Certesella larai, Bobrov & Duckert & Mitchell, 2021

Bobrov, Anatoly, Duckert, Clément & Mitchell, Edward A. D., 2021, Certesella larai (Amoebozoa: Arcellinida: Hyalospheniformes) a new soil testate amoeba species from the Dominican Republic and Chile challenges the definition of genera Certesella and Porosia, Acta Protozoologica 60, pp. 61-75 : 62-66

Certesella larai sp. nov. ( Fig. 1–7 , Sup. Fig. 1 ; Table 3 )

Description: Shell elongated pear-shaped ( Figs. 1 , 2 , 4 & Sup. Fig. 1 ), compressed with two large, rounded to irregular-elongated elliptical pores clearly visible in broad view, connected by tubes. No visible lateral pore. Punctuations and inner teeth on the neck usually absent but visible in some specimens ( Fig. 3 ). In broad view shell outline oval elongated at the fundus (aboral end of the shell), then narrowing slightly until a bulge near the area of the two large pores where the sides are approximately parallel, and narrowing again at the base of the neck. Neck relatively short with a slight bulge and then again approximately parallel near the aperture ( Figs. 1 , 2 & 4 ). Shell colourless, covered with oval plates of different sizes and shapes ( Fig. 4 ), most likely recycled idiosomes from euglyphid testate amoebae. Pores surrounded by smaller recycled idiosomes than the main body ( Fig. 4 ). Pseudostome rim smooth and somewhat wavy, lip 2–2.5 µm thick ( Figs. 2–4 ).

Measurements: Shell length: 135.8–153.4 µm, shell breadth: 56.8–68.2 µm, shell depth ca. 50 µm, aperture maximum dimension: 24.0–29.8 µm, distance from the fundus to the pores: 73.0–92.3 µm, distance from the fundus to the base (narrowest point) of the neck: 104.6– 125.0, distance between the pores: 22.8–34.1 µm, width of the neck at its narrowest point – 18.5–29.5 µm, pore length – 5.1–12.8 µm, pore width – 3.0–6.4 µm, shell length/breadth ratio 2.03–2.58 ( Table 3 ). The variability of morphological characteristics is generally low (e.g. <6% for characters 1–6 Table 3 ), and only somewhat higher for the smallest dimensions for which the accuracy of measurements is lower.

Type locality and habitat: Parque Nacional Alerce Costero , Los Ríos Region, Chile, Small Sphagnum peatland, with Fitzroya trees. In Sphagnum . Coordinates: –40.171975°; –73.491841°, elevation 1028 m. a.s.l., EM-1453 / Chi 2. Locality of the paratype specimen: Ebano Verde National Park, Dominican Republic. Broadleaf forest litter Forest approximatively three quarters of way up from the river to the ridge. Elevation 1423 m. above sea level. Coordinates: 19.0399°; –70.5193°.

Type specimen: Type: Natural History Museum of Neuchâtel, Rue des Terreaux 14, 2000 Neuchâtel, Switzerland, slide No. 95–2. Paratype: Laboratory of Soil Bioindication, Department of Soil Geography, Faculty of Soil Science, Lomonosov Moscow State University, slide No. 4–2020.

Etymology: The species name was chosen to honour our esteemed colleague Enrique Lara, as a recognition for his major contribution to the molecular taxonomy and phylogeny of testate amoebae. We believe he may be amused by the fact that we name in his honour a species which is not straightforward to classify based solely on morphological data and clearly calls for molecular phylogenetic analyses … to which he has so greatly contributed.

Comparison between the two populations: The two populations largely overlap in length and width ( Fig. 5 ) and do not differ either in general shape (Sup. Fig. 1 ) and other characters (not illustrated).

Related species: There is no possible confusion with C. australis and C. murrayi as their shape is very different ( Figs. 6 & 7 ). The two most similar species are C. certesi and C. martiali . The shell of the new species is more elongated (length/width ratio: 2.03–2.58) than Certesella martiali (1.83-1.90). The length/width ratio overlaps with C. certesi (range 1.75–2.92 based on the original description and several subsequent studies ( Certes 1889; Deflandre 1936; Heinis 1914; Penard 1911). The contrast is even clearer with the two known species of the genus Porosia – P. bigibbosa and P. paracarinata ( Table 4 ). Indeed, the dimensions of the new species do not overlap with any known species of genera Certesella and Porosia in a biplot of length vs. width ( Fig. 7 ). The somewhat irregular, wavy pseudostome lip of Certesella larai may be specific to this species; but this should be assessed by a thorough comparative morphological study.

The outline of Certesella larai is similar to other species in genus Certesella ( Figs. 6 & 7 ). However, most specimens lack the inner teeth on the neck that are considered as one of the characteristic features of this genus. While we consider it unlikely that the lack of internal teeth is an effect of phenotypic plasticity as observed for shell size in Hyalosphenia papilio ( Mulot et al. 2017) , we evaluate that the new species fits best in genus Certesella .

Figures

Fig. 1. General shape of Certesella larai n.sp. and indication of the morphometrical measurements. 1 – shell length, 2 – shell breadth, 3 – shell length / breadth ratio (not illustrated), 4 – aperture (long axis), 5 – distance from fundus to the pores, 6 – distance from fundus to base of neck, 7 – distance between the pores, 8 – width of the neck at narrowest point, 9 – pore length, 10 – pore width.

Fig. 2. Light microscopy images of Certesella larai n.sp. from Parque Nacional Alerce Costero, Los Ríos Region, Chile. Left: DIC image of the type specimen deposited at the Natural History Museum of Neuchâtel (slide 95–2). Centre and right: brightfield images of specimens from the same sample. Scale bar 20 µm.

Fig. 3. Light microscopy images of Certesella larai n.sp. from Parque Nacional Alerce Costero, Los Ríos Region, Chile, showing the detail of the pseudostome. The right image shows internal teeth fully visible on the flank of the neck (solid arrow and visible only in transparency (empty arrow). Such structures are only visible in ca. 10% of the specimens. Scale bar 10 µm.

Fig. 4. Certesella larai n.sp. scanning electron microscopy images showing the overall shape, the chitinous rim of the pseudostome, the detail of an elongated pore and the plates (presumably recycled from euglyphid testate amoebae) covering the shell.

Fig. 5. Biplot of length vs. width of two populations of Certesella larai n.sp. from Dominican Republic and Chile.

Fig. 6. Comparative overview of the morphology of all known species of genera Certesella and Porosia species.A: Certesella larai n. sp., B: C. certesi, C: C. australis, D: C. murrayi, E: C. martiali, F: Porosia paracarinata, G: P. bigibbbosa. Images are not to scale as some early images lacked a scale.

Fig. 7. Maximum range of shell length and width of the three known Certesella and Porosia species showing a lack of overlap between C. larai n.sp. and all other species from the two genera in this two-dimensional space. Each species is illustrated (images not exactly to scale).