Tropical Marine Invertebrates CAS BI 569 Phylum Echinodermata by J

Total Page：16

File Type：pdf, Size：1020Kb

Tropical Marine Invertebrates CAS BI 569 Phylum Echinodermata by J. R. Finnerty Porifera Ctenophora Cnidaria Deuterostomia Ecdysozoa Lophotrochozoa Chordata Arthropoda Annelida Hemichordata Onychophora Mollusca Echinodermata *Nematoda *Platyhelminthes Acoelomorpha Calcispongia Silicispongiae PROTOSTOMIA Phylum Phylum Phylum CHORDATA ECHINODERMATA HEMICHORDATA Blastopore -> anus Radial / equal cleavage Coelom forms by enterocoely ! Protostome = blastopore contributes to the mouth blastopore mouth anus ! Deuterostome = blastopore becomes anus blastopore anus mouth Halocynthia, a tunicate (Urochordata) Coelom Formation Protostomes: Schizocoely Deuterostomes: Enterocoely Enterocoely in a sea star Axocoel (protocoel) Gives rise to small portion of water vascular system. Hydrocoel (mesocoel) Gives rise to water vascular system. Somatocoel (metacoel) Gives rise to lining of adult body cavity. Echinoderm Metamorphosis ECHINODERM FEATURES Water vascular system and tube feet Pentaradial symmetry Coelom formation by enterocoely Water Vascular System Tube Foot Tube Foot Locomotion ECHINODERM DIVERSITY Crinoidea Asteroidea Ophiuroidea Holothuroidea Echinoidea “sea lilies” “sea stars” “brittle stars” “sea cucumbers” “urchins, sand dollars” Group Form & Habit Habitat Ossicles Feeding Special Characteristics Crinoids 5-200 arms, stalked epifaunal Internal skeleton suspension mouth upward; mucous & Of each arm feeders secreting glands on sessile podia Ophiuroids usually 5 thin arms, epifaunal ossicles in arms deposit feeders act and appear like vertebrae Asteroids usually 5 stout arms epifaunal uniformly covered predators gonads extend into each except ambulacral arm grooves stomach extrusion Echinoids regular urchins epifaunal joined to form grazers Aristotle’s lantern- /radial; irregular rigid test or deposit special grazing jaw (sand dollars— feeders bilaterally symmetrical.) Holothuroids soft-bodied, worm- epifaunal microscopic & deposit feeders -branched respiratory like, elongated oral- or embedded in body structures (tree) aboral axis, lack infanual wall -evisceration arms; Echniodermata: Crinoidea mouth ambulacral groove with cilia tube feet coelom gonad ossicl e Echinodermata: Holothuroidea Oral & Aboral surfaces.

Copy Link

Recommended publications

Systema Naturae∗
Systema Naturae∗ c Alexey B. Shipunov v. 5.802 (June 29, 2008) 7 Regnum Monera [ Bacillus ] /Bacteria Subregnum Bacteria [ 6:8Bacillus ]1 Superphylum Posibacteria [ 6:2Bacillus ] stat.m. Phylum 1. Firmicutes [ 6Bacillus ]2 Classis 1(1). Thermotogae [ 5Thermotoga ] i.s. 2(2). Mollicutes [ 5Mycoplasma ] 3(3). Clostridia [ 5Clostridium ]3 4(4). Bacilli [ 5Bacillus ] 5(5). Symbiobacteres [ 5Symbiobacterium ] Phylum 2. Actinobacteria [ 6Actynomyces ] Classis 1(6). Actinobacteres [ 5Actinomyces ] Phylum 3. Hadobacteria [ 6Deinococcus ] sed.m. Classis 1(7). Hadobacteres [ 5Deinococcus ]4 Superphylum Negibacteria [ 6:2Rhodospirillum ] stat.m. Phylum 4. Chlorobacteria [ 6Chloroflexus ]5 Classis 1(8). Ktedonobacteres [ 5Ktedonobacter ] sed.m. 2(9). Thermomicrobia [ 5Thermomicrobium ] 3(10). Chloroflexi [ 5Chloroflexus ] ∗Only recent taxa. Viruses are not included. Abbreviations and signs: sed.m. (sedis mutabilis); stat.m. (status mutabilis): s., aut i. (superior, aut interior); i.s. (incertae sedis); sed.p. (sedis possibilis); s.str. (sensu stricto); s.l. (sensu lato); incl. (inclusum); excl. (exclusum); \quotes" for environmental groups; * (asterisk) for paraphyletic taxa; / (slash) at margins for major clades (\domains"). 1Incl. \Nanobacteria" i.s. et dubitativa, \OP11 group" i.s. 2Incl. \TM7" i.s., \OP9", \OP10". 3Incl. Dictyoglomi sed.m., Fusobacteria, Thermolithobacteria. 4= Deinococcus{Thermus. 5Incl. Thermobaculum i.s. 1 4(11). Dehalococcoidetes [ 5Dehalococcoides ] 5(12). Anaerolineae [ 5Anaerolinea ]6 Phylum 5. Cyanobacteria [ 6Nostoc ] Classis 1(13). Gloeobacteres [ 5Gloeobacter ] 2(14). Chroobacteres [ 5Chroococcus ]7 3(15). Hormogoneae [ 5Nostoc ] Phylum 6. Bacteroidobacteria [ 6Bacteroides ]8 Classis 1(16). Fibrobacteres [ 5Fibrobacter ] 2(17). Chlorobi [ 5Chlorobium ] 3(18). Salinibacteres [ 5Salinibacter ] 4(19). Bacteroidetes [ 5Bacteroides ]9 Phylum 7. Spirobacteria [ 6Spirochaeta ] Classis 1(20). Spirochaetes [ 5Spirochaeta ] s.l.10 Phylum 8. Planctobacteria [ 6Planctomyces ]11 Classis 1(21).
[Show full text]
Phylum Echinodermata Phylum Echinodermata
Phylum Echinodermata Phylum Echinodermata About 7,000 species Strictly marine, mostly benthic. Typical deuterostomes. Phylum Echinodermata Class Crinoidea (sea lilies) Phylum Echinodermata Class Crinoidea Class Asteroidea (sea stars) Phylum Echinodermata Class Crinoidea Class Asteroidea Class Ophiuroidea (brittle stars and basket stars) Phylum Echinodermata Class Crinoidea Class Asteroidea Class Ophiuroidea Class Echinoidea (sea urchins and sand dollars) Phylum Echinodermata Class Crinoidea Class Asteroidea Class Ophiuroidea Class Echinoidea Class Holothuroidea (sea cucumbers) What do Echinoderms look like? Pentamerous radial symmetry. Oral and aboral surfaces. Oral surface has ambulacral grooves associated with tubefeet called podia. What do Echinoderms look like? Oral and aboral surfaces. What do Echinoderms look like? Arms (ambulacra) numbered with reference to the madreporite. Ambulacrum opposite is A then proceed couterclockwise. Ambulara C and D are the bivium, A B and E are the trivium. What do Echinoderms look like? Body wall Epidermis covers entire body. Endoskeleton of ossicles with tubefeet and dermal branchia protruding through and spines and pedicellaria on outside. What do Echinoderms look like? Body wall Ossicles can be fused into a test (urchins and sand dollars). Ossicles spread apart in cucumbers. Ossicles intermediate and variable in seastars. Muscle ﬁbers beneath ossicles. What do Echinoderms look like? Body wall Tubercles and moveable spines on skeletal plates of echinoids. Small muscles attach spines to test. What do Echinoderms look like? Water vascular system Fluid-ﬁlled canals for internal transport and locomotion. Fluid similar to sewater but has coelomcytes and organic molecules. Moved through system with cilia. What do Echinoderms look like? Water vascular system Asteroidea: Madreporite on aboral surface.
[Show full text]
Chlorophyta Is a Division of Green Algae, Informally Called
Chlorophyta is a division of green algae, informally waters of the Sargasso Sea. Many brown algae, such as called chlorophytes. The name is used in two very members of the order Fucales, commonly grow along different senses so that care is needed to determine the rocky seashores. Some members of the class are used as use by a particular author. In older classification food for humans. systems, it refers to a highly paraphyletic group of all Worldwide there are about 1500–2000 species of brown the green algae within the green plants (Viridiplantae), algae.[4] Some species are of sufficient commercial and thus includes about 7,000 species [4] [5] of mostly importance, such as Ascophyllum nodosum , that they aquatic photosynthetic eukaryotic organisms. Like the have become subjects of extensive research in their own land plants (bryophytes and tracheophytes), green algae right.[5] [4] contain chlorophylls a and b, and store food as starch Brown algae belong to a very large group, the in their plastids. Heterokontophyta, a eukaryotic group of organisms In newer classifications, it refers to one of the two distinguished most prominently by having chloroplasts clades making up the Viridiplantae, which are the surrounded by four membranes, suggesting an origin chlorophytes and the streptophytes or charophytes.[6][7] from a symbiotic relationship between a basal In this sense it includes only about 4,300 species.[3] eukaryote and another eukaryotic organism. Most brown algae contain the pigment fucoxanthin, which is responsible for the distinctive greenish-brown color that The red algae, or Rhodophyta ( / r o ʊ ˈ d ɒ f ɨ t ə / or / gives them their name.
[Show full text]
Tropical Marine Invertebrates CAS BI 569 Major Animal Characters Part 2 — Adult Bodyplan Features by J
Tropical Marine Invertebrates CAS BI 569 Major Animal Characters Part 2 — Adult Bodyplan Features by J. R. Finnerty Metazoan Characters Part II. Adult Body Plan Features CHARACTER states EPITHELIUM: present; absent; BODY LAYERS: diploblastic; triploblastic BODY CAVITIES: precoelomate; acoelomate; pseudocoelomate; eucoelomate; GUT: absent; blind sac; through-gut; SYMMETRY: asymmetrical; radial; bi-radial; bilateral; pentaradial SKELETON: “spicules;” “bones;” hydrostat; exoskeleton EPITHELIUM Sheet of cells that lines body cavities or covers outer body surfaces. E.g., skin, gut lining Creates extracellular compartments four key characteristics: 1.continuous — uninterrupted layer 2. intercellular junctions cell 3. polarity (apical vs. basal) 4. basal lamina (extracellular matrix on which basal cell surface rests; collagen secreted by cells) Ruppert et al., Figure 6.1 3 Body Layers (Germ Layers) Germ layers form during gastrulation ectoderm blastocoel blastocoel endoderm gut blastoderm BLASTULA blastopore 4 Diploblastic Condition Two germ layers, endoderm & ectoderm blastocoel blastocoel endoderm gut gut ectoderm ectoderm 5 Triploblastic Condition Three germ layers, endoderm, ectoderm, & mesoderm. blastocoel gut ectoderm Body Cavities I. Blastocoel the central cavity in the hollow blastula the 1st body cavity II. Archenteron “primitive gut” opens to the outside via the blastopore lined by endoderm III. Coelom cavity entirely lined by mesoderm A pseudocoelom is only partially lined by mesoderm. It may represent a persistent blastocoel. Character
[Show full text]
What Are Echinoderms?
What are Echinoderms? Jon Allen College of William and Mary 5 extant classes of Echinoderms Echinoidea Asteroidea Crinoidea Ophiuroidea Holothuroidea Phylum Echinodermata • General Characteristics • Water Vascular System • Pentameral (five part) Symmetry as adults • Bilateral Symmetry as larvae • Calcareous ossicles form internal skeleton • Mutable connective tissue Water Vascular System WVS Used for Locomotion Ampulla Tube foot • RED indicates muscular contraction Echinoderm Ossicles • CaCO3 ossicles form internal skeleton • Vary widely across classes (cf urchin test with sea cucmbers) • Unique stereom structure: porous structure filled with living tissue Mutable Connective (Collagenous) Tissue • MCT used for feeding in seastars • MCT allows autotomy in Seastars and Bstars • Changes in MCT are under nervous control • Two nerve types present in extracellular matrix: one softens, one hardens • Mechanism unknown: related to [Ca2+] Development and Symmetry Switch in Echinoderms 5 extant classes of Echinoderms Echinoidea Asteroidea Crinoidea Ophiuroidea Holothuroidea Crinoidea • Sea lilies (deep sea) and feather stars (shallow tropical waters) • 625 species • Filter feeders • Generally sessile but can move when agitated • Generally considered primitive among the classes • Far more numerous in fossil record than today Crinoidea • Amazing mobility for such delicate creatures • Most echinoderms are light-averse Phylum Echinodermata: Class Ophiuroidea • Defining Characteristics: – Highly developed arm ossicles form ‘vertebrae’ – 5 pairs of bursal
[Show full text]
Biology of Echinoderms
Echinoderms Branches on the Tree of Life Programs ECHINODERMS Written and photographed by David Denning and Bruce Russell Produced by BioMEDIA ASSOCIATES ©2005 - Running time 16 minutes. Order Toll Free (877) 661-5355 Order by FAX (843) 470-0237 The Phylum Echinodermata consists of about 6,000 living species, all of which are marine. This video program compares the five major classes of living echinoderms in terms of basic functional biology, evolution and ecology using living examples, animations and a few fossil species. Detailed micro- and macro- photography reveal special adaptations of echinoderms and their larval biology. (THUMBNAIL IMAGES IN THIS GUIDE ARE FROM THE VIDEO PROGRAM) Summary of the Program: Introduction - Characteristics of the Class Echinoidea phylum. spine adaptations, pedicellaria, Aristotle‘s lantern, sand dollars, urchin development, Class Asteroidea gastrulation, settlement skeleton, water vascular system, tube feet function, feeding, digestion, Class Holuthuroidea spawning, larval development, diversity symmetry, water vascular system, ossicles, defensive mechanisms, diversity, ecology Class Ophiuroidea regeneration, feeding, diversity Class Crinoidea – Topics ecology, diversity, fossil echinoderms © BioMEDIA ASSOCIATES (1 of 7) Echinoderms ... ... The characteristics that distinguish Phylum Echinodermata are: radial symmetry, internal skeleton, and water-vascular system. Echinoderms appear to be quite different than other ‘advanced’ animal phyla, having radial (spokes of a wheel) symmetry as adults, rather than bilateral (worm-like) symmetry as in other triploblastic (three cell-layer) animals. Viewers of this program will observe that echinoderm radial symmetry is secondary; echinoderms begin as bilateral free-swimming larvae and become radial at the time of metamorphosis. Also, in one echinoderm group, the sea cucumbers, partial bilateral symmetry is retained in the adult stages -- sea cucumbers are somewhat worm–like.
[Show full text]
Late Precambrian Bilaterians: Grades and Clades JAMES W
Proc. Natd. Acad. Sci. USA Vol. 91, pp. 6751-6757, July 1994 Colloquium Paper Ths par was presented at a colloquium eniled "Tempo and Mode in Evolution" organized by Walter M. Fitch and Francisco J. Ayala, held January 27-29, 1994, by the National Academy of Sciences, in Irvine, CA. Late Precambrian bilaterians: Grades and clades JAMES W. VALENTINE Museum of Paleontology and Department of Integrative Biology, University of California, Berkeley, CA 94720 ABSTRACT A broad variety of body plans and subplans decades have witnessed intense work on the early faunas, appear during a period of perhaps 8 million years (my) within and during most of that time the base of the Tommotian has the Early Cambrian, an unequaled explosion of morphological been taken as the base ofthe Cambrian. However, within the novelty, the ancestral l es represented chiefly or entirely by last few years new criteria have been developed and now the trace fossils. Evidence from the fossil record can be combined lowest Cambrian boundary is commonly based on the earliest with that from molecular phylogenetic trees to suggest that the appearance of the trace fossil Phycodes pedum (see ref. 9). lastcommon ancestor of(i) protostomes and deuterostomes was Choosing this boundary has lowered the base of the Cam- a roundish worm with a blood vascular system and (ii) of brian, enlarging that Period by about one half(Fig. 2). Despite arthropods and annelids was similar, with a hydrostatic hemo- this expansion of the Cambrian, new absolute age estimates coed; these forms are probably among trace makers of the late have caused the length of time believed to be available for the Precambrian.
[Show full text]
FISH310: Biology of Shellfishes
FISH310: Biology of Shellﬁshes Lecture Slides #3 Phylogeny and Taxonomy sorting organisms How do we classify animals? Taxonomy: naming Systematics: working out relationships among organisms Classification • All classification schemes are, in part, artificial to impose order (need to start some where using some information) – Cell number: • Acellular, One cell (_________), or More than one cell (metazoa) – Metazoa: multicellular, usu 2N, develop from blastula – Body Symmetry – Developmental Pattern (Embryology) – Evolutionary Relationship Animal Kingdom Eumetazoa: true animals Corals Anemones Parazoa: no tissues Body Symmetry • Radial symmetry • Phyla Cnidaria and Ctenophora • Known as Radiata • Any cut through center ! 2 ~ “mirror” pieces • Bilateral symmetry • Other phyla • Bilateria • Cut longitudinally to achieve mirror halves • Dorsal and ventral sides • Anterior and posterior ends • Cephalization and central nervous system • Left and right sides • Asymmetry uncommon (Porifera) Form and Life Style • The symmetry of an animal generally fits its lifestyle • Sessile or planktonic organisms often have radial symmetry • Highest survival when meet the environment equally well from all sides • Actively moving animals have bilateral symmetry • Head end is usually first to encounter food, danger, and other stimuli Developmental Pattern • Metazoa divided into two groups based on number of germ layers formed during embryogenesis – differs between radiata and bilateria • Diploblastic • Triploblastic Developmental Pattern.. • Radiata are diploblastic: two germ layers • Ectoderm, becomes the outer covering and, in some phyla, the central nervous system • Endoderm lines the developing digestive tube, or archenteron, becomes the lining of the digestive tract and organs derived from it, such as the liver and lungs of vertebrates Diploblastic http://faculty.mccfl.edu/rizkf/OCE1001/Images/cnidaria1.jpg Developmental Pattern….
[Show full text]
Cellular and Molecular Processes Leading to Embryo Formation In
Cellular and molecular processes leading to embryo formation in sponges: evidences for high conservation of processes throughout animal evolution Alexander Ereskovsky, Emmanuelle Renard, Carole Borchiellini To cite this version: Alexander Ereskovsky, Emmanuelle Renard, Carole Borchiellini. Cellular and molecular processes leading to embryo formation in sponges: evidences for high conservation of processes through- out animal evolution. Development Genes and Evolution, Springer Verlag, 2013, 223, pp.5 - 22. 10.1007/s00427-012-0399-3. hal-01456624 HAL Id: hal-01456624 https://hal.archives-ouvertes.fr/hal-01456624 Submitted on 5 Feb 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Author's personal copy Dev Genes Evol (2013) 223:5–22 DOI 10.1007/s00427-012-0399-3 REVIEW Cellular and molecular processes leading to embryo formation in sponges: evidences for high conservation of processes throughout animal evolution Alexander V. Ereskovsky & Emmanuelle Renard & Carole Borchiellini Received: 20 December 2011 /Accepted: 26 March 2012 /Published online: 29 April 2012 # Springer-Verlag 2012 Abstract The emergence of multicellularity is regarded as metamorphosis. Thus, sponges can provide information en- one of the major evolutionary events of life. This transition abling us to better understand early animal evolution at the unicellularity/pluricellularity was acquired independently molecular level but also at the cell/cell layer level.
[Show full text]
Tropical Marine Invertebrates CAS BI 569 Phylum ANNELIDA by J
Tropical Marine Invertebrates CAS BI 569 Phylum ANNELIDA by J. R. Finnerty Phylum ANNELIDA Porifera Ctenophora Cnidaria Deuterostomia Ecdysozoa Lophotrochozoa Chordata Arthropoda Annelida Hemichordata Onychophora Mollusca Echinodermata Nematoda Platyhelminthes Acoelomorpha Silicispongiae Calcispongia PROTOSTOMIA “BILATERIA” (=TRIPLOBLASTICA) Bilateral symmetry (?) Mesoderm (triploblasty) Phylum ANNELIDA Porifera Ctenophora Cnidaria Deuterostomia Ecdysozoa Lophotrochozoa Chordata Arthropoda Annelida Hemichordata Onychophora Mollusca Echinodermata Nematoda Platyhelminthes Acoelomorpha Silicispongiae Calcispongia PROTOSTOMIA “COELOMATA” True coelom Coelomata gut cavity endoderm mesoderm coelom ectoderm [note: dorso-ventral inversion] Phylum ANNELIDA Porifera Ctenophora Cnidaria Deuterostomia Ecdysozoa Lophotrochozoa Chordata Arthropoda Annelida Hemichordata Onychophora Mollusca Echinodermata Nematoda Platyhelminthes Acoelomorpha Silicispongiae Calcispongia PROTOSTOMIA PROTOSTOMIA “first mouth” blastopore contributes to mouth ventral nerve cord The Blastopore ! Forms during gastrulation ectoderm blastocoel blastocoel endoderm gut blastoderm BLASTULA blastopore The Gut “internal, epithelium-lined cavity for the digestion and absorption of food sponges lack a gut simplest gut = blind sac (Cnidaria) blastopore gives rise to dual- function mouth/anus through-guts evolve later Protostome = blastopore contributes to the mouth Deuterostome = blastopore becomes the anus; mouth is a second opening Protostomy blastopore mouth anus Deuterostomy blastopore
[Show full text]
Zoology Lab Manual
General Zoology Lab Supplement Stephen W. Ziser Department of Biology Pinnacle Campus To Accompany the Zoology Lab Manual: Smith, D. G. & M. P. Schenk Exploring Zoology: A Laboratory Guide. Morton Publishing Co. for BIOL 1413 General Zoology 2017.5 Biology 1413 Introductory Zoology – Supplement to Lab Manual; Ziser 2015.12 1 General Zoology Laboratory Exercises 1. Orientation, Lab Safety, Animal Collection . 3 2. Lab Skills & Microscopy . 14 3. Animal Cells & Tissues . 15 4. Animal Organs & Organ Systems . 17 5. Animal Reproduction . 25 6. Animal Development . 27 7. Some Animal-Like Protists . 31 8. The Animal Kingdom . 33 9. Phylum Porifera (Sponges) . 47 10. Phyla Cnidaria (Jellyfish & Corals) & Ctenophora . 49 11. Phylum Platyhelminthes (Flatworms) . 52 12. Phylum Nematoda (Roundworms) . 56 13. Phyla Rotifera . 59 14. Acanthocephala, Gastrotricha & Nematomorpha . 60 15. Phylum Mollusca (Molluscs) . 67 16. Phyla Brachiopoda & Ectoprocta . 73 17. Phylum Annelida (Segmented Worms) . 74 18. Phyla Sipuncula . 78 19. Phylum Arthropoda (I): Trilobita, Myriopoda . 79 20. Phylum Arthropoda (II): Chelicerata . 81 21. Phylum Arthropods (III): Crustacea . 86 22. Phylum Arthropods (IV): Hexapoda . 90 23. Phyla Onycophora & Tardigrada . 97 24. Phylum Echinodermata (Echinoderms) . .104 25. Phyla Chaetognatha & Hemichordata . 108 26. Phylum Chordata (I): Lower Chordates & Agnatha . 109 27. Phylum Chordata (II): Chondrichthyes & Osteichthyes . 112 28. Phylum Chordata (III): Amphibia . 115 29. Phylum Chordata (IV): Reptilia . 118 30. Phylum Chordata (V): Aves . 121 31. Phylum Chordata (VI): Mammalia . 124 Lab Reports & Assignments Identifying Animal Phyla . 39 Identifying Common Freshwater Invertebrates . 42 Lab Report for Practical #1 . 43 Lab Report for Practical #2 . 62 Identification of Insect Orders . 96 Lab Report for Practical #3 .
[Show full text]
Chaetognatha: a Phylum of Uncertain Affinity Allison Katter, Elizabeth Moshier, Leslie Schwartz
Chaetognatha: A Phylum of Uncertain Affinity Allison Katter, Elizabeth Moshier, Leslie Schwartz What are Chaetognaths? Chaetognaths are in a separate Phylum by themselves (~100 species). They are carnivorous marine invertebrates ranging in size from 2-120 mm. There are also known as “Arrow worms,” “Glass worms,” and “Tigers of the zooplankton.” Characterized by a slender transparent body, relatively large caudal fins, and anterior spines on either side of the mouth, these voracious meat-eaters catch large numbers of copepods, swallowing them whole. Their torpedo-like body shape allows them to move quickly through the water, and the large spines around their mouth helps them grab and restrain their prey. Chaetognaths alternate between swimming and floating. The fins along their body are not used to swim, but rather to help them float. A Phylogenetic mystery: The affinities of the chaetognaths have long been debated, and present day workers are far from reaching any consensus of opinion. Problems arise because of the lack of morphological and physiological diversity within the group. In addition, no unambiguous chaetognaths are preserved as fossils, so nothing about this groups evolutionary origins can be learned from the fossil record. During the past 100 years, many attempts have been made to ally the arrow worms to a bewildering variety of taxa. Proposed relatives have included nematodes, mollusks, various arthropods, rotifers, and chordates. Our objective is to analyze the current views regarding “arrow worm” phylogeny and best place them in the invertebrate cladogram of life. Phylogeny Based on Embryology and Ultrastructure Casanova (1987) discusses the possibility that the Hyman, Ducret, and Ghirardelli have concluded chaetognaths are derived from within the mollusks.
[Show full text]