Crustacean Larvae—Vision in the Plankton

Abstract

We review the visual systems of crustacean larvae, concentrating on the compound eyes of decapod and stomatopod larvae as well as the functional and behavioral aspects of their vision. Larval compound eyes of these macrurans are all built on fundamentally the same optical plan, the transparent apposition eye, which is eminently suitable for modification into the abundantly diverse optical systems of the adults. Many of these eyes contain a layer of reflective structures overlying the retina that produces a counterilluminating eyeshine, so they are unique in being camouflaged both by their transparency and by their reflection of light spectrally similar to background light to conceal the opaque retina. Besides the pair of compound eyes, at least some crustacean larvae have a non-imaging photoreceptor system based on a naupliar eye and possibly other frontal eyes. Larval compound-eye photoreceptors send axons to a large and well-developed optic lobe consisting of a series of neuropils that are similar to those of adult crustaceans and insects, implying sophisticated analysis of visual stimuli. The visual system fosters a number of advanced and flexible behaviors that permit crustacean larvae to survive extended periods in the plankton and allows them to reach acceptable adult habitats, within which to metamorphose.

Two visual systems in one eyestalk: The unusual optic lobe metamorphosis in the stomatopod Alima pacifica

“… Schematics comparing the optic lobe organization of early‐stage larvae, megalopa (decapod only) or late‐stage larvae, and adults of a typical brachyuran decapod and a stomatopod (after Cronin et al, ; Harzsch and Dawirs, ; Thoen et al, ). Upper : Development of the decapod optic neuropils involves a continuous addition of new columns in lamina (La), medulla (Me) and lobula (Lo) from three proliferation zones at the anterior edge of the optic lobe, independent of metamorphosis.…”

“…After several larval molts, the stomatopod larvae metamorphose directly into juveniles, without an intermediate megalopal stage. Like their decapod relatives, the larvae are equipped with compound eyes and well‐developed optic lobes comprising of the lamina, medulla and lobula (Cronin et al, ). But unlike all other crustaceans studied so far, a new adult compound eye develops adjacent to the larval eye in late‐stage larvae before metamorphosis (Fig.…”

“…From embryonic stages through larval and megalopal stages into the adult stage, the same neurogenesis pattern of three band-shaped proliferation zones in the optic lobes was found to constantly give rise to the new columns of lamina, medulla, and lobula (Harzsch and Dawirs, 1996;Harzsch et al, 1999). Figure 6 Schematics comparing the optic lobe organization of early-stage larvae, megalopa (decapod only) or late-stage larvae, and adults of a typical brachyuran decapod and a stomatopod (after Cronin et al, 2017;Harzsch and Dawirs, 1996;Thoen et al, 2017a). Upper: Development of the decapod optic neuropils involves a continuous addition of new columns in lamina (La), medulla (Me) and lobula (Lo) from three proliferation zones at the anterior edge of the optic lobe, independent of metamorphosis.…”

Long-Wavelength Reflecting Filters Found in the Larval Retinas of One Mantis Shrimp Family (Nannosquillidae)

“…Until this study, the larval stomatopod eye structure has been described as typical of most other planktonic crustacean larvae in the open-ocean habitats (epipelagic and mesopelagic) where they are found. Typical features of stomatopod larval visual ecology include compound eyes with a uniform array of ommatidia and a single photoreceptor type [15,16]; morphological adaptations…”

“…Compound eyes evolved in crustacean larvae to mediate visually guided behaviors such as predation and anti-predation responses, as well as migration [16,20]. The gross examination of stomatopod larval eyes from diverse taxa, however, reveals that a single family (Nannosquillidae) deviate from the typical eye structure by their possession of ISRs within the majority of their rhabdoms.…”