ISSN 1063-0740, Russian Journal of Marine Biology, 2007, Vol. 33, No. 3, pp. 145–160. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © E.V. Bogomolova, 2007, published in Biologiya Morya.
Pycnogonida, or sea spiders, are a relic group of
marine arthropods comprising more than 1200 species
. They are often included in the subphylum Chelicer-
ata, but sometimes are considered as an independent
branch within the phylum Arthropoda (as a class or sub-
phylum). The structure and biology of sea spiders are
still not clearly understood.
The larvae of sea spiders were ﬁrst described in the
middle of the 19th century ; to date the larvae are
known for about 70 species  and a signiﬁcant diver-
sity of postembryonic development has been revealed
[5, 7]. It also has been shown that numerous peculiari-
ties of larval morphology, including ﬁne details of the
latter, correlate with the pattern of development [2, 3].
However, these peculiarities were described in only a
few species of sea spiders.
This paper deals with the larval morphology of three
species of the genus
distributed in the north-
ern seas of Russia. The larvae of
1888 were described for the ﬁrst time. Our results pro-
vided some idea of the diversity of larval morphology
and development patterns in pycnogonids, within a sin-
gle family and a single genus, and allowed us to specify
the typiﬁcation of variants of postembryonic develop-
ment patterns in sea spiders.
MATERIALS AND METHODS
Hodge, 1863 were
collected in the second ten-day period of April 2003, at
a depth of 3 m, on Nil’menskii Rapids, at Nil’ma Vil-
lage, close to the White Sea Marine Biological Station
(WSMS) of the Moscow State University (MSU) (Kan-
dalaksha Bay). For the males of
1780, specimens with larvae were revealed in ﬁxed
samples from the collections of the WSMS MSU; the
samples were collected in August 1974 in Dvinskii Bay
and in August 1975 in Kandalaksha Bay. A male of
Sars, 1888 with larvae was captured on
June 17, 2004, in the “Bottleneck” of the White Sea
(RV “Kartesh”, 49.3 m deep).
The adult sea spiders were identiﬁed using keys pro-
vided in the book “Pantopoda of the Arctic Seas of
USSR” . The larvae of pycnogonids were sampled
from egg cocoons that are brooded by males on special-
ized ovigerous legs.
Males with cocoons were ﬁxed with 4% formalde-
hyde solution in seawater. The internal structure of the
larvae was studied on total glycerol preparations under
a light microscope. For scanning electron microscopy
(SEM) the ﬁxed larvae were rinsed in a detergent solu-
tion to remove alien particles and then dehydrated in an
ascending alcohol series (30–50–70–80–96–100%)
and acetone. After the dehydration the larvae were crit-
ical point dried, coated with gold and examined with a
Hitachi S-405A scanning electron microscope. The
measurements and schemes of the external structure of
the larvae were performed using SEM photos.
Larvae of Three Sea Spider Species of the Genus
(Arthropoda: Pycnogonida) from the White Sea
E. V. Bogomolova
Moscow State University, Moscow, 119992 Russia
Received September 21, 2006
—Larvae of three
species are described. For
Hodge, 1863 and
Sars, 1888 protonymphon larvae are examined, larvae of
have been studied for the
ﬁrst time. The ﬁne external morphology of larvae is studied in detail using SEM methods; the internal structure
protonymphon is additionally described. SEM data on external morphology and ﬁne surface
structures are given for several postembryonic stages of
Fabricius, 1780. Different types of
postembryonic development are revealed in examined
a “typical protonymphon” developmental pathway. A special developmental pathway named “lecithotrophic
protonymphon” is suggested for
and other Nymphonidae having large yolky eggs.
: Pycnogonida, Nymphon, postembryonic development, ﬁne morphology, developmental pathways,