Description of intracerebral ocelli in two species of North American crayfish: Orconectes limosus (Cambaridae) and Pacifastacus leniusculus (Astacidae)

Abstract

Among rnalacostracan crustaceans, intracerebral ocelli were first discovered in Isopoda, but they have been more recently reported from a crayfish (Cherax destructor) and a sandhopper (Talitrus saltator). This electron microscopic study increases the number of crayfish t a m in which intracerebral ocelli are now known to occur by two: Astacidae and Cambaridae. These photoreceptors are always integrated into the anteromedio-dorsal part of the brain and are not visible externally. Each ocellus is made up of 4-5 photoreceptor cells and is characterized by the presence of a fused rhabdom. The occurrence of different kinds of lysosomes in the cytoplasm is indicative of metabolic activity and perhaps membrane turnover. One typical feature of crayfish ocelli is their extraordinary variability in number. This trait is exemplified by individuals of Pcici&stacus leniwculus, where as inany as 14 ocelli were identified in a single brain. The arrangement of the ocelli is often not symmetrical with regard to the brain's midline and the ocelli always lack dioptric structures. Thus, it is difficult to see how they are involved in image formation. However, further research is needed to determine the precise role of these "hidden" receptors.

Brain Photoreceptor Pathways Contributing to Circadian Rhythmicity in Crayfish

“…We refer to these regions as the brain photoreceptor neuropils (BPNs) in this paper. Electron microscope studies have also shown the presence of rhabdomeric structures in Cluster 6 cells in the brains of the astacid (northern hemisphere) crayfish Orconectes limosus and Pacifastacus leniusculus (Bobkova et al, 2003). These cells, however, do not contain the dark screening pigment granules found in C. destructor.…”

“…These cells, however, do not contain the dark screening pigment granules found in C. destructor. While the structure of these cells is entirely consistent with that of the brain photoreceptors of C. destructor (Bobkova et al, 2003), physiological recordings have not yet been made of their responses to light.…”

“…Two photoreceptive systems, in addition to the compound eyes, have been identified in crayfish: caudal photoreceptors in the terminal abdominal ganglion (Prosser, 1934;Wilkens & Larimer, 1972) and brain photoreceptors in the supraesophageal ganglion (Bobkova et al, 2003;Sandeman et al, 1990). The brain photoreceptors of the parastacid (southern hemisphere) crayfish Cherax destructor, located in an anterior median brain soma Cluster (Cluster 6; nomenclature according to Sandeman et al, 1992; see Figure 1), can be visualized without staining as they contain dark screening pigment granules (see Figure 2A; Sandeman et al, 1990).…”

Circadian clocks in crustaceans: identified neuronal and cellular systems

“…The pigment granules within the BPR-cell clusters in other crayfish species such as O. limosus, P. leniusculus, and P. clarkii are, unfortunately, not as easily visible but recognised only by electron microscopy (302). It is not known whether the pigment granules within BPRs migrate in a similar way, as do those of the PP in the retinular cells (185,17,302). BPRs are histamine-ir and express cryptochrome (CRY, see also 4.3.4.…”

Anatomy and ultrastructural organisation of the eye of the Mediterranean slipper lobster,Scyllarides latus:preliminary results

“…Freshwater crayfish featured early in studies of crustacean compound eyes (parker 1891) and the visual centres in the brain have also been the subjects of numerous structural and optical studies (e.g., by Krebs 1972;Vogt 1975;Land 1978;Bryceson 1986;Frixione & perez-olvera 1991;Sandeman et al 1991;hafner & Tokarski 1998;Bobkova et al 2003). Biochemical and physiological experiments were carried out by arechiga et al (1973), walcott (1974), cummins & Goldsmith (1981), cronin & Goldsmith (1982, Eccles et al (1983), and Kashiwagi et al (2000) and results from behavioural observations have recently been summarised by delgado- Morales et al (2004).…”