#shipworms

Transition so nice, you do it twice! Shipworms begin their lives with both sets of reproductive organs; when they reach their adult stage they become fully male. At this stage they will release their sperm into the water, and then transition to female and brood fertilized eggs in their gills. After the eggs are released into the water, they will then transition back to male and start the process all over again. A shipworm may go through several cycles of transition between sexes over the course of their lives, which can span up to 3 years.

Naval Shipworm (Teredo navalis)

Family: Shipworm Family (Teredinidae)

IUCN Conservation Status: Unassessed

Despite what their name and worm-like bodies suggest, shipworms like the Naval Shipworm are actually small clams adapted to burrowing; their shells, made up of two halves called valves, are located on the front of their body and act like powerful jaws used to bore into surfaces (although there is no mouth behind these "jaws",) while their siphons (a pair of muscular tube-like structures that take food and water to the gills and release waste and gametes into the water, and which are protected by the shell in most other clam species,) are located on the opposite end of their body (labelled d and e in the image above.) Like most shipworms, the Naval Shipworm builds its burrows in submerged wood such as driftwood, and is particularly infamous for its habit of boring into hulls of wooden ship, threatening the ship's structural stability and allowing the species to spread to as the ships travel - today members of this species can be found in non-polar seas and estuaries worldwide, leaving it unclear where exactly they originate from. After settling in a piece of wood young Naval Shipworms construct a strong inner casing around themselves using mucus and calcium carbonate filtered from the water around them, and if left to their own devices they will remain in their burrows for the rest of their lives with only their siphons exposed, gaining nutrients from algae and wood shaving taken in through their inhalant ("intake") siphons (with their gills both filtering algae from inhaled water and housing mutualistic bacteria that secrete enzymes capable of digesting wood, which the shipworm could not do on its own) and periodically releasing dung, gametes or larvae from their exhalent ("outgoing") siphon. All Naval Shipworms are born as males, but some individuals develop into females as they get older - mature females take in gametes released by males to fertilize their eggs internally, and after hatching the larvae remain in their mother's gills where they are protected and given access to the nutrients she takes in until they are old enough to be released into the water, after which they (now known as "veligers") undergo further development as free-swimming, algae eating plankton before settling on a suitable piece of wood and developing into adults.

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Image Source: https://www.inaturalist.org/taxa/209057-Teredo-navalis

Ever wanted to eat rocks? Then you might be Lithoredo abatanica! This species of shipworm is unusual in that it eats not wood, but rock- specifically limestone. They have special teeth which allow them to burrow into and finely grind the rock, and excrete it as sand.

Question:

How do shipworms bore through wood?

asked by anonymous

Answer:

For clarification, the scientific name for the shipworm that I focus on here is Bankia setacea. Before I get to what I find really fascinating about this species, it is useful to view its basic anatomy. The first visual is from an article on "Bivalvia: Teredinidae" (2). Teredindae is the family in which shipworms belong to in the biological tree of life.

It should first be noted that shipworms are not worms at all; rather, they are really clams that look like worms, belonging thus to bivalvia (the class of animals that contains clams, oysters, scallops, and similar molluscs) (2). The key to understanding this anatomical diagram of this clam is shown to the right of the image.

Betcher et al, 2012 (2).

a, anus;

c, caecum;

f, foot;

g, gill;

h, heart;

i, intestine;

v, valve (shell);

aa, anterior adductor muscle;

pa, posterior adductor muscle;

st, stomach.

Please draw your attention to the lengthy gill (g), and then look at the second picture from a more recent 2014 paper (1). This is a photo of a shipworm removed from its burrow. As before, the labeling key is shown to the right.

O'Connor et al, 2014 (1).

a, anus;

b, burrow;

c, cecum;

fg, food groove;

gi, gill;

gn, gonad;

I, intestine;

m, mouth;

p, pallets;

si, siphons;

st, stomach;

v, valve

Again, I ask you to look at the clam's gill (gi). This because their gills contain a gland unique to the Teredinidae, called the gland of Deshayes. Within this gland are specialized cells that store symbiotic bacteria that make the enzymes that break down wood, called cellulolytic enzymes.  This means that these enzymes break down cellulose, the main structural component of the cell walls of trees and other plants.

"Because it requires few enzymes, and these enzymes are neatly translocated to the gut", the first paper describes, "the shipworm provides a simple model system in which to explore minimum enzymatic requirements and efficient enzyme mixtures for lignocellulose decomposition" (1). Another function of this brown, irregular mass of tissue is producing amino acids.

Here is a fantastic article on the new discovery of this digestive strategy-- with nearly 1,000 genes in the gills creating cellulolytic enzymes. These enzymes are especially interesting to researchers like Dan Distel because they convert plant biomass, or cellulose, into sugar, which can be used to make biofuels like ethanol (4).

Their capacity to degrade woody plant materials gives shipworms potential as a source of novel enzymes for industry. This is, in my view, the most important discovery that can be taken away from my answer.  If you're wondering how biofuel is made from cellulose, take a look at this infogram describing cellulosic ethanol production (5).

Thank you for asking, we're grateful for all your questions!

Answered by John M, Expert Supervisor.

Edited by Margaret G, Editor.

Citations:

Roberta M. O’Connor, Jennifer M. Fung, Koty H. Sharp, et al. Gill bacteria enable a novel digestive strategy in a wood-feeding mollusk. Proceedings of the National Academy of Sciences, Vol. 111, No. 47. (25 November 2014), pp. E5096-E5104,doi:10.1073/pnas.1413110111

Betcher MA, Fung JM, Han AW, O’Connor R, Seronay R, et al. (2012) Microbial Distribution and Abundance in the Digestive System of Five Shipworm Species (Bivalvia: Teredinidae). PLoS ONE 7(9): e45309. doi:  10.1371/journal.pone.0045309

Sherif I. Elshahawi, Amaro E. Trindade-Silva, Amro Hanora, et al. Boronated tartrolon antibiotic produced by symbiotic cellulose-degrading bacteria in shipworm gills. Proceedings of the National Academy of Sciences, Vol. 110, No. 4. (22 January 2013), pp. E295-E304, doi: 10.1073/pnas.1213892110

St. Martin, Greg. Researchers discover new digestive strategy in shipworms. November 10, 2014. News @ Northeastern: Campus & Community, Science & Technology.

Italian design studio Alcarol has expanded its collection of furniture made from resin-encased wood to include a bench patterned with holes created by shipworms. ...

By filling the gaps left by worms with resin, Alcarol freezes that decay and captures the aesthetic value of the historical poles that have endured decades of weathering in the canals of Venice.

Incidents and Reflections - 11/16/2014 by Incidentsandreflections on Mixcloud

  Article links

Society of Vertebrate Paleontology 2014 conference (Abstract book) [02:57]

Darren Naish's Patreon [25:23]

Shipworms keep symbiotic bacteria in gills (Inkfish coverage) [29:48]

Pregnant tiger keelback snakes seek out toxic prey (Not Exactly Rocket Science coverage) [36:34]

  Song links

Evil for Extra Credit - Phineas and Ferb [00:00]