Feb 28, 2013

Microphagic animals: filter feeders, suspension feeders, particulate feeders

Questions I don’t know the answer to and other miscellany:

• Why do dinoflagellate zooplankton bioluminesce, i.e. what is the function of this light?• What makes flagella and cilia move?• What is the function of the paddlefish’s rostrum? of the two lobes in front of the manta

ray intake?• Why might one expect a snake to have good binocular vision? Assuming they don’t,

what takes its place in allowing accurate strikes to apprehend single prey items?• If coining a name, then membracid ‘helmet’ might have been better called ‘cloak’:

why?.• Reading Assignment: a colleague alerts me to the fact that the paper in Nature by

Prud’homme et al. begat an argument. I’d like you to look into subsequent issues of Nature to determine what this argument is all about. Apparently some people don’t believe the helmet (cloak) is really involved with a primitive prothoracic wing. I will do the same and come back to the topic in a later lecture.

• Science is in pursuit of the truth and the truth is often presented as a model. But models (a way of thinking: e.g., Chabrier model of insect flight, so too the concept of Force, levers, are models; little drawings of flea jumps incorporating resilin are models etc.) are only true to some level of resolution.

• Science proceeds with disagreement.

Knowing what you eat and pursuing it as an item: taking a really big bite: snakes and swallowing

• In primitive land vertebrates (amphibians) the quadrate bone was part of the skull. It was immovably joined to the skull posteriorly, forming part of the fulcrum of the lower jaw/mandible.

• The braincase is a bony box of bones, developed in pieces and fused on maturation. The lower jaw, the mandible, articulates at the rear of the skull and two antagonistic muscles move it during chewing. To bite, the anterior temporal muscle (originating on the skull and inserting on the middle region of the jaw) lifts (adducts) the jaw; the digastric muscle (originating on the skull and inserting on the proximal end of the jaw) drops (abducts) the mandible.

• [What levers are involved?]

Seymouria: Permian amphibian

Michel Laurin Tree of Life

Snakes are NOT filter feeders: so how the head morphology of a filter feeder differs from that of a snake can help reveal filter feeding specializations. Both a snake and a rorqual whale need a large gape but for different reasons.

Snake gape adaptations

• Snakes choose their food in a way filter feeders can’t; they have no limbs to hold it down while tearing off pieces; the snake has to swallow the food whole.

• Jaw teeth are recurved (one-way teeth, curved in one direction like the barb on a fishook): this curving allows prey to slip in but not out.

• The quadrate pivots on the back of the skull, shifting the fulcrum of the jaw lower down greatly increasing the gape.

The jaws are flexible in the anteriormidline and can ‘walk’ forward on the prey, by alternating right andleft, loosening and setting the recurved teeth.

Some polychaete worms are tubiculous: which means tube-dwelling: they have modified the

anterior of the body into a tentacular fan for filtration: similar to commatulids but

making their own filtration current: pinnules and radioles grooved.

Branchial crown of radioles and pinnules;pinnules of one radiole overlap nearly normal to those of next radiole to make the filtration surface.

Abfrontal and laterofrontal together create an angular current which flows into the funnel of radioles through its

sides from below (blue arrows), exiting mid-funnel: these cilia are located where they have to be to ‘bail’ the

current into existence.

What is frontal? it is the aspect of the pinnule facing into the funnel: imagine the branchial crown as the prostomium (ahead of mouth) [1st metamere ] with a whorl of appendages projecting at right angles.

Mucus produced on the pinnules; frontal cilia capture food and inorganic

particles by ‘direct interception’ and moves them along the pinnule groove; more cilia tracts on radioles move the food and mucus down to the worm’s

mouth.

Sorting mechanism at mouthseparates out inorganic particles for tube construction according to size: all done by ciliary tracts.

Phylum Annelida: worms concentrating particulate food on tidal flats[‘snotworm’ is not a scientific term]

These animals are perhaps the ultimate ‘tagmatists’: the basic annelid body plan

Lives in U-shaped parchment tubes; notopodia on 12th 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

Chaetopterus in its U-shaped burrowTagma are metameres of a serially segmented body plan that are grouped for a common function.The 3 fans are grouped into a tagma that creates a current of water within the U-shaped tube.Why 3? Why not 2 or 4? Why not 1?

• The fans fit piston-like against the cylindrical wall of the parchment-like tube and they are moved in a cycle, making a power and recovery stroke, i.e., there are intrinsic promotor and remotor muscles. This beating creates a strong current within the tube (can only feed when the tide is in). Seawater is drawn in the chimney of the U-shaped tube and flows through the tube and out the other chimney. Each fan beats about 60 times a minute. 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 stretched out around the walls of the tube and a sheet of mucus secreted between them; the current draws this out (‘snot’ in water retains coherence) so soon there is a sheet of mucus trailing backward in the current continually being renewed by fresh secretion at the wings; eventually there is a bag of mucus. Particulate matter is collected in the mucus bag. 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.

• Three fans (rather than just one or two) create a smoother flow by their metachronal beating. Metachronal: phase difference between elements of a series. The flow is steadier with a three-element phased pump and this is important for filtration.

Sanderson S.L. & Wassersug 1990. Suspension-feeding vertebrates. Scientific American (March) 1990. 262: 96-101.

• Consider this paper assigned reading. It deals only with vertebrates, Subphylum Vertebrata, and does not even include any of the filter-feeding subphyla that come under the heading of Chordata: Cephalochordata (amphioxus) and Urochordata (sea squirts). S &W classify vertebrate suspension feeders into four categories: one being continuous ram feeders.

• Continuous ram feeders: paddlefish, manta ray, basking shark, megamouth shark, whale shark, some species of: anchovies, herrings, sardines, mackerels.

• These species swim through their food, (filter it like an entomologist with a beating net filtering insects out of goldenrod), creating the filtration current by swimming forward in a sustained way with the mouth open, “allowing water to escape from gill slits at the back of the head”. Here in the gills are structural devices for filtering: e.g., gill rakers.

• Baleen (rorqual*) whales [blue, minke] are ram feeders too, but intermittent ram feeders, not continuous: they don’t swim in a sustained way through their food they take gulps.

Rorqual from Norwegian ‘furrow whale’ in ref to longitudinal folds mouth to navel

dummidumwit

Paddlefishes: continuous ram feeders

Polyodontidaeprimitive chondrostean ray-finned fish with a snout or rostrum called ‘spoonbill catfish’; only 2 modern species, Chinese and American: the Chinese may be extinct

manta ray

megamouth shark

basking shark

whale shark

Wikki

prodivers

project aware

whale shark

Brian SkerryNational Geographic

whale shark

Sardines swim with their mouths open; ram filter feeders

Gill rakers: projections on gills that form part of a filter

Rorqual whale:

Blue whale; baleen