Freshwater bryozoans of Lithuania (Bryozoa)
Freshwater bryozoans of Lithuania (Bryozoa)
Ingrida Šatkauskienė 0
Jurgita Rutkauskaitė-Sucilienė 0
Vida Mildažienė 0
0 Vytautas Magnus University, Faculty of Natural Sciences, Department of Biology , Vileikos str. 8-802, 44404 Kaunas , Lithuania 2 Wright State University, Department of Biological Sciences , Dayton, OH 45435 , USA 3 Lithuanian Energy Institute , 3 Breslaujos str., LT-44403, Kaunas , Lithuania
Nine species of freshwater bryozoans were recorded in Lithuania in a survey of 18 various types of freshwater bodies. Eight species were assigned to the Class Phylactolaemata and families Plumatellidae and Cristatellidae (Plumatella repens, Plumatella fungosa, Plumatella fruticosa, Plumatella casmiana, Plumatella emarginata, Plumatella geimermassardi, Hyalinella punctata and Cristatella mucedo). The ninth species, Paludicella articulata, represented the Class Gymnolaemata. Plumatella geimermassardi and P. casmiana were recorded for the first time in Lithuania. For the plumatellids, species identification was achieved partly by analysing statoblasts' morphological ultrastructures by scanning electron microscopy.
eol>Phylactolaemata; Plumatella; statoblasts; bryozoa; Lithuania
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Freshwater bryozoans grow in colonies of minute tentacle-bearing clones (zooids) that
feed upon microscopic plankton. They are often found in ponds, lakes, and rivers,
forming a cryptic but often a significant part of the aquatic fauna
Bryozoans are important to ecosystems as filter feeders
(Wood et al. 2006)
phytoplankton from the water and producing faecal pellets that nourish benthic
meiCopyright Ingrida Šatkauskiene˙ et al. This is an open access article distributed under the terms of the Creative Commons Attribution License
(CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
(Bushnell and Rao 1974)
. The colony structure also creates important habitat
and shelter for other organisms: protozoans, rotifers, ostracods, nematodes and
(Ricciardi and Reiswig 1994)
. Bryozoans hosting certain myxozoan parasites
can spread proliferative kidney disease in fish, which is often fatal in farmed and wild
fish populations (
Grabner and El-Matbouli 2008
Bartošová-Sojková et al. 2014
In their natural habitat freshwater bryozoans are easily overlooked and, in many
areas, there is little information on the identity or distribution of species.
Fundamental studies of freshwater bryozoans in Europe were launched with a
pioneering monograph by
, which established the Class Phylactolaemata as
an exclusively freshwater group and named Plumatellidae as the largest family within
that class. A second monograph by
described species from France
following Allman’s taxonomy. Shortly afterwards a third monograph appeared from
proposing a new taxonomic scheme for the plumatellids which
has by now fallen out of use. Since those early years there have been bryozoan surveys
from a number of European countries, including the Netherlands
, Italy (
(Geimer and Massard 1986)
. In most of these works only 5–8 species were documented.
Until recently freshwater bryozoans in the Baltic region were known only from a
brief paper from Latvia
. Six species were listed using the Kraepelin
taxonomic scheme. They included Plumatella polymorpha Krpln. var. repens (L.), Krpln.,
Plumatella polymorpha Krpln. var. appressa Krpln., Plumatella polymorpha Krpln. var.
fungosa (Pall.) Krpln., Plumatella princeps Krpln. var. emarginata Allm., Cristatella
mucedo Cuv., and Paludicella ehrenbergi Bened.
provided measurements of
certain colonies and statoblasts and included some ecological information as well.
In 2015 an old master’s thesis was uncovered in Lithuania with a detailed account of
bryozoans from the area
(Satkauskiene et al. 2018)
. Written by Bronė
work covered a period of 1931–1933. Pajiedaitė collected bryozoans from widely scattered
locations in Lithuania (five districts and approximately eleven localities) including lakes,
ponds, and rivers. From microscopic examinations, she illustrated colonies and statoblasts,
prepared notes on associations with other organisms, and described substrata on which
common bryozoans were found. During her studies, Bronė Pajiedaitė prepared at least 12
bottles of fixed whole specimens and 70 high quality microscope slides
(Satkauskiene et al.
. Unfortunately, the whole specimens were apparently destroyed during World War
II (1941–1945), but the surviving microscopic slides are now deposited in Vilnius
University. Altogether Pajiedaitė described seven species of freshwater bryozoans in detail:
, Cristatella mucedo
, Plumatella fungosa
, Plumatella repens
, Plumatella emarginata
, and Hyalinella punctata
In recent years the number of freshwater bryozoans documented from Europe has
grown to 19
(Massard and Geimer 2005, 2008a; Wood and Okamura 2004)
Meanwhile from seven to eleven freshwater bryozoan species have been reported in countries
neighbouring Lithuania: Latvia, Poland, and Belarus
(Kaminski 1984, Fauna
. Based on the species diversity in other European countries, we can expect a
more diverse list of bryozoans in Lithuania as well.
The present work describes freshwater bryozoans studied in 18 freshwater bodies
Materials and methods
Climate of Lithuania
Lithuania is distinguished by a highly diverse geography: plains, hills, abundant
forests, lakes, wetlands, and Baltic Sea. The climate of the Lithuania can be described
as typical European with strong continental influence providing warm summers and
fairly severe winters. The weather is often windy and humid due to the proximity of
the Baltic Sea.
The average air temperature is 7.2 °C. July is the warmest month with an
average temperature of 18 °C. January and February are the coldest months with average
temperatures around -3.35 °C, but sometimes winter days can be much colder with
temperatures about -32.4 °C. Annual precipitation ranges from 560 to 700 mm. Snow
cover can last from 60 to 90 days. The flat landscape retains much of the precipitation,
which leads to a relatively high water level (Lithuanian Hydrometeorological Service
under the Ministry of Environment).
Characteristic of sampling sites
Our bryozoan survey was conducted during April through October 2015–2017. We
investigated localities that included different types of water bodies: lakes, ponds,
lagoons and lotic habitats (streams and rivers). Figure 1 shows regions in Lithuania that
were surveyed. Geographical details and descriptions of collecting sites are listed below
and summarized in Table 1.
Pond in Kaunas botanical garden (located in Kaunas city). Small eutrophic pond
with abundant macro- and microalgae. The bottom is sludge. Water pH is 7.89.
Linksmakalnis pond (Kaunas district). Large artificial pond, what shorelines are
overgrown by Phragmites sp. The bottom is sandy. Water pH is 7.18.
Raudondvaris, Rokai and Tribalė ponds. All these ponds located in Kaunas district
and have similar characteristics: the bottom is sand mixed with sludge, the littoral is
overgrown by Acorus calamus and Phragmites sp. in Raudondvaris and Tribalė ponds.
Vegetation on the shores of Rokai pond are rare, water birds are common here.
Water pH varies from 7.51–7.85 (Rokai and Tribalė ponds respectively) to pH 8.35
in Raudondvaris pond.
Lampėdžiai lake (located in Kaunas city). Relative large (1,252 km²), semi-artificial
lake. The bottom is sandy. Shorelines are without the trees, only Phragmites sp.
occurs occasionally in the littoral. Water pH is 8.06.
Maišia stream (located in the outskirts of Kaunas). One side of shore is overgrown by
deciduous trees, Phragmites sp. and Typha angustipholia. Water is polluted by
sewage. Water pH is 7.48.
Veršvio stream (located in western part of Kaunas city). Small and shallow stream,
that dries up in the summer. Shore is lined by trees and shrubs. Bottom is sandy.
Water pH is 7.79.
Šventupė pond (Ukmergė district). The shoreline is overgrown by shrubs and other
vegetation. Phragmites sp., Acorus calamus, Lemna minor dominates in littoral. A
small stream enters in one end of pond. Another end of the pond is connected with
Šventoji River. Water pH 7.40.
Mūša pond (Ukmergė district). Mūšia stream enters in this artificial pond. Phragmites
sp., Acorus calamus and Nymphaea lutea occur in the littoral. Water pH is 7.81.
Plateliai Lake (Plungė district) is the large lake covering about 12 km² with a
maximum depth of 47 m. Water is contributed by seventeen small streams. The Bottom
is sandy in the collecting sites.
Skyplaičiai Lake (Plungė district) covers 0.068 km² and is surrounded by a mixed
deciduous forest. The bottom is muddy; shorelines are overgrown by Phragmites sp.
According to the EU Habitats Directive, this lake is notable for its Charophyta communities.
Škilietai Lake (Trakai district) covers about 0.033 km² with maximum depth of 12 m.
The lake is surrounded by pine forest.
Elektrėnai Reservoir (Vilnius district and Trakai district) is the third largest artificial
lake in Lithuania. The reservoir measures about 0.0126 km². The lake is fed by
inflows from the Strėva River, and nine other rivulets.
Strėva River (Trakai and Kaunas district). Average current velocity is 0.1–0.3 m/s. The
bottom is sandy mixed with silt. Phragmites sp. and Nymphaea lutea grow at the
edges of the river. Water pH was 7.80 in the sampling site.
Saterečius Pond (Utena district). The pond is surrounded by marsh and mixed
deciduous forest dominated by Alnus sp. In summer the pond is almost overgrown
with macro-algae and such macrophytes as Nymphaea lutea and Stratiotes aloides.
Water pH is 6.78.
Žvirgždelis Lake (Utena district) covers an area of 0.027 km²; the bottom is silt and
Phragmites sp. dominates in littoral. Water pH is 7.03.
Snaigynas Lake (Lazdijai district). The lake covers an area of 2 km², with an average depth
of 3 m. The shores are low and overgrown by shrubs and trees. The lake bottom is
sandy in littoral. A small shallow stream flows out from this lake into Trikojis Lake.
Sampling and observations
Statoblasts were taken by net from the surface of water and aquatic plants. Bryozoan
colonies were collected from submerged branches, stones, and aquatic plants in the
littoral of the water bodies. Statoblasts and bryozoan colonies were stored in 70% ethanol.
Identification of most species was based on morphology of statoblasts and colony
(when colonies were available) using light and scanning electron microscopy (SEM)
Statoblasts characters included overall length and width, length and width of the
fenestrae, and surface micro-sculpture of statoblasts. Abbreviations used for
measurements are as follows:
ratio of the statoblast,
ventral fenestra length;
ventral fenestra width;
dorsal fenestra length;
dorsal fenestra width.
Measurements were taken from SEM images with software Original Hitachi
S3400N Scanning Electron Microscope software ver 7.3.
Statoblasts were rinsed with distilled water several times then treated by KOH in
order to remove any debris and cleaned using vortex for a few minutes. Statoblasts were
prepared for scanning electron microscopy by simple drying without sputtering. The
identification keys by
Wood and Okamura (2005)
The authors collected specimens during April through October 2015–2017. In total,
53 statoblasts and 8 colonies collected from 18 localities in Lithuania were examined.
In addition, some data collected by Bronė Pajiedaitė (1932-1934) were included in
this study for comparison. The representative specimens are deposited in the zoological
collection of Biology Department of Vytautas Magnus University.
The survey of 18 water bodies yielded nine species of freshwater bryozoans (Table 1).
Eight of these are classified with the Class Phylactolaemata: Cristatella mucedo,
Hyalinella punctata, Plumatella casmiana
, Plumatella fungosa, Plumatella
fruticosa, Plumatella geimermassardi Wood & Okamura, 2004 Plumatella repens,
and Plumatella emarginata. The ninth species, Paludicella articulata, belongs to the
Class Phylactolaemata Allman, 1856
Order Plumatellida Allman, 1856
Family Plumatellidae Allman, 1856
Plumatella repens (Linnaeus, 1758)
Material examined. Ten floatoblasts collected from ponds of Kaunas Botanical
garden, Raudondvaris pond in April 2015, and Skyplaičiai lake, collected in June 2015;
colonies collected from Raudondvaris and Rokai pond in June 2015 and July 2016
respectively. Sessoblasts were not found.
Description. Colonies were about 5–8 cm size. The transparent branches of
colonies were attached to the substratum for almost whole of their length. Floatoblasts
were identified by the broadly oval shape and the absence of tubercles on the statoblast
annulus (Fig. 2). Floatoblasts were 315–341 (325±3) μm long by 226–270 (252±4)
μm wide; L/W ratio was 1.3; VfL 144–245 (187±14) μm; VfW 126–212 (168±10)
μm(n=10); DfL 135–258 (178±14) μm; DfW126–212 (163± 9) μm (n=10). Fenestra
of floatoblasts circular, covered with rounded tubercles that become less prominent
towards the centre of fenestra. The annular nodules often described for this species have
not yet been observed in Lithuanian material.
Distribution in Europe. According to Økland and Økland (2005),
, P. repens is common in Britain, Ireland and Europe.
described P. repens as most common species in the studied lakes in Poland.
Remarks on habitat and ecology in Lithuania. Plumatella repens has been the
most commonly encountered species, with floatoblasts occurring in all surveyed sites,
include lentic and stagnant habitats. Although colonies were found in only two ponds
from listed sites, we have since become aware of colonies occurring in other lakes and
ponds not listed here.
described P. repens as most common species in Lithuania, which
can grow in various freshwater bodies. On the other hand, the exact locations of her
collecting sites were not listed in her thesis. In addition, because of early difficulty in
identifying this species, distribution reports prior to the mid-1980s are not necessarily
(Wood and Okamura 2005)
postulated close relationship between Plumatella
repens and P. fungosa based on a “short oval statoblasts” and molecular studies
confirmed a close relationship between these species
(Hirose et al. 2011)
repens can be confused with young colonies of P. fungosa (Wood and Okamura 2005).
In addition, statoblasts of P. repens are similar to those of its congeners P. nitens
Wood, 1996, P. nodulosa
, P. orbisperma
, P. recluse
, and P. rugosa
Wood, Wood, Geimer & Massard, 1998
Plumatella geimermassardi Wood & Okamura, 2004
Material examined. A few floatoblasts from Lampėdžiai Lake in April 2016. P.
geimermassardi were recorded in Lithuania for the first time. However, the species is so far
represented only by statoblasts.
Description. Floatoblasts were identified by the large dorsal fenestra with
tubercles and narrow annulus. The annulus at the poles is mostly as large as laterally
and is covered by weakly visible tubercles (Fig. 3). Length and width of floatoblast
were 311–325 (317±4) μm and 221–273 (244±15) μm (n=3) respectively. L/W ratio
1.3; DfL 199–205 (202±3) μm; DfW 174–201 (187±13) μm (n=3); VfL 200–254
(227±26) μm and VfW 185–198 (192±6) μm (n=3).
Distribution in Europe. Plumatella geimermassardi is known from England,
Ireland, Belgium, southern Norway, northern Germany, Italy and Finland
Remarks. Floatoblasts of P. geimermassardi are among the smallest floatoblasts
among all European plumatellids with an average length of around 320 μm
and Okamura 2004)
. The uniformly narrow annulus offers an easy identifying feature
characteristic for broad floatoblasts in this species. The relatively large area of dorsal
and ventral fenestrae is matched only by those of P. nitens or Stephanella hina on other
(Wood 1996; Toriumi 1955)
Plumatella fungosa (Pallas, 1768)
Material examined. A floatoblasts collected from Linksmakalnis pond (June 2015)
and Maišia stream (April 2015). Colony from Aristava pond (locates in Kėdainiai
district 55°17'07.1"N, 24°04'28.6"E and it is not included in general list of studied sites
during this survey) was taken in June 2017 (Fig. 4).
Description. The colony dark, spindle shaped, and large (15–17 cm), formed on
stems of reeds (Phragmites). Examined floatoblasts exhibited characteristic tubercles on
the floatoblast annulus (Fig. 4) and a ridge-like suture between the dorsal and ventral
valves. Dorsal floatoblast tubercles were larger on the fenestra than on the annulus. The
length of floatoblasts was 324–368 (339±5) μm; width 220–290 (254±8) μm (n=8),
L/W ratio 1.3; DfL 130–160 (147±4) μm (n=6); DfW 125–161 (144±5) μm (n=6);
VfL 214–250 (227±4) μm and VfW 205–228 (214±2) μm (n=6). However, dimen
sions of P. fungosa floatoblasts provided by
, were slightly larger: 470
μm × 290 μm. Pajiedaitė also recorded the variability in sessoblast dimensions from
different localities: 790 μm × 470 μm in Nevėžis river (Kaunas district); 480 μm × 370
μm in Lake Aukštadvaris (Trakai district), and 580 μm × 420 μm in Snaigynas Lake
(Lazdijai district) (Pajiedaite 1933). During current study sessoblasts were not found.
Distribution in Europe. According to
Wood and Okamura (2005)
P. fungosa is
widespread in Europe. It has been recorded from several places in southern Sweden and
Finland; it is common in Denmark and has been reported from Iceland (Økland and
Økland 2005) and Poland
Remarks on habitat and ecology in Lithuania. During this survey, floatoblasts of
P. fungosa were found in seven water bodies from 18 surveyed, with prevalence in
stagnant water, with neutral to slightly alkaline pH 7.01–8.15 (Table 1).
described the colonies in Kaunas Lagoon, Nevėžis River (Kaunas district) and Dubysa
River (Šiauliai district). She noted that P. fungosa often occurred in polluted water and
described colonies, found in old port of Kaunas city, where water was polluted by oil of
ships and trash. A similar observation has been made by other authors
Geimer and Massard 1986)
. Based on the available data, we consider P. fungosa to be
prevalent in Lithuania.
Remarks. Large bulky colonies of P. fungosa are easily recognizable freshwater bryozoan
species in Europe
(Wood and Okamura 2004)
. Floatoblasts of P. fungosa are
lateralyasymmetrical and distinctfrom the symmetrical floatoblasts of P. repens and P. rugosa. Molecular
studies showed a close relationship between P. repens and P. fungosa
(Hirose et al. 2011)
Plumatella emarginata (Allman, 1844)
Material examined. A few floatoblasts from Šventupė pond were collected in July 2016.
Description. Floatoblasts elongated in shape, with a circular ventral fenestra and
small dorsal fenestra, covered by tubercles. Floatoblasts were 357–489 (407±18) μm
long and 197–235 (216±6) μm (n=6) wide, L/W ratio 1.9; DfL 97–125 (107±9)
μm; DfW 60–82 (68±7) μm (n=3); VfL 101–184 (149±9) μm and VfW 110–162
(133±4) μm (n=6). The approximate size of statoblasts provided by Pajiedaite (1933)
was 560 μm long and 260 μm wide.
Distribution in Europe.
Geimer and Massard (1986)
defined the range of this
species to include most of Europe. Økland and Økland (2005) considered P.
emarginata to be a southern species, with limited distribution in Norway and Sweden.
Remarks on habitat and ecology in Lithuania. Pajiedaitė (1933) described
morphology of P. emarginata colonies, but her text is not clear about the location of
collection sites. However, the statoblasts she found were recorded from Paštys Lake
(55°42'36"N, 25°41'48"E), Satarečius pond and Dubysa River (Kaunas district,
In our survey only a few statoblasts were found in Šventupės pond (Table 1).
Wood and Okamura (2005)
noted that P. emarginata is particularly tolerant of
rapidlyflowing water. The occurrence of floatoblasts in the Neries River (Kaunas district - not
included in this study) is consistent with this observation, although colonies were not
found. From our data P. emarginata would be considered uncommon in Lithuania,
although this should be verified through further surveys.
Remarks. The species is widely distributed throughout the Holarctic
, although some reports may have confused it with similar species,
P. mukaii or P. reticulata
(Massard and Geimer 2008a)
Plumatella casmiana (Oka, 1908)
Fig. 6A, B
Material examined. Floatoblasts, leptoblasts, and colony from Linksmakalnis pond
collected from submerged branches in 20 July 2016.
Description. Colony was about 5–6 cm long. Branches of colony are short, almost
entirely attached to the substrate. The terminal parts of branches are semi-transparent
and whitish. The floatoblasts were recognized by the distinctly elongated shape of the
fenestra on both valves. Both capsuled floatoblasts and the distinctive leptoblasts were
found, along with associated colonies (Fig. 6A, B). The surface fenestra of capsulated
floatoblasts was almost smooth. Length of floatoblasts 345–432 (397±15) μm; width
188–260 (214±14) μm), L/W ratio 1.8; DfL 112–198 (154±15) μm; DfW 90–135
(113±7) μm; VfL 174–236 (205±12) μm; VfW 150–195 (167±8) (n=5). Leptoblasts
(Fig. 6B, right side) have a uniformly narrow annulus and extensive oval fenestrae;
which length was at least 1.5 times its width.
Distribution in Europe. Plumatella casmiana is currently known throughout
most of Europe
(Massard and Geimer 1995b)
Remarks on habitat and ecology in Lithuania. This is the first reported occur
rence of P. casmiana in Lithuania. Floatoblasts of P. casmiana were recorded in almost
half of the investigated water bodies (Table 1). However, colonies were found in
Linksmakalnis Pond only.
Remarks. Beyond Europe P. casmiana is widely distributed through Asia, North
America, Africa, and very likely other continents as well
(Wood and Okamura 2005)
. A unique
feature is the appearance of floatoblasts lacking the inner capsule (Figure 6B, right side).
This so-called leptoblast is capable of hatching immediately after release from the colony,
enabling populations to grow very rapidly each season. Colonies also produce conventional
capsuled floatoblasts (Figure 6B, left side) which retain the obligatory dormancy period.
Plumatella fruticosa (Allman, 1844)
Fig. 7A, B
Material examined. Colony from Rokai pond (Kaunas district) found in June 2016;
floatoblasts from pond of Kaunas Botanical garden collected in July and August 2016.
Description. The colony measured approximately 3 x 4 cm and had sparse, narrow
and upright branches. Free statoblasts are long and narrow, exhibiting a length at least
twice the width: 432–496 (459±8) μm long and 187–220 (203±4) μm (n=10) wide;
L/W ratio 2.2; DfL 120–320 (197±19) (n=10) μm; DfW 56–100 (75±6) (n=6) μm;
VfL 211–313 (266±21) (n=4) μm and VfW 74–128 (108±17) μm (n=3). Sessoblasts
were not found during this study. According to
the average size of the
floatoblasts was 590 μm long and 230 μm wide.
Distribution in Europe. Plumatella fruticosa is considered to be widespread,
especially in northern portion of Europe (Økland and Økland 2005). It is considered
common in Poland
Remarks on habitat and ecology on Lithuania. Pajiedaitė collected colonies in
Dubysa river (Šiauliai district) and Satarečius pond (Utena district) (Pajiedaitė 1933)
At first glance we could state that P. fruticosa is common in Lithuania, since during
this survey statoblasts were found in most water bodies. However, we found colonies
only in Rokai pond with sandy-mud bottom and stones in the littoral (Table 1, Fig. 7).
Thus, it is possible, that statoblasts are spread by waterfowl among various ponds and
lakes, but these may not be the preferred environment for growing colonies (Økland
and Økland 2005).
Remarks. The combined statoblast characteristics (large length/width ratio, strong
asymmetry of floatoblast and sessoblast, narrow fenestra on dorsal floatoblast valve)
distinguish P. fruticosa from all other plumatellid species
(Ricciardi and Reiswig 1994)
Molecular results provided by Hartikainen
(Hartikainen et al. 2013)
imply that P.
fruticosa is not a plumatellid and provide evidence for polyphyly in Plumatella. However,
the position of P. fruticosa remains unresolved
(Hartikainen et al. 2013)
Hyalinella punctata (Hancock, 1850)
Material examined. A few statoblasts from Veršvio stream were found in August 2015
Unfortunately, these were later lost before critical dimensions could be taken.
Description. Colonies were not observed, and species was identified according
floatoblasts. The statoblasts are larger than any other plumatellid species and show
crowded tubercles on the fenestrae of both valves.
floatoblasts by oval shape, with length 440 μm and width 230 μm. These dimensions were
slightly smaller than 500 μm and 350 μm suggested by
Wood and Okamura (2005)
Length and width of measured statoblasts during current study was 425–459 (444±7)
and 280–299 (290±4) μm, respectively (n=5).
Distribution in Europe. Hyalinella punctata has been widely reported worldwide,
including neighbouring Poland
, but verified specimens are known
only from Britain, Ireland, Europe, North America and northern Asia
Remarks on habitat and ecology in Lithuania. Few small colonies of H. punc
tata were described on Nymphaea lutea leaves in small lakes in the Zarasai district
(55°44'50"N, 25°50'4"E) and Dubysa river (Šiauliai district; 55°51'29"N, 23°08'31"E)
. During the present survey, floatoblasts of H. punctata were
recorded only in the Veršvio stream (Table 1). The available data are not sufficient to
estimate the prevalence and frequency of this species in Lithuania.
described colonies of H. punctata as “thick and
transparent with less profuse branching than in Plumatella and produce only floatoblasts,
while individual zooids are indistinct, usually arranged linearly and lack interzooidal
septa”. In fact, features distinguishing Hyalinella from Plumatella are not clear-cut
(Hirose and Mawatari 2011)
, because the diagnosis of Hyalinella is based on the
transparency and thickness of the colony wall (ectocyst), but the condition of the ectocyst
depends to some extent on environmental factors
(Wood and Okamura 2005, Hirose and
. Generic placement of some species between Plumatella and Hyalinella
has remained unstable
(Hirose and Mawatari 2011)
Family Cristatellidae Allman, 1856
Cristatella mucedo (Cuvier, 1798)
Material examined. Colony from Snaigynas lake (Lazdijai district) collected in July
2016, floatoblasts from Rokai pond found in September 2016.
Description. Colonies of C. mucedo are recognized by their elongated shape and
colourless, transparent body wall. The length of colonies found varied from 5 to 10 cm
(Pajiedaitė 1933; this study). The large statoblasts are easily recognized by circular form
with hooked spines radiating from the edges of the fenestrae on both valves (Fig. 9).
Diameter of statoblasts was about 1 mm.
Distribution in Europe. Cristatella mucedo is a common species in Lithuania,
with a Holarctic distribution, occurring in Britain, Ireland, Europe, Asia and North
(Økland and Økland 2000; Wood and Okamura 2005)
Remarks on habitat and ecology in Lithuania. During this survey a few colonies
of C. mucedo occurred in South Lithuania (Snaigynas lake), but statoblasts were found
in various water bodies of different regions of the country (Table 1).
noted that C. mucedo more often occurred in South Lithuania. She found colonies of
C. mucedo without statoblasts in June/July and noted that statoblasts inside colonies
appeared in first part of August. Numerous colonies with statoblasts were found at the
end of September and they died late autumn once the water temperature dropped to
3 °C in November 1932 (Pajiedaitė 1933).
Remarks. A more detailed discussion of the ecology and life history of C. mucedo
can be found in
Class Gymnolaemata Allman, 1856
Order Ctenostemata Busk, 1852
Family Paludicellidae Allman, 1844
Paludicella articulata (Ehrenberg, 1831)
Material examined. Two colonies from the outlet of Snaigynas Lake (Lazdijai district)
were found in May 2017. Hibernaculae were not found.
Description. The species was recognized by the slender colony branches forking at
wide angles and often growing free from the substratum. Colonies were small, about
2–3 cm. Branches of colony were transparent and shiny. Zooids 1.0–1.5 mm in length
with 16 tentacles on a circular lophophore were described by
Distribution in Europe. Paludicella articulata is known worldwide
. However, the species has not been found in Poland
Remarks on habitat and ecology in Lithuania. Paludicella articulata was re
corded by Pajiedaite (1933) in only two localities: Paštys Lake (Utena district)
(55°42'36"N, 25°41'48"E) and Satarečius pond (Utena district). Since P. articulata
tolerates cold temperatures (Økland and Økland 2005) and prefers flowing
(Wood and Okamura 2005)
it was surprising finding of this species in stagnant
Satarečius pond together with C. mucedo. Coexistence of the two species was also
, who explained it by different local conditions in the same
pond; colonies of P. articulate were observed only near a small stream flowing into the
pond. Otherwise, she noted that C. mucedo was mostly observed in the warmer waters
of Central and South Lithuania.
Økland and Økland (2005) showed positive co-occurrence of these two species
During this survey P. articulata was found in the outlet of Snaigynas lake, which is
of glacial origin and characterised by low temperature.
Remarks. Colonies of P. articulata consist of sometimes creeping but more often
elongated, mostly erect, slender zooids. There are normally three adjacent zooids: one
distal and two lateral ones
The contiguous arrangement of the
zooids and the subterminal 4-sided zooecial orifice readily distinguish the species from its
closest relative, Pottsiella erecta
(Ricciardi and Reiswig 1994)
Overall nine species of freshwater bryozoans are now known from Lithuania. This
contrasts with about 19 species reported from Europe and about 13 species from the
(Massard-Geimer and Massard-Geimer 2004; Nikulina 2006)
. Given the
fact that only a relatively few water bodies of Lithuania have been investigated so far it
is likely that the final tally of species will be higher.
The majority of surveyed pools were stagnant, neutral or slightly alkaline
(Table 1) and should have been suitable for bryozoans to grow successfully.
However, while intact colonies were found only in few sites, statoblasts were widely
distributed. The rarity of colonies in water pools might be explained by fluctuating
climatic conditions, especially the alternation of drought and rainfall. The similar
process under Lithuanian conditions was described by
, who found
P. articulata and P. repens colonies in Paštys Lake in 1931, but completely absent
the following year.
suggested this disappearance may have been
due to rising of water level after rainfall in Paštys Lake. She wrote that bryozoans
are sensitive “creatures” and cannot survive such drastic environmental change. She
went on to describe a similar situation in Nevėžis River in 1932, where after week of
rainfall, nearly all bryozoan colonies had died (Pajiedaitė 1933).
) documented the negative effects of heavy rainfall in Korea on colonies of
Another possible reason of finding small number of colonies could be the lack
of suitable substratum for the attachment of colonies. Because bryozoans are sessile
organisms, they absolutely require a solid, inert substratum on which to grow
. For example, we have found statoblasts of five bryozoan species in a pond at the
Kaunas botanical garden (Table 1). However, colonies have never been observed there,
possibly due to lack of solid substratum to which bryozoan colonies can attach. The
presence of statoblasts could be the result of waterfowl, which are known to transport
them from one site to another
(Wood and Okamura 2005)
With this study, we have now recorded 13 species of freshwater bryozoans
recorded in Baltic area: C. mucedo, P. magnifica, Fredericella indica
, Fredericella sultana
, Lophopus crystallinus
H. punctata, P. casmiana, P. emarginata, P. fruticosa, P. fungosa, P. geimermassardi,
P. repens, Stolella indica
, and P. articulata (Massard-Geimer and
Massard-Geimer 2004; Nikulina 2006)
All bryozoan species documented in Lithuania are common and widely distributed
through Europe. The composition of species found through this survey was similar to
that recorded 86 years ago, with the exception of finding two additional species for
Lithuania. The status of P. repens and P. fungosa as common freshwater bryozoan
species, and P. articulata as rare, have not changed for almost a century.
Curiously, this survey did not encounter F. sultana, which is otherwise well known
in northern Europe, Britain and Ireland
(Geimer and Massard 1986; Wood and
. Also absent was the large gelatinous species, P. magnifica, which is
currently expanding its range across Europe and is already reported from areas including
Hungary (Szekeres et al. 2013), Germany
, Czech Republic
and Vergon 2002; Balounova et al. 2011)
, and Poland (Balounová et al. 2011).
Additional bryozoan species that might be expected in Lithuania include L. crystallinus,
which is recorded in neighbouring countries as Belarus, Kaliningrad and Poland
(Nikulina 2006); also, P. rugosa, P. reticulata
, and F. indica. Since the brackish
species, Victorella pavida
Saville Kent, 1870
, is known in neighbouring Latvia, it is
likely to be found also in Lithuania.
In summary, we believe that the list of freshwater bryozoa presented here is not
final. Lithuania is an extremely watery region; there are more than 3000 lakes of a wide
variety of sizes and many rivers flow across the country. Therefore, it is very likely, that
further research will reveal additional species.
We sincerely thank Dr. Masato Hirose, University of Tokyo, and anonymous reviewer
for their careful reading of and valuable comments on the manuscript.
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