attention has been
drawn to their use in classification. Winckworth (1931) used the faecal
characters along with other criteria as a basis for the separation of
several species of the genus Nucula. Subsequently to this, Moore (1931a)
showed many illustrative examples from a variety of molluscan species.
Abbott (1954) employed successfully the faecal characters together with
other indices as a basis for removing the gastropod genus Echininus
from the family Modulidae and placing it in the Littorinidae. The more
recent work of Taylor (1966) demonstrates a difference in faecal
characters between the fresh-water gastropod families Bithyniidae and
Hydrobiidae.
On the other hand, Dinamani (1969) demonstrates that there is a
conspicuous variation in faecal characters in an animal as a result of
his recent feeding experiments on bivalves (Mytilw, Gardium), using
different algal cultures. According to his observations, the form and
type of faecal ribbon greatly vary depending upon : (1) the time ingested
material is retained within the gut; (2) the type of I ‘ food ” material
used; (3) the rate of its passage through the gut. I n the course of the
study on the seasonal change of the rate of faecal discharge in Pinctada
martensii, it was shown by Ota (1959) that during a certain period prior
to the spawning season, these pearl oysters tend to produce atypical
continuous ribbons of soft consistency and considerably flattened in
transverse section. He suggests that this characteristic change in
nature and form of the ribbons may possibly be related to certain
physiological conditions (e.g. unusual high pH value) in the animal
which take place prior to the spawning season. Moore (1931a) also
noted that in Mytilus edulis the typical pellets of well-fed animals are
ribbon-shaped and bi-crescentic in section, while the starved animals
tend to produce a thin and fragile ribbon which is often atypical in
shape.
It is apparent from Tables 111 (p. 382) and IV that the systematic
value of the faecal pellets is not always positive. While the nature and
the form of bivalve faecal pellets are variable, generally there is uniformity within a family. This familial similarity seems generally to
agree with the form of the rectum as suggested by Jegla and Greenberg
(1968). Within 45 families in which faecal pellets have been studied,
those within 20 or more are strikingly similar whereas in only some 6
403
V. USE OF PAECAL PELLETS AS A SYSTEMATIC INDEX
It has been stated that the nature and form of many bivalve faeces
although so varied are yet so constant within the smaller taxonomic
divisions that they are a useful index for identification.
Moore (1931) adduced typical examples of this sort, using a number
of British marine molluscs, and since then much attention has been
drawn to their use in classification. Winckworth (1931) used the faecal
characters along with other criteria as a basis for the separation of
several species of the genus Nucula. Subsequently to this, Moore (1931a)
showed many illustrative examples from a variety of molluscan species.
Abbott (1954) employed successfully the faecal characters together with
other indices as a basis for removing the gastropod genus Echininus
from the family Modulidae and placing it in the Littorinidae. The more
recent work of Taylor (1966) demonstrates a difference in faecal
characters between the fresh-water gastropod families Bithyniidae and
Hydrobiidae.
On the other hand, Dinamani (1969) demonstrates that there is a
conspicuous variation in faecal characters in an animal as a result of
his recent feeding experiments on bivalves (Mytilw, Gardium), using
different algal cultures. According to his observations, the form and
type of faecal ribbon greatly vary depending upon : (1) the time ingested
material is retained within the gut; (2) the type of I ‘ food ” material
used; (3) the rate of its passage through the gut. I n the course of the
study on the seasonal change of the rate of faecal discharge in Pinctada
martensii, it was shown by Ota (1959) that during a certain period prior
to the spawning season, these pearl oysters tend to produce atypical
continuous ribbons of soft consistency and considerably flattened in
transverse section. He suggests that this characteristic change in
nature and form of the ribbons may possibly be related to certain
physiological conditions (e.g. unusual high pH value) in the animal
which take place prior to the spawning season. Moore (1931a) also
noted that in Mytilus edulis the typical pellets of well-fed animals are
ribbon-shaped and bi-crescentic in section, while the starved animals
tend to produce a thin and fragile ribbon which is often atypical in
shape.
It is apparent from Tables 111 (p. 382) and IV that the systematic
value of the faecal pellets is not always positive. While the nature and
the form of bivalve faecal pellets are variable, generally there is uniformity within a family. This familial similarity seems generally to
agree with the form of the rectum as suggested by Jegla and Greenberg
(1968). Within 45 families in which faecal pellets have been studied,
those within 20 or more are strikingly similar whereas in only some 6