Pterobranchia

Hemichordates
B.s zoology

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2. INTRODUCTION TO PRESENTATION . 2 PRESENTATION TOPIC PTEROBRANCHIA Chapter # 17 Hemichordata and Invertebrate Chordates. STUDENT NAME: MOMINA BAKHTAWAR Student ID: BZOF19M001 Course code: Zol-201 Course title: Chordates Course Teacher: Prof. IRAM INAYAT Program : BS Zoology Semester : III (REGULAR) DEPARTMENT OF ZOOLOGY

3. Introduction to P terobranchia Class of Phylum hemichordata . Gk. pteron , wing+ branchia , gills 3 genera ≈ 20 species. Habitat: mostly deep oceanic water of Southern Hemisphere, few in Europeon coastal water & shallow waters near Bermuda. Size: small (0.1 to 5mm). Colonial and semi-sessile marine Animals. Deuterostomous . Mostly Tube dwellers. Sea angels. 3

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5. Body form: body divided into three regions; an anterior mouth-shield, a collar, and a trunk. Proboscis is expanded and shield like.It secretes the tube and aids in movement in tube. The collar posseses two to nine arms with numerous ciliated tentacles. The trunk is U shaped. 5

6. Tripartite body 6

7. Coenecium It is a network of tubular chambers with branching tubes that open outside. Secreted by ventral epidermis of mouth shield ( prosome ). Non- living,hollow tubes; one zooid in each tube. Tube material may be protein. The coenecium of Cephalodiscus spp. and Rhabdopleura spp. is translucent or orange due to the color of the zooid and may be embedded with detritus, such as sand or algae, which gives it a brown color (Lester 1988b, 1985, Mierzejewski and Kulicki 2003). 7

8. Types of coenecium Diversity of coenecial morphology in Cephalodiscus . (A) Cephalodiscus ( Orthoecus ) densus . (B) Cephalodiscus ( Idiothecia ) nigrescens . (C) Cephalodiscus ( Cephalodiscus ) hodgsoni . 8

9. Maintenance Functions Pterobranchs use water currents (that cilia on their arms and tentacles generate) to filter feed. Cilia trap and transport food particles toward the mouth. Although one genus has a single pair of pharyngeal slits, respiratory and excretory structures are unnecessary in animals as small as pterobranchs because gases and wastes exchange by diffusion. 9

10. Nervous system Constitutes a basiepidermal nerve net. A dorsal brain;features an anterior neuron-rich area. Concentrated parts of P-N.S are tentacle nerves,ventral stalk nerve & pair of branchial nerves in Cephalodiscus gracilis . 10

11. General anatomy of nervous system of Pterobranch ; Cephalodiscus gracilis . 11

12. Circulatory system The structure of the circulatory system is not well known. It is wholly lacunar (made up of blood spaces rather than vessels). A dorsal sinus (a sinus is a blood-filled cavity) originates from lacunae in the stomach wall and runs forward above the oesophagous and pharynx and connects to sinuses around each gonad, then continues beneath the collar ganglion and terminates in the central sinus. The central sinus is associated with a contractile heart vesicle. The central sinus gives out the ventral shield sinus that runs back beneath the buccal tube and buccal diverticulum as a pair of  peribuccal channels or a lacunae system. From these peribuccal channels or lacunae originate the main ventral sinus. This sinus extends posteriorly from the collar-trunk septum along the ventral side of the stalk and then turns dorsally at the end of the stalk and continues forward along the dorsal side of the stalk and along the dorsal side of the intestine where it disappears. In  enteropneusts  the heart vesicle and central sinus are positioned above the buccal diverticulum , whilst in  Cephalodiscus  they are positioned in front of the buccal diverticulum . 12

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14. Excretory system characteristic excretory system. Composed of contractile pericardium that encloses heart sinus that anteriorly continues into the glomerulus (highly dilated blood plexus lined by podocytes that are capable of mediating ultrafilteration into the protocoel ).The accumulated ultrafilterate leaves protocoel via proboscis pore. 14

15. Digestive system U-shaped digestive tract in trunk. Posterior pharynx,stomach and intestine. The anus opens on the dorsal side of the anterior trunk region just behind mesosome. 15

16. Rhabdopleura External Structure of the Pterobranch , Rhabdopleura . Ciliated tracts on tentacles and arms direct food particles toward the mouth (5 mm). 16

17. Reproduction and Development Both asexual and sexual. Direct development; Development to an adult body plan without an intervening larval stage with a distinct body plan. Asexual budding is common in pterobranchs and is responsible for colony formation. Pterobranchs also possess one or two gonads in the anterior trunk. Most species are dioecious , and external fertilization results in the development of a planula -like Lecithotrophic ( Having a swimming, non-feeding larva that derives its nutrition from maternally provisioned yolk) larva that lives for a time in the tube of the female. This non feeding larva eventually leaves the female’s tube, settles to the substrate, forms a cocoon, and metamorphoses into an adult. 17

18. Direct development C) Little is known about fertilization and the developmental stages of breeding pterobranchs (e.g. R. compacta ), although it is known that ciliated and pigmented larvae develop inside the coenecium . Developmental stages are indicated below each illustration and the internal organization of the germ layers is indicated (blue, ectoderm; yellow, endoderm; red, mesoderm). 18

19. Evolution of Phylogenetic Position Evolved in mid- cambrian period. Pterobranchs were considered to be related with Bryozoans.( lophophorates ). Closely related to extinct graptolites; which are often grouped as pterobranchs .(Sato et al. 2008). morphological characteristics unite enteropneusts and pterobranchs as part of the Hemichordata . These characteristics include the stomochord , collar region, glomerulus and associated kidney structures, and three paired coelomic body cavities ( Halanych 1995, Cannon et al. 2009, Sato et al. 2008). 19

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21.  Hemichordate phylogeny with limited representation of the pterobranchs and enteropneusts , showing the relationships between lineages containing the most commonly studied hemichordates, Ptychodera flava ( Ptychoderidae ), Saccoglossus kowalevskii ( Harrimaniidae ) and Rhabdopleura compacta ( Pterobranchia ), along with the deep sea family Torquaratidae [based on published data (Cameron et al., 2000; Winchell et al., 2002; Cannon et al., 2009; Osborn et al., 2012)]. 21

22. References Zoology miller and harley 5 th edi . Wikipedia. TheGlobal Diversityof Hemichordata:Data is available at http://www.marinespecies.org/aphia.php?p= taxdetails&id =1818. Determining the Composition of the Dwelling Tubes of Antarctic Pterobranchs . Pdf file. Evolutionary crossroads in developmental biology: hemichordates. Pdf file. queries… 22

23. Thank You. 23