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Figure 4 | BMC Evolutionary Biology

Figure 4

From: Development of the nervous system in Phoronopsis harmeri (Lophotrochozoa, Phoronida) reveals both deuterostome- and trochozoan-like features

Figure 4

The organization of the serotonin-like immunoreactive nervous system in a young actinotrocha (A-I) and in a 5-day-old actinotrocha (K-S). Micrographs of live animals (A, K) and Z-projections of larvae with mono- and double staining with antibodies against 5-HT (serotonin) (green),as well as by phalloidin (grey), and Hoechst (violet). (A) Lateral view of a live larva (ventral side is to the right, apical is to the top) showing apical plate (ap), esophagus (eso), stomach (st), midgut (mg), proctodaeum (pr), and tentacular ridge (tr). (B) Overview of the musculature and serotonin-like immunoreactive nervous system showing apical organ (ao) and tentacular ridge. Lateral view, ventral side is to the right, apical is at the top. (C-H) Details of the apical organ. (C) General view of the apical organ with neuropil (np) and perikarya (prk). Lateral view, apical is to the top; anterior is to the right. (D) Dorsal view of the apical organ. The thin area between apical and basal parts of the perikaryon is indicated by two arrowheads. (E) Perikaryon with pronounced thin area (two arrowheads) between apical (apt) and basal (bp) parts. (F) The same perikaryon with nucleus. Wide basal part is indicated by arrowhead. (G) The same perikaryon nucleus (arrowheads), which is located under the common row of nuclei. (H) Basal portion of the apical organ showing neuropil and bipolar or multipolar (arrowheads) perikarya. (I) Young larva with the first serotonin-like immunoreactive neurites that subsequently form the two dorsal branches of the tentacular neurite bundle (tn). Overview of the musculature and serotonin-like immunoreactive nervous system showing apical organ (ao), mouth (m), and preoral lobe (pl). Ventral view, preoral lobe bends backward. (J) The same larva; bifurcated (bf) end of left branch of the tentacular neurite bundle. The micrograph is composed of selected optical sections from the dorsal-most region of the specimen. (K) Lateral view of a 5-day-old larva showing preoral lobe, stomach, midgut, and proctodaeum. Apical is to the upper right. (L) Overview of the musculature and serotonin-like immunoreactive nervous system showing apical organ, anterior (amn) and posterior (pmn) marginal neurite bundles, tentacular neurite bundle (tn), and tentacular ridge (tr). Lateral view; preoral lobe bends backward; apical is to the upper right. Digestive tract with nonspecific staining (numerous white vesicles in the stomach and proctodaeum). (M-S) Details of the apical organ. (M) General view of the apical organ showing neuropil (np), bipolar perikarya (bn), and two dorsal branches of the tentacular neurite bundle (tn). Dorso-lateral view; anterior is to the upper right. (N) General view of an individual monopolar perikaryon showing cilium (c), apical part (ap), and basal projection (bp), which connects to the neuropil (np). (O) Two serotonin-like immunoreactive perikarya, which are adjacent to each other and form a cluster with two apical parts, two nuclei (arrowheads), and one process. (P) The same perikarya. (Q) The group of bipolar or multipolar perikarya, nuclei (arrowheads) of which are located close to the neuropil. (R) Bipolar perikaryon (arrowheads), which is located on the one branch of the tentacular neurite bundle. (S) The same perikaryon with nucleus (arrowheads).

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