Recent Discovery of Giant Shipworm Kuphus polythalamia's Unique Feeding Strategy

Kuphus polythalamia is a type of bivalve called a "shipworm" (although K. polythalamia is not a worm, nor does it live on a ship).  It is a member of the family Teredinidae. Shipworms are elongate, and have rasp-like shells for burrowing into wood. Kuphus polythalamia is unusual because of its large size.  It can reach up to five feet long and grow to almost two and a half inches in diameter.

Kuphus polythalamia  has been known of for a long time, due to the frequent discovery of their elephant tusk-like shells since the 1700s. However, the animal itself was usually long since dead and decomposed and had never been studied. Since its shells were usually dragged up in nets by fishermen, it was hard for scientists to pinpoint the exact habitat where it lived. By chance, a documentary filmed in the Phillipines showed it burrowed into the sediment of a lagoon. A team of scientists launched an expedition to that location, and brought back specimens.

They found that, unlike other shipworms, which feed on wood, which they are able to digest because of symbiotic bacteria that produce digestive enzymes to break down the wood (allowing the bacteria, in return, to obtain organic carbon from their shipworm host), Kuphus polythalamia does not eat wood.  Its digestive organs have shrunk, and it spends most of its time encased in its closed up shell, without taking in any wood.  Instead, it relies on a chemotrophic feeding strategy, meaning that it metabolises chemicals instead of sunlight (autotrophs) or organic matter (heterotrophs). Most shipworms are heterotrophic.

The way this works for Kuphus polythalamia is that it has bacteria, which live in its gills, and  metabolize sulfur. In doing this, the bacteria create organic carbon, which Kuphus polythalamia feeds on.  This is the different from the usual shipworm mutualistic symbiotic relationship.  Kuphus polythalamia's symbiotic partner bacteria do not rely on it for food.  Instead, they provide it with food by breaking down sulfur based environmental compounds that come from rotting wood in the area.  (The lagoon where Kuphus polythalamia was found had been used as a log storage pond.)

It has been hypothesized that the way this trait evolved was that Kuphus polythalamia's ancestors fed on wood, specifically wet, rotting wood, which released sulfur. They shared the enviroment with chemotrophic bacteria, and somehow, the chemotrophic bacteria got stuck in their gills. Instead of dying, the bacteria thrived, and as a byproduct of their chemosynthesis, they manufactured organic carbon, which is benificial for shipworms. This feature allowed these individuals to survive better than those without the bacteria, and for them to exploit new habitats, such as the muddy bottom of a lagoon. Eventually, they evolved into a seperate species, Kuphus polythalamia.

SOURCES:

Kuphus polythalamia: Marine Biologists Study Giant Mud-Dwelling Shipworm for First Time, Science News (April 18 2017.) Published online at    http://www.sci-news.com/biology/kuphus-polythalamia-giant-mud-dwelling-shipworm-04789.html?fbclid=IwAR3fxZweBBuujpO6eO3emt3xxHqrLv3UtBP_nfTLPibCF04NhBn_oTDmis8

Kish, Stacy W., Science Fiction Horror Wriggles Into Reality with Discovery of Giant Sulfur-Powered Shipworm (April 17 2017.)  Published online at https://healthcare.utah.edu/publicaffairs/news/2017/04/shipworm.php?fbclid=IwAR2ZHz1Ugxpz05o5Kxv0SwF_HRYYoCe0USWL3t_FvB66SbEGGN7MV1HsSH4

Daniel L. Distel, Marvin A. Altamia, et al, Discovery of Chemoautotrophic Symbiosis in the Giant Shipworm Kuphus polythalamia (Bivalvia: Teredinidae) Extends Wooden-Steps Theory, Proceedings of the National Academy of Sciences Apr 2017, 201620470.  Published online at https://www.pnas.org/content/early/2017/04/13/1620470114.full

West Indian Fighting Conchs

The West Indian Fighting Conch is the animal I picked for my project this week.  My mom had a conch shell on her desk when I was little, and I was curious about it, so I decided to learn more about conchs.

Taxonomy:
Kingdom Animalia
Phylum Mollusca
Class Gastropoda
Family Strombidae
Genus Strombus
Species pugilis.

Common name: West Indian Fighting Conch.

The West Indian Fighting Conch's maximum length is approximately 110 millimeters, though the average length is more like 90 mm.   Its range stretches from Florida across the Caribbean and all the way down to Brazil. It lives in the intertidal zone and in shallow water up to 10m generally.

It is dioecious, meaning individuals are either male or female.  Another word for this is gonochoric.  West Indian Fighting Conchs have external fertilization.

The conch starts off as a fertilized egg, which divides and becomes a meroplanktonic trochophore larva. Later it moves on to the veliger larval stage. It eventually settles down and start growing its shell. It spends this time burrowed under the sand to avoid predators.  After about four years, the conch is an adult.  It emerges from under the sand, and the cycle continues.

West Indian Fighting Conchs are herbivores, feeding on algae and other plants.
One of their predators is Octopus maya or the Mexican Four-Eyed Octopus. It has neurotoxins which can paralyze its prey, while it drills into the conch's shell.
Another predator is Homo sapiens, who usually cook their prey.  In the Florida Keys, conch fritters are a common dish.

Cool facts:

Key West calls itself "the Conch Republic" and has a conch depicted on its flag.

The reason they are called "fighting conchs" is because if you pick one up, it will jab at you with its sharp, sickle shaped operculum!

Human hunting of conchs is likely driving them to evolve to be smaller so they are less attractive prey.  This is an interesting article about it: humans affect conch evolution article.

HHMI Biointeractive Lab on Sorting Seashells.

The HHMI Lab on Sorting (i.e. classifying) Seashells was really interesting and fun.  Here is the worksheet I did as part of my assignment:

Model of a Chiton

Chitons are marine mollusks in the Class Polyplacophora.  They live in the intertidal and subtidal zones.  They all have eight armored plates on their dorsal side for protection from predators.  They can roll up into a ball when disturbed, like pill bugs do.  Their armored plates are surrounded by a soft girdle.  They have a muscular foot that they use for locomtion.

Chitons have gills for respiration which are located on their ventral side, underneath the mantle (a layer of tissue between the shell and the visceral mass), and surrounding the foot.  They have a mouth, which contains the radula, a raspy organ that they use to scrape the algae that they eat off of rocks.  They also have an anus.  They have a heart and an aorta.  Their nervous system includes a nerve ring that surrounds the mouth.  They have  primitive eyes that are part of their shell and see only pixellated images.

They are dioecious, i.e., individuals are either male or female.  The chiton's trochophore larvae  are lecithotrophic, which means "feeding on yolk". They do not go through a veliger larval stage.  Instead, they feed on their egg yolk,  growing bigger over time. They eventually fully absorb the yolk, and become adults.

One medium sized tropical species, Acanthopleura granulata, commonly known as the West Indian Fuzzy Chiton, lives in an area that stretches from Southern Florida to Panama, in the Carribean Sea. It has spines on its girdle that give it a fuzzy look, and perhaps deter predators.   It inhabits the intertidal zone, where it eats algae.

One adaptation it has is a rhythymic pattern of movement that allows it to withstand storms and rough seas.

Hamilton (1903), for example, observed a rhythmic movement of the girdle of Acanthopleura in phase with the wave period. The girdle was brought flush and tight against the substratum with each approaching wave and then was raised during the backwash. 

Peter W. Glynn, On the Ecology of the Caribbean Chitons Acanthopleura granulata Gmelin and Chiton tuberculatus Linne: Density, Mortality, Feeding, Reproduction, and Growth, SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY NUMBER 66, SMITHSONIAN INSTITUTION PRESS,  (Washington D.C., 1970), at p.5.

Another adaptation it has is the ability to tolerate a lot of sun and exposure without drying out.  (See Glynn at p. 18.)  They also exhibit "homing." that is, they move at night to feed, but return to the same area during their less active daytime hours.  (Glynn at p.7)

Their primary predators are sea stars, crabs and other crustaceans, rats, and birds.

I built a model of a chiton using aluminum tape and a large rubber band.  The plates slide to allow it to roll up.

Here is a video that shows me unrolling it.  It didn't work as smoothly as I would have liked.

Flatworms, Nematodes, Annelids and Bristle Worms

This assignment was to create a project showing the 3 types of worms we learned about: Platyhelminthes (flat worms), Nematodes (round worms) and Annelids (segmented worms) (including Polychaetes, or Bristle Worms.

All three types of marine worms have bilateral symmetry and triploblasty (three cell layers: endoderm, mesoderm and ectoderm.)

I created models of each using Tinkercad Software.

This is the flatworm, or platyhelminthes:

Flatworms have a flat body plan, a simple brain called a ganglia at their head end, eyespots that can sense light and dark,  and nerve chords that tell their muscles how to move.  They have only one opening at the end of their pharynx (a tube connecting the gut to the sole opening in their digestive tract, which serves as both mouth and anus.)  The gut spreads throughout the body.

This is a round worm, or nematode:

Round worms have a round cross section.  Thir bodies are smooth and not segmented.  They have two openings in their digestive tract, i.e. a separate mouth and anus.  

This is a segmented worm, or annelid.  It is from Class Polychaeta (a bristleworm).

Annelids have round segmented bodies.  They have well developed digestive, nervous and circulatory systems. They breathe through their skin.

The creature that I modelled is a Polychaete, or "Bristle worm."  It is an annelid that has stiff hairs or setae attached to its body by paddle-like structures called parapodia.

Here is a video of me explaining the models: