Acoelomate, Pseudocoelomate, and Coelomate Zoology Review

Vocabulary flashcards covering the characteristics, taxonomy, anatomy, and representative species of Acoelomates, Pseudocoelomates, and Coelomates.

Acoelomate

An animal that completely lacks a coelom, or formal body cavity.

Triploblastic

Having a body derived from three embryonic germ layers: endoderm, mesoderm, and ectoderm.

Endoderm (Acoelomates)

The innermost germ layer that forms the digestive tract.

Mesoderm (Acoelomates)

The middle germ layer that surrounds the organs, which form within this layer.

Ectoderm (Acoelomates)

The outermost germ layer that forms the outer skin.

Organ-system level of organization

A structural level found in flatworms and higher animals where organs work together in functional systems.

Phylum Platyhelminthes

A phylum of dorsoventrally flattened flatworms whose name derives from Greek platys ("flat") and helmins ("worm").

Parenchyma

A form of connective tissue or mesenchyme that entirely fills the spaces between organs in flatworms.

Protonephridia

Excretory and osmoregulatory structures consisting of flame cells found in flatworms.

Flame cells

Specialized excretory cells in flatworms that function in osmoregulation and waste elimination.

Anterior ganglia

A pair of nerve tissue clusters in the head region of flatworms connected to longitudinal nerve cords.

Monoecious

Having both male and female reproductive systems within a single individual.

Class Turbellaria

A class of mostly free-living, bottom-dwelling flatworms whose name derives from Latin Turbella ("little string").

Rhabdites

Rod-like structures located in the ciliated epidermis of Turbellarians.

Dugesia tigrina

A representative species example belonging to Class Turbellaria.

Microstomum sp.

A representative genus example belonging to Class Turbellaria.

Order Polycladida

Marine turbellarians possessing a plicate pharynx, highly branched intestine, radially arranged nerve cords, and completely lacking yolk glands.

Order Tricladida

Large-sized turbellarians featuring a mid-ventral mouth, a plicate pharynx with $3$ distinct branches, and a pair of ovaries with associated yolk glands.

Order Acoela

Small marine turbellarians with a ventral mouth, lacking a muscular pharynx, intestine, flame cells, gonads, and yolk glands.

Class Trematoda

Parasitic flatworms commonly called flukes, featuring an adult leaf-like or cylindrical body covered in a non-ciliated syncytial tegument and oral/ventral suckers.

Schistosoma japonicum

A species of Trematoda commonly known as the Blood fluke.

Paragonimus heterotremus

A species of Trematoda commonly known as the Lung fluke.

Fasciola hepatica

A species of Trematoda commonly known as the Sheep liver fluke.

Clonorchis sinensis

A species of Trematoda commonly known as the Chinese liver fluke in humans.

Class Monogenea

Parasitic flatworms that primarily attach to the gills and external surfaces of fish and feature direct development involving a single host.

Opisthaptor

A highly specialized posterior attachment organ in Monogeneans equipped with hooks, suckers, or clamps.

Class Cestoda

Endoparasitic flatworms known as tapeworms that completely lack a mouth and digestive tract, absorbing nutrients directly across their syncytial body wall.

Scolex

The modified anterior end of a tapeworm containing suckers, hooks, or both, used to anchor to host tissues.

Proglottids

Repeating reproductive segments forming the long chain of a tapeworm body.

Taenia solium

A species of tapeworm commonly known as the Pork tapeworm.

Taenia saginata

A species of tapeworm commonly known as the Beef tapeworm.

Diphyllobothrium latum

A species of tapeworm commonly known as the Fish tapeworm.

Dipylidium caninum

A species of tapeworm commonly known as the Dog tapeworm.

Hymenolepis nana

A species of tapeworm commonly known as the Dwarf tapeworm.

Echinococcus granulosus

A species of tapeworm commonly known as the Unilocular hydatid.

Phylum Nemertea

Ribbon worms or proboscis worms named from Greek Nemertes ("Nereids, unerring one"), possessing an eversible prey-capturing proboscis inside a rhynchocoel.

Rhynchocoel

The cavity in Nemerteans that houses the eversible prey-capturing proboscis.

Class Enopla

Nemerteans (from Greek Enoplus, meaning "armed") possessing an armature of stylets or plates on the proboscis and a common opening for the mouth and proboscis.

Class Anopla

Nemerteans (from Greek Anoplos, meaning "unarmed") characterized by the absence of stylets on the proboscis and separate openings for the mouth and proboscis.

Lineus longissimus

A species of Class Anopla commonly known as the bootlace worm.

Phylum Gnathostomulida

Jaw worms named from Greek Gnathos ("jaw") and stoma ("mouth"), averaging $0.5\,mm$ in length and living in tight interstitial spaces of fine coastal sediments.

Pseudocoel

A space or body cavity between the gut and body wall that lacks a peritoneal lining.

Hydrostatic skeleton (Pseudocoelomates)

The fluid-filled pseudocoel that functions to maintain high internal hydrostatic pressure and provide structural support.

Phylum Rotifera

Microscopic wheel animalcules named from Latin Rota ("wheel") and fera ("to bear") due to their ciliated crown (corona).

Corona

The ciliated crown on the head of rotifers that gives the illusion of rotating wheels when beating.

Mastax

The muscular pharynx containing jaws present in rotifers but absent in gastrotrichs.

Phylum Gastrotricha

Microscopic animals named from Greek Gaster ("stomach") and trichod ("hair") featuring a bristly or scaly body and lacking a corona and mastax.

Meiofauna

Microscopic benthic invertebrates residing in interstitial spaces, of which gastrotrichs form a key component.

Phylum Kinorhyncha

Marine worms named from Greek Kinein ("to move") and rhynchos ("beak"), divided into $13$ segments that bear spines and completely lack cilia.

Phylum Loricifera

A phylum described in $1983$ named from Latin Lorica ("corsalet") and Greek Phora ("bearing"), featuring a spiny head (introvert) and an abdomen surrounded by a lorica.

Introvert (Loricifera)

The spiny head of a loriciferan bearing eight oral stylets surrounding the mouth.

Phylum Priapulida

Cylindrical marine worms named from Greek Prispos (representing the Greek God of Reproduction), consisting of a proboscis, trunk, and $1$ or $2$ caudal appendages.

Phylum Nematomorpha

Horsehair or Gordian worms named from Greek Nematos ("thread") and morpho ("form"), with free-living adults and parasitic juveniles in arthropods.

Phylum Acanthocephala

Spiny-headed endoparasitic worms featuring an invaginable proboscis bearing rows of recurved spines used to attach to host intestines.

Phylum Entoprocta

Tiny stalked and sessile animals (from Greek Entos, "within", and proktos, "anus") whose bodies are called a calyx.

Calyx

The main body structure of tiny stalked and sessile animals belonging to Phylum Entoprocta.

Phylum Nematoda

A phylum of unsegmented, bilaterally symmetrical roundworms enclosed in a thick non-cellular cuticle, consisting of approximately $12{,}000$ species.

Sensory papillae

Sensory receptors concentrated around the anterior (head) and posterior (tail) regions of nematodes.

Phasmids

Specialized caudal sensory receptors in parasitic nematodes.

Copulatory spicules

A pair of structures present in male nematodes used during sperm transfer.

Enterobius vermicularis

The pinworm, seatworm, or threadworm that causes enterobiasis in humans.

Ascaris lumbricoides

The giant intestinal roundworm causing ascariasis, infecting an estimated $807\text{ million}$ to $1.2\text{ billion}$ people globally.

Trichinella spiralis

The trichina worm or porkworm causing trichinellosis through the ingestion of undercooked meat containing encysted larvae.

Trichuris trichiura

The whipworm named for its whip-like appearance with a wider handle-like posterior end, causing trichuriasis in the human large intestine.

Ancylostoma duodenale

A parasitic nematode species known as the Old World hookworm.

Necator americanus

A parasitic nematode species known as the American / New World hookworm.

Wuchereria bancrofti

A parasitic nematode species categorized as a filarial worm.

Class Aphasmidia

A class of nematodes (Enoplea) characterized by the absence of phasmids.

Class Phasmidia

A class of nematodes (Secernentea) characterized by the presence of phasmids.

Phylum Mollusca

The second-largest animal phylum after Arthropoda, named from the Latin word meaning "soft," representing unsegmented coelomates featuring a distinct head.

Metanephridia

Specialized kidneys employed for waste excretion in Phylum Mollusca.

Head-Foot (Mollusca)

The fundamental mollusk body zone containing sensory/motor organs, mouth, and a muscular foot specialized for locomotion.

Visceral Mass

The body region of a mollusk containing well-developed internal organs for digestion, excretion, and reproduction.

Mantle

A specialized tissue formed from dorsal body wall folds that hangs over the visceral mass and secretes the shell in mollusks.

Mantle Cavity

The space enfolded by the mantle that houses gills or lungs and receives discharges from digestive, excretory, and reproductive systems.

Radula

A rasping, protrusible, tongue-like organ unique to mollusks, composed primarily of chitin and used to scrape food.

Class Caudofoveata

Wormlike mollusks (from Latin Cauda, "tail", + fovea, "small pit") lacking a head, shell, and excretory organs, covered with chitinous cuticle and calcareous scales.

Class Solenogasters

Hermaphroditic wormlike mollusks (from Greek solen, "pipe", + gaster, "stomach") covered in scales and spicules, with a foot reduced to a pedal groove and lacking a radula.

Class Monoplacophora

Mollusks (from Greek monos, "one", + plax, "plate") with a single limpet-like shell covering a broad flat foot, possessing $5$ or $6$ pairs of gills and $6$ pairs of nephridia.

Class Polyplacophora

Chitons (from Greek polys, "many", + plax, "plate") featuring an elongate, dorsoventrally flattened body and a shell consisting of eight dorsal plates.

Class Scaphopoda

Tusk or tooth shells (from Greek skaphe, "trough", + podos, "foot") enclosed in a slender, tubular shell open at both ends.

Class Gastropoda

Snails and slugs (from Greek gaster, "stomach", + podos, "foot"), the largest mollusk class, characterized by body torsion and coiling.

Torsion

A $180^\circ$ twisting of the visceral mass during gastropod development that brings the anus near the head.

Class Bivalvia

Clams, oysters, mussels, and scallops (from Latin Bi, "two", + valve, "folding door") enclosed in a two-valved shell connected by a dorsal hinge, lacking a head and radula.

Class Cephalopoda

Squids, octopuses, cuttlefish, and nautiluses (from Greek kephale, "head", + podos, "foot") where the foot is modified into a siphon and tentacles surrounding the head.

Periostracum

The outer organic layer of a mollusk shell.

Prismatic Layer

The middle layer of a mollusk shell composed of calcium carbonate crystals.

Nacreous Layer

The inner smooth, pearly layer of a mollusk shell.

Phylum Annelida

Highly advanced segmented worms named from Latin Annellus ("little rings"), displaying metamerism and a closed circulatory system.

Metamerism

An anatomical arrangement characterized by the organization of the body into a linear series of similar segments both externally and internally.

Setae

Minute, rod-like chitinous bristles present on the body segments of annelids.

Parapodia

Lateral fleshy outgrowths bearing numerous setae in polychaete worms.

Prostomium

A fleshy lobe overhanging the mouth located in somite 1 of an earthworm.

Clitellum

A conspicuous glandular swelling located over somites $32$ to $37$ in earthworms that secretes material to form egg-containing cocoons.

Class Polychaeta

The largest annelid class, mostly marine, featuring a clear head with eyes and tentacles, and lateral parapodia bearing numerous setae.

Class Clitellata

Annelids characterized by the presence of a clitellum used for cocoon formation during reproduction, monoecious reproduction, and complete lack of parapodia.

Subclass Hirudinea

Leeches with a fixed body organization of $34$ segments, anterior and posterior suckers, reduced or absent setae, and medical utility in improving blood circulation.

Phylum Echinodermata

Deuterostome marine animals named from Greek echinos ("hedgehog") and derma ("skin"), exhibiting radial/pentamerous symmetry as adults and a water-vascular system.

Water-Vascular System

A remarkable hydraulic system of canals and tentacle-like tube feet with suction pads used by echinoderms for locomotion, respiration, and food gathering.

Aristotle's Lantern

A complex jaw apparatus present in Class Echinoidea (sea urchins) used for feeding.