Neural organization of first optic neuropils in the littoral crab Hemigrapsus oregonensis and the semiterrestrial species Chasmagnathus granulatus

Abstract

Crustaceans are among the most extensively distributed arthropods, occupying many ecologies and manifesting a great variety of compound eye optics; but in comparison with insects, relatively little is known about the organization and neuronal morphologies of their underlying optic neuropils. Most studies, which have been limited to descriptions of the first neuropil - the lamina - suggest that different species have approximately comparable cell types. However, such studies have been limited with regard to the types of neurons they identify and most omit their topographic relationships. It is also uncertain whether similarities, such as they are, are independent of visual ecologies. The present account describes and compares the morphologies and dispositions of monopolar and other efferent neurons as well as the organization of tangential and smaller centrifugal neurons in two grapsoid crabs, one from the S. Atlantic, the other from the N. Pacific. Because these species occupy significantly disparate ecologies we ask whether this might be reflected in differences of cell arrangements within the most peripheral levels of the visual system. The present study identifies such differences with respect to the organization of centrifugal neurons to the lamina. We also identify in both species neurons in the lamina that have hitherto not been identified in crustaceans and we draw specific comparisons between the layered organization of the grapsoid lamina and layered laminas of insects.

Neuronal processing of translational optic flow in the visual system of the shore crabCarcinus maenas

“…A more complete picture is emerging from recent work on the crab Chasmagnathus. This includes a thorough histological study based on silver staining of neurones (Sztarker et al, 2005;Sztarker et al, 2009) and a detailed analysis of the different properties of lobular neurones involved in escape responses to looming stimuli (Berón de Astrada and Tomsic, 2002;Medan et al, 2007;Oliva et al, 2007;Sztarker and Tomsic, 2008), several of which show a form of learning related to habituation (Tomsic et al, 2003). Yet none of this work refers to the term 'optic flow', nor have stimuli appropriate for the identification of neurones tuned to optic flow been used.…”

“…Unlike Chasmagnathus lobula neurones, those of C. maenas do not show strong habituation, which is an important feature of neurones that elicit escape. Indeed, there is good evidence that, although different crab species (and, to a lesser extent, different decapods) do have homologous neurones, such neurones may become specialised for different functions according to the lifestyle of the species (Sztarker et al, 2005;Sztarker et al, 2009). It is also worth pointing out that a well-studied looming neurone in locusts, the lobula giant movement detector (LGMD) is not directionally selective (Krapp and Gabbiani, 2005); therefore, looming detection and optic flow processing are not necessarily linked.…”

“…A second knowledge gap is the extent to which our two populations of neurones consist of arrays of cells with poles at different azimuth angles. Sztarker et al have now done the anatomy (Sztarker et al, 2005;Sztarker et al, 2009), so future work can build up a picture of the arrays of cells specialized for sensing translational optic flow and the extent to which they interact with each other, perhaps by electrical synapses, as do neurones with similar properties in flies (Haag and Borst, 2005). Finally, we have yet to determine the properties of neurones in the lobula plate of crabs -which may be homologous to that of insects (Strausfeld, 2005) -the area where insect optic flow neurones are found (Krapp et al, 1998).…”

Circular polarization vision in stomatopod crustaceans

“…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. It is the first optic neuropil, below the retina, and it is composed of cartridges, each of which contains the photoreceptor axons and terminals of the R1-8 cells from a single ommatidium Marshall, 2005, Thoen, 2014) (Fig.…”

“…In rows 5 and 6 of the midband the lvfs are mostly smooth compared to those of rows 1-4 which have many dendrites innervating both layers of the lamina. (Nassel, 1977, Nassel and Waterman, 1977, S. et al, 1977, Strausfeld and Nassel, 1981, Sztarker et al, 2009). These are identified by the location of their cell body (in either the proximal (PML) or distal (DML) monopolar cell layer), the location of their dendrites in the external plexiform layers and whether they are contained within a single cartridge or extend into adjacent ones (Fig 5.1D and E).…”