SOME ASPECTS O F THE BIOLOGY O F THE CHAETOGNATHS
28 1
C. Corona ciliatu
Regarding external morphology, I shall limit myself to some further
remarks about the corona ciliata (ciliary loop). This is an organ that is
to be found on the dorsal region of the body, placed either entirely on
the head or the neck or--as it occurs in some species where it has an
elongated form-extending alm to a large part of the trunk. It has
been regarded by Ritter Zahony (1911) as a good systematic feature.
A
0
C
D
E
C
D
E
F
A
B
FIG. 4. Variations of the coronu ciliuta in Sugittu. A: normal corona ; B-I?: different shapes
of ciliary loops. Above : S. inJlata; below : S. pulchru.
It must, however, be pointed out that it is difficult to observe it in
preserved specimens which must be stained for the purpose. The form
of the ciliated ring is, moreover, far from constant.
I have studcd its variations in 8. inJEata and Sagitta pulchra
Doncaster in the Red Sea and Indian Ocean (Ghirardelli, 1947) (Fig. 4).
The ring in the former is placed entirely on the head and may be
considered as made up of two distinct parts: a forward roughly
trapezoidal part, and a roundish prolongation. The form of the prolongation may vary, as may the forward part of the corona too. This
may take in some instances an ovular shape quite similar to the ring in
S. hexaptera. Incidentally, this might be another argument in favour
of the identity between the two species, about which I wrote above, but
they differ, as we said, both in the values given by the proportion of
28 1
C. Corona ciliatu
Regarding external morphology, I shall limit myself to some further
remarks about the corona ciliata (ciliary loop). This is an organ that is
to be found on the dorsal region of the body, placed either entirely on
the head or the neck or--as it occurs in some species where it has an
elongated form-extending alm to a large part of the trunk. It has
been regarded by Ritter Zahony (1911) as a good systematic feature.
A
0
C
D
E
C
D
E
F
A
B
FIG. 4. Variations of the coronu ciliuta in Sugittu. A: normal corona ; B-I?: different shapes
of ciliary loops. Above : S. inJlata; below : S. pulchru.
It must, however, be pointed out that it is difficult to observe it in
preserved specimens which must be stained for the purpose. The form
of the ciliated ring is, moreover, far from constant.
I have studcd its variations in 8. inJEata and Sagitta pulchra
Doncaster in the Red Sea and Indian Ocean (Ghirardelli, 1947) (Fig. 4).
The ring in the former is placed entirely on the head and may be
considered as made up of two distinct parts: a forward roughly
trapezoidal part, and a roundish prolongation. The form of the prolongation may vary, as may the forward part of the corona too. This
may take in some instances an ovular shape quite similar to the ring in
S. hexaptera. Incidentally, this might be another argument in favour
of the identity between the two species, about which I wrote above, but
they differ, as we said, both in the values given by the proportion of