Jan 22 lecture Odonate jetting Body plan Mollusca Bivalve foot in hydrostatic burrowing Slug floot walking on glue Notochord as hydrostatic axial skeleton

Freshwater insects that use jetting to escape and to breathe Some dragonfly immatures (Order Odonata) can jet water out of their rectum, the posterior chamber of their gut; they use funnel-shaped terminal sclerites to aim flow just like a squid siphon; telescoping in and out of abdominal segments powers water intake and outflow; filaments filled with tracheae project into rectum lumen for gas exchange.

Raptorial labium of these dragonflies modified to apprehend prey: It is extended suddenly and can grab other small insects or even small fish. Is it possible that jetting plays a useful role in speeding up this ambush attack?

A mollusc ancestral to squids, to see how foot shell & mantle cavity changed during evolution See reserve books for general anatomy of different molluscs Rupert,Fox Barnes 7 th or Brusca

streamlining dorsal view Shell is an internal remnant sunk within the mantle tissue; it is called the pen

Razor clam burrowing Winter A.G. et al Localized fluidization burrowing mechanics of Ensis directus. Journal of experimental Biology 215: (See also Inside JEB, Kathryn Knight Razor clams turn soil into quicksand to burrow.) Read Kathyrn in detail but not Winter. The foot end (anterior), the siphon end (posterior), the hinge dorsal but the animal orients normally foot end down.

An interesting picture of razor clams packaged for sale in a chinatown market in Philadelphia

Hydrostatic function of blood in haemocoel sinuses: blood is travelling at low pressure in the foot through indescriptly shaped spaces, making its way back to the heart (pump).

Biomimicry is a recently coined engineering term for building/designing devices inspired by animal adaptation. (See Kathryn Knight.) ‘Self-burying machines’; Winter is an engineer at MIT: “There are many applications that could benefit from a self-burrowing reversible anchor that embeds efficiently...” Winter’s interest in razor clam piqued by its burrowing ability: can go down >3 times body length [very fast] ; this not consistent with muscle capacity. These clams use a ‘TWO-ANCHOR SYSTEM’ One region of the animal’s body (foot) expands to form an anchor while another body region contracts (i.e., valves pulled away from the surrounding substrate; working from purchase, valves then foot then valves [like the earthworm’s chaetae] clam can burrow down (or back up) by reshaping its body hydrostatically. But the razor clam does something that helps it to burrow better: it “uses its valves to create a pocket of fluidized substrate [‘quicksand’] around its body to reduce drag”. When the valves are pulled back from the surrounding ‘soil’ (soil that is water-saturated) “it sucks more water toward its body so you get increased unpacking of the soil particles” and they won’t give support – and less resistance to penetration of the foot. [Note!!! no incurrent siphon brings down ocean water for this fluidization.]]

Median line with down arrows shows route by which blood within sinuses is displaced into foot, serving there a hydrostatic function changing foot shape. Pedal protractor muscles contract to push foot out between the valves by displacing fluid (blood) in haemocoel visceral mass sinuses into the foot Valves either push out against the surrounding substrate or not, depending on the activity of the 2 adductor muscles (only one shown); if the adductors are relaxed the ligaments hold the valves against the sand and mud at the sides of the burrow. Swollen foot expands and anchors; retractors (black) draw the animal down toward the swollen foot through quicksanded soil. Note: hinge and shells misleading re razor clam anatomy hinge but diagram illustrates muscle effects on visceral mass and foot

from Winter’s discussion: (fluid mechanics jargon, very difficult for a biologist to follow and one might be wondering exactly what he means by ‘soil’; I keep thinking of sand) As E. directus contracts its valves [my underline], it reduces the level of stress acting between the valves and the surrounding soil. [ Stress is good, but no biologist would be talking about contracting valves: the shells obviously don’t ‘contract’: he means 2 valves are pulled together by the adductor muscles inside.] At some stress level, the imbalance between horizontal and vertical stress causes the soil adjacent to the animal to fail. [This is when the soil and water mix takes on a soupy consistency that won’t support anything, i.e., ‘quicksand’.] Continued valve contraction draws pore water towards the animal, which mixes with the failed soil to create a region of localized fluidization [my boldface emphasis]”. “...the clam fluidized the [immediately] surrounding soil (fluidize, i.e., you could pour it) which dramatically reduced the drag on the shell, allowing the mollusc to pull itself down -- before the surrounding sand particles slid back into place and the soil resolidified. The energy required to move through the fluidized substrate was a fraction of that required to move through it in its nomal solid state.

Cycle of burrowing movements Fig. from Winter: In stage A, adductor relaxed so shells braced on surrounding sand by ligaments; protractors start to contract (B) pushing blood into foot and the foot probes down, gaining ground into the mud; pushing force of foot makes body move up a little (C) (relative to dashed line). Stage D, adductors contract, pulling valves together, (red indicates the space they DID occupy), pushing blood into foot to make an anchor, simultaneously squirting seawater out around valves from mantle; this water* ‘puddles’ sand; foot swells with blood into this quicksand region– the localized fluidation; displaced blood is swelling the foot maximally into the bottom anchor of the TWO ANCHOR SYSTEM. Cycle renews (F). *Its not clear whether this involves ocean water drawn in by siphons; perhaps it does if the clam is burrowing near the surface and perhaps if lower down it oscillates (?) its valves to draw in pore water (Winter)

Ensis directus burrowing motions. Ensis directus burrowing motions. The dashed line indicates the depth datum. White arrows denote valve and foot motions. Panels are snapshots of live E. directus performing burrowing motions. The red silhouette denotes valve geometry in the expanded state, before contraction. (A) Start of burrowing cycle. (B) Foot extends downward. (C) E. directus pushes on foot, causing upstroke of valves. (D) Valve contraction, which pushes blood into the foot, inflating it to form a terminal anchor. (E) Contraction of the foot, which draws valves downward. (F) Expansion of the valves, at the start of the next burrowing cycle.

Geoduck (upside down) valves cm long. Siphons up to 1 m long Siphons incurrent and excurrent so long they can’t be withdrawn in between the valves any more.. Forms of the many species of burrowing bivalves will be greatly affected by the great variety of soils (‘soil’ is a term here embracing complexities of clay, sand, organic matter etc.) in which they locomote – moving up to filter feed per the tide, down to avoid predation. The razor clam is unusually narrowed. Why this shape? Does it help it to achieve speed in burrowing that enables it to out- dig predators? What about the diversity of ridges and shell texturings on burrowing bivalves: could they be functional in gaining purchase?

Soft shell clam Mya arenaria (above). Bivalves are typically filter feeders in tidal zones, burrowing down between tides; phytoplankton filtered from water entering via incurrent siphon. Filtering of food by gills Some siphon diversity: different lengths in different species. Siphons evolve as pinched off and produced regions of posterior mantle Christopher Taylor

There are monotaxic and ditaxic gastropod species Gastropods move on their foot using “muscular waves moving along [its] ventral surface” “the force of these waves is coupled to the substratum by a thin layer of pedal mucus” Denny 1980 From Class Bivalvia species in 75 families, we go to Class Gastropoda, species. Pulmonates are a subclass of gastropoda and include land snails name is from the conversion of mantle cavity into a lung

Pedal locomotion in Pulmonates From Wikimedia Commons Arion ater, black slug Mantle cavity of pulmonates has been converted into a lung: hence ‘pulmonate snails’ of which slugs are just one sort; edges of mantle cavity seal to back except for pneumostome opening; roof of mantle cavity vascularized, no gill..

pneumostome: entry to lung Pacific Banana Slug See video of pedal waves

Long, J.H. Jr. et al The notochord of hagfish Myxine glutinosa: visco-elastic properties and mechanical functions during steady swimming. J. exp. Biol. 205: “Chordates have evolved an unique hydrostatic axial skeleton, the notochord, that is present in all taxa of that phylum early in development; it is retained in the adults of some taxa and modified by vertebral elements in others... Notochords are hypothesized to have evolved to stiffen the body (Goodrich, 1930) and to prevent body compression during muscle activation (Clark, 1964). In addition, notochords may adjust function by means of dynamically variable mechanical properties (Long et al., 1998).

Long, J.H. Jr. et al The notochord of hagfish Myxine glutinosa: visco-elastic properties and mechanical functions during steady swimming. J. exp. Biol. 205: “Chordates have evolved an unique hydrostatic axial skeleton, the notochord, that is present in all taxa of that phylum early in development; it is retained in the adults of some taxa and modified by vertebral elements in others... Notochords are hypothesized to have evolved to stiffen the body (Goodrich, 1930) and to prevent body compression during muscle activation (Clark, 1964). In addition, notochords may adjust function by means of dynamically variable mechanical properties (Long et al., 1998).

An animal having a notochord and metameric axial musculature making body waves. Anatomy of a chordate