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Fig. 4 | Frontiers in Zoology

Fig. 4

From: The antennal scape organ of Scutigera coleoptrata (Myriapoda) and a new type of arthropod tip-pore sensilla integrating scolopidial components

Fig. 4

Internal ultrastructure of the scape organ based on TEM analysis: Overview and details of distal components with emphasis on the sensory apparatus. A Medio-longitudinal section of the sensory cavity with two cone-shaped sensilla, several clusters of receptor and sheath cells, epidermal cells, as well as of one associated recto-canal epidermal gland. B Detail of a cone-shaped sensillum in longitudinal section. Note the axial projection of the secretion layer plugging and concealing the terminal pore. C The lower tip of the secretion plug tightly adjoins the truncated distal tip of a long dendritic outer segment resembling a tubular body (arrowhead). D Para-longitudinal section of a cone-shaped sensillum showing some long outer dendritic segments, encapsulated by the dendritic sheath. E–F Cross-sections of a cone-shaped sensillum at a distal level through the secretion plug (E) and at a more proximal level through the tubular body-like terminations of two long outer dendritic segments (F). Section levels are indicated in (B). G Close-up of two long outer dendritic segments slightly below the section level shown in (E). Two small additional outer dendritic segments are visible between the two main ones (arrows), tubular body characteristics are not clearly discernible. H Cross-section approximately 5 µm below (G). Note the two smaller outer dendritic segments (arrows). I–K Sequence of consecutive cross-sections illustrating the sheath cell system and dendritic apparatus of receptor cells with long outer dendritic segments. I Immediately below the sensory cone. Note the presence of the minute outer sensillum lymph space. J Section level approximately 5 µm below (I), showing the transition zone where all three sheath cells overlap. Note also the increased width of the dendritic sheath. K Section level approximately 5 µm below (J), showing the coiled path of the ciliary apparatus. ca, cavity; co, sensory cone (of cone-shaped sensillum); css, cellular profile of cone-shaped sensillum; cu, cuticle; ds, dendritic sheath; du, conducting canal; encu, endocuticle; epc, interstitial epidermal cell; esp, extracellular space; excu, exocuticle; isl, inner sensillum lymph space; mi, mitochondria; mv, microvilli; ntb, neurotubules; ods, outer dendritic segment(s); osl, outer sensillum lymph space; ovs, secretion layer; rceg, recto-canal epidermal gland; css, cellular profile of cone-shaped sensillum; shc1, first (proximal) sheath cell (scolopale cell); shc2, second (median) sheath cell; shc3, third (distal) sheath cell; spl, secretion plug; tde, terminal structures of long outer dendritic segments

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