MARINE Invertebrates BIOL 505

1. MARINE InvertebratesBIOL 505 Understanding Marine Invertebrates, Their Environments and Processes

2. Phylum Platyhelmenthes (Flatworms) General Characteristics ~ 34,000 described spp with no unique defining characteristics (synapomorphies). Has one class of free-living spp (Turbellaria) and 3 classes of exclusive parasites (Cestoda)(YUK!). More than 80 % of all flatworms are parasites – so we’ll only be talking about < 20 %. All are acoelomate, triploblastic (have a mesoderm), and bilaterally symmetrical. Much confusion about where group belongs because of questions regarding primitive or derived nature of acoelomate condition.

3. Phylum Platyhelmenthes (Flatworms) General Characteristics Although acoelomate, development is much like protostomes: spiral and (in some spp) determinate cleavage, mouth forms before anus and from the blastopore. Most spp have obvious anterior brain connected to at least 1 pair of longitudinal nerve cords. Embryonic mesoderm layer develops into loose connection of cells (parenchyma tissue). Most spp have no anus. Food enters and waste exits through single opening.

4. Phylum Platyhelmenthes (Flatworms) General Characteristics No specialized respiratory or circulatory system, although some spp have Hb. Gas exchange is through diffusion across body surface. Flat body shape provide high SA:V ratio, so gas exchange is adequate to support highly active lifestyle. Metabolic waste probably exits animal through diffusion across body surface. Most spp. Have series of special cells (protonephridia) where ultrafiltration occurs. May be important in iono- and osmoregulation, as well as waste (ammonia, urea, AA’s) elimination.

5. Phylum Platyhelmenthes (Flatworms) General Characteristics

6. Phylum Platyhelmenthes (Flatworms) General Characteristics

7. Phylum Platyhelmenthes (Flatworms) General Characteristics Most spp are simultaneous hermaphrodites, thus gamete exchanges can happen on encounters of any other individual. Usually, individuals cannot autofertilize.

8. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Only ~ 16 % of all flatworms. Very prone to dehydration due to high SA:V ratio, thus most are aquatic (mostly marine). Most of ~3,000 spp are free-living, although ~150 are commensal or parasites. A few spp considered terrestrial, but only occur in very humid conditions. Usually < 1 cm long, though some marine spp longer.

9. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Nervous system in primitive spp consists of nerve network. Compactness of system is seen in more complex spp with some spp. exhibiting a cerebral ganglion and 1 – 3 pairs of longitudinal nerve cords. Usually have 1 or more anterior pairs of eyes, as well as several sensory cells for chemicals (food), pressure changes, and mechanical stimuli. Some also have statocysts. Most aquatic spp are benthic. Body wall is ciliated, more so on ventral surface.

10. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Most spp move by secreting mucus from ventral surface and beating cilia within the mucus. To compensate for being flat and having large SA, more cilia are in contact with the substrate. This compensates for the weight of the larger animal and ability to move is not impeded by growth. Each epidermal cell is multiciliate. Locomotion involves soft waves of muscular contractions along the ventral surface (pedal waves) in one direction, anterior to posterior.

11. Phylum Platyhelmenthes (Flatworms) Class Turbellaria As wave runs length of body, small segments of ventral surface are pulled up and away from substrate. Circular muscles contract just ahead of wave, squeezing and pushing body forward. Longitudinal muscles contract just behind wave to pull body in direction of locomotion. Many pedal waves are in progress at same time. http://video.google.com/videosearch?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&um=1&q=turbellarian+movement&ie=UTF-8&sa=N&tab=iv#q=flatworm+movement&hl=en&emb=0

12. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Musculature of body wall includes longitudinal, circumferential, dorsoventral, and diagonal. These muscles are active in looping locomotion of some turbellarians.

13. Phylum Platyhelmenthes (Flatworms) Class Turbellaria • Looping movement consists of: • Attachment at anterior site. • Contraction of longitudinal muscles that bring posterior forward. • Attachment at posterior end. Release of anterior end. • Relaxation of longitudinal muscles, contraction of circular muscles. • Extension of body anteriorly. • For looping to work, worm must be able to make temporary attachments to substrate.

14. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Flatworms usually have several pairs of duo-glands, paired secretory cells on ventral surface and open to exterior. One cell of each pair produces a glue for adhesion, the other produces a chemical that dissolves the glue. x section Cilia Epithelia Circular muscle Longitudinal muscle Nerve cell Duo-glands

15. Phylum Platyhelmenthes (Flatworms) Class Turbellaria

16. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Some turbellarians can swim, through either ciliary action, or muscular contractions in vigorous, controlled waves of body wall muscles. Some benthic spp may swim when environ conditions become poor. Some spp may regularly swim and are only benthic at low tide. Some small (<1 mm) acoel spp are regularly captured in plankton samples from warm, surface ocean waters; may be permanently planktonic.

17. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Many spp have collections of small, cylindrical rhabdites, and associated rhabdoids around the body surface. These structures only found in turbellarians, and may be responsible for releasing mucus all over body as defense against predation or desiccation.

18. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Digestion Digestive system – simple. But details differ among spp. Differences in mouthparts, gut and reproductive morphology used to separate class into its 12 orders. Acoel flatworms – have simple mouth on ventral surface, and no well-formed gut cavity. Food is pushed into a packed mass of digestive cells. Acoels are ALL marine and look a little like planula larvae of cnidarians.

19. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Digestion Digestive systems in flatworms seems to increase in complexity above level of acoels. With this, increased complexity of ways to acquire food material. Guts of flatworms (above acoels) may be straight, branched, or multi-branched. Mouth is usually at end of protrusible pharynx. Some spp have separate proboscis that spears food and transfers it to the mouth opening. Most spp active carnivores, but some feed on detritus and algae, and some have symbiotic algae

20. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Digestion

21. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Digestion Digestions starts extracellularly with digestive enzymes secreted onto food material. Particles are phagocytized from gut cavity, and digestion is completed intracellularly.

22. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Reproduction Most sophisticated system (structurally and physiologically) is reproductive. Simultaneous hermaphrodites with male system most complex (almost as complex as human system). When triclad flatworms mate, each inserts penis into female opening of the other, thus sperm transfer is reciprocal. In other spp of turbellarians, copulation may be through hypodermic impregnation (where the stylets of the penis pierce the body of the partner).

23. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Reproduction

24. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Reproduction Eggs of each animal are released after fertilization and usually develop directly into mini flatworms inside a protective capsule. In most turbellarians – no free-living larval stage in life history. In some marine spp, the developing embryo produces a short-lived, microscopic, free-swimming Müller’s larva. Many also reproduce by asexual fission.

25. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Regeneration Many flatworms have excellent regenerative powers that go beyond ability to repair wounds. Accomplished through undifferentiated neoblast cells (only found in turbellarians) that maintain very versatile developmental plasticity. However, some turbellarians cannot regenerate.

26. Phylum Platyhelmenthes (Flatworms) Class Turbellaria Turbellarian Regeneration

34. Phylum Annelida (Segmented Worms) Defining Characteristics One or more pairs of chitinous setae. General Characteristics ~12,400 described spp. All adults have at least one pair chitinous bristles (setae, or chaetae). All are vermiform (worm-shaped), Soft bodies, mainly circular in x section, longer than they are wide. Most have series of repeated segments in which skin, muscles, nerves, circulatory, reproductive excretory systems are repeated (metamerism).

35. Phylum Annelida (Segmented Worms)

36. Phylum Annelida (Segmented Worms) General Characteristics Because body wall is thin, flexible, can play role in gas exchange (if kept moist) and locomotion, respectively. Even in cases where epidermis secretes cuticle, cuticle stays permeable to gases and water. So, annelids are restricted to moist (or wet) environments. Body segments usually separated by septa, thin sheets of tissue derived from mesoderm, called peritoneum. Isolates coelomic fluid in each segment form other segments. Why is this important?

37. Phylum Annelida (Segmented Worms) General Characteristics Septa allow circular and longitudinal muscle contractions to deform body wall locally, and not change hydrostatic pressure of next segment. Some wastes excreted across body surface, but usually through nephridia. Most segments have 2 nephridia, each open at both ends, (metanephridium). Coelomic fluid from previous segment taken into nephridium through nephrostome by action of cilia. As fluid passes through convoluted tubule, substances (salts, AAs, water) are reabsorbed, while others (wastes) are actively secreted into tubule.

38. Phylum Annelida (Segmented Worms) General Characteristics Final urine leaving nephridopore is different from primary urine entering nephristome. As well as outlet for metabolic waste, nephridia may help regulate osmotic content of coelomic fluid.

39. Phylum Annelida (Segmented Worms) General Characteristics

40. Phylum Annelida (Segmented Worms) General Characteristics In many spp ducts leading from gonads, fuse together with nephridial tubes. Thus, nephridia also play role is releasing gametes.

41. Phylum Annelida (Segmented Worms) General Characteristics • 3 main classes of annelids • Polychaeta • Clitellata (oligochaetes and leeches) • Echiura (peanut worm)

42. Phylum Annelida (Segmented Worms) Class Polychaeta Defining Characteristics Paired lateral outfoldings of body wall – parapodia. General Characteristics Comprises ~ 70 % of all annelid spp. Almost all are marine. Usually have at least 1 pair of eyes and at least 1 pair sensory appendages (tentacles) on the anteriormost part of the body (prostomium). Body wall extends out laterally to thin, flattened outgrowths – parapodia. Parapodial morphology is important in IDing spp.

43. Phylum Annelida (Segmented Worms) Class Polychaeta

44. Phylum Annelida (Segmented Worms) Class Polychaeta

45. Phylum Annelida (Segmented Worms) Class Polychaeta General Characteristics • Parapodia: • Increase animals exposed SA • Are highly vascularized • Function in gas exchange between animal and environment. • Have a locomotory function in many spp due to their stiffness and presence of chitinous support structures (acicula)

46. Phylum Annelida (Segmented Worms) Class Polychaeta General Characteristics • Parapodia: • Also have silicious, chitinous, and less often calcareous bristles (setae) that protrude from each parapodium. Setae also differ among spp and can be used for ID.

47. Phylum Annelida (Segmented Worms) Class Polychaeta

48. Phylum Annelida (Segmented Worms) Class Polychaeta

49. Phylum Annelida (Segmented Worms) Class Polychaeta General Characteristics Body is covered with overlapping, protective plates (elytra).

50. Phylum Annelida (Segmented Worms) Class Polychaeta General Characteristics Septa allow hydrostatic skeleton in each segment to function independently. Setae form temporary attachments to prevent backsliding. In some active burrowing forms, septa are absent, or incomplete (perforate). This allows greater volume of coelomic fluid to be used during movements. Also allows greater shape changes with extending and anchoring the proboscis into the sediment.