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Organisms Diversity & Evolution

, Volume 15, Issue 2, pp 423–428 | Cite as

Structure and ultrastructure of eyes of tornaria larvae of Glossobalanus marginatus

  • Katrin Braun
  • Sabrina Kaul-Strehlow
  • Esther Ullrich-Lüter
  • Thomas StachEmail author
Original Article

Abstract

Enteropneusts or acorn worms are marine deuterostomes that have retained many plesiomorphic characters. Thus, enteropneusts are of prime interest in evolutionary comparisons between deuterostomes and protostomes. In the present study, the larval eyes of Glossobalanus marginatus were reconstructed and described based on serial sectioning for transmission electron microscopy. The everse eyes of the late Metschnikoff/early Krohn-stage tornaria larvae of G. marginatus are epidermal structures consisting of two rows of in total 13 shading pigment cells and another two rows of 13 photoreceptor cells. The pigment cells form a shallow cup with a relatively wide opening, making the cup-shaped eye optically unsuitable for picture generation. We demonstrate that the photosensitive cells possess numerous enlarged microvilli and an unmodified apical cilium. Our ultrastructural studies thus corroborate the photoreceptor cells in the eye of G. marginatus to be of a clearly rhabdomeric type. Preliminary immunohistochemical experiments support those findings by demonstrating immunopositive reaction of the tornarian eye photoreceptors with an antibody designed against rhabdomeric sea urchin photopigment (Sp-Opsin4). Observations of living animals indicate that Late Metschnikoff/early Krohn-stage tornaria larvae are negatively phototactic, probably concordant with imminent metamorphosis.

Keywords

Deuterostome Enteropneust Hemichordate Rhabdomeric Ciliary photoreceptor 

Notes

Acknowledgments

We thank Maria I. Arnone for kindly providing the anti-Sp-Opsin4 antibody. Financial support by the Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged.

Supplementary material

13127_2015_206_Fig4_ESM.gif (196 kb)
SM1

A-G: Immunodetection of anti-Sp-Opsin4 (designed against sea urchin rhabdomeric opsin) in a tornaria larva of Glossobalanus marginatus. A: Apical view of tornaria larvae indicating area magnified in B-D; note cilia (ci) of the ciliary band. B: Higher light microscopic magnification indicated in A; arrows point to the two eyes. Rectangle demarcates area magnified in F-G. C: Immunohistochemical localization of anti-Sp-Opsin4 using confocal laser scanning microscopy showing same area as B; arrows point to the two eyes. D: Overlay of B and C. E: Higher light microscopic magnification indicated in B. F: Immunodetection of anti-Sp-Opsin4 in the respective area. G: Overlay of E and F. H-J: Immunohistochemical co-localization of antibodies raised against rhabdomeric photopigment Sp-Opsin 4 and against acetylated alpha tubulin in a tornaria larva of Glossobalanus marginatus. H: Higher light microscopic magnification showing eye depicted in SM1 E-G. I: Immunodetection of Sp-Opsin 4 using confocal laser scanning microscopy showing same area as H. J: Immunodetection of acetylated alpha tubulin using confocal laser scanning microscopy showing same area as H and I; arrowheads point to cilia in the preoral ciliary band, arrows point to neurite-like structures in the eye. ci, cilia. (GIF 196 kb)

13127_2015_206_MOESM1_ESM.tif (7.3 mb)
High Resolution Image (TIFF 7459 kb)
SM2

Animation of 3D reconstruction of eye of a Late Metschnikoff/early Krohn-stage larva of Glossobalanus marginatus. Only one row of pigment cells is shown; compare to Fig. 3c. (MPG 20350 kb)

SM3

Movie showing movement of a Late Metschnikoff/early Krohn-stage larva. Fairly straight swimming movement with the apical plate forwards is propelled by the beating of the multiciliary telotroch. The two dark eyes are clearly visible. (AVI 40033 kb)

SM4

Movie showing movement of an Agassiz-stage larva. Crawling movement, with the proboscis probing the substrate is at least partially propelled by the beating of the multiciliary telotroch. Towards the end of the movie the larva speeds up due to an increase in beat rate of telotroch cilia. Contraction of muscles in the proboscis can be seen. The two dark eyes are still visible. (AVI 36849 kb)

13127_2015_206_MOESM5_ESM.docx (23 kb)
Table SM5 (DOCX 22.7 kb)
13127_2015_206_MOESM6_ESM.docx (21 kb)
Supplementary Methods (DOCX 20 kb)

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Copyright information

© Gesellschaft für Biologische Systematik 2015

Authors and Affiliations

  • Katrin Braun
    • 1
  • Sabrina Kaul-Strehlow
    • 2
  • Esther Ullrich-Lüter
    • 3
  • Thomas Stach
    • 1
    Email author
  1. 1.Institut für Lebenswissenschaften, Vergleichende ZoologieHumboldt-Universität zu BerlinBerlinGermany
  2. 2.Department of Integrative ZoologyUniversity of ViennaViennaAustria
  3. 3.Museum für Naturkunde, Leibniz-Institut für Evolutions- und BiodiversitätsforschungBerlinGermany

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