Exercise 31

General Info: Exercise 31

Mollusca – snails, clams, octopuses, squids

Annelida – segmented worms

Both Mollusks and Annelids are coelomates (See Fig. 31.1), which means that they have a coelomic body cavity surrounded by a mesoderm and it contains a complex system of organs and compartments.

Mollusks and Annelids are also protostomes, i.e. their mouth is derived from the embryological blastopore.

Both have well developed systems of nerves, circulation, excretion, reproduction, and digestion.

Phylum Mollusca

Soft bodied animals covered by a mantle that secretes a shell (Fig. 31.2)

Their coelom reduced to a small chamber around the heart.

Circulatory system open (except in cephalopods) – this means that blood does not flow within veins but in pools of sinuses, and bathes the organs directly.

Open circulatory system has a few vessels and a heart.

The basic body plan of mollusks shows the following:

Visceral mass of organ system.

A ventral, muscular, and highly developed modified foot used for movement.

Calcium based shell

Mantle that secretes the shell; may aid in respiration or locomotion.

Some mollusks may posses a head.

Phylum Mollusca is divided into 4 classes:

Class Polyplacophora

Commonly called chitons.

Literally means organisms with many (= poly) plates ( = placo) that move (= phora).

Dorsal shell divided into 8 plates.

Ventral foot

Radula – a horny toothed organ in the mouth; scrapes food from rocks.

Class Gastropoda

Stomach (= gastro) foot (=poda) snails.

Marine rudibranch and common garden slug do not produce a shell (Fig. 31.3)

Feed with the help of a radula (Figure 13.4)

Shell is spiral or coiled.

Class Bivalvia

Two (= bi) shelled (= valvia) clams, oysters, scallops, muscles.

Mantles of left and right valves (shells) join to form ventral incurrent siphon and dorsal excurrent siphon. Both help in directing water through the clam. (Figure 31.2 b)

Posses a mantle cavity – space in between mantle and visceral mas????

Do the dissection of a of a mussel (clam). Examine the bivalve anatomy. Follow Procedure 31.1 and Figure 31.?.

Filter feed – Figure 31.6

Most bivalves produce pearls. (Ex. Pinctada???)

Natural pearls

Cultured pearls

Class Cephalopoda

Head (= cephalo) foot (= posa) squids, octopus, nautilus, etc.

Shells may be absent or reduced to an internal semmant. (Fig. 31.2) Ex: Cuttlefish

Foot modified into tentacles. (31.7)

Predatory (Ex: Loligo)

Largest eyes in Kingdom Animalia belong to squids.

Dissect a squid.

Phylum Annelida

Include earthworms and leeches

Body segmented. Segments also known as metameres

Circulatory system closed, i.e. blood flows in vessels.

Presence of setae – appendages on lateral and ventral surface which help in locomotion.

Phylum Annelida divided into 3 classes:

Class Polychaeta

Marine worms living in sediment. (Fig. 31.8)

Each segment of the body possesses a pair of appendages – parapodia

Parapodia help in movement and respiration.

Setae protrude from parapodia which gives the class it’s name (= poly) many. Setae (= chaeta).

Ex: Nereis???

Class Oligochaeta

Common species is earthworm – Lumbricus terrestris

Earthworm locomotion – involves extension, anchoring, and contraction of the circular and longitudinal muscles.

External Anatomy:

Class derives it’s name from few (=oligo) setae (=chaeta).

Lack parapodial have few setae

Mouth preceded by fleshy lobe – prostomium

Posterior to the mouth present – peristomium

Hermaphrodites – i.e. each earth worm produces BOTH egg & sperm.

Copulating worms attach at their clittela, which is present posterior to and a few segments away from the peristonium.

Sperm exit through male gonophores (segment 15) of one earthworm à To the adjacent earthworm where it is received and stored in seminal receptacles (segment 10) à copulating worms separate à the clitellum of the sperm receiving earthworm secretes a mucous band à mucous band picks up eggs from the female gonophore (segment 14) à sperms from the seminal receptacle (segment 10) à eggs fertilized in the mucous band by sperms à fertilized eggs released as cocoon (Fig 31.9 & 10)

Examine the external features of an earthworm – Procedure 31.4

Internal Anatomy

Digestive system consists of pharynx (for food ingestion), esophagus (for transport), crop (for storage), intestine (absorption) and gizzard (for maceration)

Nervous system – paired nephridia

Excretory system – ciliated nephrostomes & nephridioph(ores)

Do dissection of an earthworm (Procedure 31.5)

Class Hirudinea

Include leeches – extoparasites.

Have NO setae

Dorsoventrally flattened

Anterior and posterior suckers present which hold prey.

Hemophrodites

Sexual reproduction is as follows:

Two leeches intertwine à one leech injects a packet of sperm (spermatophore) into the other à eggs fertilized à cocoon secreted around the fertilized egg.

Kingdom Animalia

Phylum Arthropoda (Exercise 32)

Largest phylum in he Animal Kingdom

Includes spiders, ticks, mites, scorpions, centipedes, millipedes, shrimps, crabs, and insects (Fig. 32.1)

Possess rapid external skeleton – exoskeleton – made up of chitin – It provides protection, moisture barrier & place for muscle attachment.

Jointed (= arthro) appendages (= pods)

Divided in 3 subphyla – cheliceda, crustacea, and urinarama

Subphylum Chelicerata

Spiders and scorpions

Presence of chelicerae – appendages modified into feeding structures.

Pedipalps – appendages modified for capturing prey, sensing environment, or copulation.

Body divided into 2 regions –

Cephalothorax – fused head and thoracic segments.

Abdomen – posterior body region.

Lack antennae

This subphylum divided into classes

Class Merostomata (Horseshoe crabs)

Exoskeleton or carapace is horseshoe shaped (Fig. 32.2)

Chilaria – degenerated pair of legs

Book gills – site of gas exchange.

Class Pycnogonida (Sea spiders)

Carnivorous

No abdominal appendages (Fig. 32.3)

Class Arachnida (Scorpions, Ticks, DaddyLongLegs, Spiders)

Chelicernae modified as fangs to pierce prey.

Pedipalps to manipulate food.

4 pair of walking lefs and 2 body regions (Fig 32.4) (Insects on the other hand have 3 pairs of legs and 3 body regions)

Subphylum Crustacea (this subphylum has just one class.)

Class Crustacea (Crayfish, Crabs, and shrimps)

Crustacea differ from other subphylas of Arthropoda in having biramous or double branched appendages.

2 pairs of antennnae

Compound eyes with multiple lenses.

Crustaceans & Insects called mandibulates – have opposing mandibles (jaws) derived from an anterior appendage(s).

Do dissection of a crayfish. Follow procedure 32.1 and 32.2

MORPHOLOGY: Look for first antennae, second antennae, mandibles, maxillae and maxillipeds, swimmereds or pleopods, uropods, telsow (Fig. 32.7 & 32.8)

ANATOMY: look for heart, pericardial sac, gonads, cardiac stomach, pyloric stomach, esophogus, mouth, digestive gland, brain, etc. and green glands (Fig 32.9)

Green glands à excretory organ of crayfish.

Subphylum Uniramia

Single branched appendages

Divided into 3 subclasses

Class Chilopoda (centipedes) – Fig 32.10

Class Diplopoda (millipedes)