ISSN 10630740, Russian Journal of Marine Biology, 2010, Vol. 36, No. 1, pp. 1–15. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.V. Adrianov, A.S. Maiorova, 2010, published in Biologiya Morya.
Sipunculans are a group of marine unsegmented
coelomic worms considered as a particular phylum of
the animal kingdom, the Sipuncula. The phylum
Sipuncula comprises two classes, Phascolosomatidea
and Sipunculidea; their differences from each other
are determined by the structure of the complicated
tentacular apparatus of these animals. To date, after
several taxonomic revisions, the phylum Sipuncula
contains about 160 valid species .
The body of all sipunculans consists of two main
regions, a barrelshaped or cylindrical trunk and an
introvert capable of being withdrawn into the trunk.
The introvert consists of a spherical or cylindrical head
and an elongated neck area. The head of sipunculans
bears a terminal crown of ciliated tentacles. The latter
are used for feeding and through their walls gas
exchange takes place between the animal and the envi
ronment [1, 9, 34].
The size of sipunculans can differ significantly in
different species. If the introvert is withdrawn entirely,
the length of trunk region ranges from 2
(see ) and
to as much as 500–600 mm in
Siphonosoma ingens, Sipunculus indicus
(see ) and
entirely drew out introvert in some species can be sev
eral times longer than the trunk region.
Sipunculans are distributed worldwide and occur
throughout the depth range, from the intertidal area
down to the abyssal zone, inhabiting sometimes very
different habitats. In soft grounds they usually inhabit
the uppermost layer (several centimeters), although
large members of the genus
can easily bury
themselves into silty or sandy substrates down to 1 m
deep, making vertical burrows. Different species are
known to occur in mollusk clusters, thickets of sea
grasses, among rhizoids of macroalgae, in algal mats,
sponges, broken mollusk shells, in crevices of rocks
and stones, as well as in tubes of polychaetes and
empty shells of mollusks and large foraminiferans.
Some species can “drill” burrows in the carbonate
base of coral reefs, in rocks, the bones of dead whales
), and in
sunken timber (
) (see ).
, has been
found only in the decaying carcasses of whales .
, are dwellers of the interstitial zone and occur in
coarse sands and broken mollusk shells.
In local biotopes the density of sipunculans can
reach 700 specimens/m
in the limestone of coral reefs
and as much as 8000 specimens/m
in soft bottoms
[21, 35, 42]. Regarding their mode of feeding, the
sipunculans are detritophages or sestonophages. In
densely populated areas they represent important food
objects for bottom fish, crabs, starfish, gastropods and
cephalopods. For example, at the northern coast of
Sakhalin, in the Sea of Okhotsk, in some areas of
highly productive sandy shallows the sipunculan
(see ) provides more than 50%
of the entire biomass of benthos and represents one of
the major food item resources for grey whales foraging
in this area .
All sipunculans are dioecious animals; no sexual
dimorphism is shown. Fertilization is external. The
male and female gonads arise from coelomic epithe
lium cells as thin cords located along the bases of the
ventral retractor muscles. Maturation of gametes takes
Reproduction and Development of Common Species of Peanut
Worms (Sipuncula) from the Sea of Japan
A. V. Adrianov and A. S. Maiorova
Institute of Marine Biology, Far East Division, Russian Academy of Sciences, Vladivostok, 690041 Russia
Accepted September 15, 2009
—This study deals with the reproduction and development of the most common species of peanut
worms from the Sea of Japan:
Thysanocardia nigra, Themiste pyroides
the time of reproduction and larval settlement and the distribution of these species in Peter the Great Bay are
provided. The peculiarities of gametogenesis, spawning, and embryonic, larval, and postlarval development
are described. The reproductive biology of representatives of these species from the western and eastern
Pacific is examined in a comparative aspect.
: peanut worms, sipunculans, trochophore, pelagosphere, tentacular apparatus.