Cactus Worms

Origin

• Cactus worm is the colloquial name for the phylum priapulida, a small, worm-like creature that ranges in size from around 0.5 mm up to 200 mm. The name priapula derives from the ancient Phallic God, Priapos, who symbolized the regenerating power of the male gender. The scientists who first identified and categorized the species thought they resembled the human penis, hence the name. Nowadays, however, they are more commonly thought to resemble certain varieties of cactus plants.

Prosoma

• The body of a cactus worm is divided into two parts, the prosoma and the trunk. There is a mouth with five spines at its opening at the anterior end of the prosoma (the main body section). The prosoma can be folded back into the trunk of a cactus worm, which also has spines, also known as scalids at its tip.

Trunk

• Some types of cactus worm have cadual appendages on the trunk areas of their bodies. These are similar in appearance to a nest of worms and may serve a respiratory function. The body of a cactus worm has a cuticle which contains "chitin," a fibrous substance consisting mainly of polysaccharides, which forms the major parts of the exoskeletons of fungi and arthropods. The cuticle lies above the skin of a cactus worm.

Biology

• The pharynx lies behind the mouth of the phylum priapulida. This is a cavity lined with membranes which connects to the anus at the tail end of a cactus worm. Cactus worms don't have the required organs for gaseous exchange. They also lack a working circulatory system. According to the Earth Life website, however, some types of cactus worms carry a fluid containing a respiratory pigment, known as Haemerythin. This is a protein that transports oxygen in many marine invertebrates.

Gender and Maturation

• Cactus worms can be either male or female, with each usually only possessing a single testis or ovary. Fertilization occurs when both sperm and egg are ejected into an ocean or sea. The larvae form of cactus worms are protected by cuticle plates as they grow. They also shed their skins several times before growing into full adult form. Cactus worms feed on worms smaller than themselves that reside in the mud of seabeds.

Nervous System and Movement

• The cord governing the nervous system of a cactus worm runs down the front area of the body. It contains several "ganglia," which are nerve cell bodies that are usually connected by synapses. The skin of the phylum priapulida is strengthened by tiers of muscles. Cactus worms find it awkward to propel themselves to sustained motion and struggle to enter the seabed mud if extracted from it. Movement inside the mud is achieved by the position of the spines in the prosoma.