Animal Immortality

Some animals with amazingly long lifespans compared to ours, including one that can survive potentially forever, the "immortal jellyfish":

Animals with the Longest Lifespans

The most incredible is the glass sponge, possibly living up to 15,000 years. Corals and giant barrel sponges are not far behind. Other animals on the list, while impressive, fall within more imaginable ranges, e.g., Greenland sharks (400), ocean quahogs (225), and giant tortoises (possibly up to 250). It's noteworthy that all the most long-lived creatures aside from the bowhead whale (200) are invertebrates or cold-blooded vertebrates. What stops us from attaining such venerable ages? Elephants, at the bottom of the page, have about the same maximum lifespans as humans.

The Wikipedia article on the glass sponge goes into great detail about its biology and ecology but doesn't speculate why it can live so much longer than most animals:

Hexactinellid

"Biological immortality" enables some rare species to avoid aging and thus theoretically live forever. In practice, though, they're not truly deathless, since they can succumb to disease or predators.

Here's a page about the jellyfish with that extraordinary gift:

Immortal Jellyfish

In response to stress, it can hit a "reset button" and revert to its immature polyp stage. The regenerated polyp grows into an adult genetically identical to its previous incarnation. This process of "transdifferentiation," in which "an adult cell, one that is specialized for a particular tissue, can become an entirely different type of specialized cell," is being studied by scientists in search of new ways to "replace cells that have been damaged by disease." Suppose a sapient creature had a similar life cycle? If we did, would we recognize it as a type of "immortality" we'd want? Would memory and learned skills carry over from one phase of the cycle to the next? Bacteria, reproducing by fission, are technically deathless, but if they had individual identities, would that individuality be preserved through their descendants? In musing on the immortal jellyfish, the article raises the question, "If all of an organism’s cells are replaced, is it still the same individual? The genes are the same, of course."

If we consider the issue from that angle, however, almost all the cells in our bodies get replaced throughout a lifetime, too, many of them over and over. Nevertheless, we think of ourselves as the same persons, with continuity of memory, experience, and identity.

Margaret L. Carter

Carter's Crypt

A Plant-Animal Hybrid?

Here's a Wikipedia entry about the emerald green sea slug, a mollusc living in marshes, pools, and shallow creeks, which feeds on algae and incorporates their chloroplasts into its own body. It thereby not only turns green but gains the ability to nourish itself with sunlight:

Elysia Chlorotica

The slug can "capture energy directly from light, as most plants do, through the process of photosynthesis." Once it has established a stable population of chloroplasts, this creature has "been known to be able to use photosynthesis for up to a year after only a few feedings." Some research suggests that a slug may "possess photosynthesis-supporting genes within its own nuclear genome."

An article discussing its biology in less technical language:

The Green Sea Slug Steals Photosynthesizing Power from Algae

The caption on that page declares the emerald green sea slug a true "plant-animal hybrid."

Could a human being -- maybe a superhero mutant -- live on light by photosynthesis, like a tree? I've read this wouldn't be physiologically feasible because that lifestyle requires a mainly stationary existence of standing around exposing a large amount of surface area to the sun for many hours per day. Elysia Chlorotica, however, seems to live like an animal and yet derive nourishment from the sun. Suppose a larger creature with intelligence comparable to ours could do that? Wouldn't that make a cool alien species?

Margaret L. Carter

Please explore love among the monsters at Carter's Crypt.

Animal Regeneration

Here's an article about sea slugs that purposely decapitate themselves:

Decapitated Sea Slugs

It's believed they occasionally "jettison" their bodies to get rid of parasitic infestations. The abandoned torso (if that word applies to slugs) swims independently, sometimes for months, before eventually decomposing. The severed head, however, grows a whole new body, often within three weeks. Meanwhile, it continues to feed on algae as if it doesn't notice it has no digestive system, not to mention other essential organs such as a heart.

Self-amputation, called "autotomy," shows up in other species, such as lizards who let their tails detach to escape predators, then grow new tails. Starfish can generate new arms to replace severed limbs, and in some case a segment of a dismembered starfish can develop into a separate animal. In my high-school biology class, we bisected flatworms to watch the pieces regenerate over several days. Sea cucumbers sometimes eject their internal organs under stress and regrow the lost organs. Mammals, in contrast, have limited capacity for regeneration, but (according to Wikipedia) two species of African spiny mice shed large areas of skin when attacked by predators: "They can completely regenerate the autotomically released or otherwise damaged skin tissue — regrowing hair follicles, skin, sweat glands, fur and cartilage with little or no scarring."

Why do plants regularly lose limbs and grow new ones anywhere on their trunks, while most animals are much more limited in this respect? Why the difference in regenerative capacity between lizards and mammals, although they're all vertebrates? The sea slug's self-decapitation makes tales of vampires and other monsters that can re-grow lost appendages seem more plausible. The slug's independently moving detached parts remind me of a vampire novel by Freda Warrington in which a decapitated vampire regenerates a complete body from his severed head. Meanwhile, the headless corpse grows a new head; however, the resulting individual rampages mindlessly like a zombie. In the science fiction genre, I once read a story whose protagonist hosts a visiting alien at a house party. This alien's species has detachable limbs, so losing an appendage is no big deal for them. Also, this particular ET has a totally literal comprehension of English. When the protagonist compliments a concert pianist with the remark, "I wish I had her hands," the alien tries to do the host a favor by amputating those hands and presenting them as a gift. . . .

It's hoped that understanding the sea slug's remarkable ability "could one day lead to advances in regenerative medicine and other fields." Many science-fiction future technologies include medical treatments that enable injured patients to grow new organs and limbs. Maybe that vision might eventually come true.

Margaret L. Carter

Carter's Crypt

Gelatinous Houses

On the subject of alien-seeming animals inhabiting our own planet, consider the giant larvacean, undersea "gelatinous invertebrates" that look like "ghostly tadpoles" about the size of breakfast muffins:

Snot Palaces

Although the creature's photo brings to mind a jellyfish, it belongs to a different subphylum, the Tunicata. As far as I can gather from Wikipedia, they're mostly hermaphrodites, an efficient type of reproductive biology because any two members of the same species who happen to meet can produce offspring together. With bodies made mainly of water, larvaceans are filter feeders. They construct "houses" around their bodies by secreting mucus in the desired shape and blowing it up like a balloon. These delicate "snot palaces" (a nickname that belies their fragile beauty) have an inner and an outer house. The outer layer provides protection and filters water. The inner structure collects the food from the water. Since the creature's house gets clogged up quickly, it has to build a new one every couple of days. Despite the small size of the larvacean itself, its house can measure at large as one meter.

Would a larvacean's house be counted as part of its body, even though it gets frequently discarded and replaced? Animals such as snakes, after all, regularly molt their skins. The larvacean's "snot palace" isn't alive, but neither are mollusks' shells or our hair and fingernails, all of which tend to be thought of as body parts.

Could a creature composed mostly of water have a brain or a structure that serves as one? Hmm—neurons communicate by electricity, and water conducts electricity, so why couldn't a gelatinous invertebrate have an electrical network that performs brain functions? And couldn't any brain, if its environment demands higher functions for survival, develop sentience? Suppose a larvacean-like animal extruded a mucus "house" with a structure complex enough to support an intelligent electrical network? Of course, every time it replaced that structure, it would have to transfer over stored memories and skills. . . but if we can imagine a cloud of energy with sentience (as in more than one STAR TREK episode), we can imagine a mind built from water and mucus.

Margaret L. Carter

Carter's Crypt