Figure 1.
Morphology of Thyasira cf. gouldi from Bonne Bay, Newfoundland.
A. Outer view of the left shell valve, with a weakly projecting auricle (a), a well-defined submarginal sulcus (ss) forming a marginal sinus, a distinct, yet rounded, posterior fold (pf), and a rounded ventral margin (vm). B. Inner view of the right valve, revealing the absence of dentition along the hinge plate (hp). C. Scanning electron micrograph of the larval shell (∼ 181 μm diameter). D. Internal anatomy, showing a gill (g) with two demibranchs, the digestive diverticula (d), foot (f), anterior adductor (aa), posterior adductor (pa) and mantle margin, thickened at the anterior end.
Figure 2.
Light and electron micrographs of gill filaments of Thyasira cf. gouldi.
A. Symbiotic specimen. Light micrograph of a semi-thin, transverse section through four gill filaments. The ciliated frontal zone (fz) and bacteriocyte zone (bz) are highlighted. a: abfrontal end of a filament; f: frontal end of a filament. B. Symbiotic specimen. TEM of cells in the bacteriocyte zone of a gill filament, showing abundant bacteria (b), maintained extracellularly in pockets limited by extensions of host cell cytoplasm bearing microvilli (mv). Nuclei (n) and lysed remains of digested symbionts (ly) are visible in the host cell cytoplasm. C. Asymbiotic specimen. Light micrograph of a semi-thin, transverse section through two gill filaments. Note the shorter frontal (f) - abfrontal (a) length. mc: mucocyte. D, E. Asymbiotic specimen. TEM of cells in the abfrontal zone of a gill filament. Note the absence of bacteria. The epithelium is pseudostratified, with apical cells (c2) overlying basal cells (c1) containing large mitochondria (m). mv: microvilli.
Table 1.
Polymorphic nucleotide sites within sequenced 18S and 28S gene fragments of Thyasira cf. gouldi OTUs.
Table 2.
Accession numbers, Thyasira cf. gouldi OTU 18S rRNA, 28S rRNA and CO1 gene fragments.
Table 3.
Distance matrix based on CO1 (667 bp) OTU sequences.
Figure 3.
Cluster analysis of shell outlines (Elliptical Fourier Analysis).
The analysis is based on the first 10 harmonics. Shells form two groups, A and B, which differ significantly in length (indicated above the groups) based on a t-test (p<0.01). Symbols refer to operational taxonomic groups (OTUs) based on CO1, 18S and 28S rRNA sequences.
Figure 4.
Shape variation among shells along the first two principal components.
Reconstructed contours show shapes at the extremities of each axis. Symbols refer to operational taxonomic groups (OTUs) based on CO1, 18S and 28S rRNA sequences.
Figure 5.
Cluster analysis of a subset of shell outlines (Elliptical Fourier Analysis).
Shells analysed are those from group B in Figure 3. The analysis is based on the first 20 harmonics, excluding the first one. Symbols refer to operational taxonomic groups (OTUs) based on CO1, 18S and 28S rRNA sequences.
Figure 6.
Shape variation in a subset of shells along the first two principal components.
Shells analysed belong to group B in Figure 3. Reconstructed contours show shapes at the extremities of each axis. Symbols refer to operational taxonomic groups (OTUs) based on CO1, 18S and 28S rRNA sequences.
Figure 7.
Distribution of Thyasira cf. gouldi groups in Bonne Bay, NL.
Charts at each location show relative proportions of each OTU (1–3) and total number of individuals (N) used in the molecular analysis. Sampling sites are Deer Arm, Neddy's Harbour, and Southeast Arm.