Deutrostomia

PHYLUM: HEMICHORDATA Share several similarities with the chordates including pharyngeal slits dorsal nerve cord Hemichordates appear to have diverged close to a point at which the chordates originated. Hemichordates are divided into three classes that differ greatly from each other, although they show similar structure in early embryological stages PHYLUM: HEMICHORDATA This group of animals share several similarities with the chordates which includes pharyngeal slits and a dorsal nerve cord and were once classified as chordates since it was thought that they also possessed a notochord. Recent analysis has identified what was once considered a notochord to be an extension of the buccal cavity (the buccal diverticulun). Nevertheless the hemichordates appear to have diverged close to a point at which the chordates originated. Hemichordates are divided into three classes that differ greatly from each other, although they show similar structure in early embryological stages. www-biol.paisley.ac.uk Bill.smr.arizona.edu

PHYLUM: HEMICHORDATA CLASS: PTEROBRANCHIA Ten species in this class Live in colonies Larval bodies divided in to a proboscis, collar and trunk The collar expands dorsally into tentacled arms which possess cilia that direct food into ciliated grooves which carry it to the mouth The alimentary canal is U-shaped with the anus outside the fringe of tentacles In most species there is only one pair of pharyngeal slits Some are dioecious, most are hermaphroditic Fertilization is external, The sexually produced individuals then give rise to colonies by budding. CLASS: PTEROBRANCHIA Class Pterobranchia live in colonies and secrete tubes. There are about ten species in this class and they have a similar development to the acorn worms (Class Enteropneusta) with their bodies divided in to a proboscis, collar and trunk. However, the adults’ external appearance is very different from acorn worms. The collar expands dorsally into tentacled arms which possess cilia that direct food into ciliated grooves which carry it to the mouth. The alimentary canal is U-shaped with the anus outside the fringe of tentacles. In most species there is only one pair of pharyngeal slits. Some pterobranchia are dioecious, but most are hermaphroditic. Although fertilization is external, the embryos generally remain sheltered within the tubes. The sexually produced individuals then give rise to colonies by budding . These tiny marine animals tend to form large plant like colonies, whose individuals project like small flowers at the ends of a branching series of tubes. The short body is doubled-back on itself, so that the anus opens anteriorly over the back of the head. It is generally believed that they are a very primitive group rather than a degenerate hemichordate. Modern hemichordates appear to be very similar to the fossil graptolites which were abundant in the seas around the first fossil evidence of the vertebrates.Biodidac.bio.uottawa.ca

PHYLUM: HEMICHORDATA CLASS: ENTEROPNEUSTA Commonly referred to as acorn worms These animals burrow in marine sediments have worm-like bodies divided into a proboscis, collar, and trunk CLASS: ENTEROPNEUSTA Class Enteropneusta includes most of the phylum, and are commonly referred to as acorn worms. These animals burrow in marine sediments and have worm-like bodies divided into a proboscis, collar, and trunk. www.cals.ncsu.edu/course/zo150/mozley/fall/enterocoely

PHYLUM: HEMICHORDATA CLASS: ENTEROPNEUSTA General Characteristics Possess a prominent proboscis, a collar and a long slimy trunk Up to 2 metres in length Each of these three regions have a separate coelomic compartment filled with spongy tissue that provides some mechanical support Acorn worms either live in U-shaped burrows in shallow water or they burrow through marine sediment or live under rocks or seaweed General Characteristics Possess a prominent proboscis, a collar and a long slimy trunk up to 2 metres in length. Each of these three regions have a separate coelomic compartment filled with spongy tissue that provides some mechanical support, nevertheless these animals are easily broken. Acorn worms either live in U-shaped burrows in shallow water or they burrow through marine sediment or live under rocks or seaweed www.cals.ncsu.edu/course/zo150/mozley/fall/studyaids.html

PHYLUM: HEMICHORDATA CLASS: ENTEROPNEUSTA General Characteristics The proboscis is the main organ of locomotion The trunk is pulled along passively Many acorn worms feed by ingesting large quantities of mud or sand from which the gut extracts organic debris Others feed by means of cilia on the proboscis which pass the food backwards into the mouth Food particles are bound on a mucous string and are swallowed along with the water The proboscis is the main organ of locomotion, with the trunk being pulled along passively. Many acorn worms feed by ingesting large quantities of mud or sand from which the gut extracts organic debris. Others feed by means of cilia on the proboscis which pass the food backwards into the mouth. Food particles are bound on a mucous string and are swallowed along with the water.Biodidac.bio.uottawa.ca

PHYLUM: HEMICHORDATA CLASS: ENTEROPNEUSTA General Characteristics: Internal Structure The pharyngeal slits are U-shaped openings in the pharynx that can swallow water in to the pharyngeal pouches and out through the gill pores. The body: surface is the main route for respiratory exchange. The colourless blood is pumped anteriorly by a dorsal vessel into a contracting heart vessel in the proboscis and then posteriorly by a ventral vessel – an open circulatory system. the glomerulus is assumed to have an excretory function The nervous system consists largely of a diffuse network in the base of the epidermis. Along the dorsal and ventral midlines this plexus is concentrated into dorsal and ventral nerve cords which lack ganglia. In places the nerve cord is hollow and similar to the hollow dorsal nerve of the chordates. Sexes are separate and fertilization is external Internal Structure Water swallowed during feeding exits through pharyngeal slits and gill pores. The pharyngeal slits are U-shaped openings in the pharynx that can swallow water in to the pharyngeal pouches and out through the gill pores. Pharyngeal slits are sometimes called gill slits, although in these animals they have a feeding role rather than for the exchange of respiratory gases. The body: surface is the main route for respiratory exchange. The colourless blood is pumped anteriorly by a dorsal vessel into a contracting heart vessel in the proboscis and then posteriorly by a ventral vessel. The blood circulates; through sinuses, making it an open circulatory system. One such sinus, the glomerulus, is assumed to have an excretory function. The nervous system consists largely of a diffuse network in the base of the epidermis. Along the dorsal and ventral midlines this plexus is concentrated into dorsal and ventral nerve cords which lack ganglia. In places the nerve cord is hollow and similar to the hollow dorsal nerve of the chordates. Sensory receptors are scattered over the integument, especially around the proboscis. Sexes are separate in, the acorn worms although there is little to distinguish males from females. The gonads have a separate gonadopore, and fertilization is external and achieved through mass spawning initiated by the females. Embryological development is typical deuterostome. This is characterized by radial cleavage, the blastopore becoming the anus, and the coelom forms and outpocketing of the archenteron. Development is sometimes direct, although more usually a tornaria larva develops characterised by ciliary contractions which cause it to spin. The tornaria larva closely resembles the bipinnarian larva of the echinoderms.

PHYLUM: HEMICHORDATA CLASS: PLANCTOSPHAEROIDEA There is some dispute about this class as only the larvae are well known General Characteristics: Internal Structure CLASS: PLANCTOSPHAEROIDEA There is some dispute about this class as only the larvae are well known. Tolweb.org