Fig. 7

Histological micrographs of select tissues in Alviniconcha.a Increasingly magnified views (corresponding to blue-boxed regions of previous image) of branchial filaments in oblique longitudinal section: arrowhead in ii) identifies the accumulation of cellular debris in the blood lacuna within the bacteriocyte region (BR) with iii) a higher magnification view of the junction with a large blood vessel (BV in ii, likely the secondary efferent branchial vessel); b transverse section through the outer layers of the posterior digestive gland (DG) bathed in blood sinuses (BS) and enclosed in delicate muscle and epithelial layers (ML and EL); c section cut from granular tissue (GT), a spongy tissue composed of a loose, fibrous matrix, densely populated with accretions of various sizes, found throughout the cephalopedal haemocoel but particularly around the mid-posterior oesophagus (not pictured), which passes through the gonad (Go), when present; d granular deposits also accumulate in connective tissue between the DD and the stomach mucosa (Mu); e various stages of spermatogenesis could be readily identified in males examined histologically: spermatogonia, spermatocytes, spermatids, spermatozoids and spermatozoa (❶ - ❺ respectively). Image mosaics a & d are from 7 μm-thick paraffin sections (formalin-fixed); b, c (both alcohol-fixed) & e (formalin-fixed) are from 2 μm-thick LR-white sections. All tissues are from A. kojimai, except (c), which is from A. strummeri