1063-0740/04/3004- © 2004
Russian Journal of Marine Biology, Vol. 30, No. 4, 2004, pp. 288–292.
Original Russian Text Copyright © 2004 by Biologiya Morya, Kaufman.
The early developmental stages of hydrozoans have
been studied a great deal [1, 2, 12, 14, 17, 20, 21, 23,
25, 26, 34]. Most species of these animals exhibit no
regularity of cleavage. The egg cells of different and
even of the same species cleave in different ways. Each
blastomere has its own polarity axis and cleaves inde-
pendently of the others, attaining various conﬁgura-
tions (Fig. 1). Occasionally (Tubularia), cleavage syn-
chronism is disturbed and the number of blastomeres
increases in conformity with the sequence of both even
and odd numbers . Cleavage in hydrozoans also
displays a record nondeterminancy of development.
Isolated 2-, 16-, and even 32-celled blastomeres are
able to develop into a normal planula, but of a smaller
size. Normal development of hydrozoans is not
impeded by the artiﬁcial displacement of blastomeres
[30, 38, and others]. The champions of disintegration
and chaoticness of cleavage are
, and speciﬁcally
. The interrelation of blastomeres in these
species is so weak that blastomere packing represents a
disordered mass of cells not necessarily contacting
each other (Figs. 2–4). This type of cleavage is gener-
ally deﬁned as anarchical.
Likewise, cleavage in scyphozoans [4, 18, 19, 29,
37] and coral polyps [13, 22, 24, 31, 33, 35, 39, 40] is
characterized by irregularity and chaoticness. Varia-
tions in blastomere arrangement are large, and it is
sometimes impossible to ﬁnd at least two egg cells with
a similar position of the blastomeres.
The reason for this peculiar cleavage is thought to be
the general primitiveness of the structure of cnidarians
and their antiquity. The anarchical type of cleavage is
recognized to be evolutionary original and ancestral to
all other types, thus presumably conﬁrming the idea of
On Some Features of Early Embryonic Development
Stages of Cnidaria
Z. S. Kaufman
Institute of Water Problems of the North, Karelian Science Center, Russian Academy of Sciences,
Petrozavodsk, 185003 Russia
Received December 15, 2003
—Division of the life cycle of Cnidaria (except for Anthozoa) into two independent generations, poly-
poid and medusoid, i.e., metagenesis, is considered to be unjustiﬁed. Like other Metazoa, their life cycle can
be divided into three periods: embryonic, postembryonic, and deﬁnitive, i.e., according to the age [9, 10]. An
important feature of Cnidaria is the transition of some postembryonic stages to the sedentary mode of life. As
in other animals, this change results in a substantial reduction in organismic integrity and an anarchical type of
cell division. Some researchers [3, 5, 7] regard this type of cell division as original. However, the anarchical
type of cell division itself is secondary and, for this reason, cannot be ancestral to other types. The statement
that the spiral type of cell division originated from the pseudo-spiral type also arouses serious criticism. The
spiral type is caused by a change in the structure of the blastomere ooplasm rather than the appropriate arrange-
ment of blastomeres.
Cnidaria, blastomeres, cleavage, development, hydroid polyps, scyphomedusae.
A scheme of possible cleavage patterns in
(from ). a—syncytial cleavage, b—radial cleav-
age, c—scheme of the described “pseudospiral cleavage in
cut variant,” d—anarchical cleavage, e—unequal cleavage,
f—pattern of sharply asynchronous cleavage; 2, 4, 8, 16—
—stage at which
morphological gastrulation proceeds or begins.