Brachionus plicatilis, Muller, 1786

Meyer, Stephanie, Araujo, Thiago Q., Walsh, Elizabeth J., Wallace, Robert L. & Hochberg, Rick, 2023, Integrative microscopy to explore physical and nanomechanical properties of eggshells of diapausing embryos in Rotifera: a proof-of-concept study, Journal of Natural History 57, pp. 1984-2005 : 1991-1993

Phylum Rotifera :

Brachionus plicatilis

SEM

Diapausing embryos were ovoid and measured ca 134 µm in diameter (̄x = 134.0 ± 4.0 μm). The outer surface was composed of numerous smooth ridges and wrinkles, creating an overall rough surface ( Figure 2a,b ).

TEM

The shell consisted of a thick apical layer and a thin basal layer. Average shell thickness was 2.30 ± 0.22 µm (SD). The outer layer, termed the alveolar layer by Munuswamy et al. (1996), had a wavy texture ( Figure 2c,d ). Electron density was highest at the topmost and bottom portions of the alveolar layer, otherwise it had a similar electron density throughout its thickness and contained many ̍empty̾ pockets that were interconnected through electron-dense bridges. The basal layer [s1 of Munuswamy et al. (1996)] had an amorphous appearance that consisted of an electron lucent zone and a more electron-opaque zone below it ( Figure 2d ). Thin fibres were present throughout both zones.

AFM

Topography of the outer shell showed rugosity and similar attributes to those in SEM, but with fewer details ( Figure 2e ). An example force–distance curve that displays how Young̾s modulus values were collected for a single spot on one egg is shown in Figure 2f . The Young̾s modulus ranged from 12.24 to 19.85 MPa with an average of 15.81 ± 2.49 MPa (SD) ( Table 1 ). Hardness values ranged from 1.14 × 10−2 to 5.31 × 10−2 GPa with an average hardness of 1.853 × 10−2 ±1.23 × 10−2 GPa ( Table 2 ).

Figures

Figure 2. Characterisation of diapausing embryos of Brachionus plicatilis. a. Scanning Electron Microscope image of a single egg. b. Close-up of the surface of the egg. c. Ultrastructure of the shell viewed with Transmission Electron Microscopy. d. Close-up of shell ultrastructure. e. Topographic image of the external surface of an egg generated with Atomic Force Microscopy. f. Force–distance (FD) curve generated from a single location on an egg. Parameters for the position of the location on the eggshell are indicated by the cursor positions (software screenshot). Maximum force (MF, green circle) and 20% maximum force (20% MF, orange circle) are indicated on the FD curve. Abbreviations: al, alveolar layer; es, extraembryonic space (section did not include embryo); s1, sublayer. Scale bars: A = 25 µm; B = 2 µm; C = 6.5 µm; D = 1.5 µm.