ISSN:
1432-0878
Keywords:
Photoreceptor
;
Bryozoa
;
Larva
;
Ultrastructure
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The pigmented spots of bryozoan larvae have often been implicated in photoreception due to their preferential occurrence in larvae with positive phototactic behavior. Results of light and electron microscopic studies of Bugula neritina show that the larvae possess two spots, each with a basal sensory cell situated at the base of a pit-like depression. The embedment of the pit and its basal cell in a pad of subepidermal pigment cells allows for directional illumination. The basal sensory cell produces a ball-like mass of non-motile cilia. The configuration of the axoneme is typical of kinocilia and unlike the arrangement previously described for ciliary photoreceptors. Elaboration of receptor organelle membrane surface area is accomplished uniquely by multiple cilia oriented so that large portions of each cilium lie perpendicular to the direction of incident light. The pigmented spot directly contacts the underlying equatorial nerve ring which also connects with the major larval locomotor organ. The pigmented spots of B. neritina are the only potential photoreceptor structures which have been studied by electron microscopy in the three lophophorate phyla. The use of ciliary membranes as the potential photoreceptor organelle allies the bryozoan pigmented spot with the ciliary type photoreceptor which occurs most prevalently in deuterostome animals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00335542
