Encyclopedian Dictionary ( Eyespots on Protozoa ): Structure of the Eyespot and Associated Organelles

Structure of the Eyespot and Associated Organelles

From Journal of Cell Science
Observations on the Fine Structure of the Eyespot and Associated Organelles in the Dinoflagellate Glenodinium Foliaceum
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The functional and phylogenetic significance of dinoflagellate eyespots
John D. Dodge
Journal: BioSystems, ISSN: 0303-2647, Vol: 16, Issue: 3-4,Date: 1983, Pages: 259-267
Abstract: The eyespots or stigmas from five species of dinoflagellates fall into three distinct categories: independent eyespot which is not membrane bound; independent eyespot which is surrounded by three membranes; eyespot situated at the periphery of a chloroplast. In all cases the eyespot is situated behind the longitudinal groove or sulcus and there is a strand of microtubules between the eyespot and the cell covering or theca. In two cases the strand has been clearly shown to originate near the base of the longitudinal flagellum, which is the one passing over the eyespot and is also responsible for directional movement of the cell. The microtubular strand is presumed to play a part in the transmission of directional stimulation from eyespot to flagellum and a hypothesis is advanced to explain how this may be brought about. Phylogenetically, the structure of the various types of eyespots would link these dinoflagellates with euglenids and chrysophytes, and the diversity found in the dinoflagellates is probably a reflection of the diverse origin of chloroplasts in this group.

Here's a link to a full online article by him in pdf.

DINOFLAGELLATES : INVESTIGATION AND PHYLOGENETIC SPECULATION By JOHN D. DODGE. Botany Department, Royal Holloway College, Egham, Surrey, TW20 0EX, England.

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Red Eye Spots on Euglena
According to NOAA, Dr. Rochelle Sturtevant:
"The red spot is in fact an 'eyespot' - it's a very primitive eye that allows the euglena to detect light-- a big advantage for a mobile photosynthesizer."
Dr. Rochelle Sturtevant
Extension Educator
NOAA
Great Lakes Sea Grant Network
Great Lakes Environmental Research Lab

"Sharon, good to hear from you. I like diatoms and dinoflagellates. Certainly, diatoms are very important in geology, their shells are used to date rocks. Keep up the good work, it is neat to hear you talk about the eyespots and the evolution of the eye. I had not thought that far, being more vertebrate centered."
- Hans Thewissen

February 1999, Diatoms, Plants with a Touch of Glass (Article and Photo credit to Darlyne A. Murawski)

Dr. R Norman, U. Mich-Dearborn (emeritus):

'Your specimen certainly looks like a euglenid.'

Euglenids in Brackish water, samples gathered along the Atlantic Ocean (ICW/Intracoastal Waterway) which is an important detail to consider:

"Phagotrophic lineages are widespread in marine, brackish and freshwater sediments. These cells glide within the spaces between grains of sand and within the narrow interface between mud and the water column. Photoautotrophic and osmotrophic lineages mainly inhabit the water column of freshwater environments. However, relatively large and vermiform photoautotrophic species have reduced flagella and tend to creep within sediments. Several photoautotrophic species also inhabit brackish water and estuaries either in the sediments or by swimming in the water column. Only a few photoautotrophic lineages inhabit marine planktonic communities (e.g. the Eutreptiales). Some photoautotrophic species migrate vertically in marine sand in coordination with tidal and diurnal cycles (e.g. Euglena rustica and E. obtusa). These species are usually found in high abundance and form easily visible green patches in marine sand during low tides (Brown et al. 2002)."
- Tree of Life Website

Also see, Identification of Eyespot in Dinoflagellates.
"Four types of eyespot types have been distinguished in Dinoflagellates. All eyespots are situated in the sulcal area close to the flagellar roots where they are likely to be shadowed by the proximal part of the longitudinal flagellum."

"Dinoflagellates do have 4 types of eye spots. Most are not found in the marine environment."
[Reference Dodge dinoflagellate eye spots if you would like more info.]
- Dr. Steve Morton, NOAA.gov