14.5: Phylum Annelida - Biology

14.5: Phylum Annelida - Biology

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Phylum Annelida includes segmented worms. The name of the phylum is derived from the Latin word annellus, which means a small ring. Annelids show protostomic development in embryonic stages and are often called “segmented worms” due to their key characteristic of metamerism, or true segmentation.


Annelids display bilateral symmetry and are worm-like in overall morphology. Annelids have a segmented body plan wherein the internal and external morphological features are repeated in each body segment. Metamerism allows animals to become bigger by adding “compartments” while making their movement more efficient. This metamerism is thought to arise from identical teloblast cells in the embryonic stage, which give rise to identical mesodermal structures. The overall body can be divided into head, body, and pygidium (or tail). The clitellum is a reproductive structure that generates mucus that aids in sperm transfer and gives rise to a cocoon within which fertilization occurs; it appears as a fused band in the anterior third of the animal (Figure 1).


The epidermis is protected by an acellular, external cuticle, but this is much thinner than the cuticle found in the ecdysozoans and does not require periodic shedding for growth. Circular as well as longitudinal muscles are located interior to the epidermis. Chitinous hairlike extensions, anchored in the epidermis and projecting from the cuticle, called setae/chaetae are present in every segment. Annelids show the presence of a true coelom, derived from embryonic mesoderm and protostomy. Hence, they are the most advanced worms. A well-developed and complete digestive system is present in earthworms (oligochaetes) with a mouth, muscular pharynx, esophagus, crop, and gizzard being present. The gizzard leads to the intestine and ends in an anal opening. A cross-sectional view of a body segment of an earthworm (a terrestrial type of annelid) is shown in Figure 2; each segment is limited by a membranous septum that divides the coelomic cavity into a series of compartments.

Annelids possess a closed circulatory system of dorsal and ventral blood vessels that run parallel to the alimentary canal as well as capillaries that service individual tissues. In addition, these vessels are connected by transverse loops in every segment. These animals lack a well-developed respiratory system, and gas exchange occurs across the moist body surface. Excretion is facilitated by a pair of metanephridia (a type of primitive “kidney” that consists of a convoluted tubule and an open, ciliated funnel) that is present in every segment towards the ventral side. Annelids show well-developed nervous systems with a nerve ring of fused ganglia present around the pharynx. The nerve cord is ventral in position and bears enlarged nodes or ganglia in each segment.

Annelids may be either monoecious with permanent gonads (as in earthworms and leeches) or dioecious with temporary or seasonal gonads that develop (as in polychaetes). However, cross-fertilization is preferred in hermaphroditic animals. These animals may also show simultaneous hermaphroditism and participate in simultaneous sperm exchange when they are aligned for copulation.

This combination video and animation provides a closeup look at annelid anatomy.

Classification of Phylum Annelida

Phylum Annelida contains the class Polychaeta (the polychaetes) and the class Oligochaeta (the earthworms, leeches and their relatives).

Earthworms are the most abundant members of the class Oligochaeta, distinguished by the presence of the clitellum as well as few, reduced chaetae (oligo– = “few”; –chaetae = “hairs”). The number and size of chaetae are greatly diminished in Oligochaeta compared to the polychaetes (poly=many, chaetae = hairs). The many chetae of polychaetes are also arranged within fleshy, flat, paired appendages that protrude from each segment called parapodia, which may be specialized for different functions in the polychates. The subclass Hirudinea includes leeches such as Hirudo medicinalis and Hemiclepsis marginata. The class Oligochaeta includes the subclass Hirudinia and the subclass Brachiobdella. A significant difference between leeches and other annelids is the development of suckers at the anterior and posterior ends and a lack of chaetae. Additionally, the segmentation of the body wall may not correspond to the internal segmentation of the coelomic cavity. This adaptation possibly helps the leeches to elongate when they ingest copious quantities of blood from host vertebrates. The subclass Brachiobdella includes species like Branchiobdella balcanica sketi and Branchiobdella astaci, worms that show similarity with leeches as well as oligochaetes.

Learning Objectives

Phylum Annelida includes vermiform, segmented animals. Segmentation is seen in internal anatomy as well, which is called metamerism. Annelids are protostomes. These animals have well-developed neuronal and digestive systems. Some species bear a specialized band of segments known as a clitellum. Annelids show the presence numerous chitinous projections termed chaetae, and polychaetes possess parapodia. Suckers are seen in order Hirudinea. Reproductive strategies include sexual dimorphism, hermaphroditism, and serial hermaphroditism. Internal segmentation is absent in class Hirudinea.

Phragmatopoma californica

Phragmatopoma californica, commonly known as the sandcastle worm, the honeycomb worm [1] or the honeycomb tube worm, [2] is a reef-forming marine polychaete worm belonging to the family Sabellarididae. It is dark brown in color with a crown of lavender tentacles and has a length of up to about 7.5 centimeters (3.0 in). [3] The worm inhabits the Californian coast, from Sonoma County to northern Baja California. [4]

Sandcastle worms live in colonies, building tube reefs somewhat similar to sandcastles (hence the name), which are often seen on rocky beaches at medium and low tide. The sandcastles, which have a honeycomb-like outward appearance, can cover an area of up to 2 meters (6.6 ft) on a side. [3] They may share areas with mussel beds and are found in any place that provides some shelter, such as rock faces, overhanging ledges and concave shorelines. [4]

The worms remain in their tubes and are almost never seen. At low tide, when above the water, they close the entrance to their tubes with a shield-like operculum made of dark setae. When submerged, they extend their tentacles out of the tube to catch food particles and sand grains. The grains are sorted, with the best ones used to keep the tube in repair, [3] and the rest ejected. The colonies are formed by the gregarious settlement of larvae, which require contact with an existing colony to metamorphose into adult worms. [4] Gregarious settlement of this species has been linked to specific free fatty acids associated with the tubes of adult worms. [5] On rocky beaches, settlement is dependent on larval behavior in the water column and perception of chemical cues when the larvae contact the tubes. [6]

Sandcastle worms should not be confused with the similar, but more northern Sabellaria cementarium which are found from Alaska to southern California and have an amber-colored operculum. [4] Unlike P. californica, S. cementarium rarely forms colonies, does not settle gregariously, and its larvae do not respond to free fatty acids. [7]

In 2004, researchers from the University of California, Santa Barbara (UCSB) discovered that the glue used by the Phragmatopoma worm to build its protecting tube was made of specific proteins with opposite charges. [8] Those proteins are called polyphenolic proteins [9] that are used as bioadhesives. [10] They succeeded in obtaining the sequence of these adhesive proteins. [11] Inspired by these results University of Utah researchers reported in 2009 that they succeeded in duplicating the glue that the worms secrete and use to stick sand grains together underwater. [12] The typical amount of glue that the worm produces at once is approximately 100 picoliters, requiring 50 million to fill a teaspoon. [13]

They believe the glue to have applications as a biocompatible medical adhesive, for instance to repair shattered bones. [14] If found to be practicable, the synthetic glue, which is based on complex coacervates, [15] could be used to fix small bone fragments, instead of metal stabilizer devices such as pins and screws, which are challenging to use. [14] Other potential medical applications include sealing skin cuts, repair of cranio-facial bones, and corneal incisions. [13]

Obstacles include ensuring that the bond is to the substrate rather than the surface layer of the water. Another is that in order to cure, glues need to dry out. Most either do not cure underwater or set too quickly. [13]

The proteins that are the basis of its adhesive contain side chains of phosphate and amine groups, which are well-known adhesion promoters which probably helps wet the surface. The glue has two parts, with different proteins and side groups in each. The two are made separately in a gland, like an epoxy, and mix as they are secreted. [16] [17] The glue sets in about 30 seconds, probably triggered by the large difference in acidity between the acidic glue and seawater. [18] Curing takes about six hours, as the proteins cross-link, reaching the consistency of shoe leather. [13]

Existing medical superglues are highly immunogenic. Initial experiments with the new synthetic on animals show no immune response. But inside the body, the glue needs to eventually degrade, ideally at roughly the same rate as the bone or tissue regrows. Degradable versions therefore include proteins that are broken down by specialized cells. [13]

Other species that produce underwater glues include certain species of mussels, oysters, barnacles and caddisfly larvae. [13]


Some of the earliest bilaterians were wormlike, and a bilaterian body can be conceptualized as a cylinder with a gut running between two openings, the mouth and the anus. Around the gut it has an internal body cavity, a coelom or pseudocoelom. [a] Animals with this bilaterally symmetric body plan have a head (anterior) end and a tail (posterior) end as well as a back (dorsal) and a belly (ventral) therefore they also have a left side and a right side. [4] [2]

Having a front end means that this part of the body encounters stimuli, such as food, favouring cephalisation, the development of a head with sense organs and a mouth. [5] The body stretches back from the head, and many bilaterians have a combination of circular muscles that constrict the body, making it longer, and an opposing set of longitudinal muscles, that shorten the body [2] these enable soft-bodied animals with a hydrostatic skeleton to move by peristalsis. [6] Most bilaterians (Nephrozoans) have a gut that extends through the body from mouth to anus, while Xenacoelomorphs have a bag gut with one opening. Many bilaterian phyla have primary larvae which swim with cilia and have an apical organ containing sensory cells. However, there are exceptions to each of these characteristics for example, adult echinoderms are radially symmetric (unlike their larvae), and certain parasitic worms have extremely plesiomorphic body structures. [4] [2]

The hypothetical most recent common ancestor of all bilateria is termed the "Urbilaterian". [8] [9] The nature of the first bilaterian is a matter of debate. One side suggests that acoelomates gave rise to the other groups (planuloid-aceloid hypothesis by Ludwig von Graff, Elie Metchnikoff, Libbie Hyman, or Luitfried von Salvini-Plawen [nl] ), while the other poses that the first bilaterian was a coelomate organism and the main acoelomate phyla (flatworms and gastrotrichs) have lost body cavities secondarily (the Archicoelomata hypothesis and its variations such as the Gastrea by Haeckel or Sedgwick, the Bilaterosgastrea by Gösta Jägersten [sv] , or the Trochaea by Nielsen).

One hypothesis is that the original bilaterian was a bottom dwelling worm with a single body opening, similar to Xenoturbella. [3] It may have resembled the planula larvae of some cnidaria, which have some bilateral symmetry. [10]

The first evidence of bilateria in the fossil record comes from trace fossils in Ediacaran sediments, and the first bona fide bilaterian fossil is Kimberella, dating to 555 million years ago . [11] Earlier fossils are controversial the fossil Vernanimalcula may be the earliest known bilaterian, but may also represent an infilled bubble. [12] [13] Fossil embryos are known from around the time of Vernanimalcula ( 580 million years ago ), but none of these have bilaterian affinities. [14] Burrows believed to have been created by bilaterian life forms have been found in the Tacuarí Formation of Uruguay, and are believed to be at least 585 million years old. [15]

The Bilateria has traditionally been divided into two main lineages or superphyla. [16] The deuterostomes include the echinoderms, hemichordates, chordates, and a few smaller phyla. The protostomes include most of the rest, such as arthropods, annelids, mollusks, flatworms, and so forth. There are a number of differences, most notably in how the embryo develops. In particular, the first opening of the embryo becomes the mouth in protostomes, and the anus in deuterostomes. Many taxonomists now recognize at least two more superphyla among the protostomes, Ecdysozoa [17] (molting animals) and Spiralia. [17] [18] [19] [20] The arrow worms (Chaetognatha) have proven difficult to classify recent studies place them in the gnathifera. [21] [22] [23]

The traditional division of Bilateria into Deuterostomia and Protostomia was challenged when new morphological and molecular evidence found support for a sister relationship between the acoelomate taxa, Acoela and Nemertodermatida (together called Acoelomorpha), and the remaining bilaterians. [16] The latter clade was called Nephrozoa by Jondelius et al. (2002) and Eubilateria by Baguña and Riutort (2004). [16] The acoelomorph taxa had previously been considered flatworms with secondarily lost characteristics, but the new relationship suggested that the simple acoelomate worm form was the original bilaterian bodyplan and that the coelom, the digestive tract, excretory organs, and nerve cords developed in the Nephrozoa. [16] [24] Subsequently the acoelomorphs were placed in phylum Xenacoelomorpha, together with the xenoturbellids, and the sister relationship between Xenacoelomorpha and Nephrozoa confirmed in phylogenomic analyses. [24]

A modern consensus phylogenetic tree for Bilateria is shown below, although the positions of certain clades are still controversial (dashed lines) and the tree has changed considerably since 2000. [25] [23] [26] [27] [28]

1 Getting Started

The wordbiologymeans, &quotthe science of life&quot, from the Greekbios,life, andlogos,word orknowledge.Therefore, Biology is the science of Living Things. That is why Biology is sometimes known as Life Science.

The science has been divided into many subdisciplines, such as botany 1 , bacteriology, anatomy 2 , zoology, histology, mycology, embryology, parasitology, genetics 3 , molecular biol- ogy 4 , systematics, immunology, microbiology 5 , physiology, cell biology 6 , cytology, ecology 7 , and virology. Other branches of science include or are comprised in part of biology studies, including paleontology 8 , taxonomy, evolution, phycology, helimentology, protozoology, en- tomology, biochemistry, biophysics, biomathematics, bio engineering, bio climatology and anthropology.

2.1 Characteristics of life

Not all scientists agree on the definition of just what makes up life. Various characteristics describe most living things. However, with most of the characteristics listed below we can think of one or more examples that would seem to break the rule, with something nonliving being classified as living or something living classified as nonliving. Therefore we are careful not to be too dogmatic in our attempt to explain which things are living or nonliving.

  • Living things are composed ofmatter structured in an orderly waywhere simple molecules are ordered together into much larger macromolecules.

An easy way to remember this is GRIMNERD C All organisms -Grow,Respire,Interact, Move, NeedNutrients,Excrete (Waste),Reproduce,Death,Cells (Made of)

Living things aresensitive,meaning they are able torespond to stimuli.

Living things are able togrow,develop, andreproduce.

Living things are able toadaptover time by the process ofnatural selection.

All known living things use thehereditary molecule, DNA 9.

Biology - The Life Science

  • Internal functions are coordinated andregulatedso that the internal environment of a living thing is relatively constant, referred to ashomeostasis 10.

Living things are organized in the microscopic level from atoms up to cells 11. Atoms are arranged into molecules, then into macromolecules 12 , which make up organelles 13 , which work together to form cells. Beyond this, cells are organized in higher levels to form entire multicellular organisms. Cells together form tissues 14 , which make up organs, which are part of organ systems, which work together to form an entire organism. Of course, beyond this, organisms form populations which make up parts of an ecosystem. All of the Earth's ecosystems together form the diverse environment that is the earth.

sub atoms, atoms, molecules, cells, tissues, organs, organ systems, organisms, population, community, eco systems

Science is amethodologyforlearning about the world. It involves theapplication of knowledge.

The scientific method deals withsystematic investigation,reproducible results, the formation and testing ofhypotheses, andreasoning.

Reasoning can be broken down into two categories,induction(specific data is used to develop a generalized observation or conclusion) anddeduction(general information leads to specific conclusion). Most reasoning in science is done through induction.

Science as we now know it arose as a discipline in the 17th century.

The scientific method is not a step by step, linear process. It is an intuitive process, a methodology for learning about the world through the application of knowledge. Scientists must be able to have an &quotimaginative preconception&quot of what the truth is. Scientists will often observe and then hypothesize the reason why a phenomenon occurred. They use all of their knowledge and a bit of imagination, all in an attempt to uncover something that might be true. A typical scientific investigation might go like so:

Youobservethat a room appears dark, and you ponderwhythe room is dark. In an attempt to find explanations to this curiosity, your mind unravels several differenthypotheses. One hypothesis might state that the lights are turned off. Another hunch might be that the room's lightbulb has burnt out. Worst yet, you could be going blind. To discover the truth,

Biology - The Life Science

an event occurred. Experiments are then used to eliminate one of more of the possible hypotheses until one hypothesis remains. Using deduction, scientists use the principles of their hypothesis to make predictions, and then test to make sure that their predictions are confirmed. After many trials (repeatability) and all predictions have been confirmed, the hypothesis then may become a theory.

Observation- Quantitative and qualitative measurements of the world. Inference- Deriving new knowledge based upon old knowledge. Hypotheses- A suggested explanation. Rejected Hypothesis- An explanation that has been ruled out through experimentation. Accepted Hypothesis- An explanation that has not been ruled out through excessive experimentation and makes verifiable predictions that are true. Experiment- A test that is used to rule out a hypothesis or validate something already known. Scientific Method- The process of scientific investigation. Theory- A widely accepted hypothesis that stands the test of time. Often tested, and usually never rejected.

The scientific method is based primarily on the testing of hypotheses by experimentation. This involves acontrol, or subject that does not undergo the process in question. A scientist will also seek to limit variables to one or another very small number, single or minimum number of variables. The procedure is to form a hypothesis or prediction about what you believe or expect to see and then do everything you can to violate that, or falsify the hypotheses. Although this may seem unintuitive, the process serves to establish more firmly what is and what is not true.

A founding principle in science is a lack of absolute truth: the accepted explanation is the most likely and is the basis for further hypotheses as well as for falsification. All knowledge has its relative uncertainty.

Theoriesare hypotheses which have withstood repeated attempts at falsification. Common theories include evolution by natural selection and the idea that all organisms consist of cells. The scientific community asserts that much more evidence supports these two ideas than contradicts them.

Charles Darwin is most remembered today for his contribution of the theory ofevolution through natural selection. The seeds of this theory were planted in Darwin's mind through observations made on a five-year voyage through the New World on a ship called the Beagle. There, he studied fossils and the geological record, geographic distribution of organisms, the uniqueness and relatedness of island life forms, and the affinity of island forms to mainland forms. Upon his return to England, Darwin pondered over his observations and concluded that evolution must occur through natural selection. He declined, however, to publish his work because of its controversial nature. However, when another scientist, Wallace, reached similar conclusions, Darwin was convinced to publish his observations in 1859. His hypothesis revolutionized biology and has yet to be falsified by empirical data collected by mainstream scientists.

Since Darwin's day, scientists have amassed a more complete fossil record, including microorganismsandchemical fossils. These fossils have supported and added subtleties to Darwin's theories. However, the age of the Earth is now held to be much older than Darwin thought. Researchers have also uncovered some of the preliminary mysteries of the mechanism of heredity as carried out throughgeneticsandDNA, areas unknown to Darwin. Another growing area iscomparative anatomyincluding homology and analogy. Today we can see a bit of evolutionary history in thedevelopment of embryos, as certain (although not all) aspects of development recapitulate evolutionary history.

Phylum Nemertea - PowerPoint PPT Presentation is a leading presentation/slideshow sharing website. Whether your application is business, how-to, education, medicine, school, church, sales, marketing, online training or just for fun, is a great resource. And, best of all, most of its cool features are free and easy to use.

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presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!

Wiley's Textbook of Zoology for NEET and other Medical Entrance Examinations, 2020ed

The book has been organized with a structured approach as per the latest NEET syllabus requirement. A relatively conventional sequence of subjects is followed. Chapters 1 and 2 cover the diversity and classification of animal kingdom Chapters 3 and 4 elucidate structural organization in animals Chapters 5 through 11 deal with animal physiology Chapters 12 to 14 discuss reproduction in organism specifically humans and their reproductive health Chapter 15 introduces evolution Chapters 16 and 17 explains how zoology is useful for the human welfare Chapters 18 and 19 present an overview of the vast topic of biotechnology and its application.

About the Author

1 Animal Kingdom (Non-Chordata)

1.2 Basis of Classification

1.3 Classification of Animals

1.5 Phylum Coelenterata (Cnidaria)

1.7 Phylum Platyhelminthes

1.8 Phylum Aschelminthes or Nemathelminthes

2 Animal Kingdom (Chordata)

2.4 Division Gnathostomata

3 Structural Organization in Animals

3.7 Organ and Organ Systems

4.2 Analysis of Chemical Composition

4.4 Primary and Secondary Metabolites

4.10 Nature of Bonding in Polymers

4.11 Qualitative Tests for Polymers

4.12 Metabolism and its Concept

4.13 Metabolic Basis for Living&mdashAnabolic and Catabolic Pathways

4.14 Concept of Non-Equilibrium and Steady State

5 Digestion and Absorption

5.2 Different Types of Nutrition and Nutrients

5.3 Digestive System of Humans

5.5 Histology of Wall of Alimentary Canal

5.8 Neural and Hormonal Regulation in Digestion

5.9 Calorific Values of Proteins, Carbohydrates and Fats

5.10 Absorption and Assimilation of Digested Products

5.11 Disorders of Digestive System

6 Breathing and Exchange of Gases

6.3 Human Respiratory System

6.4 Mechanism of Breathing

6.5 Respiratory Volumes and Capacities

6.8 Regulation of Respiration

6.9 Disorders of Respiratory System

7 Body Fluids and Circulation

7.2 Blood&ndashAn Extracellular Fluid

7.4 Blood Groups&ndashABO and RH Group

7.8 Human Circulatory System

7.10 Regulation of Cardiac Activity

7.11 Disorders of Circulatory System

8 Excretory Products and their Elimination

8.2 Classification of Animals Based on Excretory Products

8.3 Modes of Excretion in Various Animals

8.4 The Human Excretory System

8.9 Excretion &ndash Urea and Urine Formation

8.10 Functions of the Tubules &ndash Reabsorption and Secretion

8.11 Countercurrent Mechanism of Concentration of the Filtrate

8.12 Regulation of the Kidney Function

8.14 Urine Characteristics

8.15 Role of Other Organs in Excretion

8.16 Disorders of the Excretory System

9 Locomotion and Movement

9.4 Mechanism of Muscle Contraction

9.6 Types of Skeletal Muscle Fibers

9.8 Axial Skeleton&mdashSkull and Ear Ossicles

9.9 Axial Skeleton&mdashVertebral Column

9.10 Appendicular Skeleton

9.12 Disorders of Muscular and Skeletal Systems and Joints

10 Neural Control and Coordination

10.5 Generation and Conduction of Nerve Impulse

10.6 Transmission of Impulses

10.7 Central Neural System

10.9 Divisions of Peripheral Neural System&mdashSomatic and Autonomic Neural Systems

This comprehensive course contains 47 sections with 289 self-grading lessons, including final assessments. The first section is available to try for free.

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The opening unit introduces students to the sciences, including the scientific method and the fundamental concepts of chemistry and physics that provide a framework within which learners comprehend biological processes.

  • Identify the shared characteristics of the natural sciences
  • Summarize the steps of the scientific method
  • Compare inductive reasoning with deductive reasoning
  • Describe the goals of basic science and applied science
  • Knowledge Check
  • Identify and describe the properties of life
  • Describe the levels of organization among living things
  • Recognize and interpret a phylogenetic tree
  • List examples of different subdisciplines in biology
  • Knowledge Check

The Study of Life - Final Assessment

This is the final assessment for The Study of Lif e. (Available when you subscribe.)

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Our understanding of patterns and processes in ecological systems is necessarily scale-dependent (Wiens, 1989, Levin, 1992). Structured hierarchical sampling designs can be used to quantify variability at different spatial (or temporal) scales (Andrew and Mapstone, 1987, Kotliar and Wiens, 1990). Quantifying variability is very important in order to identify relevant scales for investigating either natural processes or unnatural impacts on ecological systems (Underwood, 1992, Underwood et al., 2000, Benedetti-Cecchi, 2001).

Fauna inhabiting the holdfasts of kelp are incredibly diverse and can provide important indicators for monitoring marine ecosystems in response to many types of environmental impact, including sewage, heavy metals, oil pollution and sedimentation (Jones, 1972, Sheppard et al., 1980, Smith, 1996, Smith, 2000, Smith and Simpson, 1998). Multivariate analyses of such diverse faunal assemblages are much more powerful and informative than univariate indices for the assessment of impact (Underwood and Peterson, 1988, Clarke, 1993). One of the drawbacks of using multivariate methods is, however, that identifying and enumerating all of the organisms in an assemblage of interest can be very time consuming, especially for intensely speciose assemblages such as those found in kelp holdfasts.

Previous studies have suggested that the process of sampling such diverse assemblages may be streamlined considerably by reducing taxonomic resolution: little important information may be lost by analysing data at the level of families, or even whole phyla, rather than at the species level (Warwick, 1988, Vanderklift et al., 1996, Olsgard et al., 1998, Olsgard and Somerfield, 2000). These studies examined effects of environmental perturbation on macrobenthic soft-sediment assemblages, where large shifts in component taxa were evident. Olsgard et al. (1998) noted, however, that the strength of similarity in patterns between species-level and higher taxonomic level ordinations was not as convincing for changes among baseline or non-polluted stations. In kelp holdfast assemblages, Smith and Simpson (1993) found that impacts associated with a small sewage outfall were clearly detected using species, families, orders, classes or phyla. Furthermore, spatial variation from site to site within control locations was reduced for analyses done at higher taxonomic levels (Smith and Simpson, 1993). The extent to which higher taxonomic levels are effective surrogates for analyses of variation at different spatial scales in natural communities warrants further study.

Another possible way to streamline sampling is to focus efforts on identifying and counting only a subset of the assemblage: a single taxonomic group or indicator taxon (e.g. Daily and Ehrlich, 1995, Kitching et al., 2000). For example, Olsgard and Somerfield (2000) found that analyses of polychaetes (to either the level of species or families) gave very similar multivariate signals to those obtained using the entire assemblage at the species level. In contrast, Oliver and Beattie (1996) found that the patterns of biodiversity for individual components of terrestrial arthropod taxa (ants, beetles or spiders) were not strongly correlated with overall patterns in these assemblages. Lawton et al. (1998) cautioned strongly against inferring ecosystem-level changes in the biodiversity of terrestrial systems from a single taxonomic group (e.g. birds or butterflies). It is unknown whether or not the spatial scales of multivariate variation or biodiversity for the primary individual phyla mirror those seen for the whole assemblage in the case of kelp holdfast fauna.

In the present investigation, we describe patterns in the biodiversity of fauna inhabiting holdfasts of the kelp, Ecklonia radiata (C. Agardh) J. Agardh collected from the northeast coast of New Zealand, at several spatial scales. Holdfasts form a discrete and structurally complex habitat for a wide diversity of marine organisms. For example, an Australian study of E. radiata holdfast fauna recorded over 385 species in 152 families and 10 phyla, and this list did not include species of compound ascidians, hydroids or bryozoans, and platyhelminthes, sipunculids and nemerteans were assessed only as a count for the phylum (Smith et al., 1996). Despite the fact that forests of Ecklonia are widespread in northern New Zealand, forming an important habitat in subtidal marine systems (Schiel, 1990), this is the first quantitative study, to our knowledge, of assemblages inhabiting Ecklonia holdfasts in this region.

The purpose of the present investigation was to document the biodiversity of the New Zealand holdfast fauna at different spatial scales for several major taxonomic groups and at several taxonomic levels. Smith (2000) provided a recent review of ecological factors known to affect assemblages inhabiting holdfasts of kelp and concluded that holdfast fauna are sensitive indicators which can lead to predictive models of various kinds of stress in shallow coastal environments. Our interest was to further assess the potential use of holdfast communities as a multivariate environmental indicator, especially in the New Zealand context. We expected that biological differences in mechanisms of reproduction and dispersal, and differences in biogeographical historical patterns of speciation for different phylogenetic groups would lead to different patterns of variation at different spatial scales for the major phyla. In particular, we examined the following hypotheses: 1.

Multivariate variation and biodiversity at different spatial scales will vary for different phyla

Proportional abundances of the phyla will vary at large spatial scales

Analyses at lower levels of taxonomic resolution (e.g. class, phylum) will show similar results to analyses done at higher levels of resolution (e.g. species, genus) and

Analyses of subsets of the total assemblage consisting of the most abundant and diverse phyla will show similar patterns to analyses for the whole assemblage.

To test these hypotheses, we used several recently developed multivariate methods, including partitioning of multivariate variation on the basis of community dissimilarities (Anderson, 2001a). We also used second-stage non-metric multi-dimensional scaling ordinations, to visualise and compare patterns of similarity among several different dissimilarity matrices (Somerfield and Clarke, 1995). In addition, analyses of biodiversity included not just measures of overall abundance and richness (the number of species), but also taxonomic breadth, which measures the degree of relatedness among species (Clarke and Warwick, 1998).

8.9 View Prepared Slides of Trematoda

  1. Clonorchis sinensis w.m. (Figure 8.7).
    • Identify: oral and ventral suckers, pharynx, esophagus, dead-end intestine, reproductive structures, excretory pore
  2. Clonorchis sinensis eggs (Figure 8.8).
    • Identify: oral and ventral suckers, pharynx, esophagus, dead-end intestine, reproductive structures, excretory pore
  3. Fasciola hepatica w.m. (Figure 8.9).
    • Identify: mouth, oral and ventral suckers, pharynx, uterus, intestine

Figure 8.7: Clonorchis sinensis.

Figure 8.8: Clonorchis sinensis eggs.

Figure 8.9: Fasciola hepatica.


Alitta succinea has an elongate, cylindrical body, divided into up to 160 segments. The prostomium is pear-shaped, with four eyes, two frontal antennae, and a pair of stout conical palps. The prostomium is flanked by four pairs of tentacular cirri. The posterior pair of tentacular cirri is longest, and can reach back to chaetigers 4-15. Ventrally and anteriorly, the muscular extendable proboscis consists of two rings, terminating in a pair of amber-colored jaws, with 4-9 teeth each. It is possible to see it only when the organism is relaxed. The proboscis is marked by patches of amber-colored denticles (paragnaths) arranged in species-specific patterns (see Pettibone (1963), Sato (2013) and Villalobos-Guerrero and Carrera-Parra (2015), for descriptions of these patterns in A. succinea). These patterns and details of chaetal structure (acicula, homogomph, heterogomph, spiniger, falciger), are needed for identification of species (Pettibone 1963 Blake and Ruff in Carlton 2007 Sato 2013 Villalobos-Guerrero and Carrera-Parra 2015), but will not be dealt with here.

The parapodia vary greatly in form from anterior to posterior, with the posterior appendages being longer and more elongated in shape. The two anterior-most parapodiae are not fully biramous. The subsequent anterior parapodia are divided into two branches, which are in turn divided into smaller lobes, called ligules. The dorsal lobe is called the notopodium. It has a dorsal cirrus, which does not extend beyond the ligules. The dorsal ligule is large and triangular, the lowest (ventral) one is smaller, and the middle one, called the prechaetal lobe, is smallest, about 1-2 to 2/3 the size of the ventral ligule, and bears a bundle of thin chaetae. The neuropodium has a dorsal ligule, a broader median post chaetal lobe, with a bundle of thicker chaetae, a ventral ligule, and a ventral cirrus. The parapodia start to change in the middle of the worm and are longer and different in structure in the posterior region. The dorsal ligule is long and strap-shaped, with the dorsal cirrus near the tip, the middle ligule reduced or absent, and the lower one short and conical. The neuropodium is more like that of the anterior region, except that the postchaetal ligule is missing (Pettibone 1963 Sato 2013).

Specimens of A. succinea range up to 170 mm. The worm is brownish anteriorly, with the prostomium and bases of the parapodia darkly pigmented. The rest of the body can be greenish, greenish-yellow, or pale reddish, and sometimes with white or dark dots. A red dorsal blood vessel runs down the midline of the body. This species is found in a wide range of habitats, including mud and sand bottoms, oyster beds, fouling communities, etc., and often occurs in brackish waters (Pettibone 1963).

Alitta succinea undergoes a dramatic morphological change (epitoky) when breeding, with both sexes changing into a 'heteronereis' form. The segments become compressed in the antero-posterior direction, so that the worm's body is shorter (14-55 mm in males 30-75 mm in females). The eyes are enlarged, especially in males. The body becomes divided into three sections, an anterior section of 13-18 segments with unchanged chaetae, a middle section of 29-56 segment, with flattened parapodia and paddle-like chaetae, and a posterior 'tail' with un-modified chaetae. The body of the male becomes bright red, with a white tail, while the female is paler, white to yellow-green. During this mating period, the adults swarm and swim at the surface (Pettibone 1963).

The planktotrophic larval stages were described by Banse (1954) and Kinne (1954). Hansen (1999) shows an illustration of a 6-chaetiger larva. Villalobos-Guerrero and Carrera-Parra (2015) re-described Alitta succinea, using exclusively material from the North Sea, Germany, near the type locality, whereas previous authors had combined features from multiple locations. They consider the globally reported 'A. succinea' to be a complex of species of unresolved native-invasion status. They examined worms previously A. succinea from Eastern Tropical Pacific in Mexico and Guatemala, and restored an earlier species name, A. acutifolia. Their work suggests that detailed morphological and genetic examination of 'A. succinea' populations worldwide will be needed to resolve their identity and invasion status.

Watch the video: Phylum Annelida (September 2022).


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