Invertebrates Sleep

Transparent octopus larvae showing the brain,
the white cloudy stuff between its eyes. 

My science-geek book club just finished reading Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness by Peter Godfrey-Smith. This got me going down the rabbit hole, not of consciousness exactly, but sleep. 

 

Since Octopods are wicked smart, the expectation is that their sleep patterns would be akin to those of vertebrates, most of which are kind of smart, while other lowly dumb invertebrates would exhibit different sleep patterns. On the other hand, since sleep is an ancient process, maybe braininess does not influence the pattern.

 

Jellys and flatworms have sleep-like states and lack a centralized nervous system, suggesting that sleep appeared early in the history of animal life. Thus sleep appears to be a fundamental biological function for all animals; well, maybe not sponges. It’s very hard to tell if a sponge is sleeping. We know some reasons for sleep, such as cell maintenance (see below), and sleep has even been proposed as a vital adaptive strategy that allows organisms to optimize fitness in a world with day and night (a diurnal environment). Though that seems an unlikely primary reason for sleep, it may explain the napping of some jellys.

 

Some Cnidarians NAP!!!

The upside-down jelly, Cassiopea andromeda, naps! The midday nap occurs in both controlled laboratory settings and the wild. In C. andromeda, which lives in an symbiosis with a photosynthetic dinoflagellate, sleep patterns are strongly influenced by the light/dark cycle. Napping bottom-up during the day allows its symbionts to bask in sunlight. I wish I had symbionts so I could justify a nap every day. Just to be clear, I do nap every day, I just want more justification for doing so. 

 

Cellular Maintenance and Genomic Integrity

The primary function of sleep is to provide a period for neural maintenance that is inadequate during wakefulness. In diurnal and crepuscular species*, wakefulness is associated with continuous sensory input and metabolic activity, which leads to neuronal DNA damage via reactive oxygen species (ROS) and UV radiation. Sleep enables DNA repair and supports genomic integrity. 

*Crepuscular organism are those that are active in the intervals between dark and light (high activity at dusk and dawn).

Sleep is also associated with autophagy. In this process, cells degrade damaged components and other waste. In vertebrates, this activity interacts with the brain’s glymphatic system to clear metabolic waste products that accumulate during periods of high activity. 

 

In vertebrates, the glymphatic system is the brain's waste clearance pathway, using cerebrospinal fluid (CSF) to flush metabolic byproducts and toxins, particularly during deep sleep, by moving fluid along the spaces surrounding arteries and veins. Its main function appears to be waste removal, but nutrient distribution, and maintenance of fluid balance also occur; some invertebrates may use their hemolymph in a similar way. For context, knowledge of the glymphatic system is relatively recent, first described in 2012, so expect some revelations that may alter our thinking. It’s a big deal since dysfunction of the glymphatic system is linked to neurodegenerative diseases such as Alzheimer's,highlighting the importance of adequate sleep for its activity.

 

Are there other deep-seated needs beyond cell maintenance/ physical restoration for sleep? And, back to our initial inquiry, is octopus sleep different because they are wicked smart?

 

It turns out that, yes, octopus sleep is more complex than that of other invertebrates. It consists of distinct stages, with a pattern of alternation between quiet sleep and active sleep. While many invertebrates, such as jellyfish, scorpions, and honeybees, exhibit a single restful state characterized by behavioral calm and elevated arousal thresholds, the octopus displays a sophisticated active sleep phase that includes rapid eye movements, body twitches, and vivid changes in skin patterning and texture. These active bouts can involve the octopus rapidly transitioning through a diverse set of skin patterns that resemble those seen while the animal is awake.

 

Electrophysiologically, octopus sleep also exhibits signatures that differ from those of other studied invertebrates: During quiet sleep, the octopus brain generates 12–18 Hz oscillations in regions associated with learning and memory, resembling mammalian sleep in both regularity and length. Insects, Drosophila, and honeybees do not exhibit electrophysiological slow-wave action comparable to that observed in vertebrates. In the jellyfish Cassiopea, sleep is defined more simply as a reduction in pulsation frequency and is regulated primarily by light and hydrostatic pressure rather than by complex alternating brain states.

 

The complexity of octopus sleep is evidence of convergent evolution, given their large brains and behavioral sophistication. Their two-stage sleep pattern thus mirrors that of vertebrates, although some differences are expected given their 550 million years of evolutionary separation. Unlike simpler invertebrates that essentially power down, the octopus brain appears to remain computationally active during its sleep, potentially engaging in refinement of its skin pattern control or memory consolidation.

 

But wait!

Crayfish adopt a distinct side-lying posture associated with slow-wave brain activity, elevated arousal thresholds, and regulation similar to that of mammals. They exhibit 15–20 Hz slow-wave brain activity during sleep and may have up to three phases (drowsy, transition, and deep), though they may not include a wave-like, REM-like neural phase. Observations indicate that these sleep states in crayfish are accompanied by fluctuations in cardiorespiratory power, suggesting multiple complex sleep phases and a functional autonomic nervous system. 

 

Is this because crayfish are smart…or at least smarter than we previously expected? How about lobsters and crabs, their relatives? So much to look into…get started. 

 

Quick Summary

Sleep is an ancient biological necessity that evolved long before the development of complex brains. Over time, the diversity of species have extended to a variety of sleep patterns that may be associated with smarts. However, the need for cellular maintenance remains across all animals. Well, maybe not sponges; how do you tell if a sponge is sleeping?

A 3D printed octopus. 

 

Sources and Further Readings

Aguillon R, Harduf A, Sagi D, Simon-Blecher N, Levy O, & Appelbaum L. 2026. DNA damage modulates sleep drive in basal cnidarians with divergent chronotypes. Nature Communications 17 (3): https://doi.org/10.1038/s41467-025-67400-5

 

Godfrey-Smith P. 2016. Other minds: The octopus, the sea, and the deep origins of consciousness. Farrar, Straus and Giroux.

 

Iliff JJ, Wang M, Liao Y, et al. A paravascular pathway facilitates CSF flow through the brain

parenchyma and the clearance of interstitial solutes, including amyloid β. Sci Transl Med. 2012;

4:147ra111.10.1126/scitranslmed.3003748

 

Lesku JA, & Ly LMT. 2017. Sleep Origins: Restful Jellyfish Are Sleeping Jellyfish. Current Biology 27(18): R1014–R1016.

 

Meisel DV, Byrne RA, Mather JA, & Kuba M. 2011. Behavioral sleep in Octopus vulgaris. Vie et Milieu, Life and Environment 61(4): 185–190.

 

Mendoza-Angeles K, Hernández-Falcón J, & Ramón F. 2010. Slow waves during sleep in crayfish. Origin and spread. The Journal of Experimental Biology 213(12): 2154–2164.

 

Nath RD, Bedbrook CN, Abrams MJ, Basinger T, Bois JS, Prober DA, Sternberg PW, Gradinaru V, & Goentoro L. 2017. The Jellyfish Cassiopea Exhibits a Sleep-like State. Current Biology 27(19):  2984–2990.

 

Osorio-Palacios M, Montiel-Trejo L, Oliver-Domínguez I, Hernández-Falcón J, & Mendoza-Ángeles K. 2021. Sleep Phases in Crayfish: Relationship Between Brain Electrical Activity and Autonomic Variables. Frontiers in Neuroscience 15: 694924.

 

Osorio-Palacios M, Oliver-Domínguez I, Montiel-Trejo L, Hernández-Falcón J, & Mendoza-Ángeles K. 2021. Sleep in crayfish: Relationships between brain electrical activity and autonomic variables. AIP Conference Proceedings 2348(1): 050024.

 

Pophale A, Shimizu K, Mano T, Iglesias TL, Martin K, Hiroi M, Asada K, García Andaluz P, Van Dinh TT, Meshulam L, & Reiter S. 2023. Wake-like skin patterning and neural activity during octopus sleep. Nature 619(7968): 129–134.

 

Ramón F, Hernández-Falcón J, Nguyen B, & Bullock TH. 2004. Slow wave sleep in crayfish. Proceedings of the National Academy of Sciences 101(32): 11857–11861.

Siegel, JM. 2008. Do all animals sleep? Trends in Neurosciences 31(4): 208–213.

 

Tobler, I. 1988. Evolution and Comparative Physiology of Sleep in Animals. In Clinical Physiology of Sleep (pp. 21–30). American Physiological Society.

 

Ullern H, Schnur P, Boccara CN, & Knævelsrud H. 2025. Rest, Repair, Repeat: The Complex Relationship of Autophagy and Sleep. Journal of Molecular Biology 437(18): 169227.