ISSN 1063-0740, Russian Journal of Marine Biology, 2007, Vol. 33, No. 5, pp. 338–342. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © O.M. Ivanova-Kazas, 2007, published in Biologiya Morya.
In 2006 the Russian Academy of Sciences and other
scientiﬁc institutions celebrated the centenary of the
birth of Acad. Artemii Vasil’evich Ivanov. One of his
most important contributions to zoology was investiga-
tions of the organization and development of a new ani-
mal phylum, the Pogonophora. Pogonophorans are
such peculiar animals that their systematic position was
a subject of lovely discussions for several decades.
A.V. Ivanov, whose contribution to the knowledge on
the organization and development of pogonophorans
was the most important, considered them as an inde-
pendent phylum, which in many respects is close to
Deuterostomia. However, not all zoologists shared this
point of view and many of them considered pogono-
phorans as aberrant polychaetes. After the publication
of the last paper by A.V. Ivanov dealing with this prob-
lem , the pogonophorans were studied not by mor-
phologists, but rather by taxonomists, mostly interested
in description of new species and compilation of iden-
tiﬁcation keys based on purely external characteristics.
Therefore, the afﬁnity of pogonophorans to annelids
has been widely accepted and the illusion arose that the
problem had been resolved once and for all and that
there is nothing more to discuss.
However, the afﬁnity of pogonophorans to annelids
is based on superﬁcial similarities of adult animals that
are due to their similar sedentary mode of life.
Although the followers of this theory refer to some
The Editorial Board of “Biologiya Morya” would like to express
sincere thanks to O.M. Ivanova-Kazas for kindly submitted this
paper dedicated to the jubilee of Acad. A.V. Ivanov. The paper is
published as is, without any changes.
characters of ontogenesis in pogonophorans, like the
presence of spiral cleavage, the larvae of a metatro-
chophore type, polymerism, and the primary heteron-
omy of segments, they do not show a fundamental
understanding of what is hidden beyond these charac-
ters and to what extent the latter could support their par-
ticular point of view. Let us discuss these characters in
some more detail.
Egg cleavage in pogonophorans
is strikingly dif-
ferent from the typical strictly determinate spiral cleav-
age of polychaetes (Fig. 1). However, the cleavage
undoubtedly demonstrates similarities with the spiral
cleavage that in different species is expressed to a dif-
ferent extent. To designate the blastomeres in
, it appeared possible to use the termino-
logical system worked out for the case of spiral cleav-
age . Sometimes, the characteristic of spiral cleavage
alternating dexiotropic and leotropic displacements of
blastometeres is almost not expressed in pogono-
phorans, therefore the arrangement shows a certain
resemblance to radial cleavage.
The differences in the cleavage pattern between
show that this process
varies strongly within the phylum Pogonophora,
depending on egg shape and the proportion of yolk in
the eggs. However, there is a signiﬁcant difference
between the cleavage in polychaetes and pogono-
phorans that is related to the prospective value of blas-
tomeres. In polychaetes such important primordia as
ectoblast 2d and mesoblast 4d are derivatives of the
postero-dorsal quadrant D, whereas in pogonophorans
a great role in development is played by anterior quad-
On the Problem of the Origin of Pogonophora
O. M. Ivanova-Kazas
Received May 17, 2007
—A number of embryological features of the Pogonophora suggest that they could not derive from
the Polychaeta and are closely related to Deuterostomia. These are: (1) traces of spiral cleavage that sharply
differ the from cleavage of polychaetes in the prospective value of blastomeres; (2) enterocoelic formation of
mesoderm; (3) the larva most closely resembles
that has just completed metamorphosis; proto-,
meso-, and metasoma of pogonophoran larva correspond (or are homologous) to the proboscis, collar, and trunk
respectively; while the telosoma can be regarded as an organ appearing late in phylogenesis
that serves to burrow into the bottom; (4) larvae of
have a transitory mouth located, as it is the case
in Enteropneusta, between proto- and mesosoma, very far from the posterior end, where there is closed blasto-
pore; therefore, the former can be considered as a secondary mouth; (5) the asymmetrical development of the
anterior pair of coeloms in Pogonophora, Echinodermata, and Amphioxus allows ﬁnding homologies between
organs developing from these coeloms.