Presentation on theme: "Lab this week a bell-ringer; starts at 3 pm SHARP!!! Term test coming up next week Monday October 6 in lecture (Its not in February as it mistakenly says."— Presentation transcript:
Lab this week a bell-ringer; starts at 3 pm SHARP!!! Term test coming up next week Monday October 6 in lecture (Its not in February as it mistakenly says on the website.) Sources: R.B. Clark, Dynamics in Metazoan Evolution – the coelom as hydrostatic skeleton Frank Brown Jr., Selected Invertebrate Types McCurley R.S. & Kier W.M The functional morphology of starfish tube feet: the role of a crossed-fiber helical array in movement. Biological Bulletin 188:
Metamerism and Tagmata “ Of all the countless shapes and forms that triploblastic metazoan animals take, the least complicated …the least specialized, is vermiform. Vermiform: worm-shaped: longer than diameter cylindrical [A worm consists] …from a mechanical point of view, of a flexible muscular body wall enclosing an incompressible, but deformable medium which has a constant volume and in which fluid pressures can be transmitted.” R.B. Clark p. 31 Dynamics in Metazoan Evolution. Because the force (pressure) made by body-wall muscle within the fluid cavity is everywhere the same, to get locomotory changes effective in different body regions one needs to partition the medium into metameres/segments. Functionally metameres are locomotory modules that enable the creation of peristaltic body waves and forces adequate for burrowing. Annelids are metameric worms and their coelom is a hydrostatic skeleton.
Caribbean reef advice: don’t touch: fire coral, Millepora not a true coral (Anthozoa), but a Hydrozoa; very variable form per substratum.
Hermodice carunculata Photo from Paddy Ryan Fireworm, bristleworm Homology of chaetae Annelid diversity Bonaire fringing reef
Good place to see invertebrate diversity. Photos from Paddy Ryan website ‘worms’ Filogranella spp.? Protula bispiralis New Zealand Steinbeck: Sea of Cortez, Ed Ricketts, Hansen Sea Cow (see Wikkipedia) sessile
ABC News Leeches: blood- feeders with gut tube dominated by a sacculate pharynx for blood storage. discontinuous, feeders; integument annulations are not homologous with ancestral metameres. Most species of annelid are marine, errant* polychaetes. Annelida have a coelom. Metameres are grouped sometimes into tagmata: a tagma is a series of metameres adapted for a Particular function. Nereis *Knight errant wanderer How does a leech move without a partitioned coelom? Loss of septa
“Arenicola lugworm, both burrows and feeds by forcefully everting its proboscis into the sand and then retracting it with its load of sand. The burrow is enlarged by firm muscular peristaltic waves which also pass anteriorly. Organic material in the sand [falling out of the water column, brought in by the tides] is digested [extracellularly] and absorbed as the material passes through the gut.” (F. Brown, Selected Invert. Types)
Arenicola, lugworm: ocean flats tidal detritus feeder Ingests from shaft of ‘puddled’ sand and castings ejected at the surface at other end of burrow. Coelomic pressure everts pharynx for burrowing/feeding in lugworm. Some worms evert jaws from inside pharynx and capture prey. Malcolm Storey Proboscis eversion in burrowing see p R.B. Clark, Dynamics…
Arenicola, gills in middle third of animal, notopodium protects. Neuropodia are ventrolaterally located and comprise dorsoventrally elongated muscular ridges – obtains purchase in burrow. Each neuropodium has a longitudinal slit-like opening into a chaetal sac. The sac contains large hook- like setae (chaetae) or crochets (not visible here). F.A. Brown, Selected Invertebrate Types. neuropodium notopodium gill Gills: fine branches increased surface area, metameric on annelid body. (What is the difference between a gill and a lung?).
Parapodia comprised of neuropodium (ventrolateral) and notopodium (dorsolateral). Parapodia serve as paddles for locomotion and sites of gas exchange. Neuropodium is the lower half of a parapodium, nearer to the ventrally located nerve chord. (Annelids and arthropods contrast with vertebrates in this respect: vertebrate nerve cords are always dorsally situated.) Notum means ‘back’ so the upper, more dorsal, half of the parapodium is nearer the back, hence notopodium. neuropodium notopodium notum
The parapodia act as paddles, strengthened by aciculae (modified chaetae). There are muscles that can retract parapodia slightly, reducing impedance forces relative to power-stroke forces; parapodia protraction by localized increase in coelomic fluid pressure (?). Parapodium has locomotory function but also a respiratory function – gas exchange. Blood in a closed vessel system circulates out into the parapodia where there is a capillary bed for gas exchange. Movement maintains diffusion gradients steep. Parapodia have at least two functions. neuropodium notopodium Setal/chaetal bundle Parapodia of an errant polychaete, Nereis. aciculum coelom Muscles, circulars Muscles longitudinals
Phylum Annelida: concentrates organic food* filtering it from silt and inorganic particles using mucus and a seawater current. Lives in U-shaped secreted parchment tubes constructed in tidal flats; notopodia on 12 th segment are wing-like, aliform, produced; epithelium of these wings is ciliated and richly supplied with glands that secrete mucus. Notopodia of segments 14, 15 and 16 are modified into circular fans that just fit against the tube walls. Chaetopterus paired aliform notopodia fan notopodium parapodia suckerr
The fans fit piston-like against the cylindrical wall of the tube and are moved in a to- fro cycle, making a power then a recovery stroke; there are intrinsic promotor and remotor fan muscles. Fans create a strong current within the tube (of course only when the tide is in). Seawater is drawn in the chimney of the U-shaped tube, flows down across the burrow, up and out the other chimney. Each fan beats about 60 times a minute in active feeding. Ventrally there are suckers gripping the tube wall; if the fans are to work properly they must be properly anchored. The paired aliform notopodia are deployed against the walls of the tube and they secrete a sheet of mucus drawn rearward in the current created by the fans. Initially the current draws this ‘sock’out (mucus in water retains coherence). Streams of mucus trailing backward in the current, continually being renewed by fresh secretion at the wings, tapers ‘downstream’ into a bag. Particulate matter is filtered/trapped in this mucus bag. (Food of a sediment feeder: micro-organisms such as diatoms, detritus tissue from prey events etc. Bottoms of water bodies accumulate organic detritus.)
The 3 fans of this annelid are a tagma that functions as a pump: 3 metameres specializing to create a current of water within the U-shaped ‘parchement’ tube. Imagine it as it isn’t. Why 3 fans? Why not 2 or 4? Why not just 1? Chaetopterus Tagmatization supreme suckerr
Three fans instead of two or one create a smoother flow by their metachronal beating. Metachronal: refers to the phase difference between elements of a series. The flow is steadier with a three-element phased pump and this is important for filtration. The animal can move the bag about a little within the tube by muscles associated with the ‘wings’ and so avoid incoming material that is undesirable. The ciliated cup collects and rolls up the bag and then a midline ciliary tract carries this food ball anteriorly to the mouth for ingestion.
Potter wasp pedicel or petiole. Insect has two ‘necks’, one behind the head, and one between the thorax and abdomen: making both the abdomen and the head mobile relative to the thorax (the locomotory tagma). One might say there are 4 tagmata: thorax, head, abdomen and the petiole (a tagma of one segment). Torre- Bueno: “petiole: a stem or stalk; the slender segment between the thorax and abdomen in certain Diptera and many Hymenoptera; in the latter a pedicel formed of only one segment, or the first segment of a two-segmented pedicel in ants*; in plants the slender stalk of a leaf.” Petiole provides tagma manoeverability for stingingand immobilizing prey or for carrying prey (?). Hymenoptera pedicel Some other tagmata Head is a tagma: derived from fused segments.
Orthopteran Cyphoderris illustrates a segmented abdomen adapted for ventilation When acoustic insects stridulate the abdomen telescopes in and out like a little bellows, ventilating the tracheal system (tracheal sacs). Just as we breathe more heavily under exertion, so the katydid shows more rapid abdominal movements when singing. The retention of telescopic segmentation in the abdomen of many insects allows this ventilating function. gkmorris
Spiders evolved from serially segmented ancestors; they have two tagmata: cephalothorax/soma, opisthosoma/abdomen; intervening pedicel creates mobility of abdomen tip for creating silk structures. Maydianne Andrade
‘opistho-’ means behind or to the back. Spider opisthosoma is the ‘to-the-back’ tagma; it houses silk glands and spinnerets and the tagma gets necessary manoeverability for silk disposition (web-building) from the pedicel, a constricted ‘neck’ connecting the locomotory tagma and the weaving organ. (Some primitive spiders have segmented opisthosomas; but most have lost this segmentation. Opisthosomas house book lungs and can be the basis for hydraulic extension of the legs with fluid. Spider spinnerets terminal on opisthosoma
Water vascular system of these animals is unique to them; it is a *hydraulic mechanism (Kier): a system of vessels and chambers arising from a tubular ring around the mouth called the ring canal; in an asteroid one radial canal travels into each of the arms. They have a coelom but the water vascular system is separate from the coelom (apparently). Ambulacral grooves below each arm lined with tube feet or podia. Phylum Echinodermata *Where movement or shape change occurs through actual displacement of fluid from one location to another.
Asteroid echinoderms have an exoskeleton. In their dermis are embedded calcareous plates (inorganic salt Calcium Carbonate) called ossicles; the skin thus consists of ossicles of various shape separated by collagen- fibre connective tissue. Above each tube foot inside the arm is a vesicle called an ampulla encircled by ampullar muscles; their contraction will push incompressible fluid out of the ampulla, displacing it into the tube foot. (in the case of earthworm segments the fluid is not displaced from its container but it is here. There is a valve within the side branch to the radial canal – a one-way valve that closes to prevent backflow of the fluid into the water vascular system
Fig. from Frank Brown, Selected Invertebrate Types.
Ampulla is squeezed by ampullar or protractor muscles; the fluid is displaced down into the lumen of the tube foot; because of the crossed fibre helical connective tissue array in the wall of the tube foot (CFHCTA) the accordioned tube- foot wall smooths out as the foot protracts, i.e., lengthens. Hydraulic System
McCurley R.S. & Kier W.M The functional morphology of starfish tube feet: the role of a crossed-fiber helical array in movement. Biological Bulletin 188: The great importance of helical fibres in the functioning of tube feet is explained by Kier, but see also this paper by McCurley. The cylindrical tube foot extends when the ampullar muscles contract and displace fluid into it. Stress distribution in a fluid-filled cylinder is not uniform (as per annelid metameres): hoop stress [force acting to increase diameter] is twice as large as longitudinal stress. [Imagine it as isn’t.] In the absence of connective tissue fibres in the tube foot walls when fluid pressure increased in the tube foot it would swell more in diameter than it lengthened; the helical fibres oppose this diameter increase so that there is an increase in length rather than diameter.
How can a connective tissue fibre which is relatively inextensible (“stiff in tension”) serve to prevent diameter change while allowing lengthening? The answer is the pitch of the helix changes. p. 207, Fig. 10 McCurley Tube foot model: treat it as a cylinder and consider this cylinder “wrapped by a single turn of an inextensible helical fiber. Fibre angle θ is the angle that the helical fibre makes with the long axis of the cylinder (tube foot) When tube foot is at its shortest, θ is 90 degrees When tube foot is at its maximal extension θ is 0 degrees Confirm this for yourself by drawing a lengthened and shortened version of his modelled single-turn cylinder, see Fig. 10 of McCurley