Invertebrate Zoology Lecture Exam 2

This is covering the 5 chapters for the exam on 10/18/2024, anything bolded is important characters that Dr. Christensen is likely to ask about in the exam. Other featuring of phrases is information that is also important to understanding the content

Phylum Gastrotrichia

Phylum Gastrotrichia

• Name means “stomach hair”, these are all cilia on the ventral surface, with tufts on the head.

• Found in marine and freshwater environments

• They have structures that look like “toes”, which has adhesive tubes within (duo glands)

• Bi layer cuticle (skin), that is not molted.

• Complete gut

• Acoelomate (without cavity)

• Hermaphrodites or participate in parthenogenesis and are direct developers

Phylum Dicyemida

• Obligate symbiosis with nephridia of cephalopod (think octopus and squid) molluscs

• Asexual and sexual reproduction

• 2 adult forms possible:

  • Nematogens - asexual: vermiform (worm-like) larva

    • 20-30 ciliated cells with an axial cell that acts as the reproductive center, the axoblast develops within the axial cell and becomes new nematogens

  • Rhombogens - sexual: infusoriform (circular) larva

Phylum Chaetognatha

• Name means “bristle jaw”

• Marine species

• Planktonic (few are benthic, deep sea)

• Transparent body

• Body

  • Head - ocelli, grasping spines , teeth, hood

  • Trunk - paired lateral fins

  • Tail - single caudal fin

• 4 bands of longitudinal muscle

• 4 coelomic cavities, 1 in head, 2 in trunk, 1 in tail

• Complete digestive system

• Contain tetradotoxin against prey

• Ciliary fences around face to sense vibrations in the water

• No gas exchange or excretory organs (they do diffusion)

• They have a nervous system (cerebral and ventral ganglion, eyes with ocelli, and sensory cilia)

• Simultaneous hermaphrodite (can self, no internal copulation, exchange of spermatophores) with direct development.

What are defining characteristics of Phylum Gnathifera

• Pharyngeal jaws

• Blastocoelomate

• Eutely

Blastocoelomate

an invertebrate animal with a three-layered body and a pseudocoel, or "false cavity"

Eutely

a condition in which an organism has a fixed number of cells that remains constant throughout its life

Phylum Rotifera

• Name means “wheel bearer” - their wheel has ciliated corona

• Muscular pharynx with jaws

• Toe has adhesive glands

• Syncytial epidermis

• Mostly freshwater and freeliving, it is possible for it to be marine or semiterrestrial, and omnivorous

• 28% of described species are parasitic within vertebrate hosts

• Intracellular cuticle is not molted.

• Body

  • Head, trunk, foot (1-4 toes, pedal glands, can be used for locomotion)

Syncytial

a mass of protoplasm containing many cell nuclei

Rotifera: Head

Two main parts:

• Corona with a trochus and cingulum (used for feeding and locomotion

• Mastax - muscular pharynx with teeth (trophi)

Rotifera has…

complete digestive system with gastric glands (oooo complex girly) and a bilobed brain (smart gorl), two longitudinal nerve cords, sensory bristle, sensory systems, ocelli

Gnathifera is…

a group of organisms with complex structures for such small creatures, remember complicated!!!!

How are rotiferans specialized

They experience cryptobiosis, which is a state of suspended life functions to survive during a time of change or lack of resources.

Rotifer osmoregulation

Use of protonephridia (primitive kidney) and bladder where nitrogenous wastes diffuse across the body wall

Rotifer reproductive strategies

• Sexual and asexual processes possible

• Sexual - dimorphic, with internal fertilization

• Parthenogenesis, asexual, females only.

• They also have a cycle that combines the two methods.

Monogonota

• One gonad

• Influenced by seasonal and environmental cues

1. Amictic phase - 2N which is done by mitosis, this phase follows parthenogenesis and is always female diploids.

2. Environmental stimuli causes meiosis to occur, haploid males and females occur in where they are eggs and sperm, with fertilization diploid female eggs are made.

3. They are hatched and follow the parthenogenesis cycle.

Subclass Acanthocephala

• Meaning prickly head

• 1-2 ligament sacs that support the gonads

• Have a proboscis with intracellular hook

• All are parasitic in vertebrates, with an intermediate host in arthropods

• They were previously placed in a separate grouping but molecular data places them as rotifers.

• Three body parts:

  • Proboscis - hollow and retractable with hooks or spines

  • Neck

  • Trunk with pseudocoel

• No main organ systems and reduced sensory structures - since they do not need to develop them if they get broken down food from host.

• Reproduction - mostly gonad, separate sexes (internal fertilization, males have a cement gland, and females have ovarian ball and uterine ball), acanthor (mature embryo) larvae

Phylum Gnathostomulida

• Name means “jaw mouth”

• Related to rotifers

• Wormlike

• Lives in marine sediment

• Acoelomate

• Ciliated outer surface, each cell has a single cilium

• Incomplete digestive system

• Simultaneous hermaphrodites, internal fertilization, and direct development.

Phylum Micrognathozoa

• Single species

• 2 part head with complex set of 4 jaws

• Dorsal and lateral epidermal plates

• Ciliated ventral epidermis (ciliophores), they swim in a spiral.

• Posterior adhesive structure

• 3 pairs of protonephridia structures (primitive kidneys)

• Might be only female, but since very few have been found, there is no way of knowing.

Phylum Cycliophora

• Name means “small wheel”

• A few species have been described

• Symbiont with lobsters and other decapods

• Chordoid larva with mesodermal rod of muscle cells

• Acoelomate

• Ring of compound cilia around the male

• Cuticle present

• U-shaped gut

• Adhesive disc

• Feeding structure and brain are replaced periodically via budding

• Asexual and sexual production, female asexual larvae, sexual chordoid larvae and prometheus larvae that is timed to release when the host molts

Chordoid larva

develops from an embryo that grows inside a chordoid cyst and engulfs the tissue of the mother animal. Once freed from the cyst, the chordoid larva can swim to a new host

What are nemerteans?

ribbon worms

Phylum Nemertea

• Name means snout cavity

• Mostly marine with a few freshwater and terrestrial species

• Can be small (1cm) to very long (30m)

• Eversible proboscis contained in a fluid filled schizocoelous chamber - Rhyncocoel

• They superficially resemble flatworms, with their ciliated epidermis that secretes mucus

• Proboscis - moves in and outward via hydrostatic pressure, has a retractor muscle, may have a stylet and poison gland, not connected to gut typically.

• Most are predatory and leave a chemical trail, if they do not have the stylet, they will entangle the pray with their proboscis.

• Asexual and sexual reproduction

  • Asexual - fragmentation

  • Sexual - Dioecious, spawn through pores and ruptures out the body, external fertilization, spiral determinant cleavage, direct development or pilidium larvae

Eversible

something can be turned inside out or outward

Rhyncocoel

a fluid-filled cavity in certain invertebrates, particularly nemertean worms, that houses the worm's proboscis

Schizocoelous

relating to a type of embryonic development in which a solid mass of mesodermal tissue splits to form secondary body cavities, or coeloms

How do nemerteans and platyhelminthes resemble each other?

• Ciliated skin

• Dorso-ventrally flattened

• Circular, longitudinal, and a third layer of muscle

• Ladder like nervous system

• Similar sensory structures such as ocelli, chemo- and mechano- receptors and cephalic grooves

• Nephridial system (function similar to kidney)

How do nemerteans and platyhelminthes differ?

• Nemerteans:

  • Closed circulatory system - lateral vessels and lacuna, no heart, the vessels contract to pump fluids around the body

    • This allows for a larger size, more muscles, more activity

  • One way digestive system, mouth and anus present, allows for continuous eating since they don’t spit digested waste back out of the mouth, they have regional specialization (organs we also have, esophagus, stomach, intestine with diverticula, and anus)

spiral determinant cleavage

a type of cell division that results in determinate cells, which means the fate of each cell is predetermined early in development

Pilidium larvae

meaning “cap” because the typical pilidium larva is shaped like a hat with earflaps that are pulled down over the ears

Phylum mollusca

• Found in all habitats - many species

• 7 classes

• Eucoelomate and bilateral symmetry

• Unsegmented body

• Protostome body

• Visceral mass in concentrated along the back

• Characteristics:

  • Mantle - epithelium that covers body and excretes spicules or shell, with three layers. house the organs

  • Radula - circular band of teeth (odontophore)

  • Foot - ventral muscles

• Open circulatory system - hemocoel

  • Heart composed of 2 atria and a ventricle, respiratory pigments are Hb and Hemocyanin

• Well developed nervous system

• Complete gut - specialization with digestive glands

• Complex excretion metanephridia

  • Heart-kidney complex

    • Podocytes in the atria (ultrafiltration)

    • Nephrostome open to pericardium

• Trochophore larvae

  • Veliger

Shell layers

• Periostracum - outer

• Prismatic - middle

• Nacreous - inner

Hemocoel

the primary body cavity of most invertebrates, containing circulatory fluid

Podocytes

specialized cells in the kidney that help maintain the glomerular filtration barrier and prevent plasma proteins from entering the urinary tract

Trochophore

planktonic larva of certain invertebrates, including some mollusks and polychaete worms, having a roughly spherical body, a band of cilia, and a spinning motion.

Veliger

the final larval stage of certain mollusks, having two ciliated flaps for swimming and feeding.

Class Aplocophora

• Worm like

• No shell - has scales

• Rudimentary mantle on the posterior region

• Foot reduced or absent

• Close relative of chitons

Class Monoplacophora

• Single, cap-like shell

• Primitive

• Deep sea

• Repeating pairs of organs

  • 3-6 pairs of ctenidia, 3-7 pairs of metanephridia, 2 pairs of gonads, 2 pairs of atria

Ctenidia

respiratory organs, or gills, found in many mollusks, including bivalves, cephalopods, Polyplacophorans, and aquatic gastropods

Class Polyplacophora

• Known as chitons

• Flattened and elongated

• Found on hard substrates, many are intertidal

• 8 dorsal plates that overlap

• Mantle forms a thick girdle that can obscure plates

• Broad ventral foot with pedal waves

• Mantle encircles foot

• 6-80 pairs of ctenidia

• 1 pair of nephridia

• No eyes, tentacles, or sugar glands

Class Gastropods

• Stomach foot

• Largest group of mollusks in all habitats

• Muscular creep foot with pedal waves, monotactic vs. ditactic

• Head with statocysts, eyes, and tentacles

• Complex radula and crystalline style

• Mantle cavity

  • Ctenidia

  • Osphradia

  • Hypobranchial gland

• Asymmetric coiled shell

  • Operculum

  • Columellar muscle

  • Reduction or organs on the right side - dextral

• Herbivorous or predatory

Osphradia

a sensory organ in most aquatic mollusks that tests the quality of water passing to the gills

Operculum

anatomical feature, a stiff structure resembling a lid or a small door that opens and closes, and thus controls contact between the outside world and an internal part of an animal

Columellar muscle

adductor muscles of bivalves shorten to close the shell or relax to allow the shell to spring open, enabling the mollusk to extend its foot

Dextral

of or on the right side or the right hand

Gastropod torsion

• Rotation of the body 90 to 180 degrees during development

• Mantle cavity moves towards the anterior and the posterior is now located above the head

• Gut and nervous system is twisted

• Detorsion

Detorsion

the process of correcting an abnormal twist or torsion in the body

To avoid fouling in gastropods

• Hole in the shell would weaken the shell

• Mantle folded to make a siphon to increase gas exchange

• Change water flow direction - left to right, anus on the right.

Class Gastropoda

Subgroups:

• Prosobranchia - typical gastropod

• Ophistobranchia - pteropods, nudibranchs

  • incomplete torsion or detorsion

  • Shell reduced or absent

  • Rhinophores

  • Reduction/loss of ctenidia

    • cerrata

• Pulmonata - Lung snails

  • Pneumostome - no ctenidia

Rhinophores

one of a pair of chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy

Cerrata

dorsal and lateral outgrowths on the upper surfaces of the body of these nudibranchs

Pneumostome

breathing pore is a respiratory opening of the external body anatomy of an air-breathing land slug

Gastropod reproduction

• Prosobranchs are diecious

• Opistobranchs and pulmonates are hermaphroditic

  • Reciprocal insemination

  • Internal fertilization

• Hatch as veligers or direct developers

Class Scaphopoda

• Tusk shells

• All marine

• Lack ctenidia, heart/circulatory system, and osphradium

• All live in sediment

• Feeding tentacles are called captacula

Class Bivalvia

• Two valves (shells) connected by a hinge joint

• Includes clams, oysters, mussels, and scallops

• Marine and freshwater

• Lack of cephalization (head)

• Large mantle cavity

• Sedentary (does not move)

• Absence of radula (mouth)

• Lateral compression of the body

• Shells grows from a point called the umbo

• The shell is opened and closed by 1 or 2 adductor muscles

• Foot is anterior and gills are posterior

• Water enters and leaves posteriorally through the siphons.

• Siphons are a modified mantle, Bottom one in incurrent (bring water in), top is excurrent (pushing water out), this helps with gas exchange.

Subclasses of Bivalvia

3 subclasses:

• Protobranchia - Primitive, deep sea

• Lamellibranchia - greatly enlarged gills used for feeding purposes

• Septibranchia - predatory and very rare

Protobranchia Feeding

• Gills are small and used for gas exchange

• Have tentacles around the mouth that secrete mucus and traps food particles. They are sorted by size by labial palps. They have pseudofeces.

Labial palps

a pair of symmetrical flaps in bivalves that are involved in feeding. functional for particle processing.

pseudofeces

specialized method of expulsion that filter-feeding bivalve mollusks (and filter-feeding gastropod mollusks) use in order to get rid of suspended particles such as particles of grit which cannot be used as food, and which have been rejected by the animal.

Lamellibranchia feeding

• Large gills = large surface area and v-shaped. Very efficient at gas exchange.

• Surface are ciliated in the gills that create lateral water currents, food moves through the front food grooves. Food is sorted by the labial palps

Septibranchia feeding

• Gills form a septum and create suction to force food in

Bivalve digestion

• Food is passed from the mouth to the esophagus

• Drawn into stomach by rotation of the crystalline style

  • Protein and digestive enzymes

  • Style sac is ciliated - causes rotation and produces a new crystalline stle

  • Abrades against the gastric shield, and grinds the food and releases digestive enzymes.

Class Cephalopoda

• Name means “head foot”

• All marine

• Most are predatory and have a beak used for crunching prey

• Elongated along dorso-ventro axis

• Fastest, largest, and most intelligent mollusks

• Shell divided by septa, reduction in shell allows for speed, pen used for ink.

• Foot modified to form funnel, arms, and tentacles - with suckers!

• Closed circulatory system - systemic heart, 2 branchial hearts, blood pigments is hemocyanin (blue blood)

• Ink sacs

• Photophores can emit light

• Chromatophores and iridocytes are specialized pigment cells, innervated, they can help with mating and threat displays as well as camo to prevent predation.

• Nervous system well developed with multilobed brain, eyes, and giant axons.

Subclass Nautiloidea

• External shell present

• Lives in an outer chamber of the shell, which other parts of shell are filled with gas and low density liquid, siphuncle

• Located in the Indo-Pacific

• Deep water

Siphuncle

a tube-like tissue that runs through the shell of a cephalopod mollusk to help it maintain neutral buoyancy

Subclass Coleoidea

• Mantle greatly thickened

• Jet propulsion

  • Powered by siphon

  • Squid are constantly swimming, using the fins is a slow process

• Cuttlefish and Octopods are in this groups.

• Octopods hide and crawl

• Reproduction

  • Gonochoristic

  • Internal fertilization - males have specialized arms (hectocotylus)

  • Direct developers

Gonochoristic

having separate sexes, or being dioecious

Hectocotylus

a modified arm used by male octopuses and some other cephalopods to transfer sperm to the female.