The bootlace worm ( Lineus longissimus ) is a fascinating creature, renowned for its extreme length and unique feeding habits. This article delves into the diet and prey of this remarkable animal, exploring its biology, habitat, and other intriguing aspects.
What is a Bootlace Worm?
Appropriately named, the bootlace worm ( Lineus longissimus ) is a species of ribbon worm, which are known for their long, slender bodies. The bootlace worm in particular is often credited with being the longest species in this group, and perhaps one of the longest known animals in the world. Though they're only about 5 to 10 mm (0.20 to 0.39 in) around, most bootlace worms can be anywhere from 10 to 15 m (32 to 49 ft) long. Some reports of individuals as long as 30 to 55 m (98 to 180 ft) have been recorded, but few have been confirmed. L. longissimus is relatively uniform in appearance, with a dark purple or brown body and few distinct facial features.
Habitat and Distribution
Like most other ribbon worms, the bootlace worm is a marine species. They're most often found along the coasts of northern Europe, especially washed up on beaches or in tide pools. Lineus longissimus can be found on Norway's and Britain's coasts, on the Danish east coast and also on Sweden's west coast. Bootlace worms are indigenous to the northeastern Atlantic Ocean. The worms like to bundle themselves up underneath large boulders by the shore. Other hangout spots include rock fissures, beds of kelp and natural seaside pools. Offshore, bootlace worms frequent sunlit parts of the ocean floor, winding their sinuous bodies through beds of muck and seashells. Noted for its dark complexion, Lineus longissimus comes in shades of black and chocolatey brown. The skin may appear iridescent or striped, at least to our fancy human eyes. Ribbon worms cannot "see" images like we can. Bootlace worms can be found bundled up beneath large boulders by the shore or by rock fissures, beds of kelp and natural seaside pools.
Anatomy and Physiology
L. longissimus has a fairly basic anatomy; it has no heart or spine, and a simple digestive system. The blood of a ribbon worm is held in a series of vessels. When the walls of these constrict, the blood inside is pushed in one direction or another, allowing it to circulate through the body. The general body plan of ribbon worms is very similar to that of turbellarians. They exhibit bilateral symmetry and have a body shape that is cylindrical anteriorly yet flattened posteriorly. The body of a ribbon worm is triploblastic, meaning they have three layers of tissue (endoderm, mesoderm, and ectoderm). Ribbon worms have an epidermis with external cilia to help them move, as well as specialized gland cells. In addition, ribbon worms possess a complete digestive system (i.e., mouth, foregut, stomach, and intestine with an anus at the tip of their tail). Ribbon worms have a nervous system that usually consists of a four-lobed brain with ganglia positioned around the rhynchocoel and connected to paired longitudinal nerve trunks or, in some, middorsal and midventral trunks. Most ribbon worms have chemoreceptors and ocelli that detect light but cannot form actual images. Their excretory system has two coiled canals that are branched with specialized flame cells to filter out soluble waste products.
Feeding Habits: The Proboscis in Action
Bootlace worms feed through a tube known as a proboscis. They feed opportunistically on a variety of other invertebrates, including mussels, clams, annelids, and crustaceans, as well as animal carcasses. When a bootlace worm encounters a potential meal, it expels a special feeding structure called the "proboscis" from a special pouch inside its mouth. The force that propels the probiscis towards its prey also turns it inside out. When a bootlace finds prey, it uses strong muscles to squeeze out the proboscis. The bootlace also produces a sticky mucus that basically glues the worm to its meal. It then ties itself around the prey like a ribbon on a birthday package. It can then pull the prey in through its mouth, just below the proboscis, and swallow it whole.
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Bootlace worms use a tubular feeding structure called the "proboscis" that they force from a special internal pouch when needed. Usually, it's tucked away in a specialized pouch. However, when the need arises, a ribbon worm applies pressure to the area. That force drives the proboscis tube outside the body by - quite literally - flipping it inside-out. Ribbon worms eat a variety of different things, like crabs, snails and animal carcasses. A few species are even herbivorous. Having a quick-draw proboscis really helps these legless animals catch and manipulate food. Sometimes, the proboscis is also used as a digging tool.
Diet and Prey
The favorite prey items of nemerteans are annelids (segmented worms), clams, crustaceans, and other small invertebrates. As all nemerteans, the bootlace worm is a predator and hunts its prey between the rocks on sandy shores, stunning them with its long poisonous proboscis and then swallowing them whole. Once they find their prey, the bootlace worm latches on and injects a neurotoxin that paralyses or kills its target.
Defense Mechanisms
When L. longissimus itself becomes prey, typically by larger crustaceans or fish, it secretes a toxin-filled mucus from its skin that impairs the predators and allows the worm to escape-- much like another worm-like creature, the hagfish. Handling bootlace worms is not a pleasant experience. Naturalists have learned that the bootlace worm's defensive mucus is loaded with peptide toxins. Researchers who participated in that 2018 study have said the most common of these peptides (called "nemertide α-1") probably isn't poisonous to human beings or other mammals. Lab tests showed that exposure to nemertide α-1 interferes with nerve and muscle function in green crabs (Carcinus maenas) and Dubia roaches (Blaptica dubia). As a second line of defense, many ribbon worms are poisonous and taste bad. Several species contain tetrodotoxin, the infamous pufferfish venom that can induce paralysis and death by asphyxia.
Reproduction and Lifespan
Little is known about L. longissimus's reproductive biology. The group it belongs to, ribbon worms, are highly variable and have distinct male and female sexes, or individuals can carry the gonads of both. Marine ribbon worms usually have separate sexes and temporary sex organs. Rows of gonads line the inside of their bodies to produce either eggs or sperm. Sexually reproductive ribbon worms often release eggs and sperm into the water, where they fertilize and become microscopic larvae. Most ribbon worms have direct development: a miniature version of the worm hatches from a fertilized egg. However, the young of one group of ribbon worms, the heteronemerteans, emerge in a bizarre larval stage that looks like a flying saucer. After a few weeks to months living and feeding in the open ocean, a small worm develops inside and, when it’s ready, it eats its way out of the original larva encasing.
Ribbon worms, including the bootlace worm, can also split into segments when disturbed; each segment then has the ability to fully regenerate an entire body. Many ribbon worms can regenerate when a predator takes a bite, healing their broken ends. One worm species, Ramphogordius sanguineus, has an exceptional ability to regenerate: if any part of their body is severed (except for the very tip of their tail where there are no nerves), it can regrow into a new worm. The lifespan of the bootlace worm is also unknown, although it's likely only 1-2 years, like most other ribbon worms. Life span has been reported in one species Paranemertes peregrina at about eighteen months.
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Conservation Status
The bootlace worm has not been evaluated by the IUCN.
Potential Applications of Bootlace Worm Toxins
These toxins are still under-researched, but could be a promising avenue of exploration for a multitude of pesticide applications. The German cockroach, the fruit fly, and the notorious Varroa mite, a killer of bees, have all been tested with these toxins and have died spectacularly. This could be great news for agriculturalists looking for a biopesticide that (hopefully) doesn’t cause too much collateral damage. Who knows? In the near future, products derived from the bootlace worm's stinky mucus may keep pest insects from ruining farms and cash crops.
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