Attention, San Francisco parents who want to gratify their child with a cheap pet: Grab a bucket and head on down to Ocean Beach, where the sands were recently bathed with thousands of squishy, purple-blue jelly creatures that are cute as a button—and almost certainly not-toxic to humans, to boot!

Well, some of them probably remain fun to poke and joggle, but as they've been washing up all week no doubt many are dead and smelling like fish intestines. The mass arrival of the sea dweller Velella velella, also known as the "By-the-Wind Sailor," began on the West Coast earlier this month and has been sporadically sliming beaches from Northern California all up the Oregon coast. The ones pictured above during a different velella fest in 2004 are sandy and hard to see. Here's what a fresh one looks like up close:

There's great photographic coverage of this slippery invasion at Reddit, and people are slinging velella shots left and right on social media. 

"Freaky. I saw a few of those at Marshall Beach yesterday and assumed they were jellyfish that had seen better days."  This comment cracked me up; I wonder what a "better day" looks like for a jellyfish.

Swimming around the ocean, carefree.

Very cool looking creatures!

So they're not jellyfish?

I'm confused, and not very good with genus',  I think they might be jellyfish?

Velella is a cosmopolitan genus of free-floating hydrozoans that live on the surface of the open ocean. There is only one known species, Velella velella, in the genus.[1]Velella velella is commonly known by the names sea raft, by-the-wind sailor, purple sail, little sail, or simply Velella.[2]

These small cnidarians are part of a specialised ocean surface community which includes the better-known cnidarian siphonophore, the Portuguese Man o' War. Specialized predatory gastropod mollusks prey on these cnidarians. Such predators include nudibranchs (sea slugs) in the genus Glaucus and purple snails in the genus Janthina[citation needed].

Like many Hydrozoa, Velella velella has a bipartite life cycle, with a sort of alternation of generations. The deep blue by-the-wind sailors that are recognized by many beach-goers are the polyp phase of the life cycle. Each "individual" with its sail is really a hydroid colony, with many polyps that feed on ocean plankton and are connected by a canal system that enables the colony to share whatever food is ingested by individual polyps. Each by-the-wind sailor is a colony of all-male or all-female polyps. The colony has several different kinds of polyps, some of which are both feeding and reproductive, called gonozooids, and others protective, called dactylozooids.[4]

The gonozooids each produce numerous tiny jellyfish by an asexual budding process, so that each Velella colony produces thousands of tiny jellyfish (medusae), each about 1 mm high and wide, over several weeks. The tiny medusae are each provided with many zooxanthellae, single-celled endosymbiotic organisms typically also found in corals and some sea anemones, that can utilize sunlight to provide energy to the jellyfish. Curiously, although a healthy captive Velella will release many medusae under the microscope and thus must do the same in the sea, the medusae of Velella are rarely captured in the plankton and very little is known about their natural history. The medusae develop to sexual maturity within about three weeks in the laboratory and their free-spawned eggs and sperm develop into a planktonic larva called a conaria, which develops into a new floating Velella hydroid colony.[4]

Hydrozoa (hydrozoans) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most living in salt water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in fresh water. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.

So... Not jellyfish but related to jellyfish. Fascinating!