Fig. 1

Maja brachydactyla. Gross morphology and development of the midgut caeca. Anterior caeca (A–B): newly hatched zoea I (A) and juvenile 12 days post-hatching (B). Posterior caecum (C–D): newly hatched zoea I (C) and juvenile 12 days post-hatching (D). Isolated midgut tract and associated caeca, newly hatched zoea I (E). Midgut caeca, adult (F–G): anterior caeca (F), and posterior caecum (G). Isolated midgut tract and associated caeca, adult (H). Midgut tract and associated caeca, megalopa 6 days post-hatching, micro-CT rendered image reconstructions, dorsal section (I–J). Anterior caeca, megalopa 6 days post-hatching, micro-CT rendered image reconstruction, transversal section (K). Length growth of the midgut caeca from hatching to the first juvenile stage (L–N): right anterior caecum (L), left anterior caecum (M), and posterior caecum (N). Scale bars (μm): 25 (A–D), 50 (E), 100 (K), 250 (I–J); (mm): 2 (F–G), 10 (H). Abbreviations: AC, anterior caeca; arrow, midgut-hindgut junction; arrowhead, junction between the posterior midgut caecum and the midgut tract; asterisk, stomach-midgut junction; CS, cardiac stomach; HGT, hindgut tract; MGG, midgut gland; MGT, midgut tract; PC, posterior caecum; PS, pyloric stomach