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Velvet worms are enigmatic creatures with peculiar bodies, surprising social behavior, and unconventional mating rituals. They are found in tropical regions and certain temperate areas in the southern hemisphere. Despite their adorable name, these extraordinary animals can be a nightmare for their prey.
10. Slime Attacks
Velvet worms exhibit an ancient and bizarre trait that seems straight out of a science fiction novel. They can eject a sticky slime up to 30 centimeters (1 ft) to immobilize their prey.
Produced within two glands, which together account for about 10 percent of the velvet worm's body mass, the slime is expelled through muscular contractions and forced out of two specially adapted legs. The slime is projected like a sprinkler and rapidly solidifies, trapping the prey in place.
Once the prey is paralyzed, the velvet worm devours it. Researchers were astounded to find that the spray is guided by fluid movement through the oral tubes, not by muscular action.
As the fluid moves through the oral tubes, the appendages flop around like a loose hose. These oscillations produce the necessary 'sprinkler effect' to ensnare prey, allowing the velvet worm to continue with its even more unsettling methods of feeding.
9. Jointless Stub Feet
Velvet worms are inherently bizarre. Even their seemingly normal body parts exhibit peculiar adaptations. For instance, rows of legs stretch along each side of the velvet worm's body, resembling a centipede. While each leg appears typical at first glance, a closer inspection reveals a complete lack of joints.
Velvet worms have 'stub feet'—simple, fluid-filled structures that operate through hydrostatic action. These stub feet resemble blobs.
These feet can be flexed and compressed in various directions. Without a skeleton, the velvet worm relies on hydrostatic pressure to walk and support its body. By alternating fluid pressure, its appendages move in pairs, lifting upward as its body ripples. The worm’s slow but effective 'hydrostatic locomotion' allows it to move with ease.
The animal’s flexibility enables it to traverse a variety of surfaces in its environment with relative ease. Each leg ends in a slightly recessed, sharp claw, allowing the velvet worm to cling tightly as it moves on its jointless legs.
8. Impressive Fangs
Once the velvet worm identifies a vulnerable area on its prey, it uses its large, curved fangs—comprising both inner and outer sets of fangs—to tear into the victim. Unusually, the jaws move along the body, rather than opening and closing in a perpendicular motion like those of other arthropods.
The smooth, powerful claws are made of chitin and reinforced with biochemical substances known as phenols and chinons. While the base of the claws contains a consistent mix of materials, the tips are fortified with calcium, making them more durable and resistant to wear as they subdue prey.
The inner fangs are equipped with multiple denticles, while the outer fangs feature a single point. These robust fangs, attached to powerful muscles, are highly effective in processing prey once it has been immobilized by the worm's slime.
Concealed by the soft mouthparts, the fangs could cause a painful bite if a human handles the creature carelessly. Studies have revealed tanning and hardening in certain parts of the jaws, along with structural patterns displaying arthropod-like features. This hardening is a crucial adaptation for the velvet worm as it tears into the tough exoskeletons of arthropod prey.
7. Velvet Worm Sociology And Group Hunting
Not all velvet worms are solitary. The highly evolved Australian species Euperipatoides rowelli is a pack hunter with a sophisticated social structure and hierarchy, typically led by a female. Members of these groups can capture larger prey through coordinated slime attacks. The social hierarchy is rigidly enforced, resembling the pack dynamics of wolves or a pride of small lions.
The largest, most dominant worm will drive the others away, feasting alone for an extended period before the rest of the group has a chance to eat. This hierarchical structure is uncommon in arthropods. It is believed that these creatures are related, with cooperative groups of up to 15 velvet worms exhibiting behaviors that some traditional anthropologists argue are uniquely human.
Despite their relatively primitive nature, these invertebrates display this complex behavior. The combination of powerful hunting strategies and group collaboration makes Euperipatoides rowelli, and potentially other velvet worm species, highly effective predators.
6. Antenna-Based Investigation Of Prey
Using the long antennae extending from its head, the velvet worm gently probes potential prey by tapping or brushing its body to assess whether it's a suitable meal. Through the antennae, it gathers information on nutritional value, potential threats, and size, quickly retracting them after each probe to avoid being detected by its prospective meal.
Once the velvet worm determines the prey is appropriate, it uses varying degrees of force, applying slime to immobilize the target before its jaws dismember the prey and assist in consumption. Since slime is precious and takes time to replenish, deciding if a meal is worth the effort is a strategic cost-benefit decision that has proven effective for the velvet worm.
5. Misplaced Reproductive Organs
The reproduction process of velvet worms is as strange and disturbing as their feeding habits. However, the most significant bodily damage during reproduction is caused by a particular female velvet worm after mating with a chosen male.
Male velvet worms in the Peripatopsidae family do not directly inseminate females; instead, they deposit sperm packets on the female's skin. The female then secretes an enzyme that dissolves both the sperm packet's casing and part of her own skin. Through this self-inflicted wound, she absorbs the sperm, which then circulates through her bloodstream after the sperm cluster disassembles.
The transportation of certain sperm is assisted by funnel-like structures, while others are directed straight into storage compartments. Australian velvet worm expert Noel Tait from Macquarie University uncovered that males of several newly discovered species possess reproductive organs on their heads, which they insert into the female's genitalia.
Additionally, it appears that skin absorption-based mating methods remain an option if a female has already been inseminated. One velvet worm species has abandoned traditional sexual reproduction with two partners and instead reproduces asexually by cloning itself to create offspring.
4. A Living Fossil Of Research Interest
Velvet worms possess a unique evolutionary biology that intrigues scientists. Belonging to their own phylum, Onychophora, they stand apart as an entirely distinctive form of animal life. With 110 species, their evolutionary past seems to span hundreds of millions of years.
Although velvet worms are terrestrial creatures today, they appear to be linked to marine species found in the fossil record, including animals that closely resemble the present-day velvet worms found crawling on land. Some fossils of their ancestors are estimated to be around 300 million years old.
Their marine ancestors are even more ancient, dating back 500 million years. Beyond their possible marine origins, velvet worms are increasingly considered by scientists to be a key evolutionary link between annelid worms, such as earthworms, and arthropods.
While the exact relationship between velvet worms, arthropods, and annelid worms remains unproven, evidence suggests that velvet worms are more closely related to arthropods than to true worms. Recent research has even linked a peculiar fossil creature with legs to the velvet worm. Notably, the powerful jaws of the velvet worm are believed to have evolved from modified legs.
3. Oxygen-Free Blood And Blood-Bathed Organs
In humans and many animal species, the bloodstream serves primarily to deliver oxygen to essential organs, tissues, and cells. However, velvet worms do not possess a conventional circulatory system. Instead, they absorb oxygen via the same tubules that prevent them from retaining water, making them reliant on humid environments.
Unlike most animals, velvet worms lack blood vessels such as arteries and veins. Instead, their internal organs are enclosed in a body cavity, which is filled with blood that both nourishes and eliminates waste. This blood circulates throughout the body via a remarkably long, tube-shaped heart.
Interestingly, the circulatory fluid in a velvet worm does not carry significant amounts of oxygen. To supply oxygen to its organs, the velvet worm utilizes a direct delivery respiration system. Oxygen enters through spiracles—tiny openings in the skin that are connected to delicate air tubes, allowing the worm to bypass the blood for oxygen transfer.
2. Hydrophobic Exoskeletons
Velvet worms derive their name from the soft, velvety texture of their skin, which is covered with dermal papillae that have hydrophobic (water-repellent) scales. These adaptations help the worms thrive in the moist forest environments they inhabit.
Velvet worms inhale through openings called trachea, which are scattered across their body. These openings remain permanently open, exposing the worms to the constant risk of drying out. Consequently, they can only survive in habitats that maintain their moisture.
To prevent absorbing too much water and causing their skin to become overly damp, velvet worms developed a covering of fine papillae, each made up of tiny, overlapping scales. These scales help to repel excess moisture, allowing the velvet worm to stay hydrated in its humid environment without becoming waterlogged.
1. External Enzymatic Prey Digestion
Being captured by a velvet worm is both a physically and chemically intricate process for the prey, and it can be a bit unsettling for a human to witness. The unsettling aspect is partly due to the worm’s habit of enzymatically digesting the prey even before it is consumed.
Once the prey is coated in the worm's slime, it uses its powerful jaws to tear open the exoskeleton or skin of the prey, depending on the species. The worm then injects potent enzymes into the prey’s body cavity through the wound in its exoskeleton. The prey dissolves into a chemical soup, which the velvet worm ingests as a slurry of pre-digested material.
This efficient method eliminates the need for extensive chewing or separating the soft flesh from the hard body parts. The velvet worm also consumes any slime that has enveloped the prey, ingesting the liquefied portion of the animal along with the meal.
