Phylum Mesozoa

Today's animal phylum is a rather obscure one, so obscure that I wasn't able to find a properly licensed image to use. If it helps, here is an image of a member of Class Rhombozoa. 

Mesozoa comes from the Greek for "middle animal" and is a phylum that contains creatures having traits of both protists and flatworms. Though some include this on the list of animal phyla, others do not. This is mainly due to very fuzzy relationships to other animal groups. Studies have shown relationships to both the flat- and roundworms, along with some mesozoans being closer to segmented worms, molluscs, and other invertebrates. Despite similarities, these differences have lead some to split Mesozoa into several phyla based on closest relation. Others maintain their status as a single phylum.

Mesozoans are parasites and show many of the characteristics that are seen in other parasitic creatures. The body form of these animals is very simple, lacking a number of basic systems. They have no nervous system or digestive tract. This simplified body form is likely derived from more complex ancestors, with extra parts being lost when they had become parasitic. Their method of reproduction is quite unusual, with development occurring inside of other cells. No other animal group has shown this sort of method.

Phylum Mesozoa includes two classes: Class Orthonectida and Class Rhombozoa. Orthonectida members can parasitize a variety of invertebrate, marine hosts, while the Rhombozoa members are only found in the kidney-like nephridia of cephalopods.

Source is Biology of the Invertebrates.

Mismark Case Study: Gordon Setter

A Gordon setter in the breed's only acceptable color.

The Gordon setter is one of a small number of setter breeds, which also includes the English setter, Irish setter, and Irish red and white setter. Though the Gordon setter now only comes in one acceptable color, the breed's history included a number of other colors that are now considered to be mismarks. Part of why these colors are in the breed is due to its relationship with the other setters. So, what are these mismarks?

• Incorrect tan markings
• Dogs with more or less than than required in the standard
• Liver
• Inherited on the Brown locus, a dog must be bb to be liver
• Red
• Inherited on the Extension locus, a dog must be ee to be recessive red
• Too much white
• Inherited on the Spotting locus, a dog with a variety of genotypes can have too much white

Too much white

Looking at these mismarks, they are all recessively inherited except in dogs that are genetically solid but have too much residual white. All of theses colors were well known when the breed was young. Much like the Irish setter, the predominant color in the early years of the breed is actually not what you think it would be when looking at modern dogs. Gordons were once mostly tricolor with some dogs being solid black and tan, liver, or red, but the white markings and other colors fell out of favor and led to the production of the breed you see today.

This dog appears to be liver

The current breed standard for the Gordon only allows for black and tan dogs with specific tan markings. Dogs that are anything other than black and tan are disqualified and anything more than a small bit of white on the chest is not allowed. A dog with more or less than the required tan would be penalized, despite the fact that ten markings can vary greatly on dogs that are all genetically atat tan pointed. So far, it is known that there are modifiers that control this amount of tan, but it isn't known where they are or how they are inherited.

Too much tan

This is a case where color standard is based on, basically, fashion. What once was popular was no longer liked by those who wrote the breed standard, and thus those other colors faded into obscurity. However, since the colors are basically all recessively inherited, they continue to pop up on occasion in litters that are born today. These past decisions are really problematic when looking at the breed's history and what this holds for the future.

Too little tan

Since Gordon setters were originally hunting dogs, the main thing that they should be bred for is working ability. This was at least true of setters past. However, modern Gordons have a lot more emphasis placed on type and show potential. It remains true that Gordons were developed as working dogs and color has no affect on working ability. It also has no affect on health or temperament, which are both important to people who wish to have a happy life living with a dog, particularly if the dog is meant to be a pet. If breeders wish to emphasize the Gordon setter's place as a working breed and its ability to do field work, why should they place any emphasis on color?

Another major concern in the Gordon setter and any other breed is a loss of genetic diversity due to selective breeding. Since Gordons of only one color were favored, a lot of diversity was lost rather early on in the breed. Continued shunning of off-color dogs only drops more potential sources of genetic diversity from the breed and risks loss of some very good, sound individuals based on a silly cosmetic preference.

Sources are the American Kennel Club, Gordon Setter Club of New South Wales, and Gambit Gordon Setters. Images are from Wikimedia Commons or Flickr.com under Creative Commons licenses: one, two, three, four, five.

Invasive Species: Apple Snail

An apple snail (Pomacea canaliculata), also known as a miracle snail

Apple snails are native to the Amazon basin on down to parts of Argentina and are quite large-bodied, growing up to ten centimeters. They have become invasive in a large swath of South and Eastern Asia, as well as Guam, the Dominican Republic, Papua New Guinea, Hawaii, and parts of the continental United States. Introduction has been through the aquarium trade, the nursery trade as eggs attached to plants,and through attempts to use them as a food source. They are also known to escape captivity.

The first transports of this species out of its native range began in the 1980's. After attempts to sell the snails as food, they escaped and began becoming crop pests. The species is known to feed on such plants as rice and taro, causing major damage to important food sources, but they also feed on water chestnut, lotus, and other plants. Since they are aquatic, the species spreads quickly and easily in watery environments. They pose a threat to native plant species in and have been linked to the decline of several species of native snail. Mainly due to crop damage, the economic losses these snails have caused in some countries are huge.

Egg mass, scale 5cm

The most important management method thus far is prevention. Spread of the snails must be prevented, particularly to potentially vulnerable areas such as wetlands in India and Australia. Simple things such as copper barriers have proven effective at preventing spread of infestations. Eradication of the pest is done where possible, but cannot be done when there are too many snails. As much as possible, egg masses and hatched snails are removed from effected areas. So far this has been the most viable form of control. Other methods, such as pesticides and biological controls via predators, have not worked out so well. One big concern for any of these methods involves concerns over the environment. Hand removal, on the other hand, as minimal effect if any.

This species is currently on the list of 100 World's Worst Invasives at #73. 

Images are from Wikimedia Commons and are under a Creative Commons license or are copyright free: one, two.