Limnotrachelobdella okae

Do you like eating fish? Well so do some leeches. Most people only know about the leeches that feed on humans, but there are also numerous other species of leeches out there, and many of them are found in the sea. As the saying goes, "there are plenty of fish in the sea", so they are often the target of these leeches' appetites. And if you're going to be farming fish in the sea, there's a chance that you have inadvertently opened up an all-you-can-eat buffet for some hungry leeches.

Top left: Limnotrachelobdella okae attached to the base of a fish's dorsal fin, Top centre: a leech attached to a fish's tail fin, Top right: a lesion caused by the leech's feeding. Bottom: A mature Limnotrachelobdella okae leech
Photos from Fig. 2 and Fig. 3 of the paper.

The Mi-iuy Croaker (Miichthys miiuy) or 鮸鱼 is a popular food fish in China, where it is considered to be not just tasty and highly nutritious, but may also have medicinal properties. Because of the high demand for this fish, it is farmed in sea cages to ensure continuous supply without threatening wild stocks. But as with farming on land, having a lot of animals in a single place makes them extremely vulnerable to parasites.

In January 2025, there was an outbreak of marine leeches at a croaker farm off the coast of Raoping County in the Guangdong Province. Fish began dying off at the start of January, with fish mortality peaking towards the end of month, before tapering off over the course of February and March. At its peak, the sea cages that housed the croakers were swarming with leeches, and over a hundred thousand kilograms of fish were killed by their feasting.

So what exactly were the slithery killers that dined and dashed at that fish farm? Researchers were able to identify those thirsty blood-suckers as a species of leech called Limnotrachelobdella okae. It belongs to the Piscicolidae family - a group of leeches that mostly specialise in parasitising fish. When the leeches entered the sea cage, they just grab onto whichever part of a fish and start sucking, but they mostly focused on the part of the body which had thin skin and plenty of blood vessels. This included the fins, mouth, the edge of the gill covers, the tail, and the belly of the fish. Limnotrachelobdella okae are big leeches, reaching 12-15 cm in length, and having just a few of those big suckers on a fish would render it anaemic in no time.

When the researchers examined the parasitised fish, they found that not only did these fish have severely depleted blood cells as result of the leech's ravenous appetite, they also suffered internal injuries to their internal organs including their liver, spleen, and kidneys. This is due to depleted blood flow to those organs, because under anaemic conditions, blood flow is preferentially directed to organs with high oxygen demands such as the heart and the brain, and this comes at the expense of the other organs. And unlike our kidneys, the "head kidney" in fish also produces new blood cells, rather like our bone marrow. So the reduction of blood flow into the fish's head kidney also reduces its capacity to replenish that lost blood.

So why did the outbreak happen when it did? Well, it might have something to do with leech's temperature preference. Limnotrachelobdella okae seems to prefer water at a chilly 5-10°C. When the researchers kept some of the leeches in aquariums set at different levels of salinity and temperature, they found that the leeches thrived in cold, salty water, but if it gets above 20°C they start dying in droves. This might explain why the swarm of leeches suddenly appeared in January, since that is the coldest month in China. As the year progressed and the weather got progressively warmer, the number of leeches declined and their threat ended once the water temperature reached 20.5°C in April.

Parasites are just like any other organisms in the environment, their activities are deeply tied with climatic conditions. So understanding parasite ecology can help us better prepare for their emergence. Because sometimes winter doesn't just bring cold wind and snow, it could also be bringing leeches in tow.

Reference:

Che, S., Mo, Z., Zhang, H., Tang, H., Dan, X., & Li, Y. (2026). First report of marine leech Limnotrachelobdella okae infestation in miiuy croaker (Miichthys miiuy): an emerging threat to Chinese mariculture. Veterinary Parasitology, 341:110637.

Acanthobdella peledina

In the cold rivers and lakes of the arctic and subarctic region, there live some rather peculiar worms with a face full of tiny hooks and an appetite for blood. These worms live as ectoparasites of fish, and they belong to a group called Acanthobdellida - relatives of leeches that seem to have gone down their own evolutionary path. These worms have also been called "hook-faced fish worms" and the entire group consists of only two known species - Acanthobdella peledina and Paracanthobdella livanowi. 

Top: Acanthobdella peledina on a grayling.
Bottom: Scanning electron micrograph of the whole worm (left) and close-up of the anterior body region (right).
Photos from Figure 1, 6, and 7 of the paper

Their mouthpart has been described as being a less sophisticated version of a leech's mouthpart - they lack the saw-edged jaws or the extensible proboscis found in many leeches, nor do they have the muscular sucker which surrounds the mouth. Instead, they have a protrusible pharynx and a series of hooks on the first five segments of the body, which they use to attach themselves to their fishy hosts. 

They have previously been considered to be a "missing link" between leeches and the rest of the Clitellata - the group of segmented worms that also includes earthworms and tubifex worms - as they have certain features which are commonly found in other clitellate worms but are absent in leeches. This includes having tiny bristles (called chaeta) on their segments, and a reproductive system similar to those found in earthworms.

Acanthobdella peledina is found all across the subarctic, where they range from being relatively rare to being found on over two-thirds of the fish at a given location. Given it is so widely distributed, with populations scattered across different geographical locales, could each of those distinct populations actually be different species? A group of researchers set out to determine whether there are actually more species of these hook-faced worms than meets the eye. Furthermore, they also wanted to find out how closely related Acanthobdella and Paracanthobdella are to each other. They did so by comparing museum specimens of hook-faced worms which have been collected from sites across the subarctic, including Norway, Sweden, Finland, Alaska, and Russia. 

Aside from examining their anatomical features, the researchers also compared five different key marker genes from these worms. Some of those DNA segments came from the mitochondria, others from the cell's nucleus. The reason for comparing multiple genes is that each has their own histories, and may offer different perspectives on the organism's evolutionary history. It is like interviewing different witnesses at a crime scene.  Unfortunately, for whatever reasons, the DNA of these worms proved to be particularly challenging to amplify and sequence, so for most specimens they were only able to sequence up to four of the five genetic markers they were aiming for, with some specimens only yielding sequences for two of the genes. Despite that limitation, the researchers were able to use the sequences they obtained to resolve the hook-faced worm's evolutionary history.

Despite their wide distribution across the arctic and subarctic regions, Acanthobdella peledina does appear to be a single, widespread species. While the Alaskan population of worms are genetically distinct from the Nordic population, they are not dissimilar enough for them to be considered as separate species. Furthermore, based on their analysis, the two living species of hook-faced worms are quite closely related to each other. In fact, it seems they had only diverged from each other just prior to the last ice age. So, far from being some kind of "missing link" between leeches and other clitellate worms, these hook-faced worms belong to their own distinct group.

But while the two living species had shared a common history until relatively recently, the hook-faced worms as a group had evolutionarily split off from the leeches a long time ago. Based on available data on these worms, this might have occurred during the early Cenozoic as the ancestors of the hook-faced worms became specialised on arctic freshwater fishes that arose during that era, such as salmonids.

So it might have been the pursuit of salmonids that had sent these worms down their own distinct path - a story which is probably relatable to any fly fishers out there.

Reference:

de Carle, D. B., Gajda, Ł., Bielecki, A., Cios, S., Cichocka, J. M., Golden, H. E., Gryska, A. D., Sokolov, S., Shedko, M. B., Knudsen, R., Utevsky, S., Świątek, P. & Tessler, M. (2022). Recent evolution of ancient Arctic leech relatives: systematics of Acanthobdellida. Zoological Journal of the Linnean Society 196: 149-168.

Pterobdellina vernadskyi

If you've ever been out hiking in the wilderness, you would know that there is no shortage of tiny animals out there that love nothing more than to feast on your blood. They range from mosquitoes to midges, from fleas to ticks, and of course, let's not forget about leeches - a group of animals so synonymous with blood-sucking that its name is also used as a term for exploiting the life blood of others.

But leeches aren't just found out in the bushes, there are hundreds of species of blood-sucking leeches that are actually aquatic, feeding mostly on amphibians and fishes. In fact, spare a thought for the fishes, which have a whole family of jawless leeches called Piscicolidae that are after their blood.

Left (top) Antarctic toothfish with P. vernadskyi leeches on its body surface, and (bottom) in its mouth. Photos by Gennadiy Shandikov from Fig. 1 of the paper.
Right: Two live specimens of P. vernadskyi (the left leech has a spermatophore in its clitellum) from Fig. 2 of the paper
 

For fish, there is no escape from these leeches as they are found in a wide range of aquatic habitats, ranging from freshwater to the marine environment. They target a wide range of hosts, from trout and carp, to rays and sharks. Even in the inky depths of the deep sea, there are hungry leeches waiting for a tasty fish to swim by, and it is one of these deep sea leeches that is featured in today's post.

This post is about a newly described species of fish leech - Pterobdellina vernadskyi - which has been found parasitising the Antarctic toothfish (Dissostichus mawsoni) in the cold dark waters of Antarctica. The researchers who described this species collected them from fish that were caught by longline commercial fishing vessels - Antarctic toothfish are highly valued on the commercial market, where they are often sold alongside the Patagonian toothfish as "Chilean Sea Bass".

While most of the fish that the researchers encountered only had one or two leeches, some were afflicted with ten or more, and one unlucky fish was covered in twenty eight leeches all over its body. They tend to favour attaching to either the dorsal surface of the fish, or inside the mouth, where they are more sheltered. And P. vernadskyi can grow rather large compared to other fish leeches, reaching about 8 cm in length - so roughly the size of your finger.

Aside from its sheer size, another thing that differentiates it from other leeches are series of distinct, zig-zag ridges along its back and fin-like projections along its sides. It is not entirely clear what purpose those structures serve for the leech, though there are other deep sea ectoparasites which also have some unusual external structures. The researchers suggested that perhaps they serve some kind of sensory function that allows to leech to find their host, or they might be adaptations to the low oxygen levels of its environment, increasing the leech's surface area so it can absorb more oxygen from the surrounding waters.

In additional to those external features, it is worth mentioning that this leech's host, the Antarctic toothfish, is notable for producing antifreeze glycoproteins in its blood, which allows it to dwell in such frigid waters. But this additive would surely have some implications for the digestive system and physiology of P. vernadskyi compared with other fish leech that feed on hosts with more conventional blood.

Since the Antarctic toothfish can be found dwelling as deep as 2600 m below sea level, this would make P. vernadskyi the deepest Antarctican leech that has ever been recorded. However, it is NOT the deepest depths that a leech has ever ventured. That title goes to Johanssonia extrema which has been found in the hadal zone over 8700 m below sea level in the Kuril–Kamchatka Trench, where the waters are still and the pressures are crushingly immense.

Pterobdellina vernadskyi is just one out of two dozen different species of fish leeches that have been recorded from Antarctica, and there are a number of other leeches which have been reported from deep sea habitats. It would be safe to say that P. venadskyi, and other marine leeches that have been described in the scientific literature, represents only the tip of the iceberg. Where there are fish, there are leeches.

Reference:

Utevsky, А., Solod, R., & Utevsky, S. (2021). A new deep-sea fish leech of the bipolar genus Pterobdellina stat. rev.(Hirudinea: Piscicolidae) parasitic on the Antarctic toothfish Dissostichus mawsoni (Perciformes: Nototheniidae). Marine Biodiversity 51: 15.

Dinobdella ferox

When it comes to parasitology, sometimes you have to get really up close with your study organism, as one researcher in Taiwan did in trying to figure out the behaviour of Dinobdella ferox - a species of leech that has a habit of getting into some uncomfortable (for its host) places.

Dinobdella belongs to a family of leeches call the Praobdellidae - unlike other leeches that simply latch onto their host's skin and start sucking, Dinobdella and most other praobdellid leeches attach themselves to and feed from the host's mucous membranes - which means they either crawl up the host's nose, or occasionally even up their urethra or anus. Because of their habit of hiding themselves in parts of the host where the sun doesn't shine, it is rather difficult to figure out just what exactly what they get up to when they are attached to the host (aside from sucking blood).

Top: a D. ferox leech poking out of Dr Lai's nose., Bottom: a D. ferox leech which has emerged after the infection period
From Fig. 1. of the paper

Dr Yi-Te Lai at National Taiwan University decided to put his body on the line in the name of science, and infected himself with some D. ferox leeches, diligently documenting his own health and the leeches' behaviour throughout entire duration. He conducted three trials, each time administering himself with a different D. ferox leech - and you can see him demonstrating his procedure for self-infection in this video.

During this period, in addition to documenting the leech's behaviour based on his first hand experience, Dr Lai also took regular trips to a local clinical laboratory to examine the leech via endoscopy, and take measurements of his red and white blood cell counts to see what effects the leech's feeding might have on his blood works.

Some of the symptoms he experienced during the leeches' residency were to be expected, including nasal congestion, mild stinging sensations and some nosebleeds. But despite the leech's feeding, he found that both his red and white blood cell count held steady during the infection period, and his body was able to compensate for the blood loss. Furthermore, despite their activities in the nasal passage, they can be remarkably camera shy and were pretty good at hiding from the endoscope.

And those leeches had a ravenous appetite - during the course of their stay (which can range from 24-75 days), they grew to five to ten times their original length, and increased their body mass by up to 380 times. The juvenile leech starts out as a tiny dark mote just 3-4 millimetres long, but by the end of their stay, they were big enough to be easily noticeable when they decide to poke their head out.

Cohabiting with a bunch of nose leeches allowed Dr Lai to make round-the-clock observations and record behaviours which might not have been previously documented. After about a month into the infection period, the leeches started getting restless and were looking for a new host, and this behaviour manifested itself in some disconcerting ways.

When D. ferox starts looking for a new host, it develops an attraction to darkness and water. According to Dr Lai's account, whenever he was in a dark place such as in the middle of watching a movie at a theatre, the leeches came poking out of his nose. But this wasn't the only time when they made their presence noticeable - they also got nosy when he went about some of his daily routines like showering or washing his face. This overlapped with the ceasing of bleeding-related symptoms - which meant the leeches had finished feeding.

With their cohabitation coming to an end, Dr Lai tested out some methods for removing such leeches which have been reported in the scientific literature. His self-experimentation showed that while the leech can be coaxed out with a bowl of water, this only worked at later stages of the infection, presumably after the leech has finish feeding and was ready to move on. Once they were out, they made one final contribution to science - they were preserved in a vial of 95% ethanol and are now held at the Academia Sinica collection in Taiwan.

There is a bit of a tradition among parasitologists to infect themselves with all manners of parasites to learn more about their study organisms or test out various techniques for treatment. In this case, through self-infection, one researcher was able to shine some light on a leech which usual prefers hanging out in dark places.

Reference:
Lai, Y. T. (2019). Beyond the epistaxis: Voluntary nasal leech (Dinobdella ferox) infestation revealed the leech behaviours and the host symptoms through the parasitic period. Parasitology 11: 1477-1485

Batracobdella algira

Leeches and amphibians frequently interact with each other in nature, usually with the amphibian serving as food for the leeches, whether as eggs, tadpoles, or adults. Of course, the thing that most people know about leeches is their appetite for blood, and those that parasitise amphibians are no different. Most amphibians usually survive their blood-letting encounter with leeches (with some exceptions), but some leech can transmit blood-borne parasites and may be an additional source of stress for their hosts during unstable environmental conditions. While there have been some studies on interactions between leeches and amphibians, most of them have been on those found in freshwater environments, and less is known about the terrestrial species.

Photo collage of Batracbdella leeches on salamanders from Fig 2 of this paper and Fig 1 of this paper

Batracobdella is a genus of leech that is usually associated with amphibians, as denoted by their scientific name which basically translates into "frog leech". The study that I am discussing in this post focused on Batracobdella algira, a species of green leech found in Europe which has been found to feed on a wide range of different amphibians. Among its list of hosts are European cave salamanders.

These cave salamanders are confined to southeastern France and Italy, and are unique among salamanders in that they lack lungs and breath entirely through their skin. Batracobdella algira is the only known ectoparasite of those secretive amphibians, and while there have been some records of leeches on these salamanders, next to nothing is known about their ecology or the impact they might be having on their hosts.

A group of researchers carried out a study of these salamanders and their leeches at various caves in Sardinia, Italy. They looked through 26 different caves and found that while some caves were leech hotspots where thirty percent of the salamanders were infected with at least a leech or two, there were other caves where leeches were scarce, and only one in a hundred salamanders had a leech. The caves that were home to lots of leeches also tend to have water with higher dissolved mineral content. While there's nothing about the mineralised water themselves that are attracting leeches, such hard water means there is active water flow through the cave network and the researchers suggested that might be how leeches are infiltrating and distribute themselves throughout the caves.

They researchers found that bigger salamanders tend to get more leeches, possibly because they present a bigger and juicier target. They also noticed that whereas adult leeches tend to be found by themselves on the host, smaller leeches tend to be found in groups which might be a brood that have dropped off by an adult leech. Some leeches can be great parents, and are known to provide parental care for their brood. So those clumps of baby leeches might have been placed there by their mother to give them the best possible start in life.

For all that blood-letting, the salamanders didn't seem to be fazed by the leeches and were in fairly good health. When the researchers compared the body condition of the leech-infected salamander with the leech-free ones, they didn't find any significant difference between them, though admittedly, that is a single, very simplified measure of their condition

Infected salamanders might be doing something to compensate for being fed on by those leeches. Indeed, the researchers found that infected salamanders were more likely to be found at the cave entrance, and it is possible that was because those salamander have to spend more time looking for food. Also, it is not known if the leeches transmit blood-borne parasites (as other amphibian-feeding leeches have been recorded to) or if they alter host immunological response in some way.

With amphibian populations declining all over the world due to climate change, habitat loss, pollutants, over-exploitation, and the deadly amphibian chytrid fungus, it is more important than ever to learn more about the parasites and symbionts that live on/in amphibians, and the effects that they have on their hosts.

References:
Lunghi, E., Ficetola, G. F., Mulargia, M., Cogoni, R., Veith, M., Corti, C., & Manenti, R. (2018). Batracobdella leeches, environmental features and Hydromantes salamanders. International Journal for Parasitology: Parasites and Wildlife. 7: 48-53.

P.S. Speaking of leeches, earlier this year, I illustrated my own tribute to the medicinal leech in the form of  another Parasite Monster Girl - meet Dr Delilah the Leech Monster Girl Doctor.

Marsupiobdella africana

Leeches are not endearing animals and many are literal blood-suckers. As a result they often evoke a sense of disgust in most people, and the term "leech" is usually used in a derogatory way. But most people might not realise that leeches also has a warm, maternal side too, one which is amply demonstrated in the kangaroo leech, Marsupiobdella africana. But this leech does not parasitise the kangaroo - indeed, in southern Africa where M. africanus is found there are no kangaroos - the reason it has that name actually has more to do with how it reproduces

Left: A pair of mating leech.                                   Right: Leeches riding on the legs of  a crab      (from Fig. 1 of the paper)

Marsupiobdella africana makes a living sucking blood from Xenopus laevis - the African clawed frog which is commonly used as a laboratory model for developmental biology research. When it reach sexual maturity, the leech detaches from its frog host to find a suitable mate. Some do so by simply crawling around in the environment, but they are also known to hitch-hike on the legs on crabs as if they some kind of crustacean-based Uber, admittedly an armoured, multi-legged one.

Top: Leech with spermatophore attached
Middle: Leech with filled brood pouch
Bottom: Young leeches emerging
from brood pouch
From Fig. 2 of the paper

These leech are hermaphrodites, and each individual take turns being the sperm depositor and the recipient. Mating between kangaroo leech is a very different affair to how you might imagine it, and from our perspective it is not very romantic. Instead of bringing their respective genitalia together, the leech playing the sperm depositor role actually pulls out a spermatophore - which is something like a biological hypodermic syringe filled with sperm - and stabs it into the recipient, which may end up being tagged with one to three of those sperm packets.

If the prospect of being harpooned with a sperm-filled syringe is not daunting enough, the recipient also make a habit of collecting a bunch of spermatophores from a number of different depositors, probably to ensure they can have the cream of the crop (so to speak). Once the spermatophore has made its mark, the sperm it carries are able to make their own way to the egg, no matter where the spermatophore may have initially landed on the leech's body. At this point it is not entirely clear how they accomplish this.

Once the eggs are fertilised, the sperm recipient, now playing the role of mother leech, transfer the eggs (which can be as many as 50) to a brood pouch in her belly (which is where the name kangaroo leech came from). There they will be protected and nurtured. Once the eggs hatch, the baby leeches continue to receive nutrient from their mother through her body wall and into their posterior suckers. Those developing leeches will stay in the pouch for four weeks. As a final send-off, the mother leech will find an unsuspecting clawed frog, and the young leeches are "released explosively" over the surface of the frog, thus ensuring that those blood-suckers will get the best possible start to their own lives.

Marsupiobdella africana - a loving and nurturing blood-sucker which wants nothing but the best for its babies (see also another blood sucker which goes to great lengths to care for its brood here).

Reference:
Kruger, N., & Du Preez, L. (2015). Reproductive strategies of the kangaroo leech, Marsupiobdella africana (Glossiphoniidae). International Journal for Parasitology: Parasites and Wildlife 4: 142-147.

Mysidobdella californiensis

Photo taken from Figure 3 of the paper

Marine leeches are commonly known to feed on various vertebrate hosts - mainly fish and sea turtles. However, today's parasite stands out from the pack by associating itself with an arthropod. Instead of fish or turtles, Mysidobdella californiensis sticks its sucker onto mysid shrimps. Mysids are also known as opossum shrimps because the females have a little brood pouch (called a marsupium) in which they carry developing young.

The discovery of Mysidobdella californiensis actually occurred rather serendipitously. Back in the summer and fall of 2010, an unprecedentedly huge swarm of mysid shrimp appeared off the central Californian coast. Some of those shrimps got sucked into the water clarification system at the Bodega Marine Laboratory. With all this shrimp in the system, the lab staff began collecting them opportunistically for fish food. But then, they started noticing these little leeches attached to the shrimps, so they made a concerted effort to collect the shrimps directly from the water clarifier, and examine them under the microscope.

What they found were tiny leeches about 1.5 cm (a bit above half an inch) long. Approximately one in every six shrimp were found to have leeches on them, and each infected shrimp was carrying between one to three leeches. Seeing as this is a new species, at this stage very little is known about its biology except what can be inferred based on what we know of a related species - M. borealis - which has been studied in slightly more details. It is unclear whether M. californiensis (and related species) merely hitch-hike on the shrimp and use it to carry them to potential hosts, or if they in fact feed on the shrimp. In laboratory trials on M. borealis, the leeches refused to feed on any of the fishes that they were presented with, and none of the leeches were found to have fish blood cells in their gut. It is possible that Mysidobdella as a genus specialise in feeding on mysid shrimps. If that is indeed the case, then Mysidobdella would be the only marine leech known to feed on the blood of invertebrates rather than vertebrates. However, mysid blood has yet to be found in the gut of these leeches, so at least at this point, the diet of M. californiensis remains a mystery.

Reference:
Burreson, E.M., Kim, B. and Passarelli, J.K. (2012) A New Species of Mysidobdella (Hirudinida: Piscicolidae) from Mysids along the California Coast. Journal of Parasitology 98: 341-343.

October 1 - Placobdella papillifera

Closely related to a glossiphoniid leech we saw earlier, Placobdella papillifera is a pretty leech distributed in North American freshwater habitats. P. papillifera is a blood-feeder, feeding on turtles (and sometimes alligators!). This leech was found under a rock in Savannah River in South Carolina. There are two pictures shown here, one showing the papillae on the dorsal surface and one showing the smooth ventral region. This leech was large, filling out the entire bottom of a petri dish! (Click on the thumbnail to get a good look at its pretty papillae.)

Contributed by Jessica Light.

September 14 - Cystobranchus virginicus

Today's parasite may be an example of a parasite turned predator over the course of evolution. Cystobranchus virginicus is a fish leech (Family Piscicoloidae), similar to a leech we saw earlier this year. Like other fish leeches, C. virginicus supposedly uses its long proboscis to feed on fish blood. However, this leech also has been documented to feed on fish eggs, an infrequently documented behavior (egg-feeding had only been observed in 5 or 6 other leech species). During a study examining fish mating systems, C. virginicus appeared in the redds (gravel nests where fish eggs are deposited) of at least four different fish species. Although not actually observed feeding on the fish eggs, these leeches were distended in shape and had the same translucent yellow color as the fish eggs when collected. Interestingly, no one has ever observed C. virginicus feeding on fish blood. It’s possible that the entire diet of this leech now consists solely of eggs, a potential concern if egg feeding results in high mortality and decreased fitness of the host fish species.

Contributed by Jessica Light.
See this paper for more info.

August 31 - Placobdelloides jaegerskioeldi

Yesterday, you met Oculotrema hippopotami, a parasite of hippos that lives under their eyelids. Now, today, meet a parasite from the other end. The leech, Placobdelloides jaegerskioeldi, lives in the last 10 centimeters of the rectum of hippopotamuses and feeds on blood through that delicate tissue. A few years ago, I did some pretty exciting fieldwork in South Africa collecting these critters with Mark Siddall. But, don't worry - it was not necessary for anyone to reach up into the backside of any hippos (nor distract them on the other end). We were able to obtain some specimens when a nuisance hippo had to be culled by the Park Service there and the rangers very kindly removed some tissue with leeches attached for us (click on photo for a better view of the adult plus several of its offspring). However, we still spent a very harrowing morning poking around a river, looking for more samples, with hippos just 30 feet away or so. These leeches were collected as part of a larger project that we were conducting on the endosymbiotic bacteria that they have.

May 22 - Placobdella parasitica

Today's parasite, the leech Placobdella parasitica is an excellent parent. Not only can it perform both motherly and fatherly duties simultaneously (it's a hermaphrodite), it also takes good care of its young. These leeches spend most of their lives on turtles, particularly snapping turtles, where they will feed on the blood primarily around the leg pits and tail (where the turtle's formidable jaws can't reach them.) They brood their young on their ventral surface protecting them there until they are big enough to feed on their own, which sometimes means transporting them to their first meal. Despite the caring nature of the leeches post reproduction, the conception of those young is actually quite violent. Leeches will stab small spermatophores into each other in a process known as traumatic insemination. Yipes.

Photo by Mark Siddall.

April 16 - Tyrranobdella rex

A new genus and species of leech, Tyrranobdella rex Phillips et al. 2010 with enormous teeth was described in the journal PLoS ONE on Wednesday of this week. Found feeding from the nose of a 9 yr old child in the upper Amazon by Renzo Arouco-Brown of the School of Medicine at the Universidad Peruana Cayetano Heredia, this new T. rex is known from 3 nasopharyngeal cases, and may well be the first leech species for which Homo sapiens is the type-host.

Phylogenetic work in the publication demonstrates that T. rex is part of a larger evolutionary group of mammal-specific endoparasites, the Praobdellidae, which includes the terrible ferocious leech (Dinobdella ferox) from Asia as well as African and Mexican pests. Mucosal leech infestations by members of this family typically involve the naries, pharynx and hypopharynx, though more alarming mucosal infestation sites are noted by Anna Phillips of the American Museum of Natural History and her co-authors. While leeches are not typically thought to be significant parasites of humans, praobdellid leeches like T. rex have been known to cause life-threatening conditions that range from choking to severe anemia and even death.

In addition to Phillips and Arauco-Brown, authors of this new and formidable T. rex include Mark Siddall and Alejandro Oceguera-Figueroa, also of the American Museum of Natural History, Gloria P.Gomez of the Department of Microbiology at the Universidad Peruana Cayetano Heredia in Lima, María Beltrán of the Enteroparasitology Laboratory at the Peruvian Public Health Center, and Lai Y-Te of the National Taiwan University in Taipei.

Contributed by Mark Siddall.

February 20 - Zeylanicobdella arugamensis

The piscicolid leeches inhabit marine environments and take their blood meals from fish hosts. Recently, these leeches were found on mudskippers – unusual fish in the goby family that are amphibious, spending part of their time out of the water. Zeylanicobdella arugamensis was discovered feeding from the mudskipper Scartelaos tenuis, which lives in the Persian Gulf and leeches also readily attached to a second species, Periophthalmus waltoni, in aquaria (shown in photo). Although this second fish species is sympatric with S. tenuis, the authors of the paper did not find any leeches on them in the wild. They proposed that perhaps in nature, P. waltoni spends too much time out of the water and thus the leeches prefer the more aquatic S. tenuis. Z. arugamensis has a wide distribution in the Indian Ocean and infects numerous species of fish, but this was the first time one had ever been found on mudskippers.

Photo kindly provided by Gianluca Polgar.

January 25 - Branchellion torpedinis

Leeches are a class of annelids that has many members that feed exclusively on blood and are often found ectoparasitic on their hosts. Branchellion torpedinis is a piscicolid leech that infects a wide range of elasmobranchs (sharks, rays and skates). The individual shown here came from The Georgia Aquarium collection, but they can be found on cownose rays and sawfish along the Atlantic coast. The frilly gills on the side help with respiration. Unlike many leeches, which glue a handful of cocoons containing eggs to the substrate, this species is a supreme egg layer and instead casts large quantities of eggs into the water, more like a monogenean parasite.

Contributed by Alistair Dove.