March 27/2024

Snails & Slugs (Gastropoda)

Snails and Slugs (Gastropoda) (molluscs.at)

Introduction

Snails are among those animal groups everybody knows. After rain snails can be seen crawling around on bushes, trees, walls, & roads at a proverbially slow pace.

The Roman snail (Helix pomatia) is a common & well known snail species. This largest native snail (10 cm body length & 4 cm shell diameter) can be found especially in bushes besides roads or on the wood front, where it crawl around mostly in the cool evening hours. If we take a closer look we also find snails on tree trunks in the forest, under decaying wood, on walls & rocks faces. Snails can also be found in settlements & gardens.

That is where snails & especially the large slugs are regarded with much less sympathy, as they may inflict noticeable damage to vegetable & flower beds, not to mention fields & plantations. Not only the large slugs, but also their smaller relatives, are prosecuted with traps & poison. Poison applied to snails naturally also hampers animals that generally feed on snails, such as hedgehogs & toads.

Are snails a garden pest?

Other species, among them notably the Roman snail, generally are picked & eaten. The history of snails as human food can be retraced as far as to prehistoric times. Especially when food was rare peasants are said to have relied on the collecting of snails. From excavations at Roman sites we know that Roman legionaries distributed snails as transportable food in all of the Empire, which is why those snails, notable Helix species, colloquially are referred to as Roman snails. As did the legions of Rome, so did the soldiers of France during Napoleon's campaigns in 19th century Europe. Roman snails in hibernation close their shell with a calcareous lid, which means they are a natural food tin. To be able to rise & sell snails in an economically feasible way, it is necessary to establish a snail farm, in French also referred to as Héliciculture.

 Snail farming

Actually these are only a few of the largest & most various group of molluscs. Altogether there are estimated to be as many as 43,000 species of snails, which is about 78% of all molluscs that by no means only live on land. Snails with a recognizable spiral shell can also be found in rivers, ponds, & other fresh water bodies. So we often encounter pond snails (e.g. Lymnaea stagnalis) in garden ponds, where in contrary to their garden-dwelling relatives, they usually do not inflict any damage.

In the sea, there are snails as well, as on land. There are snails on coastal rock faces, on the ocean floor in various depths, on coral reefs, & even on sea floor hot vents, where steaming hot water emerges into the sea.

Moreover there are sea snails that, on the first sight, might not even be recognized as snails. So the nudibranchs with their colourful dorsal protrusions are snails as well as the ormer or abalone (Haliotis) that with its ear-shaped shell more resembles a mussel, than a snail. In English, snails & other sea molluscs provided with a shell are called just that – shells.

Morphology

Comparing the snail groups mentioned or displayed, besides characters typical for molluscs, there can also be found characters typical for all snails, whatever they may look like from outside.

Snail Morphology

Foot

Most snails have got a noticeable muscular crawling foot with a flat sole, the animal uses to move slowly but visibly. Besides this crawling motion, as it can be seen among ground-living snails from limpets up to terrestrial snails, there are many alternative methods of locomotion. So many snails also are able to use their foot for digging. Among sea snails, notably among sea slugs, there are species that can swim the free water.

Head

At a snail foot's front end, a head can be seen provided with eyes & a variable number of tentacles. Most (not all) terrestrial snails equipped with 4 tentacles, the remaining snail species only have 2 tentacles at their disposition, that may look like threads or even have the shape of ears.

Operculum

At their foot's rear end many water living snails (& few terrestrial species) carry a calcareous lid (operculum) that closes the shell aperture, when the snail withdraws. Using their sabre-shaped lid, conches are even able not only to defend themselves, but also to move in jumps by pushing their operculum into the ground & jerking themselves forward.

Radula

Like other molluscs, snails as well feed using their rasp tongue (radula). From the composition of their radula & the shape of their teeth, different snail groups may be distinguished, such as the primeval docoglossan (meaning beam tongue) limpets or the carnivorous toxoglossan (meaning venom tongue) cone shells. The main function of the radula, whatever its appearance, bases on the same principle, a rasp tongue with tiny chitin teeth is used for food provision. The number & shape of teeth however is dependent on the type of nutrition, as it is among mammals. Herbivorous snails usually have many similarly shaped broad toothlets, the cone shell, on the other hand, having only one harpoon-shaped tooth, that, like a snake tooth, is connected to a venom gland & injects the venom into the prey's body.

Shell

Snails' shells mainly protect the snail's backside, but also several internal organs that are assembled in the dorsal visceral hump. As among other molluscs, among snails as well the shell is produced by cells of the mantle, the tissue coat protecting the snail's backside as well as its visceral hump. Originally snail shells differ noticeably from other mollusc shells, such as a Nautilus's, as they are asymmetrically coiled to one side of the body.

Torsion

Basically the snail shell's form can be retraced to a process in the snail's embryonic development, during which mantle & visceral hump alike perform a 180° clockwise turn, so that the pallial cavity with the respiratory organs comes from a rear to a frontal position. This is the situation present among most sea snails, so those are called Prosobranchia (front gill snails). Among other groups after the torsion there is a counter clockwise detorsion, moving the pallial cavity to a position on the right side of the body, behind the heart. This situation can be found among the Opisthobranchia (hind gill snails) & Pulmonata (lung snails).

In primeval snail groups the 2 main neural pathways run straight & parallel from front to back. After the torsion, in the prosobranch stage, those nerves are crossed, a situation referred to as chiastoneury, those snail groups thus also called Streptoneura (crossed nerve snails). In contrary to that, after the detorsion the nerves lay straight & parallel again, which is why opisthobranch & pulmonate snails are grouped as Euthyneura (straight nerve snails).

Most fresh water & land snails (scientifically referred to as limnic & terrestrial gastropods) maintain a special status, as their gills are reduced completely. Instead oxygen diffuses into the blood by the thin walls of a network of capillary blood vessels in the pallial cavity, which is why these capillary blood vessels are also called a snail lung, hence those snail groups are referred to as lung snails, scientifically called Pulmonata.

Systematics

The result of the situations described above, regarding respiratory & neural systems of snails is a systematic arrangement of snail groups published by Thiele (1929 – 1932), that, until today is the prevailing snail system in most museums & schools. According to Thiele the class Gastropoda (snails) is divided as follows:

Gastropoda

Prosobranchia

Opisthobranchia

Pulmonata

Though, this does not comply with the situation as it looks like since new snail groups were found near sea floor hot vents (already mentioned above). Those snail groups should belong to the prosobranch snails regarding the location of their respiratory organs. Though, other organ systems suggest a relationship closer to the opisthobranch snails. This discovery was supported by a new method of biological examination: molecular genetics & the comparison of genetic sequences.

As a reliable scientific system has to show the evolutionary relationship between the groups in question, the prevailing gastropod system had to undergo a major revision, which has since then been undertaken mainly by Haszprunar, Ponder, & Lindberg. As a consequence today there is a system, in which the gastropods are divided into Pulmonata & Opisthobranchia (grouped as Euthyneura) on one hand, & several streptoneuran groups on the other hand.

Apart from the characteristically wound snail shell there are quite a few other types of shells, that are not without difficulties to be recognized as a snail's shell. A limpet, for example, has got a noticeable spire only in its juvenile stage. Afterwards the spire disappears & the shell, by lateral growth, gets its cup-like shape, optimally adapted to life on rock faces in midst of surf. Cowry shells characteristic shell form develops when the outermost whorl grows over the rest of the spire, which is why only the outermost whorl can bee seen, the others situated in the shell's interior.

Collections

Especially when at the end of the Middle Ages the great exploring voyages brought home information on many new kinds of animals, collections of sea shells became a common hobby among rich merchants & nobles. Many of these collections made the basis for today natural history museums' collections. Today, collecting shells for a hobby is so common that there is even a market for collective shells. On the other hand many, especially rare snail species, are threatened by extinction, as they are collected & killed for collections. That is why a responsible collector should think seriously about the ecological consequences of his collecting.

The science of shells today is called conchology, in contrary to malacology meaning the biology of molluscs.

*NOTE Snails in this post include Esme, Atticus, Cosmo, & Speedy. Photos courtesy  of C.L.I.

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*Next week is E.B.W. Critter Corner's annual Cat Month!!!

March 20/2024

Honey Badger Facts, Pictures: Complete Species Guide

2/16/2024 

by Active Wild Admin

activewild.com

Meet The Honey Badger: Introduction

The honey badger (also known as a ratel) is a mammal in the weasel family. It is found in Africa, the Middle East, & India.

One of the largest species of the weasel family Mustelidae, the honey badger has a reputation for toughness. Its thick skin, powerful claws, & teeth allow it to defend itself against animals much larger than itself.

How To Recognize A Honey Badger

The honey badger has a squat, powerfully-built body, relatively short legs, & a short, bushy tail. Its eyes are small & dark & its ears barely protrude from the head.

The honey badger's thick fur is black on the face, sides & undersides, & pale grey / white on the top of the head, neck & back. Its tough, loose-fitting skin is a defensive adaptation; even if the honey badger finds itself clamped in a larger animal’s jaws, thanks to its loose skin it is able to turn round to bite the would-be predator.

Each of the honey badger's feet has 5 strong, curved claws, with the claws of the forepaws being longer than those of the hindpaws. Its teeth are short & sharp.

Honey Badger Facts: Size

The honey badger is the largest mustelid (member of the weasel family, Mustelidae) found in Africa, & one of the largest overall, being smaller than a wolverine (the largest Musteild), & only slightly smaller than the greater hog badger & European badger.

On average, honey badgers are around 55 to 77 centimeters (22 to 30 inches) in length, with the tail adding another 17 to 30 centimeters (7 to 12 inches). Honey badgers weigh between 5 & 16 kilograms (11 & 35 pounds), with males weighing more than females.

Honey badgers are around the same weight as the jackal species with which they share part of their range.

Where IS The Honey Badger Found?

Despite being found across a wide area, which includes most of Africa, much of the Middle East & part of Asia, the honey badger’s population density is very low.

In Africa, the honey badger is mostly found south of the Sahara desert. The honey badger is also found in several Middle Eastern countries (including Saudi Arabia, Yemen, & Iran), in western Asia & in India.

Habitat

The honey badger is extremely adaptable, & is able to live in a wide range of habitats, including rainforests, savannas, grasslands, & deserts.

Behavior

Adult honey badgers usually live alone, only pairing up during the breeding season. They are primarily nocturnal, but can be active at any time of the day, especially in areas uninhabited by humans.

The honey badger usually digs its own burrow, but will also use the abandoned burrows of other animals, including those of the aardvark & various fox species.

The honey badger’s burrow is relatively simple, consisting of just a tunnel & a resting chamber. It rarely exceeds 3 m (10 ft.) in length & 1.5 m (5 ft.) in depth. The honey badger will fiercely defend its burrow from larger animals who wander too close.

The honey badger is not strongly territorial. A male honey badger has a large home range, which can cover up to 500 km2 (193 square miles). This will take in the home ranges of several females, & will also overlap with the home ranges of other males. Honey badgers leave scent markings to communicate with each other.

Honey badgers produce a range of sounds, including grunts, growls, & whines. When they meet they will sniff each other & roll around, leaving scent marks on the ground.

The honey badger is a highly intelligent animal & there is some evidence of it using objects as tools. Captive animals have been observed piling objects on top of each other in order to escape from an enclosure. Another individual was seen to move a log in order to be able to reach some food.

Diet

The honey badger is an omnivore (it eats both meat & plants), although meat forms the bulk of its diet. Although it hunts most of its own prey, it will scavenge food, & also steal food from other predators.

The honey badger is an opportunistic generalist hunter (i.e. it will eat pretty much whatever it can get its paws on), & does not have a specialized diet. It eats a wide range of animals. Any animal smaller than the honey badger is potential prey, as are mid-sized species & the young of large species such as antelopes.

Small mammals make up the majority of the honey badger’s diet, but it will also eat reptiles (including snakes) & birds.

The honey badger seeks out both honey & bee larvae from wild bee nests & beehives – a behavior that gave the honey badger its name.

Predators

The honey badger is not an easy meal, & has few natural predators. However, despite its tough reputation, the honey badger is not at the top of the food chain.

Large predators such as the lion, leopard & African rock python will prey on the honey badger, although usually only as a last resort if no other food is available. Black-backed jackals have been known to prey on honey badger cubs.

Honey Badger Family & Related Animals

The honey badger is a mammal, & a member of the order Carnivora. If belongs to the family Mustelidae (the weasel family), & is the only animal of genus Mellivora.

Other mustelids (members of the family Mustelidae) include weasels, badgers, otters, martens, & the wolverine.

Despite its name, the honey badger isn’t closely related to other badger species. Its closest living relatives are the martens.

Honey Badger Subspecies

Currently, 12 honey badger subspecies are recognized. These include the Cape ratel, Indian ratel, and black ratel (which is all black in color).

The various subspecies are found in different locations, & are distinguished by differences in size & coat markings.

Honey Badger Life Cycle

Male & female honey badgers only come together for a short time to mate, after which time the male resumes its usual solitary lifestyle. The female digs a burrow & gives birth to a single cub (very occasionally to twins) after a gestation period of 50 to 70 days.

A newborn honey badger cub is blind & hairless, & completely reliant on its mother. Even after reaching adult size at 6 months old, the cub will remain with its mother for at least another 8 months as it learns how to fend for itself.

Is The Honey Badger Endangered?

Despite being a rare animal, the honey badger is found across a wide area & currently is not endangered. The species is rated "Least Concern" by the IUCN. However, the honey badger population is thought to be decreasing.

Honey badgers are hunted by local people for food & for use in traditional medicines. They are also killed by local beekeepers who believe that the species is a threat to their livelihood.

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March 13/2024

 

Baby Sea Stars Are Voracious Predators That Might Just Save an Ecosystem

By Roxanne Hoorn

2/27/2024

atlasobscura.com

ALONG THE NORTHERN PACIFIC COAST, bright orange, blue, green, & pink sea stars hunt along the seafloor. The animals have as many as 24 arms & can get big, reaching the diameter of a bicycle tire, or about 3 feet across. Moving up to 200 feet an hour, these sea stars are fast—& furious. The sunflower sea star has a reputation as a vicious predator in its kelp forest ecosystem, swallowing prey—such as spiny sea urchin & hard-shelled mussels—whole.

While the adults may be impressive in size, new research shows that juveniles smaller than the eraser on a pencil may be the most voracious consumers. In a lab setting, they ate up to 10 times as much, proportionally, as adults. Being hungry isn’t uncommon for growing young, but in this case, it could have major implications for conservation.

That’s because sunflower sea stars are crucial predators for a healthy kelp forest ecosystem. While they’re not picky eaters, & will make a meal of anything from mussels to sea cucumbers, they primarily eat sea urchins, which helps keep the urchin population from exploding & overgrazing the kelp. The sea stars’ role in maintaining balance in their ecosystem is so important that scientists consider them a keystone species—remove the keystone, & the whole system can crumble. “It’s like a game of Jenga,” says biologist Jason Hodin at University of Washington’s Friday Harbor Laboratories. “You can remove a few pieces, but then you remove that one & everything sort of collapses.”

In 2013, the Jenga tower began to fall. A disease called Sea Star Wasting—which is still not well understood—struck on the West Coast. It reduced healthy sea stars to piles of rotten goo. “The sea stars essentially melt until there’s no tissue,” says senior aquarist Jennifer Burney at the Aquarium of the Pacific in California. “When you pick one up, it would be falling apart like a pile of wet tissue paper.”

Sunflower stars were hit the hardest, wiping out up to 90% of the population. Before, these voracious creatures covered a 2,000-mile-long range, from Alaska to Baja California. Now, sunflower stars have almost completely disappeared from California kelp forests, & the species overall is listed as critically endangered by the International Union for Conservation of Nature.

With the absence of the not-so-gentle giants, their sea urchin prey began to flourish, overgrazing the kelp forests many creatures rely on. “I think it’s difficult to overstate how shocking the kelp forest disappearance in California was during the last 10 years,” says Hodin. “That highlighted these generally understood connections between sea stars & urchins & kelp.”

In 2019, Hodin & his colleagues at Friday Harbor Laboratories, in the San Juan Islands, decided to take action. Through the support of The Nature Conservancy, they launched a breeding program focused on raising robust sea stars that would eventually be reintroduced to the dwindling kelp forests.

The problem was that no one had ever done that before, & not a lot was known about the life cycle of sea stars. No one was sure what juveniles ate, or how long raising them would take. During the project, Hodin & colleagues discovered that baby sea stars go from the size of a sand grain to that of a silver dollar in about a year, slowly adding arms as they continue to grow in their second year & beyond. We don’t even know how long they live, but given their massive manhole cover size, it’s likely a long time.

Through trial & error, & a lot of spawning, Friday Harbor Laboratories became the first to successfully breed the tricky species. The population begun with 30 wild-caught sunflower stars & is now “bursting at the seams,” says Hodin. Hundreds of stars now fill both the lab & several outdoor study tanks, as well as experimental cages out in the water. As word of the lab’s success spread, other aquarists across the country wanted to help. In August 2023, the Association of Zoos & Aquariums formed the Saving Animals From Extinction Sunflower Sea Star program, which has inspired groups across the country to successfully spawn their own sunflower sea stars, from California to Nebraska, & study how to protect the species.

While the goal of the work has always been to breed sea stars for release, Hodin says the proliferation of baby stars has also given him “the opportunity to do something that I’ve always wanted to do, which is trying to figure out what’s going on in the very, very early cryptic life stages of these stars.”

In their first year of life, sunflower stars grow from the size of a grain of sand to that of a silver dollar; born with 5 arms, they'll continue to add appendages throughout their life.

Inside the lab, Hodin points out rows of small plastic compartments—which are actually bead organizers—that he calls “mini condos.” Each one will hold a juvenile sunflower star the size of the period at the end of this sentence. Carefully, aided by a microscope, researchers use a pipette to transfer one tiny, 5-armed sea star into its new home. Then they add an even smaller sea urchin larva.

At first, tiny sunflower stars will eat an urchin or 2 a day. About a month later—when they’ve already grown 10 times in size—they really get ravenous, says Hodin. At this point, feeding is more like the scene in Jurassic Park where they lower the cow into the raptor pen. While previous studies at the lab showed adult sea stars eat one adult urchin every other day or so—or at most 2 per day—the babies were seen eating an average of 10 urchins a day.

Right now, Hodin stresses he doesn’t want to jump to any conclusions—the team’s findings are awaiting peer review, & he plans to test his theory outside the lab. But he & his peers believe a fuller understanding of juvenile sea stars could influence the conservation strategy for the species—& for the entire kelp forest ecosystem. “These young life stages may actually be particularly key in understanding the ecology of kelp forests,” he says. “It’s not a huge logical leap to think that there might be some important ecological stories there that we’re not telling.”

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March 6/2024

Bizarre, alien-like creature discovered deep in Atlantic Ocean has 20 gangly arms

By Ben Turner 

livescience.com

8/18/2023

Researchers have discovered an otherworldly, 20-tentacled creature lurking in the freezing depths of the Antarctic Ocean.

Resembling an alien or a Lovecraftian horror, the Antarctic strawberry feather star (Promachocrinus fragarius) is one of 4 new species of crinoids that scientists found at the bottom of the ocean. Crinoids are a group of eerie, perfectly symmetrical creatures that include sea lilies & sea feathers. Sea lilies attach themselves to the ocean floor with a stalk, while sea feathers abandon their stalk upon reaching maturity to waft themselves through the sea with mesmerizing, synchronized swishes of their arms.

Prior to the discovery, there was thought to be only one species of Antarctic feather star, Promachocrinus kerguelensis. But the new research has revealed that at least 8 species of the strange creatures live in the waters surrounding the southernmost continent, at depths ranging from about 330 to 3,300 feet (100 to 1,000 meters).

To discover the new animals, whose colors range from purple to dark red, researchers trawled a net across patches of the Southern Ocean to collect samples of the creatures. After performing a DNA analysis, the researchers classified the creatures into 4 new species. 

Intrigued by their findings, the researchers then took a closer look at sea feather specimens that were captured between 2008 & 2017 & were presumed to be P. kerguelensis. Their efforts netted them a discovery of 4 more new species — bringing the total to 8.

The Antarctic strawberry feather star gets its name from the strawberry-like nub on its body, from which stringlike appendages called cirri protrude anchor the animal to the seafloor. When feather stars take flight, they spread their arms wide & paddle with rhythmic pulses, dancing through the water & capturing plankton with thousands of tiny, mucousy filaments along their arms.

Crinoids like these dominated the young seas of our planet, but they were largely wiped out — along with 95% of life on Earth — during the Permian mass extinction roughly 251 million years ago.

The researchers published their findings July 14/2023 in the journal Invertebrate Systematics.

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