Classification and biodiversity — AS & A Level Marine Science (9693) questions by topic
Seahorse and clownfish anatomy, the defining features of echinoderms like crown-of-thorns starfish, and interpreting population decline data for snow crabs sit within this 14-question topic from 2023 to 2025 papers, worth 8 to 17 marks.
State, suggest, explain, identify and describe are the top command words, and identify on a labelled diagram means a precise, ruled line to the correct structure rather than a circled region. Examiners report specific labelling mix-ups, like pectoral and pelvic fins confused, so checking a labelled or written answer against instant marking is a direct way to catch that kind of slip before it repeats.
What examiners look for
- A recurring criticism is mislabelling pelvic fins as pectoral, or the dorsal fin as caudal, on anatomical diagrams.
- Examiners note labelling answers marked down for drawing a circle around the fin that also included other parts of the fish.
- Reports flag confusion over zooxanthellae, with some candidates believing they occupy trophic level 2 and eat phytoplankton, or that they are eaten by the sea anemone.
- A common error was not knowing that zooxanthellae are photosynthetic organisms living within host tissue and providing it with nutrients.
- Strong answers labelled features with ruled straight lines touching the structure, named a Chordate feature such as a notochord, and linked zooxanthellae photosynthesis and nematocyst predation to the correct trophic levels.
May–June 2025, Paper 31
Seahorses belong to the phylum Chordata. They are small bony fish which live in shallow sheltered waters such as seagrass beds and estuaries. They are poor swimmers and rest by…
Answer this question and get it marked →May–June 2025, Paper 32
Snow crabs (Chionoecetes opilio) live in cold waters at depths of up to 1800 m. They feed on detritus and other invertebrates. They are commercially important but their numbers…
Answer this question and get it marked →The European green crab (Carcinus maenas) is one of the most invasive species in the world's oceans. Originally from the north-east Atlantic and Baltic Sea, it has spread across…
Answer this question and get it marked →May–June 2025, Paper 33
Snow crabs (Chionoecetes opilio) live in cold waters at depths of up to 1800 m. They feed on detritus and other invertebrates. They are commercially important but their numbers…
Answer this question and get it marked →The European green crab (Carcinus maenas) is one of the most invasive species in the world's oceans. Originally from the north-east Atlantic and Baltic Sea, it has spread across…
Answer this question and get it marked →May–June 2024, Paper 11
Fig. 2.1 shows an ascidian and Fig. 2.2 shows a reef shark. Both organisms are in the phylum Chordata. State two features both organisms have in common during their early…
Answer this question and get it marked →May–June 2024, Paper 12
Fig. 3.1 shows a blue shark, Prionace glauca. Three fins are labelled A, B and C: A is on the tail, B is on the underside (paired), and C is on the back. On Fig. 3.1, identify the…
Answer this question and get it marked →May–June 2024, Paper 13
Fig. 3.1 shows a blue shark, Prionace glauca. Three fins are labelled A, B and C: A is on the tail, B is on the underside (paired), and C is on the back. On Fig. 3.1, identify the…
Answer this question and get it marked →October–November 2024, Paper 11
Crown-of-thorns starfish (COTS), Acanthaster planci, are echinoderms that feed on coral. State two features typical of echinoderms.
Answer this question and get it marked →October–November 2024, Paper 12
Crown-of-thorns starfish (COTS), Acanthaster planci, are echinoderms that feed on coral. State two features typical of echinoderms.
Answer this question and get it marked →October–November 2024, Paper 13
Crown-of-thorns starfish (COTS), Acanthaster planci, are echinoderms that feed on coral. State two features typical of echinoderms.
Answer this question and get it marked →May–June 2023, Paper 11
Complete Fig. 1.1 by sorting the features of seagrass and macroalgae shown in the box below. Features provided in the box: blade, flowers, gas bladder, holdfast, photosynthetic,…
Answer this question and get it marked →Fig. 4.1 shows a clownfish species living with sea anemones (a photograph of clownfish among the tentacles of an anemone). Label the pectoral fin and caudal fin of one clownfish…
Answer this question and get it marked →Describe the differences between cartilaginous and bony fish.
Answer this question and get it marked →Other AS & A Level Marine Science topics
- Marine organisms and physiology (58)
- Water and physical oceanography (43)
- Mangroves and coastal ecosystems (37)
- Marine ecosystems and energy flow (36)
- Investigative skills (28)
- Fisheries and mariculture (26)
- Aquaculture (21)
- Human impacts and pollution (16)
- Coral reefs (14)
- Earth structure and plate tectonics (12)
- Conservation and management (11)