Eukrohnia hamata (Möbius, 1875)
The dominant arrow worm of Arctic basins
Size
- body up to 4.5 cm
Color & Characteristics
- Body semi-flacid & translucent, eyes without pigmentation & close together
- 1 pair of very elongated fins spanning trunk and tail, with incomplete rays
- Head narrow, tail 19-24% of length
- Each side of head with 8-10 hooks (serrated in juveniles), no anterior and 23-25 posterior teeth
- Collarette becomes developed in maturing animals, as does a marsupium in the tail region
- Semininal vesicles conical, separated from both posterior and tail fins
- Ovaries of medium length, with large eggs
Habitat
- Bipolar? Most records are polar and subpolar, but it appears to be cosmopolitan
- Oceanic: in arctic deeper epipelagic (>50 m) and mesopelagic (200-1000m); in subarctic, mesopelagic and bathypelagic (1000-3000 m); deepr in subtropical waters
Feeding
- An ambush predator, detecting motion with numerous tiny hairs along body
- Pey seized with hooks during a rapid lunge, ratched whole down throat with aid of teeth
- Prey size largely determined by head width
- Diet poorly known, likely composed of copepods, ostracods, and larvaceans in lower numbers
Life cycle
- Protandrous (releasing sperm first, then producing eggs)
- Fertilized eggs released as 2 sacs into a marsupium and carrieduntil hatching, with ~200 eggs per clutch
- ~2.5 mm at hatching, released early to mid-summer
- generation time inferred by size-frequency, 1 generation per year in Arctic, life expectancy unknown
Page Author: Russ Hopcroft
Created: November 15, 2011