USABO Biosystematics Exam
Questions & Answers (Grade A+)
Calcarea, Silicea (sponges) -
correct answer ✅Lack true tissues; have choanocytes (collar cells-
flagellated cells that ingest bacteria and tiny food particles)
Cnidaria (hydras, jellies, sea anemones, corals) -
correct answer ✅Unique stinging structures (nematocysts)
housed in special cells (cnidocytes); diploblastic, radially
symmetrical, gastrovascular cavity
Plathyhelminthes -
correct answer ✅Dorsoventrally flattened, unsegmented
acoelomates; gastrovascular cavity or no digestive tract
Rotifera (rotifers) -
correct answer ✅Pseudocoelomates with alimentary canal
(digestive tube with mouth and anus); jaws (trophi) in pharynx;
head with ciliated crown
Lophophorates: Ectoprocta, Brachipoda -
correct answer ✅Coelomates with lophophores (feeding
structures bearing ciliated tentacles)
, USABO Biosystematics Exam
Questions & Answers (Grade A+)
Mollusca (clams, snails, squids) -
correct answer ✅Coielomates with three main body parts
(muscular foot, visceral mass, mantle); coelom reduced; most have
hard shell made of calcium carbonate
Annelida (segmented worms) -
correct answer ✅Coelomates with segmented body wall and
internal organs (except digestive tract, which is unsegmented)
Nematoda (roundworms) -
correct answer ✅Cylindrical, unsegmented pseudocoelomates
with tapered ends; no circulator system; undergo ecdysis
Arthopoda (crustaceans, insects, spiders) -
correct answer ✅Coelomates with segmented body, jointed
appendages, and exoskeleton made of protein and chitin
Echinodermata (sea stars, sea urchins) -
correct answer ✅Coelomates with bilaterally symmetrical larvae
and five-part body organiziation as adults; unique water vascular
system; endoskeleton
Questions & Answers (Grade A+)
Calcarea, Silicea (sponges) -
correct answer ✅Lack true tissues; have choanocytes (collar cells-
flagellated cells that ingest bacteria and tiny food particles)
Cnidaria (hydras, jellies, sea anemones, corals) -
correct answer ✅Unique stinging structures (nematocysts)
housed in special cells (cnidocytes); diploblastic, radially
symmetrical, gastrovascular cavity
Plathyhelminthes -
correct answer ✅Dorsoventrally flattened, unsegmented
acoelomates; gastrovascular cavity or no digestive tract
Rotifera (rotifers) -
correct answer ✅Pseudocoelomates with alimentary canal
(digestive tube with mouth and anus); jaws (trophi) in pharynx;
head with ciliated crown
Lophophorates: Ectoprocta, Brachipoda -
correct answer ✅Coelomates with lophophores (feeding
structures bearing ciliated tentacles)
, USABO Biosystematics Exam
Questions & Answers (Grade A+)
Mollusca (clams, snails, squids) -
correct answer ✅Coielomates with three main body parts
(muscular foot, visceral mass, mantle); coelom reduced; most have
hard shell made of calcium carbonate
Annelida (segmented worms) -
correct answer ✅Coelomates with segmented body wall and
internal organs (except digestive tract, which is unsegmented)
Nematoda (roundworms) -
correct answer ✅Cylindrical, unsegmented pseudocoelomates
with tapered ends; no circulator system; undergo ecdysis
Arthopoda (crustaceans, insects, spiders) -
correct answer ✅Coelomates with segmented body, jointed
appendages, and exoskeleton made of protein and chitin
Echinodermata (sea stars, sea urchins) -
correct answer ✅Coelomates with bilaterally symmetrical larvae
and five-part body organiziation as adults; unique water vascular
system; endoskeleton
