SCATOLOGICAL STUDIES OF THE BIVALVIA (MOLLUSCA)
407
less pellets may have evolved directly from sculptured pellets. If, as
suggested here, the primitive fecal pellet is the sculptured rod type,
there has been considerable similarity in the development of fecal pellet
types among diverse groups." He continues, " In general, the separaPelseneer (191 I)
loor Order PROTOBRANCH~A
' ""l Order FILIBRANCHIA
n
Order PSEUDOLAMELLIBRANCHIA
_ I
FT
EULAMELLIERANCHIA
0 r der SEPTIBRA NCHIA
1 2 3 4 5 6 7 8 9 1011
Pellet- types
Frequency distribution of types of pellets produced by the bivalve orders
Protobranchia, Filibranchia, Pseudolamellibranchia, Eulamellibranchia and Septibranchia (Pelseneer, 191 1).
Fig. 22.
tion of pellet constituents seems to be a primitive trait with composition being more nearly uniform in advanced forms." Arakawa (1962)
described the probable course of descent of the bivalve pellets in his
preliminary communication and suggested that the common anc2stral
407
less pellets may have evolved directly from sculptured pellets. If, as
suggested here, the primitive fecal pellet is the sculptured rod type,
there has been considerable similarity in the development of fecal pellet
types among diverse groups." He continues, " In general, the separaPelseneer (191 I)
loor Order PROTOBRANCH~A
' ""l Order FILIBRANCHIA
n
Order PSEUDOLAMELLIBRANCHIA
_ I
FT
EULAMELLIERANCHIA
0 r der SEPTIBRA NCHIA
1 2 3 4 5 6 7 8 9 1011
Pellet- types
Frequency distribution of types of pellets produced by the bivalve orders
Protobranchia, Filibranchia, Pseudolamellibranchia, Eulamellibranchia and Septibranchia (Pelseneer, 191 1).
Fig. 22.
tion of pellet constituents seems to be a primitive trait with composition being more nearly uniform in advanced forms." Arakawa (1962)
described the probable course of descent of the bivalve pellets in his
preliminary communication and suggested that the common anc2stral