Showing posts with label marine biology. Show all posts
Showing posts with label marine biology. Show all posts

Thursday, March 18, 2021

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

Thursday, June 11, 2020

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