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ISSN 0012-4966, Doklady Biological Sciences, 2018, Vol. 478, pp. 22–25. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © N.N. Rimskaya-Korsakova, N.P. Karaseva, E.N. Temereva, V.V. Malakhov, 2018, published in Doklady Akademii Nauk, 2018, Vol. 478, No. 4, pp. 491–494.
Protonephridial Excretory System in Vestimentifera
(Siboglinidae, Annelida)
N. N. Rimskaya-Korsakova
a,
*, N. P. Karaseva
a
, E. N. Temereva
a
,
and
Corresponding Member of the RAS
V. V. Malakhov
a,b
Received October 3, 2017
Abstract—Ultrastructural study of the excretory tree of vestimentifera Ridgeia piscesae has shown that it con-
sists of tubules that are blind at their distal ends. The tubules are lined with ciliated cells and have one or two
multiciliated terminal cell(s) at the distal ends. In the tubule walls, there are putative ultrafiltration sites. The
excretory tree tubules are interpreted as the secondary protonephridia.
DOI: 10.1134/S0012496618010064
Vestimentiferans (Annelida: Siboglinidae) are
deep-sea tube worms inhabiting reduced environ-
ments, such as hydrocarbon seepages and hydrother-
mal vents. Adult vestimentiferans have no mouth or
gut, but they have a special organ, trophosome, with
chemoautotrophic endosymbiotic bacteria living in its
cells. Vestimentiferan position in the animal kingdom
remained uncertain for a long time. They are currently
considered as a kind of sedentary annelids of the
Siboglinidae family, the group Sedentaria [1, 2].
Organization of the excretory system is an extraor-
dinary feature of vestimentiferans. It consists of the
so-called “excretory tree,” which adjoins from behind
to the brain, from where paired ducts extend to pass
into the excretory channels. The channel extensions
form excretory sacks. Excretory channels extend to the
dorsal side to terminate by the paired excretory pores
on the obturacle base. To date, the excretory tree
structure is known in detail on the basis of histological
studies. Interpretation of this structure in the pub-
lished data is rather contradictory. Van Der Land and
Nørrevang [3] believe that the excretory tree tubes
open into the narrow coelomic spaces of the connec-
tive tissue. Gardiner and Jones [4] assume that the
tubes open into the perivascular coelom. Southward
[5] noted the cells with cilia flame in Ridgeia but with-
out structural details. Malakhov et al. [6] considered
the excretory tree to be an organ consisting of blind
tubules at the distal end of which there are multicili-
ated terminal cells. They referred to the vestimentif-
eran excretory system as protonephridial type. Schulze
[7] has criticized this opinion because she believed
that protonephridia cannot be exactly identified by
electron microscopy.
The object of this study was the vestimentiferan
Ridgeia piscesae; ultrastructure of its excretory tree was
examined.
R. piscesae specimens were collected in 1986 on the
Axial Mountain of the underwater Juan de Fuca Ridge
(46°00' N, 130°04' W) at a depth of 1545 m. After fix-
ation in 3% glutaraldehyde solution in sea water and
then in 1% osmiumtetroxid in sea water, the material
was embedded in Spurr resin (Merck, Germany). Thin
sections were prepared using a Histo Jumbo diamond
knife (DiATOME, United States) on a Leica EM UC7
ultramicrotome (Leica Microsystems, Germany). The
sections were transferred into copper blend and con-
trasted with uranyl acetate and lead citrate. The mate-
rial was examined using a JEOL JEM 1011 transmis-
sion electron microscope (JEOL, Japan).
The evidence obtained by section examination
under a transmission electron microscope indicates
that the excretory tubules are the blind channels of 4–
6 μm in diameter (Figs. 1, 2a). Tubule wall is formed
by multiciliated cells with the longitudinal oval nuclei
and light cytoplasm (Figs. 1, 2b). One or two multicil-
iated terminal cells are located on the distal tubule
ends (Figs. 1, 2b). Terminal cells differ from the tubule
wall cells by the complex lobed nuclei and their cyto-
plasm is denser (Figs. 2a, 2b). Each terminal cell has
numerous cilia of typical structure. From the basal
bodies, streaked roots penetrate the cells. At the
periphery, a bundle of cilia is surrounded by the
microvillar outgrowths extending parallel to cilia
(Figs. 1, 2b).
The excretory tree tubules are covered with a thin
layer of the extracellular matrix (EM). Between the
tubules, there are narrow gaps that are hemocoel lacu-
nae filled with electronically dense contents (Fig. 2c).
GENERAL BIOLOGY
a
Moscow State University, Moscow, Russia
b
Far East Federal University, Vladivostok, Russia
*e-mail: nadezdarkorsakova@gmail.com
@Phil_Robichaud
@deepthiw
@JoseServera