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.

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.

Figure 2. 

Plumatella repens. Scanning electron micrograph of floatoblasts showing dorsal valve (left) and ventral valve (right). Scale bars: 200 μm.

According to Økland and Økland (2005), Wood and Okamura (2005), P. repens is common in Britain, Ireland and Europe. Kaminski (1984) described P. repens as most common species in the studied lakes in Poland.

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.

Pajiedaitė (1933) 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 reliable (Wood and Okamura 2005).

Lacourt (1968) 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). Plumatella 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 Wood, 2001, P. orbisperma (Kellicott, 1882), P. recluse Smith, 1992, and P. rugosa Wood, Wood, Geimer & Massard, 1998 (Massard and Geimer 2008a).

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.

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).

Figure 3. 

Plumatella geimermassardi. Scanning electron micrograph of the floatoblast ventral valve showing the uniformly narrow annulus. Scale bar: 100 μm.

Plumatella geimermassardi is known from England, Ireland, Belgium, southern Norway, northern Germany, Italy and Finland (Wood and Okamura 2005).

Floatoblasts of P. geimermassardi are among the smallest floatoblasts among all European plumatellids with an average length of around 320 µm (Wood 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 continents (Wood 1996; Toriumi 1955).

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).

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, dimensions of P. fungosa floatoblasts provided by Pajiedaitė (1933), 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.

Figure 4. 

Plumatella fungosa. Scanning electron micrograph showing characteristic tubercles on the floatoblast annulus. Scale bar: 100 μm.

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 (Kaminski 1984).

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). Pajiedaitė (1933) 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 (Bushnell 1966; Geimer and Massard 1986). Based on the available data, we consider P. fungosa to be prevalent in Lithuania.

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).

A few floatoblasts from Šventupė pond were collected in July 2016.

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.

Figure 5. 

Plumatella emarginata floatoblast valves. The dorsal valve (left) has a characteristically small central fenestra; in the ventral valve (right) the fenestra is nearly circular. Scale bar: 100 µm.

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.

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, 55°12'12"N, 23°30'28"E).

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 rapidly-flowing 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.

The species is widely distributed throughout the Holarctic (Wood and Okamura 2005), although some reports may have confused it with similar species, P. mukaii or P. reticulata (Massard and Geimer 2008a).

Floatoblasts, leptoblasts, and colony from Linksmakalnis pond collected from submerged branches in 20 July 2016.

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.

Figure 6. 

Plumatella casmiana. A Portion of a colony showing crowded zooids almost entirely attached to the substratum B Dorsal valve of floatoblast (left) and leptoblast (right). Scale bars: 1 mm (A), 100 µm (B).

Plumatella casmiana is currently known throughout most of Europe (Massard and Geimer 1995b).

This is the first reported occurrence 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.

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.

Colony from Rokai pond (Kaunas district) found in June 2016; floatoblasts from pond of Kaunas Botanical garden collected in July and August 2016.

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 Pajiedaitė (1933) the average size of the floatoblasts was 590 μm long and 230 μm wide.

Plumatella fruticosa is considered to be widespread, especially in northern portion of Europe (Økland and Økland 2005). It is considered common in Poland (Kaminski 1984).

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).

Figure 7. 

Plumatella fruticosa. A Colony showing upright zooids and branches (B) Scanning electron micrograph showing floatoblast ventral valve with characteristic long, narrow shape. Scale bars: 3 mm (A); 200 μm (B).

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).

A few statoblasts from Veršvio stream were found in August 2015 Unfortunately, these were later lost before critical dimensions could be taken.

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. Pajiedaitė (1933) described 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).

Figure 8. 

Hyalinella punctata. Scanning electron micrograph showing the floatoblast ventral valve. Scale bar: 300 μm.

Hyalinella punctata has been widely reported worldwide, including neighbouring Poland (Kaminski 1984), but verified specimens are known only from Britain, Ireland, Europe, North America and northern Asia (Wood and Okamura 2005).

Few small colonies of H. punctata 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) by Pajiedaitė (1933). 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.

Hancock (1850) 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 Mawatari 2011). Generic placement of some species between Plumatella and Hyalinella has remained unstable (Hirose and Mawatari 2011).

Colony from Snaigynas lake (Lazdijai district) collected in July 2016, floatoblasts from Rokai pond found in September 2016.

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.

Figure 9. 

Cristatella mucedo. Scanning electron micrograph showing floatoblast with characteristic spines. Scale bar: 500 μm.

Cristatella mucedo is a common species in Lithuania, with a Holarctic distribution, occurring in Britain, Ireland, Europe, Asia and North America (Økland and Økland 2000; Wood and Okamura 2005).

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). Pajiedaitė (1933) 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).

A more detailed discussion of the ecology and life history of C. mucedo can be found in Okamura (1997).

Two colonies from the outlet of Snaigynas Lake (Lazdijai district) were found in May 2017. Hibernaculae were not found.

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 Pajiedaitė (1933).

Figure 10. 

Fragment colony of Paludicella articulata. Scale bar: 1 mm.

Paludicella articulata is known worldwide (Wood and Okamura 2005). However, the species has not been found in Poland (Kaminski 1984).

Paludicella articulata was recorded 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 water (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 noted by Pajiedaitė (1933), 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 in Norway.

During this survey P. articulata was found in the outlet of Snaigynas lake, which is of glacial origin and characterised by low temperature.

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 (Davenport 1891) 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).