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Figure 2 | BMC Developmental Biology

Figure 2

From: A detailed staging scheme for late larval development in Strongylocentrotus purpuratus focused on readily-visible juvenile structures within the rudiment

Figure 2

Examples of skeletogenic developmental stages of S. purpuratus larvae as defined in Table2(arabic numerals). All images (except as indicated) are rudiment close-up views in same orientation (i.e., abanal view, sensu [37]) as indicated in A (earlier stages) and N (later stages). E, F, G, K, M are anal views. Insets in C-M: schematic views of defining skeletogenic features for stage in question, not drawn to scale; see also Table 2. Drawing (A) and corresponding live image (B) of representative early skeletogenic stage larva. (C) Stage 1: spicule dot (white arrow). (D) Stage 2: spicule (white arrow). (E) Stage 3: tube foot spicule dot (white arrow). (F) Stage 4: tri-radiate tube foot spicule (white arrowhead); multi-branched spicule (white arrow), fated to form ocular plate 1 (see [34, 35]). White asterisk indicates ocular plate 5 –a non-rudiment skeletal character not included in our scheme– which forms off of the left PO rod (see [43]). (G) Stage 5: spine primordium (6-sided star- white arrow; note also spine lumen visible at this and later stages). (H) Also Stage 5: incomplete TF ring (black arrow); multi-branched spicule indicated (black arrowhead) is fated to form the interambulacral skeleton at the base of an adult spine in interambulacrum 1 (sensu [34, 35]; but see [44]). Note this view is looking down on the left side of larva. (I) Stage 6: spine primordium (white arrowhead) with base of spine (black arrowhead) extending orthogonal to that. (J) Stage 7: pre-spine (fronds present with no cross hatches; white arrowhead), and TF ring with 2nd ring <1/2 complete (white arrow). Larva viewed from left side. (K) Stage 8: adult spine with cross hatches (white arrowhead); juvenile spine (white arrow) indicated for comparison; anal view. (L) Stage 9: TF ring with 2nd ring >1/2 complete (white arrow is pointing directly to a gap in 2nd ring). (M) Stage 10: TF ring with 2nd ring complete (white arrow); anal view. (N) schematic of larva as seen in panels I-M with larger rudiment and spines becoming recognizable. (O) Stage 10. Whole larva (oriented as in N) showing, in addition to the rudiment, several of the non-rudiment juvenile skeletal characters that we do not incorporate in our staging scheme (see also Additional file 1: Figure S1 and [43]): genital plate 5 (white arrow), posterior juvenile spines articulating with genital plate 4 (white arrowhead) and right side posterior juvenile spine (black arrow; see [45]). Ocular 5 is indicated in panel F. Note that schematic does not show PO arms for simplicity. Abbreviations: Ala – anterolateral arms; M – Mouth; St – stomach; PD – postdorsal arms; PO – postoral arms, PrO – preoral arms. Scale bars B – 300 μm; C-D: 70 μm; E- 80 μm; F-M – 70 μm; O - 200 μm

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