269 1 Institute of Zoology, Bulgarian Academy of Sciences, Blvd. Tsar Osvoboditel 1, 1000 Sofia, Bulgaria Fax: (3592) 9888-28-97; e-mail: Golemansky@zoology.bas.bg; mtodorov@zoology.bas.bg ACTA ZOOLOGICA BULGARICA Acta zool. bulg., 57 (3), 2005: 269-278 Psammonobiotus invaginatus sp.n.  a New Psammobiotic Testate Amoeba (Rhizopoda: Gromiida) from the Black Sea and a Morphometric Data of the Known Psammonobiotus spp. Vassil Golemansky 1 , Milcho Todorov 1 Abstract: A new psammobiotic testate amoeba Psammonobiotus invaginatus sp. n., isolated from the supralittoral sand of Bulgarian Black Sea coast is described using LM and SEM. The morphology and biometry of this new species are discussed. Furthermore, comparative morphometrical data for all known Psammonobiotus species are presented. Key words: biometry, Black Sea, description, psammon, Psammonobiotus invaginatus, Rhizopoda. Introduction The genus Psammonobiotus, with the type species P. communis was first described from the hygropsammon of the tectonic freshwater Lake Ohrid, Macedonia (GOLEMANSKY 1967). Some years later it was proved that P. communis is a widespread interstitial inhabitant of the sub-surface water of littoral and supralittoral sand beaches of many seas and oceans. This species is considered as an eurybiotic psammobiont with a cosmopolitan distribution (GOLEMANSKY 1970A, 1970B, 1971, 1973, 1974A, 1980, 1986, CHARDEZ 1972, 1977, SUDZUKI 1977, 1979). In the meantime, 7 new species of the genus Psammonobiotus were described from the supralittoral psammal of different seas (GOLEMANSKY 1970c, 1970d, 1973, CHARDEZ 1972, 1977; VUCETICH and ESCALANTE 1983). Another undetermined Psammonobiotus species was also observed (GOLEMANSKY 1973, NICHOLLS and MCISAAC 2004), that was later described as P. dziwnowi (NICHOLLS 2005). The majority of the Psammonobiotus species inhabit the sub-surface interstitial water of the supralittoral sand beaches of different marine localities, although P. com- munis, P. linearis and P. dziwnowi have also been found in the beach sands of some large freshwater lakes: Lake Ohrid and Lake Prespa (GOLEMANSKY 1967, 1994) and the Laurentian Great Lakes (NICHOLLS and MCISAAC 2004, NICHOLLS 2005). Recently, in our investigations of the interstitial rhizopods of the sandy Black Sea littoral, we observed a rich population of an unknown Psammonobiotus, whose morphological characteristics are quite different from those of known species. The main aim of the present article is to accomplish a morphological description of the 270 observed new species and to present comparative morphometrical data for all known Psammonobiotus species. Materials and Methods Samples of about 200 cm 3 of nearshore supralittoral sand from the Bulgarian Black Sea coast, especially from the Central sand beach of Sozopol, were collected on 2 October 2003. The samples were collected from the holes (25-30 cm deep) with sub- surface water. The physicochemical parameters of the sub-surface water were measured at sampling place using Waterproof Multifunction Meter CX - 401. The temperature of the water was 21°C, the salinity, 14.5  and the oxygen, 3.8 mg/l. Living samples were examined 12-15 days after their collection in the Laboratory of the Institute of Zoology (Sofia) with a light microscope NU-2 (Zeiss-Jena) using 10x and 40x objectives and PK 12.5x oculars lens. Shell structure was examined also by Zeiss phase-contrast. The isolation of some specimens for microscope slides was performed with a micropipette. The isolated specimens were washed in fresh water, then mounted in a standard slide/ cover glass preparation with Canada Balsam. The biometric characterization of the species was made according to SCHÖNBORN et al. (1983). The following parameters were calculated: arithmetic mean ( x ); median (M); standard deviation (SD); standard error of mean (SE); coefficient of variation in % (CV); extreme values (Min and Max); number of examined specimens (n). Size measurements of shells were made by light microscopy at 400x magnification. For the majority of the described Psammonobiotus species the ratio L/W, given in Table 2 is not original, and is calculated by us on the basis of the mean dimensions of the shells, according to different authors. Consequently, these ratios are approximate, but likely provide enough information to be used as comparative data for taxonomic purpose. The median data for L/W ratios of 4 taxa, printed in bold in Table 2 (P. communis, P. linearis, P. dziwnowi and P. invaginatus) are original (NICHOLLS and MCISAAC 2004, NICHOLLS 2005). For scanning electron microscopy (SEM) the shells were isolated, cleaned by several washes with distilled water, mounted directly on stubs and air-dried. The shells were coated evenly with gold in vacuum coating unit. The microphotographs were obtained by using a Phillips SEM 515, operating at 25 kV. Results and Discussion Psammonobiotus invaginatus sp. n. Figs 1-9, 11A. Class Filosea; Order Gromiida; Family Psammonobiotidae. Diagnosis. The shell is ovoid to nearly circular in outline in ventral or dorsal views, with a circular collar surrounding the aperture (Figs 1, 2, 6, 7, 11A). In lateral view the shell has a concave, rarely flat ventral wall. The dorsal wall is rounded. The shell depth is about a half of the width (Figs 3, 4, 11A). The shell is translucent, pale brown, fragile and collapsed when is dried. The aperture is relatively large and nearly circular in outline (Figs 1, 2, 5, 7, 8, 11A). The diameter of the flared collar is about 2/3 of the shell width and its periphery is translucent and flexible (Figs 1, 2, 5, 7). The shell structure is a typical one for the genus Psammonobiotus. The shell is composed of small flattish particles disposed on an organic matrix (Figs 1, 5, 7, 9).