by Rick O'Connor | Aug 23, 2024
Roundworms differ from flatworms in that… well… they are round. You might recall from Part 1 of this series that flatworms were flat which helps with exchange of materials inside and out of the body. Flatworms were acoelomates – they lack an interior body cavity and thus lack internal organs. So, gas exchange (etc.) must occur through the skin. And a flat body increases the surface area in order to do this more efficiently.
A common nematode.
Photo: University of Florida
But roundworms are round, which reduces this surface area and reduces the efficiency of material exchange through the skin. Though gas exchange through the skin does happen, it is not as efficient. So, there is the need for internal organs and that means there is a need for an internal body cavity to hold these organs. But with the roundworms there is only a partial cavity, not a complete one, and the term pseudocoelomate is used for them. Though the round body has adaptations to deal with gas exchange, it is a better shape for burrowing in the soil and sediment.
There are about 25,000 described species of roundworms, though some estimate there may be at least 500,000. They are placed in the Phylum Nematoda and are often called nematodes. Nematodes live within the interstitial spaces of soil, sediment, and benthic plant communities. They have been found in the polar regions, the tropics, the bottom of the sea, and in deserts – they are everywhere. They are usually in high numbers. One square meter of mud from a beach in Holland had over 4,000,000 nematodes. Scientists have estimated that an acre of farmland may have at least 1 billion of them. A decomposing apple on the ground in an orchard had about 90,000 nematodes. So, they are found everywhere and usually in great abundance. There are parasitic forms as well and they attack almost all groups of plants and animals. Food crops, livestock, and humans have made this group of nematodes a concern in our society.
Like many pseudocoelomates, nematodes have an anterior end with a mouth, but no distinct head – rather two tapered ends. Most of the free-living nematodes are less than 3mm (0.1in), but some soil nematodes can reach lengths of 7mm (0.3in) and there are marine nematodes that can reach 5cm (2in.) – it is a group of small worms.
Roundworms usually need water in order to move, even the soil species. They typically wriggle and undulate, similar to a snake, when moving and under a microscope they wriggle quite fast. In aquatic habitats they may swim for a short distance, and a few terrestrial species can crawl through dry sand.
Marine Nematode – Dr. Roy P. E. Yanong, UF/IFAS Tropical Aquaculture Lab
Many free-living nematodes are carnivorous and feed on tiny animals and other nematodes. Some feed on microscopic algae and fungi. Some terrestrial species pierce the roots of plants and digest the material within. Many marine species will feed on detritus lying on the seafloor. The carnivorous species may possess small teeth, and many have a stylet they can use to pierce prey or the plant root to access food. The mouth leads to a long digestive tract and eventually an anus – nematodes have a complete digestive tract.
The brain is basically a nerve ring near the head that leads to numerous nerve chords that run the length of the body. Sensory cells are most associated with the sense of touch and smell.
Having separate sexes is the rule for nematodes, but not for all. Males are usually much smaller and usually have a hooked posterior end which they use to hold the female during mating. 50-100 eggs are usually produced and laid within the environment.
Farmers and horticulturists are familiar with these free-living nematodes, but it is the parasitic ones that are most known to the general public. There are many different forms of parasitism within nematodes. Dr. L.H. Hyman categorized them as follows:
- Ectoparasites that feed on the external cells of plants – using their stylet to pierce the plant tissue and remove nutrients.
- Endoparasites of plants. Juveniles of some nematodes enter plants and feed on tissue. This can cause tissue death and gall-like structures.
- Some free-living nematodes, while juveniles, will enter the bodies of invertebrates and feed on the tissue when the invertebrate dies.
- Endoparasites within invertebrates as juveniles, but the adult stage is free-living.
- Some are plant parasites as juveniles and animal parasites as adults. The females live within the bodies of plant eating insects, where they give birth to their young. When the insects pierce the plant tissue, the juveniles enter the plant and begin feeding on it. When they mature into adults, they re-enter the insects and the cycle begins again.
- Those that live within animals. The eggs, or newly hatched young, may be free-living for a short period, where they find new animal hosts, but the majority of the life cycle occurs within the animal. Many known to us infect dogs, cats, pigs, cattle, horses, chickens, fish, and humans.
Heartworms, pinworms, and hook worms are names you may have heard. For dog nematodes, the eggs are released into the environment by the dog’s feces. Another dog eats this feces and becomes infected.
The nematode known as Ascaris lumbricoides is the most common parasitic worm in humans. It has been estimated that almost 1 billion people are infected with it. Female Ascaris release developing eggs into the environment via human feces. Other humans become infected after swallowing food or water containing the eggs. Once inside the human, the eggs hatch and penetrate the tissue moving into the heart and eventually the lungs. From here they crawl up the trachea inducing a coughing response which is followed by a swallowing response that moves the developing juvenile worm into the esophagus and eventually back to the intestines where the cycle begins again. Infections of this worm are more common where sanitation systems are not adequate and/or human feces are used as a fertilizer.
Hookworms are another human parasite that feed on blood and can cause serious infections in humans due to blood and tissue loss. Fertilized eggs of this worm are laid in the environment and re-enter new human host as developing juveniles by penetrating their skin. Once in the new host the developing worms are carried to the lungs via the circulatory system and work their way into the pharynx, are swallowed, and eventually end up in the intestine. Not all hookworm juveniles penetrate through the skin but rather enter the body when the person unknowingly consumes human feces. This can happen from not washing your hands or food (if human waste is used as fertilizer). Pinworms and whipworms are other nematodes that have similar life cycles. In Asia there are some nematodes that are passed to humans by biting insects.
The roundworm known as the nematode is a common issue for farmers, horticulturists, and as a parasite in some parts of the world. Their lifestyles, while being a potential problem for us, have been very successful for them. In the next edition in this series, we will learn more about the most advanced worms on our planet – the segmented worms. We will begin with the polychaetes.
References
Barnes, R.D. (1980). Invertebrate Zoology. Saunders Publishing. Philadelphia PA. pp. 1089.
Ascaris lumbricoides. 2024. Wikipedia. https://en.wikipedia.org/wiki/Ascaris_lumbricoides.
by Thomas Derbes II | Aug 23, 2024
Oysters are not only powerful filterers, they also provide a home and habitat for many marine organisms. Most of these organisms will fall off while the oysters are being harvested or cleaned, but some will stay behind and can be found inside or outside of your oyster on the half shell. Seeing some of these creatures might give you the “heebie jeebies” about eating the oyster, they are perfectly safe and can either be removed or, in some cases, consumed for luck. These creatures include mud worms (Polydora websteri), “pea crabs” (Pinnotheres ostreum or Zaops ostreus), and “mud crabs” (Panopeus herbstii, Hexapanopeus angustifrons or Rhithropanopeus harrisii).
Mud Worms (Polydora websteri)
A Mud Worm in an Oyster – Louisiana Sea Grant
One of the more common marine organisms you can find on an oyster is the oyster mud worm. These worms are typically red in color and form a symbiotic relationship with the oyster. Mud worms can be found in both farmed and wild harvest oysters throughout the United States. These worms will typically form a “mud blister” and emerge when the oyster has been harvested. Even though the worms look menacing and unsightly, they are a sign of a fresh harvest and a good environment. Mud worms do not pose any threat to humans and can be consumed.
If you find a mud worm on your next oyster and are still unsure, just simply remove the worm and dispose of it. Dr. John Supan, retired professor and past director of Louisiana Sea Grant’s Oyster Research Laboratory on Grand Isle, mentioned in an article that oyster mud worms “are absolutely harmless and naturally occurring,” and “if a consumer is offended by it while eating raw oysters, just wipe it off and ask your waiter/waitress for another napkin. Better yet, if there are children at the table, ask for a clear glass of water to drop the worm in. They are beautiful swimmers and can be quite entertaining.”
“Pea Crabs” (Pinnotheres ostreum or Zaops ostreus)
“Pea Crabs” are in fact two different species of crabs lumped together under one name. Pea crabs include the actual pea crab (Pinnotheres ostreum) and the oyster crab (Zaops ostreus). These crabs are so closely associated with oysters that their species name contains some form of the Latin word “ostreum” meaning oyster! Pea crabs are known as kleptoparasites and will embed themselves into the gills of an oyster and steal food from the host oyster. Even though they steal food, they seem to pose no threat to the oyster and are a sign of a healthy marine ecosystem.
A Cute Little Pea Crab – (C)2013 T. Michael Williams
Pea crabs are soft-bodied and round, giving them the pea name. Pea crabs can be found throughout the Atlantic coast, but are more concentrated in coastal areas from Georgia to Virginia. While they might look like an alien from another planet, they are considered a delicacy and are typically consumed along with the oyster. If you are brave enough to slurp down a pea crab, you might just be rewarded with a little luck. According to White Stone Oysters, “historians and foodies alike agree that finding a pea crab isn’t just a small treat, it’s also a sign of good luck!”
“Mud Crabs” (Panopeus herbstii, Hexapanopeus angustifrons or Rhithropanopeus harrisii)
Smooth Mud Crab – Florida Shellfish Lab
Just like pea crabs, “mud crabs” is another name for two different species of crabs commonly found in oysters. These crabs, the Harris Mud Crab (Rhithropanopeus harrisii), Smooth Mud Crab (Hexapanopeus angustifrons), and the Atlantic mud crab (Panopeus herbstii) to name just a few, reach a maximum size of 2 to 8 centimeters and are hard-bodied, unlike the pea crabs. Mud crabs can survive a wide range of salinities, but need cover to survive as these crabs are common prey for most of the oyster habitat dwellers, such as catfish (Ariopsis felis), redfish (Sciaenops ocellatus), and sheepshead (Archosargus probatocephalus). These crabs are not beneficial to an oyster environment as they will seek out young oysters and consume them by breaking the shell with their strong claws. If you find a mud crab in your oyster, this is one to dispose of before consuming. However, these crabs typically live on the outside of an oyster and are typically only found when you buy a sack of oysters and do not have an effect on the quality of the oyster.
Don’t Be Afraid
Hopefully this article has helped shed some light on the creatures you might experience when shucking or consuming oysters. Here is a helpful online tool to help identify some marine organisms associated with clam and oyster farms (Click Here). While most of the organisms can be consumed, we recommend the mud crabs be disposed of due to their hard shells. Remember, some of these organisms can bring you luck and with college football season around the corner, some of us might need all the luck we can get! Bring on the pea crabs!
References Hyperlinked Above
by Thomas Derbes II | Aug 10, 2024
Many of us are given that Birds and the Bees talk; another majority have had to give it as an adult to their kids. It is usually an awkward talk, but someone had to step up to the plate and put on a straight face. I am happy to be the one today to discuss one section of the Birds and the Bees of the Sea, batch spawning. Batch spawning, also known as broadcast spawning, is the coordinated release of gametes (sperm and eggs) into the water column. Batch spawning is not just relegated to fish, many species of invertebrates also batch spawn. Some of the most commonly encountered batch spawners include Florida Pompano (Trachinotus carolinus), Eastern Oyster (Crassostrea virginica), Red Drum (Sciaenops ocellatus), Red Snapper (Lutjanus campechanus), and Gag Grouper (Mycteroperca microlepis), to name a few. In fact, most gamefish species in the Gulf of Mexico are batch spawners. This has its advantages, but also has its major disadvantages. We will dive headfirst into a few representative species of saltwater organisms that batch spawn, and their respective life stages to help shed some light on reproduction in the marine world.
Baby Snapper – Thomas Derbes II
Eastern Oysters are a perfect representative for invertebrate batch spawning. I have gone over their life cycle in a previous article (Click Here), but I will just quickly go over their spawning habits and life history. Eastern Oysters typically spawn during the changing of the seasons, particularly from Spring to Summer and Summer to Fall. As humans, we see these changing temperatures and weather fronts as an opportunity for a new wardrobe, but these changes are triggers for oysters to spawn. Once one oyster releases their gametes into the water all of the mature oysters in the area will start releasing their gametes. Waiting to sense for other gametes in the water is a very smart tactic. This allows for a coordinated spawn between masses of oysters and (hopefully) increases the fertilization rate of the eggs. Since oysters cannot move, batch spawning is the most beneficial way for them to reproduce. Females can release anywhere from 2 to 70 million eggs in one spawning event, with only a dozen or so becoming adults. Since they are batch spawners, the larvae are left unprotected by the parents and suspended in the water column for the first few weeks, leaving them susceptible to predation by filter feeders and bad water quality. Once the larvae have reached the pediveliger stage, they will settle out and “walk” along the bottom of the estuary until they find a suitable place to call home, usually another oyster or hard substrate. After 1-3 years, the oyster will mature and begin batch spawning when conditions are ripe, and the cycle continues!
The Oyster Life Cycle – Maryland Sea Grant
Fish in the Lutjanidae (snapper) family are the perfect representative for batch spawning with fish. Snappers of all species are known to congregate and have mass spawning events typically around a full moon. The mutton snapper (Lutjanus analis) of South Florida and the Florida Keys are very well known for their ability to form massive congregations of tens of thousands of fish along the reef starting in April. Once the spawning commences, the mutton snapper will form a small subgroup of up to 20 fish in the late afternoon. This subgroup will travel to depths of up to 100ft to perform their spawning event. During this event, the female will signal to the males that she is about to release her eggs. The males will then rub up against the side of the female snapper, helping her release eggs while simultaneously releasing their milt (sperm). When the milt is released, the sperm is activated by the seawater and begins to swim. Eventually, the eggs are fertilized and an embryo is formed.
Massive Two-spot red snapper aggregation ready to spawn in Palau – R.J. Hamilton
18 – 24 hours later, the embryo is now a larval fish consisting of a yolk sac and lacking a mouth, eyes, and most organs. The yolk sac consists of amino acids and other nutrients that provide energy to the developing larvae. These larval fish have until their yolk sac runs out to develop the lacking vital organs, which usually takes between 24 – 48 hours. Only a very small percent of juvenile snapper make it to adulthood due to predation during their larval stage and predation as a juvenile. In fact, sharks and other large predators will prey on the snapper as they congregate and spawn, and filter feeders like manta rays are known to pass through an active spawning congregation to consume all the fertilized eggs and larval fish.
Well, I hope I didn’t scar anyone too badly. Batch spawning is fairly common in the marine biology world, and you can sometimes experience a spawning event without even knowing it. As for positives, this allows for many eggs to be fertilized at a time multiple times a season and for the larval fish and shellfish to be distributed through the estuary and reef via tides and waves. A major negative is the vulnerability of the juvenile and larval fish and shellfish, but the sheer number of eggs produced and fertilized helps outweigh the high potential for predation and unexplained loss of fertilized eggs and juveniles.
References:
Oyster Spawning: https://www.umces.edu/news/the-life-of-an-oyster-spawning
Mutton Snapper Species Spawning Profile: https://geo.gcoos.org/restore/species_profiles/Mutton%20Snapper/
Mutton Snapper Aquaculture Profile: https://srac.msstate.edu/pdfs/Fact%20Sheets/725%20Species%20Profile-%20Mutton%20Snapper.pdf
by Rick O'Connor | Aug 10, 2024
I bet that for most of you, this is not only a worm you have never seen – it is a worm you have never heard of before. I learned about them first in college, which was almost 50 years ago, and have never seen one. But, other than the earthworm, the world of worms is basically hidden from us.
A nemertean worm.
Photo: Okinawa Institute of Science
Nemerteans are a group of about 1300 species in the Phylum Nemertea and are often called ribbon or proboscis worms. They do possess a proboscis used to capture prey. Most are marine and live on the bottom both near the beach and a great depth. They are more temperate than tropical and do have a few parasitic forms.
Adult Nemertea Worms – Terra C. Hiebert, PhD, Oregon University
In appearance they resemble flatworms but are larger and more elongated. Most are less than 20cm (8in) but some species along the Atlantic coast can reach 2m (7ft). The head end can be lobed or even spatula looking. Some species are pale in color and others quite colorful. Most nemerteans move over the substrate on a trail of slime produced by their skin. Some species can swim.
As mentioned, the proboscis is used to capture prey. It is a tube-like structure held in a sac near the head. When prey is detected, they can launch the proboscis out and over the victim. Sticky secretions help hold on to the prey while they ingest. Many species are armed with a stylet, dart, that is attached to the proboscis and is driven into the prey like a spear. From there toxins, secreted from the base of the proboscis are injected into the prey.
For many species the proboscis is connected to the digestive tract via a tube, there is no true mouth, but they do possess an anus. They are all carnivorous and feed on a variety of small living and dead invertebrates. Their menu includes annelid worms, mollusk, and crustaceans.
Nemerteans do possess a brain and most find their prey using chemoreception, though some species must literally bump into their prey to find it. They have multiple eyes that can detect light, and, like the true flatworms, they are negatively phototaxic. They are nocturnal by habitat and is probably why most of us have never seen one.
Many nemerteans, particularly the larger ones, have a habit of fragmenting when irritated, creating new worms. Most species have separate sexes and fertilization of the gametes is external (fertilization occurs in the environment).
Nemerteans are an interesting group of semi-large, sometimes toxic, hunters who prowl through the marine waters at night hunting prey. Seen by few, maybe one evening, while exploring or floundering, you may see one.
In Part 3 we will begin to explore a group of worms that are more round than flat. The Gastrotrichs.
Reference
Barnes, R.D. (1980). Invertebrate Zoology. Saunders Publishing. Philadelphia PA. pp. 1089.
by Rick O'Connor | Aug 10, 2024
I was recently conducting a survey for diamondback terrapins from my paddleboard in a small estuarine lagoon within the Pensacola Bay System. Even if we do not find our target species during these surveys – I, and our volunteers, see all sorts of other cool wildlife. On this trip I was treated to nesting osprey, a kingfisher, large blue crabs, and even a swimming eel. But one neat encounter was the numerous stingrays.
The Atlantic Stingray is one of the common members of the ray group who does possess a venomous spine.
Photo: Florida Museum of Natural History
They were lying in the sand and grassbeds, lots of them, and they all seemed to be of one species – the Atlantic stingray. My brain immediately went to “breeding season”, but when I checked the literature, I found that it was not breeding season, but pupping season – the babies were being born.
Atlantic Stingray (Dasyatis sabina) are true stingrays in the family Dasyatidae. This means they do possess the replaceable serrated venomous barb that makes these animals so famous. They are one of the smaller members of this family. Females can reach a disk width of two feet while the smaller males will only reach about one foot. Atlantic stingrays are a warm water species, migrating if they need to find suitable temperatures. They have been found in water as deep as 80 feet but are more common in the warmer shallower waters near shore. They are very common in our estuaries and being euryhaline (they tolerate a large range of salinity), are found in freshwater systems. There is a population that lives in the St. Johns River. Atlantic stingrays feed on a variety of benthic invertebrates and have special cells in the nose to detect the weak electric fields their prey give off while buried in the sediment. They also like to bury in the sand to ambush prey as they move by.
Breeding occurs in the fall. The smaller males possess two modified fins called claspers connected to their anal fins that are used to transfer sperm to the female. The males have modified teeth they can use to bite the fins of the females. They do this to hold on and make sperm transfer more successful.
The females do not begin to ovulate until spring. So, though they receive the sperm in the fall, fertilization does not occur until the spring. Instead of laying eggs, as some rays and skates do, baby Atlantic stingrays develop within the mother. This is not the same as mammals, who produce a placental to feed the developing young, but more like an internal egg with no hard shell. The embryo is attached to, and feeds from, a yolk sac. Gestation takes about 60 days at which time the yolk sac is depleted, and the young must emerge. Birth usually occurs in late July and early August, and each female will produce 1-4 small pups whose disk are about 10cm (4in.) wide. It was this birthing/pupping period I witnessed.
I returned the following day to search for terrapins and the number of stingrays was significantly fewer. It may be that the birthing process is fast, and the adults leave the coves afterwards. It may have been because that day was the day Hurricane Debby was making landfall east of us and the water levels were abnormally high – something the rays may have noticed and decided to leave – I am not sure.
I was really hoping to see the young rays swimming around – I did not – but plan to search again soon. Stingrays make many people nervous. I witnessed several adult rays whose tails had been cut off – which is very unfortunate – but they are actually cool creatures and fun to watch while paddleboarding. Maybe I will see a baby soon.
References
Dasyatis sabina. 2023. Florida Museum of Natural History. https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/dasyatis-sabina/.
Johnson, M.R., Snelson Jr., F.F. 1996. Reproductive Life History of the Atlantic Stingray, Dasyatis sabina (Pisces, Dasyatidae), in Freshwater St. Johns River, Florida. Bulletin of Marine Science, 59(1): 74-88.
