This exam is worth 50 points, 25% of lecture grade.

Shorter Answer (20/50 points). 5 points each.

  1. How is water flow directed in the mantle cavity of different Gastropods to maximize sanitation and oxygen exchange efficiency? ( at least 3 types)

    2. Keyhole Limpets: cleft in mantle, hole in shell, two pairs ctenidia drive water through mantle cavity to hole, anus near hole.

    Abalone: cleft mantle, perforated shell with anterior incurrent and posterior excurrent holes, anus near excurrent holes

    Busycon: a prosobranch with an incurrent siphon on left, ctendia drive water left to right over head with anus on right.

    In all, one way direction of flow, water and blood flow in opposite direction (counter current exchange), anus placed near excurrent water stream

  2. Describe the association between locomotion and body plan in Polychaetes, Oligochaetes, and Hirudinea. (consider the coelom and external features)

    3. Polychaetes: crawling, swimming, burrowing with spacious segmented hydrostatic coelom, parapodia and setae. Some sedentary types with incomplete septa

    Oligochaetes: burrowing with spacious segmented coelom, longitudinal and circular muscles, but streamlined with no parapodia and reduced setae

    Hirudinea: anterior, posterior suckers for inch-worm locomotion; absent are segmented coelom, parapodia, setae

  3. How are Cirripedia (barnacles) specialized for a sessile adult life? (consider feeding, reproduction, dispersal, and site selection)

    4. Cirri with passive and active feeding, simultaneous hermaphrodites and extendable penis so every neighbor is a potential mate, planktonic feeding nauplius larva for dispersal, and specialized cyprid larva for settlement with sensory capacity to find appropriate substrate, hard calcareous exoskeleton for protection.

  4. Compare a fully benthic and fully pelagic Decapod crustacean. How is the body plan modified in the transition?

Pelagic (shrimp): long abdomen and short thorax. Laterally flat. Thoracic and abdominal appendages for feeding or swimming,

Benthic (crabs): long thorax, some fused to head, and short abdomen. Abdomen folded and fused to thorax. D-V flattened and laterally extended, heavy appendages. Pleopods reduced, not used in locomotion. One pair maxillae chelate.

Changes from swimming to crawling locomotion.

 

Essay questions. Each question is worth 15 pts.

1. Describe the major trends of body plan modification among molluscan classes. Now, using one structure (shell, foot, mantle, radula), describe how it is specifically adapted for life in different habitats.

 

Monoplacophora: broad foot, mantle cavity expanded around margin, low visceral hump, multiple ctenidia, "segmentation"

Polyplacophora: shell divided into plates, broad foot, mantle cavity expanded around margin, low visceral hump, rasping radula, multiple ctenidia

Gastropoda: high visceral hump, cephalization, coiled shell, torsion (mantle cavity anterior), diverse radula

Bivalvia: two-valved shell, laterally flattened, wedged-shaped foot, reduced cephalization, enlarged mantle cavity, enlarged ctenidia, radula absent

Cephalopoda: foot modified to arms and tentacles, visceral hump stretch D-V, body axis switched (D-V to anterior-posterior), super-cephalization, shell reduced or absent, mantle cavity spacious for locomotion.

 

EX. Foot: broad and entire ventral surface in chitons for attachment on waveswept rock; wedge/hatched shaped for burrowing in soft sediment in some bivalves; reduced and finger-like in mussels (bivalves) to help attach byssal threads; extended to arms, tentacles in pelagic or mobile predatory cephalopods; stretched and flattened into wings or fins for swimming (flying) in pelagic gastropods (heteropod prosobranchs, pteropod opisthobranchs).

 

EX. Shell: reduced to supporting rod, chambered for bouyancy in pelagic cephalopods; hinged, laterally flattened and streamlined in benthic infauna (bivalves); protective refuge (spiralled and large aperture) for benthic snails (gastropods); flattened profile and split into plates for epibenthic chitons (polyplacophora) on wave-swept coasts.

2. How do errant versus sedentary Polychaetes differ in terms of regional specialization in body plans and feeding modes? How are these locomotion modes associated with feeding modes, and what structures perform what functions?

Errant:

cephalization, homonomous segments (all the same), with well-developed parapodia and setae. Some with fusion of anterior segments to form head.

Parapodia functions as paddle.

For swimming or surface locomotion (epibenthic), often predatory.

 

Sedendary:

reduced cephalization, more regional specialization. Parapodia restricted or diverged regionally.

Function of anterior parapodia as anchors in tubes, as gills. One suspension feeder uses diverged parapodia (aliform notopodia, fan parapodia) for mucus-net feeding. Function of posterior parapodia for swimming in epitokes, gills, or reduced to absent.

Feeding modes generally are deposit and suspension feeding. Head tentacles used as feeding structures

 

3. Why are planktonic suspension feeding crustaceans important? How are basic Arthropod body plan and appendages adapted for suspension feeding in different crustaceans (Copepods, Branchiopods, Cirripedia, Euphausiids)? Which appendages are used?

Important link in the food web: energy transfer to higher trophic consumers

primary consumers that convert primary production into food for larger animals. Abundant in oceans. Dominant member of plankton

 

Copepods: 2nd antennae (current) and maxillae (trapping appendages) for feeding, 1st antennae for parachute, thoracic appendages for locomotion (abdominal appendages absent). Can accumulate lipids for floatation, or be flat for greater surface friction against sinking.

Branchiopods: thoracic appendages for feeding, leaf or comb like with setae, antennae for locomotion

Cirripedia: sedentary but use cirri (thoracic appendages) with long setae for food capture. Because they are sedentary, they can use passive feeding. Abdomen and all other appendages reduced or absent.

Euphausiids: thoracic appendages, well-developed abdominal appendages for locomotion