Neural organization of afferent pathways from the stomatopod compound eye

Abstract

Crustaceans and insects share many similarities of brain organization suggesting that their common ancestor possessed some components of those shared features. Stomatopods (mantis shrimps) are basal eumalacostracan crustaceans famous for their elaborate visual system, the most complex of which possesses 12 types of color photoreceptors and the ability to detect both linearly and circularly polarized light. Here, using a palette of histological methods we describe neurons and their neuropils most immediately associated with the stomatopod retina. We first provide a general overview of the major neuropil structures in the eyestalks lateral protocerebrum, with respect to the optical pathways originating from the six rows of specialized ommatidia in the stomatopod's eye, termed the midband. We then focus on the structure and neuronal types of the lamina, the first optic neuropil in the stomatopod visual system. Using Golgi impregnations to resolve single neurons we identify cells in different parts of the lamina corresponding to the three different regions of the stomatopod eye (midband and the upper and lower eye halves). While the optic cartridges relating to the spectral and polarization sensitive midband ommatidia show some specializations not found in the lamina serving the upper and lower eye halves, the general morphology of the midband lamina reflects cell types elsewhere in the lamina and cell types described for other species of Eumalacostraca.

Circular polarization vision in stomatopod crustaceans

“…Beneath the lobula lies the lateral protocerebrum which is composed of several smaller structures, many of which are yet to be named. Initial investigation into the optic neuropils (Kleinlogel et al, 2003, Kleinlogel and Marshall, 2005, Thoen et al, 2017 revealed they follow a similar layout to what is seen in other crustaceans, but that the midband pathway is distinctly visible throughout the three first optic lobes. The lamina ganglionaris is the best studied optic neuropil in crustaceans (Hamori and Horridge, 1966, Nassel, 1975, Nassel and Waterman, 1977, Strausfeld and Nassel, 1981, Sztarker et al, 2009.…”

“…Like other arthropods, stomatopods have three nested optical neuropils, termed the lamina, medulla and lobula (Strausfeld and Nassel, 1981, Schiff et al, 1986, Schiff, 1987, Kleinlogel et al, 2003, Kleinlogel and Marshall, 2005, Thoen et al, 2017 (Fig 1.5 A, B), which are located in the eye stalk. Beneath the lobula lies the lateral protocerebrum which is composed of several smaller structures, many of which are yet to be named.…”

“…1.5C). The likely function of the lamina is to encode the spatiotemporal image from the mosaic from the photoreceptors, sharpen the contrast and establish parallel pathways for the processing of colour and polarization (Thoen et al, 2017). The midband cartridges appears as a swelling across the lamina (Fig.…”

“…1.5D, E), however no significant differences have been observed in the structure between the hemisphere and midband cartridges, other than overall size and shape. This suggests that chromatic, achromatic and polarization information is processed using a similar set of cells and that any complex colour processing probably does not take place in the lamina (Strausfeld and Nassel, 1981, Thoen, 2014, Thoen et al, 2017.…”

“…Thoen et al (2017) speculated that the large midband terminals result from the processing required for the quick responses during eye scans. The medulla encodes many different types of visual information, including colour and polarization, and is expected to house many different cell types, such as in insects (Strausfeld, 1976, Strausfeld andNassel, 1981).…”