New data to the knowledge on the Harpacticoida ( Crustacea , Copepoda ) fauna in Poland

Harpacticoida is the least known group of Copepoda in freshwater habitats in Poland, although they are very common and very abundant in the continental waters. The last detailed taxonomic studies of Harpacticoida in Polish inland waters were carried out about 100 years ago. A faunistic and ecological review of 12 harpacticoid species from north-eastern Poland is presented herein for the first time. Two species new to the Polish fauna were recorded: Elaphoidella elaphoides (Chappuis, 1923) and Bryocamptus (Rheocamptus) spinulosus (Borutzky, 1934). Bryocamptus spinulosus is morphologically close to B. zschokkei (Schmeil, 1893). The latter species is considered to be widely distributed in Poland, yet many records of B. zschokkei might in fact refer to B. spinulosus. Distinguishing features of these species were described in detail.


INTRODUCTION
Harpacticoid copepods are meiobenthic crustaceans that are common and occasionally very abundant in both marine and freshwater environments (Błędzki 2004).Harpacticoida is one of the least known animal groups in Poland (Drzycimski 1985).The last taxonomic studies of Harpacticoida in Polish inland waters were carried out about 100 years ago, among others by Wierzejski (1883), Demel (1922), Minkiewicz (1924).Moreover, except for Wigry Lake and its neighbourhood (Drzycimski 1985), there is no information about Harpacticoida from northeastern Poland.We know much more about the group in the coastal waters of the Baltic Sea (Drzycimski 1991;Drzycimski 1993;Drzycimski 1997).The fauna of Poland and Southern Baltic includes 80 species, but only 28 species have so far been recorded from freshwater habitats.In the last century very little research has been done on the harpacticoids in the country (Błędzki 2004).The aim of my investigations was to explore the harpacticoid fauna and its peculiarities in different types of freshwater habitats in north-eastern Poland.

MATERIALS AND METHODS
Harpacticoids were collected in north-eastern Poland between 2010-2014.A total of 141 samples were collected from the different freshwater habitats (lakes, river, springs, underground water) and microhabitats (aquatic plants, peat bog, on the surface of freshwater bivalves) (Table 1).The samples were obtained by different water samplers, depending on the habitat (Karpowicz 2017).The water was filtered through a plankton net with mesh size of 50 µm and fixed with 4% formaline.Harpacticoids were sorted out from the samples under a stereo microscope in the laboratory.Microscope slides were prepared using Hoyer's mounting medium, as it immediately makes the embedded specimen transparent, which is helpful in fast species diagnostics.Also, it allows to store the slides for a relatively long time (Cielecka et al. 2009).Voucher specimens of the identified species are deposited in the Department of Hydrobiology, University of Bialystok.List of deposited species (slides) with their localization and habitat type are given in Table 1.Abbreviations used in the text: P1-P5: thoracic legs numbers; exp: exopodite; enp: endopodite RESULTS AND DISCUSSION Harpacticoida had the highest frequency of occurrence in moss and peat bogs around humic lakes (84%) and in Stratiotetum aloides vegetation (83%).In these habitats harpacticoids occurred also in high numbers (Table 2).The highest abundance was found in the Stratiotetum aloides association in Lake Bełdany (160 indiv.l -1 ) and in mosses near humic lakes (90 indiv.l -1 ).These habitats were usually dominated by one or two highly abundant species.Despite their low abundance, harpacticoids constituted the most important component of crustacean zooplankton in in springs and groundwater.Twelve harpacticoid species belonging to three families (Canthocamptidae, Ameiridae, Parastenocarididae) were found in NE Poland.Two species new to the Polish fauna were recorded: Elaphoidella elaphoides (Chappuis, 1923) and Bryocamptus (Rheocamptus) spinulosus (Borutzky, 1934).Bryocamptus spinulosus is closely related to B. zschokkei which is widespread and very common in Holarctic (Ishida 1987;Błędzki 2004).I speculate that many records of B. zschokkei in Poland might actually refer to B. spinulosus.
Brief information on the geographic distribution, biology, ecology as well as the distinguishing features of the species recorded in north-eastern Poland is presented below.
Ge ner al d istrib utio n a nd b iolo gy.Whole Europe.Geographic distribution of P. brevipes is likely influenced by the distribution of sphagnous peat bogs, the preferred habitat of the species (Borutzky 1952).
Ge ner al distr ib utio n a nd biolo gy.Widespread in Europe and Asia, mainly in large lakes and rivers.Chappuis (1927) observed N. hibernica in the gill cavity of the common crayfish.Jakubisiak (1929) found the species in the water system of Poznan city.Those specimens slightly differed from the typical form and were named by Jakubisiak (1929) as Nitocra hibernica var.hyalina (see also Borutzky 1952).

Nitokra divaricata Chappuis, 1923
Lo catio n, eco lo gy.Single female was found in Stratiotes aloides vegetation of Lake Tyrkło in the Masurian Lakeland, however, the species is known as a commensal of common crayfish (Janetzky et al. 1996).
Ge ner al d istr ib utio n a nd biolo gy.Nitokra divaricata is known from the Russian Federation, Romania, Germany and Poland.It lives in the gill cavity and on the body surface of common crayfish, and its species range likely overlaps with the range of these decapods (Borutzky 1952).
Distinguishing features.Nitokra divaricata is closely related to N. hibernica, and these species exhibit great similarity in the structure of the swimming legs.The two species can be distinguished by the morphology of P1 and P5.Proximal segment of endopodite of P1 reaching middle of distal segment of exopodite in N. diverciata.
Ge ner al distrib utio n a nd biolo gy.Widespread in Poland (Błędzki 2004), and occurs almost throughout Europe.Associated mainly with sphagnous swamps.The species has been encountered in the littoral of stagnant water bodies with silty bottoms and in springs where it often shows developmental aberrancies.Absent from the tundra zone (Borutzky 1952).
Ge ner al d istr ib utio n a nd biolo gy.Lowland water bodies of Europe, North Africa and Asia (Borutzky 1952).Widespread in Poland (Błędzki 2004).The range of the subgenus Brehmiella is mostly restricted to the Holarctic region (Borutzky 1952).

Pesceus schmeili (Mrázek, 1893)
Lo catio n, e colo gy.Only females were found on the surface of zebra mussel (Dreissena polymorpha) from Lake Boczne in the Masurian Lakeland.
Ge ner al d istr ib utio n a nd biolo gy.Palaearctic, inhabits various types of water bodies, from large lakes where it is common in benthos and reaches considerable depths, to lowland swamps and springs (Borutzky 1952).Pesceus schmeili s. str.occurs throughout Europe up to and including Ural region.Widespread in Poland (Drzycimski 1985).Polycyclic (Sarvala 1990;Fefilova 2007) and oligosaprobic (Sarkka 1995).
Distinguishing features.Caudal rami widely divergent, almost three times as long as wide, with slightly narrowed and pointed tips.Outer and inner margins of caudal rami hairy.
Ge ner al distrib utio n a nd biolo gy.Widespread in Poland (Błędzki 2004) and occurs almost throughout Europe (Borutzky 1952).Elaphoidella gracilis inhabits various types of water bodies, yet it prefers sphagnous peat swamp and it is particularly abundant in small pools (Borutzky 1952).

Elaphoidella elaphoides
Lo catio n, eco lo gy.Dominant species in groundwater (wells) of Ogrodniczki and Ciasne villages near Białystok city.Only females and copepodites were found.
Ge ner al d istrib utio n a nd b iolo gy.The species is new to the Polish fauna.Elaphoidella elaphoides is considered to be a stygophilic species that recently invaded the subterranean waters (cave, hyporheic and phreatic waters).Widespread in epigean and underground waters of Europe, i.e.Greece, Italy, Turkey (Pesce 1985), Balkan Penisula, Germany (Borutzky 1952), Austria, Czech Republic (Janetzky et al. 1996).

Bryocamptus (Rheocamptus) spinulosus
Remar ks.New species to the Polish fauna.Bryocamptus spinulosus is morphologically close to B. zschokkei (Schmeil, 1893).The latter species is considered to be widely distributed in Poland, yet many records of B. zschokkei might in fact refer to B. spinulosus.
Ge ner al distrib utio n a nd biolo gy.The B. zschokkei group is widespread in Holarctic.The typical form of B. zschokkei is a cold-water stenothermal form, found in the littoral of alpine lakes or in cold springs and brooks.In lowland regions it is confined to cold http://rcin.org.plsprings, very close to their issue, where moist moss is its favorite habitat (Borutzky 1952).Bryocamptus spinulosus has been reported from Slovakia, Czech Republic (Sterba 1968), mountain brooks and springs in the North Caucasus (Borutzky 1952), Albania and Bulgaria (Apostolov 2004) and caves in NE Romania (Meleg et al. 2011).
Distinguishing features.Bryocamptus spinulosus is morphologically very close to B. zschokkei.The Bryocamptus zschokkei group is highly variable.Differences from the typical form have been described by Schmeil, and relate to the armature of the body segments, limbs and even the number of leg segments.In B. spinulosus the swimming legs have the same segmentation pattern as what is observed in B. zschokkei group.The setal formula of leg 1−4 in the B. zschokkei group is as follows (according to Janetzky et al. 1996): In the springs of Knyszyn Primaeval Forest B. spinulosus shows two-segmented endopodites in P2 and P3 (Fig. 23).The setal formula of leg 1−4 is as follows: Basiendopodite and exopodite of P5 with 6 and 5 setae, respectively (Fig. 25).The structure of the inner apical caudal seta (Fig. 22) and P5 (Fig. 25) of the female are distinguish B. spinulosus from B. zschokkei.The inner apical caudal seta of B. spinulosus is serpentine-like with much widened base (Borutzky, 1934), which is very characteristics feature of this species.Caudal rami almost as long as wide (Fig. 22).Anal operculum with 4 large denticles (Fig. 22), which differs from the state (5 denticles) mentioned in the original description (Borutzky 1934).Antennule eight-segmented (Fig. 24).
Bryocamptus zschokkei zschokkei var.tatrensis, described by Minkiewicz (1916) from water bodies in the Tatra mountains and subsequently found in Lake Wigry and other parts of Poland, differ from B. spinulosus in few features only, i.e. differences in leg armature, row of spinules on the body segments (Walter 2015).
Gener al distrib utio n and biolo gy.Cold-water, European species, most frequently found in highland water bodies, rarely in cold spring in lowland regions (Borutzky 1952).It has been recorded from lowland springs and rivers in Poland (Drzycimski 1985) and Estonia (Fefilova 2010).
Ge ner al d istr ib utio n a nd biolo gy.Widespread in Europe and North America, except the tundra zone.Also known from North Africa.It inhabits different types of surface waterbodies and groundwater too (Fefilova 2010).It was most often found in moist moss cushions in swamps of lowland or transitional type, with avoidance of higher acidity swamps (Borutzky 1952).

Table 1 .
List of deposited harpacticoid species with their localization and habitat type.

Table 2 .
The occurrence of Harpacticoida in various types of aquatic habitats in NE Poland.