1063-0740/02/2805- $27.00 © 2002
Russian Journal of Marine Biology, Vol. 28, No. 5, 2002, pp. 329–335.
Original Russian Text Copyright © 2002 by Biologiya Morya, Shukalyuk.
The life cycle of rhizocephalan barnacles comprises
two stages, a free-living larval stage and a parasitic
stage that performs the function of sexual reproduction.
The males are reduced to spermatogenic tissue that is
cultivated by the female in speciﬁc male receptacles.
The parasitic female organism consists of two parts: the
interna, a portion of the parasite located within the
hemocoel of the host (a decapod crustacean), and the
externa, a portion of the organism of the parasite
located on the surface of the host [2, 8, 9]. Inside the
organism of the host, the interna develops a system of
branching roots consisting of trophic canals and trans-
porting trunks and a reproductive system comprising
the primordia of the forthcoming externae, the nuclei.
The externa appears only in the period of sexual repro-
duction and is constructed of highly differentiated tis-
sues of the lobed ovary of paired male receptacles and
the mantle. The entire organism is covered with a cuti-
cle; the latter is thick on the surface of the externa and
thin on the surface of the interna. The complication of
the life cycle due to the parasitic mode of life in the
rhizocephalans results in the development of species
with colonial organization in several families (Pelto-
gastridae, Sacculinidae, Duplorbidae, and Thompsoni-
idae). The colonies develop as a result of asexual repro-
duction via budding of the interna and the subsequent
development of numerous externae . The possibili-
ties of asexual reproduction at the stage of interna in
have already been discussed else-
where. Thus, Takahashi and Lützen  have found
numerous nuclei in an interna and revealed, although
only on a single occasion, the connections between two
nuclei via the common root system. Later on, the inter-
connections between numerous nuclei at different
stages of development, uniting them into a solid sys-
tem, were revealed and discussed [1, 3].
The target of this project was to study the histologi-
cal organization in the interna of
ferentiation in its cell and tissue elements, and morpho-
genesis of the primordia of the externae and the host’s
tissues surrounding the interna.
MATERIALS AND METHODS
The materials were collected at the Marine Biologi-
cal Station of the Institute of Marine Biology, FED,
RAS, in Vostok Bay of the Sea of Japan during July and
August from 1997 to 1999. We examined the internae
 parasitizing coastal crabs
(De Haan). For our intravital
and histological studies, the pieces of interna were iso-
lated from the crabs bearing the externae of
For histological studies, the internae isolated from
their crab hosts were ﬁxed with Bouin ﬂuid, embedded
into parafﬁn following the standard technique, sec-
tioned, and stained with Caracci hematoxylin–eosin.
For semithin sectioning, the material was ﬁxed with
2.5% gluteraldehyde solution in seawater, postﬁxed
with 1% OsO
, and embedded into an Epon. The sec-
tions were stained with methylene blue.
Organization of Interna in
A. I. Shukalyuk
Institute of Marine Biology, Far East Division, Russian Academy of Sciences, Vladivostok, 690041 Russia
Received February 7, 2002
—We performed histological studies on trophic and reproductive systems of colonial interna in
, a parasite of the coastal crab
The trophic system that performs
functions of absorption, accumulation, and transportation of nutrients from the hemolymph of the host com-
prises the trophic epithelium of distal canals and transporting trunks. The reproductive system of interna consist
of nuclei (early stages of development of the primordia of externae) and the primordia of externae in later stages
of development. It has been shown that during morphogenesis of the nucleus two primordia arise, a primordium
of the externa itself and a primordium of its trophic system. In the primordium of the ovary, we found oogonia;
early oocytes and vitellogenic oocytes were found in the ovaries of the late primordia of the externae. The dam-
aging effects of the interna on the ovaries and testes of the crab host are discussed. Thus, we have found numer-
ous elements of reproductive and trophic systems in the colonial interna of
The term individual
is proposed to be used for the externa in rhizocephalan barnacles with its trophic system.
: rhizocephalan barnacles, interna, coloniality.