Lepidodermella squamata 1841

Lepidodermella aff. squamata (Dujardin, 1841)

Fig. 36

Chaetonotus squamatus Dujardin, 1841: 664, fig. 18.

France.

POLAND • 2 adults; Kraków, Botanical Garden, Jubilee Greenhouse, site 2; 50°03'38" N, 19°57'30" E; 15 Nov. 2013; M. Kolicka leg.; NHC (photomicrographs, also in the author's collection).

Lepidodermella squamata is a widely distributed species or, more precisely, in the light of the current data, it represents sets of cryptic or morphologically similar species noted in Europe, inter alia reported from Bulgaria (Valkanov 1937), Germany (Remane 1935–36), Great Britain (Martin 1981), Italy (Mola 1932), Poland (Roszczak 1936; Kisielewska & Kisielewski 1986 a, 1986 b, 1986 c), Romania (Rudescu 1967), Sweden (Kånneby 2011) and Switzerland (Greuter 1917); also reported from Argentina (Grosso & Drahg 1984), Australia (Hochberg 2005), Brazil (Kisielewski 1991), Canada (Schwank 1990), East Africa (Daday 1910), India (Naidu & Rao 2004), Israel (Kisielewski 1999), Japan (Sudzuki 1971), South Korea (Lee & Chang 2000), the United States (Bryce 1924) and Uruguay (Cordero 1918).

Lepidodermella squamata (Dujardin, 1841) is one of the four earliest described gastrotrich species (Balsamo et al. 2014). This taxon is distributed worldwide and is very common in very different habitats (from freshwater and brackish psammon to micro-reservoirs in bromeliad leaves); however, in light of molecular data and on the basis of morphological evidence, it constitutes not one but at least a few morphologically very similar species, i.e., a complex of pseudocryptic or cryptic species (Fregni et al. 1998; Kånneby et al. 2012).

Both of the specimens reported here corresponded well with the original species description (Dujardin 1841) and with later records and the emended descriptions by Balsamo (1983) and Kisielewski (1984, 1997 a) (Fig. 36). A detailed discussion of the shape of the scales and comparisons between the studied specimens and L. squamata in the literature are considerably impeded by the noticeable differences in the shape and distribution of the scales that were presented by various authors and by intraspecific variability (e.g., Rudescu 1967; Roszczak 1969; Balsamo 1983; Schwank 1990; Kisielewski 1997 a), but the type and shape of the scales in the main covering remain consistent with Balsamo (1983) and Kisielewski (1984, 1997 a). All of the main morphometric characteristics of L. aff. squamata are within the range given in the literature (Rudescu 1967; Roszczak 1969; Balsamo 1983; Schwank 1990; Kisielewski 1984, 1997 a). The body length of studied adult specimens varied from 146.2 to 153.5 μm; the length of the pharynx from 45.7 to 47.3 μm; the intestine length from 75.5 to 82.1 μm; there were 19 total longitudinal rows of scales (5D +4DL+4L+4LV+ 2V), with 29–31 scales in the central row. The main clear differences between the studied specimens and L. squamata are the possession of one pair of scales with keels and rudimental but rigid spines on the dorsolateral area of the furcal appendages. Scales with keels or spines were listed neither in the original description nor in the main taxonomic reports on L. squamata; thus, I could not determine that the specimens undoubtedly belonged to this nominal taxon. Moreover, the present specimens possessed three pairs of dorsal sensory bristles, but this features cannot be a valid diagnostic character, since it was omitted in the original description and most previous works.

The epiphytic species found in the Jubilee Greenhouse in Kraków increase the number of Gastrotricha known from Poland to 105 and those known from palm houses to 24 species (see Kolicka 2016). This is also the first recorded presence of gastrotrichs in aquatic plants in an artificial habitat. It is worth emphasising that these chaetonotids were found on vegetation cultivated from seeds or small seedling shoots in reservoirs that were cleaned on a yearly basis, including a partial replacement of the bottom sediment. The species composition changed between the first and second sample collections. The presence of different species could have been caused by two factors, namely the reservoir cleaning which took place between the collection of the samples and the change of plant species arrangement. Perhaps some of the gastrotrich species did not survive the seasonal cleaning and replacement of sediments, or some new taxa from the second sample collection were ones that were unintentionally imported into the Jubilee Greenhouse or were present on different plant species brought from another part of the reservoir. Observations of epiphytic gastrotrichs and species community changes may increase our knowledge of the colonisation abilities of Gastroticha because they suggest three ways of inhabitation of specific plants: 1) the gastrotrichs were brought in their resting egg stages on seeds or seedlings to the reservoir and survived the transfer to the nursery tank during the annual cleaning procedure; 2) gastrotrichs were introduced to the reservoir with the bottom sediments, they grew in abundance and subsequently they also moved to the submerged plants from the benthic communities; 3) the resting eggs of various gastrotrich species were brought yearly to the reservoirs in uncontrolled ways and some taxa found appropriate conditions to live in the bottom sediments while others were able to live only on aquatic vegetation.

Kisielewski (1990) suggested that submerged plants were the last freshwater habitat to be colonised by gastrotrichs after their expansion from marine waters. Possible routes of gastrotrich transfer from sediments to aquatic plants or from aquatic plants to sediments remain unconfirmed. Chaetonotids, as small benthic or epibenthic invertebrates without any free-swimming life stages, possess very limited abilities to actively move long distances. However, the active movement of Gastrotricha into vegetation rooted in a reservoir bottom does not seem to be impossible. On the other hand, transport by the water column itself seems to be a task requiring external factors in the form of water tides or larger, more actively swimming animals which could drag the gastrotrichs or their eggs from the bottom sediments to the submerged plants. The very long spines on the trunk of Chaetonotus (Hystricochaetonotus) horridus sp. nov. and C. (H.) inaequabilis sp. nov., as well as the very long lateral to ventral spines in C. (C.) invitatus sp. nov., may be a crucial adaptation to an epibenthic or epiphytic lifestyle. The presence of a long spine could increase the likelihood of elevation from sediments to vegetation and allow this species to stay on submerged plants by increasing the bearing surface (Kisielewski 1991).

The presence of as many as three species that are new to science and two newly recorded species in such a relatively well-studied country as Poland may suggest the foreign origin of the newly found taxa. Although we do not know the place of origin of the new species, the newly observed Chaetonotus (Chaetonotus) paucisquamatus Kisielewski, 1991 and C. (Zonochaeta) cestacanthus Balsamo, 1990 were previously known only from their terra typica in Brazil and Italy, respectively. Both regions have a relatively high annual temperature and more stable climatic conditions than those observed in natural Polish habitats (e.g., Hijmans et al. 2005). It is possible that these species were accidentally imported to the Jubilee Greenhouse along with the subsoil (potted plants, sand, peat or, less probably, in the manure) or with the water containing fish, and they found appropriate living conditions. It cannot be excluded that the resting eggs of these species are widely spread in a temperate climate zone via natural (air currents, surface runoffs, dispersion with larger animals) or anthropogenic (long-distance transport of goods and people) means, but do not find favourable conditions for development and/or the creation of a stable population (e.g., due to long, cold winters). On the other hand, the taxa recorded in the Kraków greenhouse were not found in any previously studied palm houses (see Kolicka et al. 2013; Kolicka 2014, 2016), which may suggest that the aquatic vegetation plays a crucial, habitat-forming role for these chaetonotids. This research could confirm that urban greenhouses may be considered as biodiversity hot-spots in a strongly industrialised world and that they provide conditions for communities composed of species from different habitats and world regions.