MSCI345 Worms, Worms, Wonderful Worms (and a few other things, too)

Protostomia

* the mouth forms before the anus during gastrulation
* tend to have mosaic development, which means that the cells formed by cleavage have their developmental fates determined right away, and those fates can’t be changed.
* tend to form their coeloms through schizocoely. In other words, their internal body cavities tend to form from splits that appear in the embryonic mesoderm.

Spiralia

united primarily by having spiral cleavage during early development; can be divided into two sub-groups: the Gnathifera and the Platytrochozoa.

Gnathifera

united by having complex jaws made of the polysaccharide chitin. There are several sub-groups, but only two that I expect you to know: rotifers and arrow worms.

Rotifera

* are very tiny (usually microscopic) animals that live in water (either freshwater or saltwater).
* They have an unsegmented, tapered body with a distinctive corona
* have a **complete gut**, with the mouth at the head end and an anus near their tail end.
* these animals are considered **pseudocoelomates**.
* They have a **simple nervous system**.
*  they have **no gills or other respiratory system** and **no circulatory system**.

corona

A feature found in Rotifers that usually consists of two whorls of cilia used to generate feeding currents that carry food particles to the mouth. When viewed under a microscope, the corona resembles two counter-rotating circular saw blades.

Chaetognatha

(Arrow worms); **voracious stealth predators**.

* They have long, slender, flat bodies with a distinct head and some fins.
* They are a few mm to a few cm long. and most are transparent
* They have complex jaws with frightful-looking **chitinous** spines that function as fangs to capture prey
* They have a **complete gut** with mouth at anterior end and anus at posterior end.
* they are said to be **eucoelomate** (“true coelom”).
*  they have **no gills or other respiratory system** and **no circulatory system**.

Platytrochozoa

This is the sister taxon to the Gnathiferans within the Spiralia. It’s name is a combination of its two main sub-groups: the Platyhelminthes (flatworms) and the Lophotrochozoans (several groups including annelids and mollusks).

Platyhelminthes

(Flatworms)

* They range in size from microscopic to almost 30 m (100 feet) long, but all have a very **flat body**, rarely more than 1 or 2 mm thick.
* flatworms can do all their needed gas exchange by diffusion alone, so **they do not have a respiratory system or a circulatory system**.
* flatworms are a solid mass of tissue with no body cavity. That means they are described as being **acoelomate**
* Most free-living flatworms have a **blind gut**.
* On the inside, the gut is usually highly branched, with extensions reaching throughout the body to deliver nutrients by diffusion.
* Flatworms have a **simple nervous system**, but they do have **ganglia** and **nerves**
* have a set of tiny tubes leading out of the body that collectively act as a **simple excretory system** capable of excreting nitrogenous waste in a urine-like liquid while retaining desired solutes for osmoregulation

blind gut

means dead-end with only one opening that serves as both mouth and anus.

ganglia

clusters of nerve cells that perform simple information processing, kind of like a “mini-brain

nerve

bundles of nerve cells running in parallel that act like electrical cables to transmit information from one part of the animal’s body to another

Class Turbellaria

(Platyhelminthes)

* free living flatworms; mostly predators or scavengers
* many species of free-living marine flatworms are brightly colored and exceptionally beautiful

Class Trematoda

(Platyhelminthes)

* flukes; parasitic
* Flukes are common internal parasites of marine animals, just as they are of terrestrial animals

Class Cestoda

(Platyhelminthes)

* tapeworms; parasitic
* Some of these, like the tapeworms found in whale intestines, can be over 30 m (100 feet) long!
* Note that tapeworms have distinct segments, so they are easily confused with the segmented worms in phylum Annelida. However, the segments in tapeworms are generally flattened, whereas those in annelids tend to be round in cross-section, or at least not really flat

Lophotrochozoa

Most of them have a trochophore larva, and some have a specialized feeding structure called a lophophore. The group name comes from merging lophophore + trochophore.

Nemertea

(Ribbon worms)

* They have a long, very slender, limp, stretchy body and range in size from just a few mm long to over 50 meters (160 feet) long!
* The outer surface of the **body is covered with cilia**. In smaller species, propulsion may be done entirely by these cilia
* They are **eucoelomate**
* The most distinctive feature of this phylum is an **eversible proboscis with venom** used for capturing prey.
* Ribbon worms may be drab or very brightly colored
* They have a **complete gut** for more efficient and complete processing of food
* They have a **closed** **circulatory system** formed by a circular blood vessel, but they have no heart! Fluid is “pumped” just by body movements.
* They have no gills or other specialized respiratory structures; gas exchange occurs directly through the surface of their slender body.
* They have a **simple nervous system with ganglia and nerves**, but nothing sophisticated enough to be considered a brain.

complete gut

One-way flow of food through a complete gut is advantageous, because it allows different parts of the gut to specialize for different purposes.

Annelida

(Segmented Worms)

* have a **segmented** body plan (otherwise known as a **metameric** body plan), except in a few subgroups
* These animals are **eucoelomate**. Each fluid-filled segment of the worm contains its own mesoderm-lined portion of the well-developed coelom (**hydrocoel**)
* **Hydrostatic skeleton**: The worm uses the incompressibility of water, in combination with muscle contractions to pressurize and stiffen the segment.
* Each segment has **longitudinal muscles** (which the worm uses to shorten or bend the segment) and **circumferential muscle** (which the worm uses to elongate the segment).
* They have a **closed circulatory system,** just like humans do, but annelids typically have 5 or more separate hearts instead of just one.
* Most annelids have bristles called **setae** along their sides. These setae may be short or very long. They are used for traction and/or defense and probably serve a tactile sensory function

Class Clitellata

(Annelida)

* Unranked group: **Oligochaeta** (earthworms and relatives).
* These are mostly terrestrial and won’t be considered further in this course.
* Unranked group: **Hirudinea** (leeches).
* Although most leeches are terrestrial, there are a few marine species.
* Leeches are mostly ectoparasites that feed by attaching to the skin of their host using a mouth that resembles a suction cup, rasping or slicing through the skin once attached, and sucking out blood or other body fluids.

Class Polychaeta

(Annelida)

* Polychaetes have a pair of paddle-like appendages, called **parapodia,** protruding from the right and left sides of each segment. These are often used like feet or paddles to aid in crawling or swimming locomotion.
* Each parapodium (the singular of parapodia) typically has stiff, hair-like bristles (**setae**) projecting from it. In some species, these setae are very short and almost invisible. In others they are very long, giving the worm a shaggy appearance.

Errantia

(Annelida; Polychaeta)

* almost all **free-living**, which means they are able to crawl or swim around freely, even if they dig burrows or conceal themselves in tubes much of the time. In contrast, the “tube worms” discussed below are obligate tube dwellers and typically secrete a special tube they live in for their entire life rather than just digging a burrow.
* A **polyphyletic group** united by how they move rather than by evolutionary ancestry.
* Most errant polychaetes are **predatory**. Some have very impressive mandibles and can inflict painful bites. Others have venomous, fiberglass-like bristles. So be careful if you handle errant polychaetes!
* Examples of common species include clam worms, sand worms, blood worms, bristle worms, scale worms, and bobbit worms

Tube worms

(Annelida; Polychaeta)

* Most groups of polychaetes **spend their entire lives living inside tubes** they secrete themselves
* the segmented body is normally hidden from view inside the tube, and all you see are the tentacles or gills extended from the open end of the tube for feeding and/or gas exchange.
* Not a taxonomic group based on evolutionary history; rather, it is __a description of how and where these worms typically live__, and the group is **polyphyletic**.

Serpulid worms

(Annelida; Polychaeta; Tube worm)

* These worms secrete **calcium carbonate tubes**, which are usually hard and white or cream in color, as if made of plaster or limestone.
* The gills, which protrude from the open end of the tube and are normally used both for gas exchange and filter-feeding, are often fluffy or frilly looking, so some of these worms are commonly called **feather-duster worms**.
* They have an **operculum**, which is basically a tiny trap door they can close over the open end of their tube after they retract their gills inside to protect their delicate and vital gills from damage by predators.
* Examples include the very colorful **Christmas Tree worms** found on tropical coral reefs.

Sabellid worms

(Annelida; Polychaeta; Tube worm)

* Are similar to serpulids in general appearance, and they, too, are often nicknamed feather-duster worms; however, sabellids **do** __**not**__ **have calcium carbonate tubes** and they **do** __**not**__ **have an operculum**.
* Their tubes may be made of parchment-like material, or they may be made by gluing sand grains or bits of shell together.
* Local examples include some feather-duster worms, such as those in the genus ***Eudistylia***, which have parchment-like tubes, and sandcastle worms (genus ***Phragmatopoma*****)**

Siboglinid worms

(Annelida; Polychaeta; Tube worm)

* “Beard worms”
* Only discovered within the past few decades, as they are **associated with deep-sea hydrothermal vents**.
* Some species are **up to 2 m tall, with white tubes and bright red plume-like gills**.
* Very unusual. **No mouth or gut**. They rely on **endosymbiotic chemosynthetic prokaryotes** living inside their tuft of gills to generate energy from inorganic molecules and to absorb other nutrients from the water near deep-sea hydrothermal vents.
* Not recognized as annelids until genetic work confirmed their true ancestry. Originally placed into two phyla called **Pogonophora** and **Vestimintifera.**

Osedax worms

(Annelida; Polychaeta; Tube worm)

* Affectionately known as **bone-eating snot flowers** or zombie worms.
* They have a snot-like appearance
* They were first discovered in Monterey Bay in 2002 by MBARI during an ROV dive on a dead whale carcass. The worms feed on lipids in the skeletons of dead whales in the deep sea. 
* About 20 species have since been discovered around the world, all in the genus (***Osedax***)
* These worms are probably a sub-group of siboglinid worms.
* **Hundreds or thousands of individuals growing on dead whale bones resemble a carpet of reddish-brown fuzz on the bones.**  
* The branched tail end of the female worms burrow into the bones like the roots of a tree and **extract energy from the fats and oils in the bone**.
* All of the visible adult worms are female.
* Each female contains a **“harem” of dozens to hundreds of tiny males inside her body**, where they produce sperm to fertilize her eggs.

Spionid worms

(Annelida; Polychaeta; Tube worm)

* These are usually very small and easily overlooked.
* They can be distinguished from other types of tube worms by **a single pair of long, slender, fleshy tentacles** protruding from the end of their tube.

Terebellid worms

(Annelida; Polychaeta; Tube worm)

* “Spaghetti worms”
* These tubeworms have dozens or hundreds of very long, light-colored**, spaghetti-looking tentacles that radiate out in all directions along the bottom from the tube opening**, which is usually flush with the seafloor. (The worm’s body is hidden in its tube, which is usually buried in sediment or hidden in cracks among rocks.)
* The tentacles may be just a few mm long, or many meters long, depending on the size and species of terebellid.
* These worms are **detritivores**, and the tentacles are **feeding tentacles**. Each tentacle has a U-shaped cross-section that forms a little mucus-filled trough. The trough is lined with cilia that beat to create a flow of mucus toward the mouth. This acts like **a conveyor belt** to transport food particles along the U-shaped channel to the worm’s mouth. 

Sipunculids

(Annelida but no segments)

* “Peanut Worms”


* They are usually small, plump, unsegmented little blobs with a long, retractable, tube-like extension (called the **introvert**) at the anterior end.
* The introvert looks like a long, flexible neck. It ends in a mouth that often has a ring of short, **ciliated tentacles used for feeding**. The introvert can be extended for feeding, or pulled back within itself by turning it inside-out.
* Most worms are **deposit feeders** that keep their body hidden in mud or rock crevices, extending only their skinny introvert to feed.
* They have **no circulatory system or respiratory system**, but they do have a **complete gut.**

Echiurans

(Annelida but no segments)

* “Spoon worms”
* These worms are generally, plump, sausage-looking worms with a little **spoon-like protrusion at the mouth end**. The spoon is often ringed with bristles.
* Our most famous local example is the **Fat Innkeeper Worm** (also known as the **Weenie Worm** for its resemblance to a certain human organ), *Urechis caupo*.