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Here, There and Everywhere : The Radiolar Eyes of Fan Worms (Annelida, Sabellidae)

Bok, Michael J. LU ; Capa, María and Nilsson, Dan Eric LU (2016) In Integrative and Comparative Biology 56(5). p.784-795
Abstract

Fan worms (Annelida: Sabellidae) possess some of the strangest eyes in nature. Their eponymous fans are composed of two sets of radiolar tentacles that project from the head up out of the worm's protective tube into the water column. Primarily used for respiration and feeding, these radioles are also often involved in photoreception. They display a surprising diversity of eyes of varying levels of sophistication, ranging from scattered single ocelli to compound eyes with up to hundreds of facets. These photoreceptors could represent a relatively recent evolutionary development to cope with a sessile, tube-dwelling lifestyle, and the primary cerebral eyes (haplessly positioned within the tube most of the time) amount to little more than... (More)

Fan worms (Annelida: Sabellidae) possess some of the strangest eyes in nature. Their eponymous fans are composed of two sets of radiolar tentacles that project from the head up out of the worm's protective tube into the water column. Primarily used for respiration and feeding, these radioles are also often involved in photoreception. They display a surprising diversity of eyes of varying levels of sophistication, ranging from scattered single ocelli to compound eyes with up to hundreds of facets. These photoreceptors could represent a relatively recent evolutionary development to cope with a sessile, tube-dwelling lifestyle, and the primary cerebral eyes (haplessly positioned within the tube most of the time) amount to little more than minute pigment cups with scant visual potential. The radiolar eyes on the other hand, appear to function as visual burglar alarms for detecting looming predators and eliciting a startle response for the worm to rapidly retreat within its fortified tube. Despite sometimes resembling arthropod compound eyes, the radiolar photoreceptors have many canonically vertebrate-like physiological characteristics. Considering the unusual and apparently recently evolved nature of the fan worm radiolar photoreceptors, these animals are an excellent case for examining the emergence of novel visual systems, the development of rudimentary visually guided behaviors, and the function of distributed sensory systems. Here, we review over 100 years of investigations into the anatomical diversity of sabellid radiolar photoreceptors and eyes in an evolutionary and functional context. We provide new information on radiolar eye structure in several species of fan worms, and we attempt to organize the various eye types and ocellar structures into meaningful hierarchies. We discuss the developmental, evolutionary, and functional significance of the radiolar eyes and highlight areas of future interest in deciphering their unique nature.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Integrative and Comparative Biology
volume
56
issue
5
pages
12 pages
publisher
Oxford University Press
external identifiers
  • scopus:84996536314
  • wos:000386081100005
ISSN
1540-7063
DOI
10.1093/icb/icw089
language
English
LU publication?
yes
id
c6fb6868-5cff-4284-aaba-89c0ea30d7b3
date added to LUP
2016-12-12 11:03:53
date last changed
2017-10-29 04:55:26
@article{c6fb6868-5cff-4284-aaba-89c0ea30d7b3,
  abstract     = {<p>Fan worms (Annelida: Sabellidae) possess some of the strangest eyes in nature. Their eponymous fans are composed of two sets of radiolar tentacles that project from the head up out of the worm's protective tube into the water column. Primarily used for respiration and feeding, these radioles are also often involved in photoreception. They display a surprising diversity of eyes of varying levels of sophistication, ranging from scattered single ocelli to compound eyes with up to hundreds of facets. These photoreceptors could represent a relatively recent evolutionary development to cope with a sessile, tube-dwelling lifestyle, and the primary cerebral eyes (haplessly positioned within the tube most of the time) amount to little more than minute pigment cups with scant visual potential. The radiolar eyes on the other hand, appear to function as visual burglar alarms for detecting looming predators and eliciting a startle response for the worm to rapidly retreat within its fortified tube. Despite sometimes resembling arthropod compound eyes, the radiolar photoreceptors have many canonically vertebrate-like physiological characteristics. Considering the unusual and apparently recently evolved nature of the fan worm radiolar photoreceptors, these animals are an excellent case for examining the emergence of novel visual systems, the development of rudimentary visually guided behaviors, and the function of distributed sensory systems. Here, we review over 100 years of investigations into the anatomical diversity of sabellid radiolar photoreceptors and eyes in an evolutionary and functional context. We provide new information on radiolar eye structure in several species of fan worms, and we attempt to organize the various eye types and ocellar structures into meaningful hierarchies. We discuss the developmental, evolutionary, and functional significance of the radiolar eyes and highlight areas of future interest in deciphering their unique nature.</p>},
  author       = {Bok, Michael J. and Capa, María and Nilsson, Dan Eric},
  issn         = {1540-7063},
  language     = {eng},
  month        = {11},
  number       = {5},
  pages        = {784--795},
  publisher    = {Oxford University Press},
  series       = {Integrative and Comparative Biology},
  title        = {Here, There and Everywhere : The Radiolar Eyes of Fan Worms (Annelida, Sabellidae)},
  url          = {http://dx.doi.org/10.1093/icb/icw089},
  volume       = {56},
  year         = {2016},
}