Diagram of gill position and cross-section through a lamella showing ascending and descending limbs of a filament.

<p>A: Gill position within a valve showing positioning of the anterior adductor (aa) and posterior adductor muscles (pa), budding zone (bz) and filaments (fi). B: A dorso-ventral section though a eulamellibranch showing the foot (ft), gill base (gb), inner demibranch (id), interlamellar junction (ilj), interlamellar space (ils), mantle (m) and outer demibranch (od). Used with permission from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193637#pone.0193637.ref038" target="_blank">38</a>].</p

Description of the three stages of juvenile gill development based upon observations during this study.

<p>The age (months) at which individuals begin to display particular structures/developments is approximate and no attempt has been made to postulate when development of certain structures begins if they were not directly observed during this study. The number of inner demibranch (ID) and outer demibranch (OD) filaments are the number observed during this study and may differ depending upon population or other parameters.</p

Main anatomical features of juvenile mussels.

<p>a) Foot (FO), unreflected filaments (FI), gill axis (GA), left and right labial palps (LP). b) Distal tips of filaments are joined to each other by thin tissue connections (arrow heads); c) Gill reflection of the inner demibranch. Thin tissue connections join filaments at the ventral bend (VB) and the thicker fused dorsal bend (FDB) joins the terminal ends of the ascending arms. All three cilia types are present on the ascending limbs (AL); lateral cilia (LC), laterofrontal cirri (LFC) and frontal cilia (FC). The ascending limb is longer on medial filaments compared to those at either anterior or posterior ends (to the left and right of frame). Other features of note are the filament abfrontal surface (AS), descending limb (DL) and mantle (MA); d) Oral groove on inner demibranch (left) and absence of groove on outer demibranch (right); e) Ciliary junctions between approximately filaments 11–14 (*), after which tissue junctions were present (†); f) Right ID, OD and labial palps (LP). Inset: Labial palps are highly ciliated on the inner surface but devoid of cilia externally.</p

Interfilamentary space vs length (mm) and age (months).

<p>There was no significant trend of interfilamentary space with length nor age.</p

Scatter plot of the number of inner ‘vs’ outer demibranch filaments.

<p>The number of inner demibranch filaments is able to predict the number of outer demibranch filaments and accounted for 99% of the explained variability in number of outer demibranch filaments.</p

Summary of main periods during the first approximately 4 years post-excystment outlining whether the mortality risk is deemed to be low, medium or high and which factors may contribute to increased mortality during those periods.

<p>Possible mitigation measures are also provided.</p

Summary information about the ranges of shell length (mm) and number of inner demibranch (ID) filaments for the different age cohorts.

<p>The number of specimens considered is also provided (n).</p