Psammonobiotus dinarica Bakovic & Siemensma, 2023

Bakovic, Najla, Siemensma, Ferry, Puljas, Sanja, Bakovic, Robert, Ozimec, Roman, Ostojic, Ana & Mesic, Zrinka, 2023, First data on testate amoebae associated with the endemic cave bivalve Congeria jalzici Morton & Bilandzija, 2013 with a description of Psammonobiotus dinarica sp. nov., Subterranean Biology 45, pp. 53-74 : 53

Psammonobiotus dinarica Bakovic & Siemensma sp. nov.

Plates 2F , 3A-E

Diagnosis.

Shell is bilaterally symmetrical, in dorsal and ventral views spherical to ovoid in outline and in lateral view compressed with a length/height ratio of about 2.3. A funnel-shaped collar extends from a kidney-shaped oral aperture. In lateral view, the angle of the plane of this pseudostome collar is usually zero degrees, but can sometimes be as high as 33°. The translucent and fragile organic shell is covered with small irregularly-shaped thin and flat quartz particles. Larger particles are located on the dorsal and distal part of the shell and smaller particles on the ventral side. The rim of the collar is covered with relatively large flat particles. The organic matrix is colorless to dark brown. Length including the collar 45-54 μm; main body width 26-30 μm, height 17-30 μm; collar 20-29 μm across (n=6).

Etymology.

The specific name refers to the area where the species was found, the Dinarides or Dinaric Alps, Latin: Psammonobiotus dinarica , a mountain range in, among others, Croatia and Bosnia and Herzegovina.

Type material.

Three slides, one with the holotype and two with paratypes, were mounted in HYDRO-Matrix on glass slides and deposited in the collection of the Croatian Biospeleological Society under accession numbers TAM4 (holotype), TAM5 and TAM6 (paratypes).

Type locality.

Croatia, Lika region, Lipovo polje, Dražice ponor, 44°46'20.2"N, 15°11'10.6"E, 10 November 2018, H. Bilandžija leg.

Differential diagnosis.

There are several testate amoebae similar in shape and size to P. dinarica : Centropyxis platystoma , Psammonobiotus communis , P. septentrialis and P. minutus , some Centropyxiella and Corythionella species, and Conicocassis pontigulasiformis . Centropyxis platystoma was described by Penard in 1890, but in 1902 he considered this species identical to Leidy’s C. constricta (Penard, 1890, 1902). Since he originally described it as Difflugia platystoma , the shell must have looked to him as that of a Difflugia , with a dense covering of quartz particles. Penard described the shell as “pierreuse”, stony. This is different from P. dinarica , where the shell is covered with tiny flat particles. In the original description, Penard showed a drawing of the visor with a strongly inwardly curved edge, in contrast to the edge of the collar of P. dinarica which is not curved. P. dinarica can be distinguished from P. septentrialis and P. minutus by its larger size, 45-54 μm long versus 10-12 μm and 23-30 μm, respectively (Golemansky 1970; Chardez 1977 a). The size is about the same as P. communis , 45-54 μm ( Golemansky 1967) versus 33-52 μm, but P. dinarica can be distinguished from the latter by the kidney-shaped aperture. P. dinarica also bears some resemblance to Conicocassis pontigulasiformis , but this species is much larger, 82-90 µm, and the test wall has a much more pronounced granular organic cement and a circular aperture ( Nasser and Patterson 2015). P. dinarica can be distinguished from Centropyxiella arenaria by its kidney-shaped aperture, and from C. elegans and C. lucida by its smaller size, length 45-54 μm versus 70-80 µm and 70-81 µm, respectively ( Golemansky and Todorov 2007). It can be distinguished from similarly shaped Corythionella species ( Golemansky 1970b) by the presence of small elliptical or oval idiosomes in the latter genus.

Biogeography and habitats.

Psammonobiotus dinarica was found in the Dinaric karst of Croatia and in Bosnia and Herzegovina, in the caves Dražice ponor, Markov ponor (both Lipovo polje, CRO) (Fig. 1 , Table 1 ), Jopićeva cave-Bent system (Krnjak, CRO) and Matešićeva-Popovačka cave system (Slunj, CRO) ( Baković N., unpublished data). One empty shell was found in a small karst spring near the Jopićeva cave-Bent system (Krnjak, CRO) ( Baković N., unpublished data). This species was also reported in the Velika Bukovačka and the Listvača cave (both in Bosnia and Herzegovina) ( Baković et al. 2019). The altitude of these localities ranges from 210 to 950 m.a.s.l. The species inhabits surface sediments of permanent cave streams (dominant), sediments of small cave standing waters (sinter pools and clay pools) and transitional habitats (hygropetric). Only one observation of P. dinarica on the shell of a living Congeria jalzici was noted.

The following ranges of physio-chemical parameters were present in the habitat of this species: water temperature 5.4-10.7 °C, pH 7.62-8.11, conductivity 161-338 µS /cm. It was only occasionally present in all investigated habitats, but always at low densities (up to 3.3 ind. in 1 ml of aquatic sediment).

Remarks.

The genus Psammonobiotus contains nine beach sand-dwelling species, six recorded only from marine and brackish waters ( Golemansky and Todorov 2004), one exclusively from freshwater ( P. dziwnowi ) ( Nicholls 2005) and two also from marine and freshwater bodies ( P. communis and P. linearis ) ( Golemansky and Todorov 2004). P. dinarica is the second Psammonobiotus species to be reported exclusively from a freshwater biotope. All species known to date have been collected from the psammon from beaches of marine water bodies and some large freshwater lakes ( Golemansky and Todorov 2005). The presence of P. dinarica in a (freshwater) cave system can therefore be called surprising. However, it is not the first Psammonobiotus species to have been found in another ecosystem. The website arcella.nl reports the presence of Psammonobiotus species in a relatively small lake, in organic sediment of a small shallow freshwater ditch, in organic sediment of an isolated pond and in the soil of a peat bog, all in the Netherlands ( Siemensma 2021). It shows that our knowledge about the presence and distribution of Psammonobiotus species in freshwater and soil biotopes is still very limited.

Regarding the presence of light, all species of the genus Psammonobiotus primarily inhabit aphotic biotopes - cave sediments ( P. dinarica ) and interstitial sand habitats (all other species) ( Golemansky and Todorov 2005).

Although living specimens of P. dinarica have been observed, pseudopodia could never be observed as these specimens were always firmly attached to sediment particles. The brown color, if present, disappears rapidly when the shell is embedded in HYDRO-Matrix.

Figures

Figure 1. Research location and hydrographic map showing the main permanent and temporary water bodies and the hydrotechnical tunnel (DAN - Dankov ponor, DRA - Drazice ponor, MAR - Markov ponor, BUK - Buklina, PRA - Prazina pecina, CAK - Pecina u Cakovcu, HOR - Horvatova pecina, SAM - Samograd).

Plate 2. A Parmulina sp. B Euglypha laevis C Trinema lineare D Tracheleuglypha dentata E Phryganella paradoxa F Psammonobiotus dinarica sp. nov. G Cryptodifflugia oviformis H Testacea sp 1 I Testacea sp. 2 J Testacea sp. 3 (stacked image) K Centropyxis laevigata. Scale bars: 20 µm (A, I-K); 10 µm (B-H).

Plate 3. Psammonobiotus dinarica A shell in ventral view (type specimen) B shell in lateral view (type specimen) C shell in ventral view D shell in lateral view E kidney-shaped aperture. Scale bars: 20 µm. A-D stacked photomicrographs.