Chapter 7: Marine Invertebrates Bilateral Symmetry and the Advancements of the Worms

Oh, to be a Worm! Adaptive trends exhibited by worm phyla: Bilateral symmetry Cephalization –development of a head region Coelom development Increasing development of nervous sensory systems.

Bilateral Symmetry “Bilateral symmetry refers to a basic animal body plan in which one plane of symmetry exists to create two mirror-image halves.” Sumich (1999) An Introduction to the Biology of Marine Life gecko.gc.maricopa.edu/.../platyhelminthes/ platyhel.htm Planaria

Bilateral Symmetry Organisms with bilateral symmetry have developed an anterior “head” region and a posterior “tail” region. In addition they also display a top or back side (dorsal) and a belly or underside (ventral).

Worms with Direction “Animals with a front end [anterior] region generally move in a forward direction.” Villee, et. Al. (1989) Biology Thus the tendency would naturally be to concentrate sensory organs in this anterior region to detect changes in the environment. – Leads to more active predation – More sophisticated behaviors This process is termed “cephalization” – from the Greek for “getting a head”

A Bit About Germ Layers Early in embryonic development, the structures of most animals develop from three tissue layers call germ layers. Ectoderm – outer layer Mesoderm – middle layer Endoderm – inner layer Digestive cavity

As organisms become more sophisticated anatomically, the development of a body cavity or coelom [see-luhm] is observed. The coelom is lined by mesoderm tissue and is essentially an open tube within the organism’s body in which digestive, reproductive and other organs arise. A Tube-Within-A-Tube

‘Tubular’ Terminology Animals can either be Acoelomate – no body cavity Pseudocoelomate – a body cavity develops between the body wall (ectoderm) and the internal organs (endoderm). Usually filled with fluid. Coelomate – the body cavity is completely lined with tissue from the mesoderm.

Advantages of a Coelom It allows for more extensive growth of the organs such as those of the digestive tract. It permits the formation of an efficient circulatory system with a heart that can drive the blood through the vessels without them being restricted by a compact body. The fluid in the coelom can transport or move materials faster than by diffusion. The fluid can also generate a more efficient hydrostatic force against which muscles can act. The muscles of the digestive tract can become independent of the muscles of the body wall permitting more variation in movement of both sets of muscles. The coelom provides a space for gonads to develop during breeding season or for young to grow in those animals which give birth to live young. From Dr. Kent Simmons, Campus Manitoba Web

PHYLUM: Platyhelminthes Flatworms – A Tiny “Inch” Forward Exhibit bilateral symmetry and cephalization Acoelomate Mouth and anus are still shared Simplest organisms with well-developed organs Have a simple brain called a ganglia in the head with two nerve cords that extend the length of the body.

Flatworms Turbellarians – Planarians – Marine, free-living Trematodes – Flukes – Mostly parasitic Cestodes – Tapeworms – Parasites that live in the intestines of vertebrates (including humans!) Anatomy of a Flatworm

Flatworms – Another Look Anatomical diagram of a planarian – a typical flatworm found in both fresh and marine waters as well as terrestrial habitats Flatworm Media Planaria Swimming Turbellarians Trematode infection of salamanders Warning: Colonoscopy showing tapeworm !

PHYLUM: Nemertinea Proboscis Worms/ Ribbon Worms Simplest animals to possess definite organ systems. Almost exclusively marine Possess a proboscis – a long, hollow, muscular tube which can be everted from the head to capture food or for defense.

Proboscis Worms/ Ribbon Worms Are truly a “tube-within-a-tube.” The digestive tract is a complete tube with mouth at one end and anus at the other. First example of separate circulatory and digestive systems Acoelomates Non-parasitic, mostly benthic Claim to fame – one species has been observed up to 30 m long (the longest invertebrate!)

PHYLUM: Nematoda Roundworms Most common worms in the world – inhabit almost every species of plant and animal. Mostly parasitic, some benthic Have a tough, outer covering called a cuticle which keeps them from drying out. Sexes separate and dimorphic – separate male and females that look different (male smaller)

Roundworms Pseudocoelomates Have a cavity filled with incompressible fluid which acts as a hydrostatic skeleton. – Cavity is not completely lined by mesoderm. – When muscles in the body wall contract they flex and squeeze against this fluid causing the shape of the worm to deform and therefore move. – Excellent technique for sediment burrowing. Roundworm in cat gut Marine roundworm Good slide show of various roundworm images

20,000 species including marine and terrestrial species (e.g. earthworms) Defining characteristics – Body divided into segmented units called metameres. – Chaetae (or setae) – hair- like structures on each segment PHYLUM: Annelida Segmented Worms

Other Innovations of Annelids Digestive tract (or gut) extends through all segments. Coelomates – Acts as a hydrostatic skeleton – Organism can move each segment individually. This permits localized and more efficient movement. Have a closed circulatory system In aquatic species, respiratory exchange is through gills

Annelid Classes Polychaeta – All marine, may be free-swimming or live in benthic aggregations – Include bloodworms, sandworms, lugworms, bristle worms, fan worms, feather duster worms, beard worms, etc. Oligochaeta – Aquatic or terrestrial, live in mud or sand bottoms’ – Include earthworms Hirudinea – Mostly freshwater, but some marine species – Leeches

Polychaete Biology Anatomy: – Chaetae emerge from flat parapodia which are stiff extensions on each body segment Life History: – Have a planktonic larval stage called a trochophore – As adults, some crawl on bottom, others burrow, others build tubes and live in aggregations, while still others remain planktonic Feeding: – Some are carnivorous, some are suspension feeders, and others are deposit feeders. – Crawling worms have well developed parapodia, a proboscis, and jaws. – Suspension feeding worms often have tentacles, cilia, or mucus to capture prey

Serpula vermicularis – reef building tube worm

Common lug worm (Arenicola marina) Plymouth, Devon, England

Lug worm casts on the coast of North Ireland

King Ragworm (Nereis virens)

Tubeworm (Spirorbis tridentatus) Batten Bay, Mount Batten, Plymouth, Devon.)

Myrianida pachycera, a polychaete (worm) (60x)

Christmas tree worms on coral head

Trochophore larvae of a bristle worm Note the bristles anchored in the body for swimming and the reddish eye spots.

Polychaete sandworms - Notice the tubes sticking up from the mud. Some sandy beaches can contain up to 32,000 polychaete worms/m 2 that consume 3 tons of sand/ year.

Feather duster worms, Bimini, Bahamas

Polychaete epitokes swarming. Glover’s Reef, Belize

Pogonophora beard worms Deep water species – live near hydrothermal vents No mouth or gut Tuft of tentacles absorbs dissolved nutrients from the water Symbiotic bacteria inside the worm use these nutrients to make food. Formerly classified in their own phylum

Oligochaeta Found in mud/sand bottoms Usually deposit feeders Lack parapodia Includes the common earthworm

Hirudinea leeches Usually parasitic and blood- sucking Inject a chemical into prey that is both an anticoagulant and an anesthetic. Have a sucker on anterior and posterior. Lack parapodia

Sipuncula peanut worms Strictly marine Unsegmented Burrow in shallow water soft bottom sediments Possess a long anterior portion that can be retracted into the body. Deposit feeder 1-35 cm long Approximately 320 species

Echiura innkeepers/ spoon worms proboscis Strictly marine Unsegmented, though now classified with annelids Have a non-retractable, spoon- like proboscis for gathering organic material. One species creates a U-shaped burrow that is often shared with other organisms. Deposit feeder Approximately 135 species

Unifying Characteristics of Worms Ubiquitous in marine environment (benthic, parasitic, free swimming) Usually small Responsible for mixing marine sediments. Recycle bacteria and detritus into the food chain. Have highly developed feeding appendages and digestive systems. Important food for higher invertebrates and some fish. May have important health effects on marine vertebrates

Image Citations Brown, Hugh. “Serpulid polychaete worm” Digital Image. Serpulid reefs. The Scottish Association for Marine Science (SAMS). 5 January Fiege, Dieter. “Glyceridae” Digital Image. Senchenbergische Naturforschende Gesellschaft January “Leech.” Digital Image. Annelids Live Invertebrates – Niles Biological, Inc Niles Biological, Inc. 5 Jaunary 2009 Rouse, Greg. “Chaetae of an Annelid” Digital Image. Annelida Tree of Life Web Project. 5 January 2009 Rouse, Greg. “Myrianida pachycera, a polychaete.” Digital Image. Nikon Small World – Gallery Nikon Small World – Photomicrography Competition. 5 January Siddal, Mark. “Medicinal leech” Digital Image. Leech on Me Science Friday Newsbriefs. 5 January “Social feather duster worm close-up” Digital Image. ReefNews January “Swarming polychaetes” Digital Image. Rpolychaete epitokes Ryan Photographic. 5 January “Trocophore larvae” Digital Image. Bristleworms and their larva Mic-UK: Bristle worms. 5 January Veitch, Nick. “Lug worm casts” Digital Image. Wikimedia Commons January 2009.