Fig. 2

Whole mounts, histological cross-sections and electron microscopical images of O. fusiformis at 7 dpf. Light microscopic images of entire larvae (a), toluidin-blue stained cross-sections (b, d, e) and electron microscopy (c, f). Note that the sectional planes of b, d, e are indicated by red lines in a. There are three planes. The position of the electron microscopical detail is indicated by red rectangles. a Early developmental stage 7 dpf. Ventral (including the mouth opening) is left, apical is up. The animal exhibits a well-developed ciliary band (cb), a distinct esophagus (es) and a defined midgut (mg). b In cross-sections of the esophagus region the prominent blastocoel is visible, which occupies most of the space within the larval episphere. The inset shows the esophageal region (es) and the position of the epidermis (ep) in higher magnification. c The outer epidermis (ep) is composed of a monolayer of epidermal cells and a prominent cuticle (cu). The underlying basal lamina (bl) borders directly borders the large blastocoel (bc) being a primary body cavity. The inset in (c) shows a higher magnification of the basal lamina (bl). d A cross-section in the plane of the apical organ (ao) reveals the presence of distinct muscle bundles (mu) and the circumesophageal connective (cc) framing the esophagus (es). The inset shows the the apical organ (ao) in higher magnification. e The blastocoel (bc) occupies most of the larva. The inset in (e) shows the epidermis (ep) lateral to the apical organ. f The central tissue is covered by a basal lamina directly bordering the internal blastocoel (bc). The inset in (f) shows a higher magnification of the basal lamina (bl). an, anus; ao, apical organ; bc, blastocoel; bl, basal lamina; cb, ciliary band; cc, circumesophageal connective; ci, cilium; cu, cuticle; ep, epidermis; es, esophagus;; hg, hindgut; mg, midgut; mu, muscle bundle; ne, nerve; nu, nucleus; tr, trunk region. Scale bars = 100 μm (b, d, e), 1 μm (c, f) and 500 nm (inset in c and f). The scale bars only refer to the main images in b, d and e, not to the insets