Figure 2
From: The homology and function of the lung plates in extant and fossil coelacanths
Extant and fossil coelacanth lung plates. (a) Virtual transverse section of an ossified plate of the extant coelacanth Latimeria chalumnae (adult specimen CCC 24). (b) Virtual section of an ossified plate of the fossil coelacanth Axelrodichthys araripensis from the Lower Cretaceous of the Santana Formation, Araripe Basin, Brazil (‘Josa collection’ MNHN, Paris); asterisk 1, external surface; asterisk 2, internal surface. (c) Histological thin section of a Latimeria chalumnae lung plate (adult specimen CCC 5, azocarmin coloration). (d) Close-up of boxed area in (c), focussing on collagen fibres at the extremity of the plate, which corresponds to the non-mineralised region. (e) Close-up of boxed area in (c), focussing on mineralised portion of the plate comprising proteoglycans, collagenous fibres, and spheritic mineralisation. (f) Ground cross-thin section of Axelrodichthys araripensis (UERJ-PMB 143) lung plate showing central artefactual fracture. (g) Close-up of boxed area in (f), focussing on weakness zone. (h) Histological thin section of a Latimeria chalumnae lung plate (haematoxylin/eosin coloration, adult specimen CCC 24); black arrows point to mineralised globules with a radiating arrangement; arrowhead points to osteocyte lacunae. (i) Ground cross-thin section of Axelrodichthys araripensis lung plate (UERJ-PMB 143); black arrows point to mineralised globules with a radiating arrangement. (j) Histological thin section of an ossified plate of the extant coelacanth Latimeria chalumnae (adult specimen CCC 24); arrowheads point to star-shaped osteocytes and arrow to canaliculi. (k) Ground cross-thin section of an Axelrodichthys araripensis lung plate (UERJ-PMB 143); arrowheads point to star-shaped osteocytes with ramified canaliculi for cytoplasmic processes. Ext. surf., external surface; Int. surf., internal surface; Min., mineralised portion; m. col. f., mineralised collagen fibres; n. m. col. f., non-mineralised collagen fibres; n. min., non-mineralised portion; prot, proteoglycans; sph. min., spheritic mineralisation; w. z., weakness zone. Scale bars, 500 µm (a–c,f) 100 µm (d,e,i) 2 µm (g) 20 µm (h) 50 µm (j,k).
