I Can’t Sleep - Jellyfish | Gentle Bedtime Reading for Sleep

Episode Date: July 23, 2025

Unwind with this calm bedtime reading designed to bring peace and ease sleepless nights. Tonight’s soothing sleep story explores the fascinating world of jellyfish, those graceful, ancient creatures that drift through the oceans. You’ll discover their biology, life cycle, and unique role in marine ecosystems, all while relaxing to Benjamin’s steady, peaceful narration. There’s no whispering or hypnosis—just fact-filled, tranquil storytelling to help relieve stress, anxiety, and insomnia. Press play, settle in, and let your thoughts float away with the gentle rhythm of the sea. Want More? Request a Topic: https://www.icantsleeppodcast.com/request-a-topic Ad-Free Episodes: https://icantsleep.supportingcast.fm/ Shop Sleep-Friendly Products: https://www.icantsleeppodcast.com/sponsors Join the discussion on Discord: https://discord.gg/myhGhVUhn7 This content is derived from the Wikipedia article on Jellyfish, available under the Creative Commons Attribution-ShareAlike (CC BY-SA) license. Read the full article: Wikipedia - Jellyfish. Learn more about your ad choices. Visit megaphone.fm/adchoices

You're listening to a Glassbox media podcast. What if I told you that most of the modern day self-help advice you've been hearing could actually make you worse? The key to a better life isn't about feel-good gimmicks that sound catchy. The Mentally Stronger Podcast gives you access to a licensed therapist who shares science-backed tools that will actually change your life. Hi, I'm Amy Morin, psychotherapist, mental strength trainer, and international best-selling author. In each episode, we cover research-back strategies, like how to stop relying on willpower and start creating habits for lasting change. And the five mental strength-building exercises you can do from your couch. I also speak to world-class experts like Dr. Nicole Kane, who shares how to permanently heal anxiety by addressing the root cause.

With over 200 episodes in our catalog, this podcast is for you if you're ready to crush self-doubt, conquer challenges, and become stronger than ever with therapist-approved strategies that can change your life. Listen to Mentally Stronger with therapist Amy Morin, wherever you get your podcasts. Welcome to the I Can't Sleep Podcast, where I help you drift off one fact at a time. I'm your host, Benjamin Boster, and today let's fall asleep learning about jellyfish. Jellyfish, also known as Sea Jellies or Simply Jellies, are the Medusis phase of certain gelatinous members of the sub-phylum Magusazoa, which is a major part of the Phylam Nidaria. Jellyfish are mainly free-swimming marine animals, although a few are anchored to

the seabed by stalks rather than being motile. They are made by an umbrella-shaped main body, made of mesoglia, known as the bell, and a collection of trailing tentacles on the underside. Via pulsating contractions, the bell can provide propulsions for locomotion through open water. The tentacles are armed with stinging cells and may be used to capture prey or to defend against predators. Jellyfish are found all over the world,

from surface waters to the deep sea. Cepozoans, the true jellyfish, are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Large, often colorful jellyfish are common in coastal zones worldwide. The medusae of most species are fast-growing, and mature within a few months, then die soon after breeding. but the polyp stage attached to the seabed may be much more long-lived. Jellyfish have been in existence for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal group.

The name jellyfish, in use since 1796, has traditionally been applied to Medusay and all similar animals, including the comb jellies. The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word fish, with its modern connotation of an animal with a backbone, though shellfish, cuttlefish, and starfish are not vertebrates either. In scientific literature, jelly and jellyfish have been used interchangeably. Many sources refer to only syphozoans as true jellyfish. A group of jellyfish is called a smack or a smuck. The term jellyfish broadly corresponds to Medusay,

that is a life cycle stage in the Medusazoa. The American evolutionary biologist Paul and Cartwright gives the following general definition. Typically, Magisazzoan Nidarians have a pelagic, predatory jellyfish stage in their life cycle. Starazons are the exceptions, as they are stalked. The Miriam-Webster dictionary defines jellyfish as follows. A free-swimming marine silenterate that is the sexually reproducing form of a hydrozone or cyphazone, and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells.

Given that jellyfish is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies and certain salps jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the Megesozoa. The subphylum Mejizzoa includes all Nidarians with a Medusa stage in their life cycle. The basic cycle is egg, planula larvae, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost.

The subphilum include the major tax system. Siphazoa, large jellyfish, cubozoa, box jellyfish, and hydrozoa, small jellyfish, and excludes anthezoa, corals and sea anemones. This suggests that the Medusa form evolved after the polyps. Medusazoans have tetramar asymmetry, with parts in four or multiples of four. The four major classes of Medusa-Zoan Nideria are, Cipazoa are sometimes called true jellyfish, though they are no more truly jellyfish than the others listed here. They have tetra-radial symmetry.

Most have tentacles around the outer margin of the bull-shaped bell, and long oral arms around the mouth in the center of the sub-umbrella. Cubazoa, box jellyfish, have a rounded box-shaped bell, and their valerium assists them to swim more quickly. Box jellyfish may be related more closely to syphozoan jellyfish than either are to the hydrozoa. Hydrozoa medusae also have tetraradio symmetry, nearly always have a vellum, diaphragm used in swimming, attached just inside the bell margin, do not have oral arms, but a much smaller central stock-like structure, the manubrium with terminal mouth opening,

and are distinguished by the absence of cells in the mesoglia. Hydrozoas show great diversity of lifestyle, some species maintain the polyb form for their entire life, and do not form medusa at all, such as hydra, which is hence not considered a jellyfish. And a few are entirely medusal and have no polyb form. Storazoa stocked jellyfish, are characterized by a Medusa form that is generally Cecil, oriented upside down,

and with a stock emerging from the apex of the bell, which attaches to the substrate. At least some Storozoa also have a polyp form that alternates with the megesoid portion of the life cycle. Until recently, Storozoa were classified with a ciphazoa. There are over 200 species of syphozoa, about 50 species of Storozoa, about 50 species of cubozoa, and the hydrozoa includes about 1,000 to 1,500 species that produce Medusae, but many more species that do not. Since jellyfish have no hard parts, fossils are rare. The oldest unambiguous fossil of a free-swimming medusa is Burgosso Medusa from the mid-Cambrian Burgess Shale of Canada, which is likely either a stem group of box jellyfish, Cuba-Zoa, or a Craspida, the clade including Storazoa, Cuba-Zoa, and Ciphasoa.

Other claimed records from the Cambrian of China and Utah in the United States are uncertain. and possibly represent tenophores instead. The main feature of a true jellyfish is the umbrella-shaped bell. This is a hollow structure consisting of a mass of transparent jelly-like matter, known as mesaglia, which forms the hydrostatic skeleton of the animal. The mesoglia is 95% or more composed of water, and also contains collagen and other fibrous proteins. as well as wandering amoebicides that can engulf debris and bacteria.

The mesaglia is bordered by the epidermis on the outside and the gastrodermis on the inside. The edge of the bell is often divided into rounded lobes, known as lapids, which allow the bell to flex. In the gaps or niches between the lapids are dangling rudimentary sense organs known as rapalia, and the margin of the bell often bears tentacles.

On the underside of the bell is the maneuverium, a stock-like structure hanging down from the center. There are often four oral arms connected to the maneuverium streaming away into the water below. The mouth opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed. This is subdivided by the, 4-6 septa into a central stomach and four gastric pockets.

Near the free edges of the septa, gastric filaments extend into the gastric cavity. These are armed with nematocides and enzyme-producing cells and play a role in subduing and digesting the prey. In some cyphozoans, the gastric cavity is joined to radio canals, which branch extensively and may join a marginal ring canal. Cilia in these canals circulate the fluids in a regular direction. The box jellyfish is largely similar in structure. It is a squareish box-like bell.

A short pedallium or stalk hangs from each of the four lower corners. One or more long slender tentacles are attached to each pedalium. The rim of the bell is folded inwards to form a shell. known as a valerium, which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing the box jelly to swim faster than true jellyfish. Hydrozoans are also similar, usually with just four tentacles at the edge of the bell, although many hydrozoans are colonial and may not have a free-living medusal stage. Stock jellyfish are attached to a solid surface by a basil disc, and resemble a polyp, the oral end of which has partially developed into a medusa with

tentacle-bearing lobes and a central manubrium with four-sided mouth. Most jellyfish do not have specialized systems for osmeregulation, respiration, and circulation, and do not have a central nervous system. Nematocytes, which deliver the sting, are located mostly on the tentacles. True jellyfish also have them around the mouth and stomach. Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermas. They have limited control over their movement, but can navigate with the pulsations of the bell-like body. Some species are active swimmers. most of the time, while others largely drift.

The rophalia contained rudimentary sense organs, which are able to detect light, water-borne vibrations, odor, and orientation. A loose network of nerves called a nerve-ned is located in the epidermis. Although traditionally thought not to have a central nervous system, nerve-net concentration and ganglion-like structures could be considered to constitute one in most species.

A jellyfish detects stimuli and transmits impulses both throughout the nerve net and around a circular nerve ring to other nerve cells. The ruffalial ganglia contain pacemaker neurons, which controls swimming rate and direction. In many species of jellyfish, the rothalia include a celli. light-sensitive organs able to tell light from dark.

These are generally pigment-spot ocelli, which have some of their cells pigmented. Therophalia are suspended on stalks with heavy crystals of calcium carbonate at one end, acting like gyroscopes to orient the eyes skyward. Certain jellyfish look upward at the mangrove canopy, while making a daily migration from mangrove swamps, into the open lagoon where they feed and back again. Box jellyfish have more advanced vision than the other groups.

Each individual has 24 eyes, two of which are capable of seeing color, and four parallel information processing areas that act in competition, supposedly making them one of the few kinds of animals to have a 360-degree view of its environment. The study of jellyfish eye evolution is an intermediary to a better understanding of how visual systems evolved on Earth.

Jellyfish exhibit immense variation in visual systems, ranging from photoreceptive cell patches, seeing in simple photoreceptive systems, to more derived complex eyes, seen in box jellyfish. Major topics of jellyfish visual system research, with an emphasis on box jellyfish, include the evolution of jellyfish vision from simple to complex visual systems,

the eye morphology and molecular structures of box jellyfish, including comparisons to vertebrate eyes, and various uses of vision, including task-guided behaviors and niche specialization. Experimental evidence for photosensitivity and photoreception in nadirians antecedes the mid-1900s, and a rich body of research has since covered evolution of visual systems than jellyfish. Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes.

More ancestral visual systems incorporate extraocular vision, vision without eyes, that encompass numerous receptors dedicated to do. single-function behaviors. More derived visual systems comprise perception that is capable of multiple task-guided behaviors. Although they lack a true brain, Naderian jellyfish have a ring-nerves system that plays a significant role in motor and sensory activity. This net of nerves is responsible for muscle contraction and movement and culminates the emergence of photosensitive structures. Across Nideria, there is large variation in the systems that underlie photosensitivity.

Photosensitive structures range from non-specialized groups of cells to more conventional eyes, similar to those of vertebrates. The general evolutionary steps to develop complex vision include from more ancestral to more derived states, non-directional photoreception, directional photoreception, low-resolution vision, and high-resolution vision. Increased habitat and task complexity

has favored the high-resolution visual systems common and derived nidarians, such as box jellyfish. Basal visual systems observed in various nidarians, Exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception, a form of non-directional photoreception, is the most basic form of light sensitivity and guides a variety of behaviors among Nidarians. It can function to regulate circadian rhythm, as seen in eyeless hydrozoans,

another light guided behaviors responsive to the intensity and spectrum of light. Extraocular photoreception can function additionally in positive phototaxis in planula larvae of hydrozones, as well as in avoiding harmful amounts of UV radiation via negative phototaxis. Directional photoreception, the ability to perceive direction of incoming light, allows for more complex phototactic responses to light and likely evolved by means of membrane stacking. The resulting behavioral responses can range from guided spawning events

timed by moonlight to shadow responses for potential predator avoidance. Light-guided behaviors are observed in numerous cyphozoans, including the common moon jelly, Aurelia Rita, which migrates in response to changes in ambient light and solar position, even though they lack proper eyes. The low-resolution visual system of box jellyfish is more derived than directional photoreception, and thus box jellyfish vision represents the most basic form of true vision, in which multiple directional photoreceptors combine to create the first imaging and spatial resolution. This is different from the high-resolution vision that is observed in camera or compound eyes of vertebrates,

encephalopods that rely on focusing optics. Critically, the visual systems of box jellyfish are responsible for guiding multiple tasks or behaviors in contrast to less derived visual systems than other jellyfish that guide single behavioral functions. These behaviors include phototaxis based on sunlight, positive, or shadows, negative, obstacle avoidance, and control of swim pulse rate. Box jellyfish possess proper eyes, similar to vertebrates, that allow them to inhabit environments that lesser-derived Medusa cannot. In fact, they are considered the only class in the clade Magysozoa that have behaviors necessitating spatial resolution and genuine vision. However, the lens in their eyes are more functionally similar to cup eyes exhibited in low-resolution

organisms and have very little to no focusing capability. The lack of the ability to focus is due to the focal length, exceeding the dilestine, distance to the retina, thus generating unfocused images and limiting spatial resolution. The visual system is still sufficient for Box jellyfish to produce an image to help with tasks, such as object avoidance. Box jellyfish eyes are a visual system that is sophisticated in numerous ways. These intricacies include the considerable variation within the morphology of box jellyfish eyes, including their task behavior specification, and the molecular makeup of their eyes, including photoreceptors, opson, lenses, and synapses. The comparison of these attributes to more derived

visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred, and puts into perspective how box jellyfish can play the role as an evolutionary developmental model for all visual systems. Box jellyfish visual systems are both diverse and complex, comprising multiple photo systems. There's likely considerable variation in visual properties between species of box jellyfish, given the significant interspecies morphological and physiological variation. eyes tend to differ in size and shape, along with number of receptors, including opson's, and physiology across species of box jellyfish.

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms, such as vertebrates. Their 24 eyes fit into four different morphological categories. These categories consist of two large, morphologically different medial eyes, a lower and upper-lensed eye, containing spherical lenses, a lateral pair of pigment slit eyes, and a lateral pair of pigment pit eyes. The eyes are situated on Rofalia, small sensory structures, which serve sensory functions of the box jellyfish, and arise from the cavities of the X umbrella, the surface of the body on the side of the bells of the jellyfish.

The two large eyes are located on the midline of the club and are considered complex because they contain lenses. The four remaining eyes lie laterally on either side of each ruffalia and are considered simple. The simple eyes are observed as small and vaginated cups of epithelium. that have developed pigmentation. The larger of the complex eyes contains a cellular cornea, created by a mono-aciliated epithelium, cellular lens,

homogenous capsule to the lens, vitreous body with prismatic elements, and a retina of pigmented cells. The smaller of the complex eyes is said to be slightly less complex, given that it lacks a capsule, but otherwise contains the same structure as the larger eye. Box jellyfish have multiple photosystems that comprise different sets of eyes. Evidence includes immunocitochemical and molecular data

that show photopigment differences among the different morphological eye types and physiological experiments done on box jellyfish to suggest behavioral differences among photosystems. Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors. Box jellyfish eyes primarily use CPRCs, ciliary photoreceptor cells, similar to that of vertebrate eyes. These cells undergo phototransduction cascades, process of light absorption by photoreceptors that are triggered by C-Opsons. Available opson sequences suggest that there are two types of opsons possessed by all nadarians, including an ancient phylogenetic opson, and a sister's ciliary opson to the sea opsons group.

Box jellyfish could have both ciliary and nidops, nidaryans, which is something not previously believed to appear in the same retina. Nevertheless, it is not entirely evident whether nidarians, possess multiple options that are capable of having distinctive spectral sensitivities. Comparative research on genetic and molecular makeup of box jellyfish's eyes versus more derived eyes seen in vertebrates and cephalopods, focuses on lenses and crystalline composition, synapses, and packs genes and their implied evidence for shared primordial

ancestral genes in eye evolution. Box jellyfish eyes are said to be an evolutionary development model of all eyes based on their evolutionary recruitment of crystallins and packs genes. Research done on box jellyfish, including Tripodalia cystophora, has suggested that they possess a single Pax gene, Pax B. Pax B functions by binding to crystalline promoters and activating them. Pax B in situ hybridization resulted in Pax B expression in the lens, retina, and statisists. These results and the rejection of the prior hypothesis that Pax 6 was an ancestral Pax gene in eyes

has led to the conclusion that Pax B was a primordial gene in an eye evolution, and that the eyes of all organisms likely share a common ancestor. The lens structure of box jellyfish appears very similar to those of other organisms, but the crystallins are distinct in both function and appearance. Weak reactions were seen within the CERA, and there were very weak sequence similarities within the crystallins, among vertebrate and invertebrate lenses. This is likely due to differences in lower molecular weight proteins

and the subsequent lack of immunological reactions was antiserra that other organisms lenses exhibit. Jellyfish range from about 1 millimeter in bell height and diameter to nearly 2 meters in bell height and diameter. The tentacles and mouth parts usually extend beyond this bell dimension. The smallest jellyfish are the peculiar creeping jellyfish in the genera Storaucladia and elytheria. which have bell discs from 0.5 millimeters to a few millimeters in diameter,

with short tentacles that extend out beyond this, which these jellyfish used to move across the surface of seaweed or the bottoms of rocky pools. Many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope. They can reproduce asexually by fission, splitting in half. Other very small jellyfish have bells about one millimeter are the hydromedusae of many species that have just been released from their parent polyps.

Some of these live only a few minutes before shedding their gametes in the plankton and then dying, while others will grow in the plankton for weeks or months. The lion's main jellyfish, Cyania capillata, was long-sighted as the largest jellyfish and arguably the longest animal in the world,

with fine thread-like tentacles that may extend up to 36.5 meters long, though most are nowhere near that large. They have a moderately painful but rarely fatal sting. The increasingly common giant, Namura's jellyfish, found in some but not all years in the waters of Japan, Korea and China, in summer and autumn, is another candidate for largest jellyfish, in terms of diameter and weight, since the largest Nomura's jellyfish in late autumn

can reach two meters in bell diameter and about 200 kilograms in weight, with average specimens frequently reaching 0.9 meters in bell diameter and about 150 kilograms in weight. The large bell mass of the giant Nomura's jellyfish can dwarf a diver and is nearly always much greater than the lion's mane, whose bell diameter can reach one meter.