The giant (>3 m) parasitic nematode Crassicauda magna infects kogiid whales, although only 3 studies to date have provided detailed descriptions of these worms, all based upon fragmented specimens. These fragments were found within the neck region of kogiids, an unusual anatomic site for this genus of parasites. C. magna is a species-specific parasite among kogiids, infecting only pygmy sperm whales Kogia breviceps, and with a primarily cervico-thoracic distribution. To date, however, the pattern of habitat use within the host and transmission path of this parasite remain unknown. We used detailed dissections (n = 12), histological examination of host tissues (n = 2), and scanning electron microscopy of excised nematodes (n = 7) to enhance our understanding of this host-parasite relationship. Results revealed that a critical habitat for the parasite is an exocrine gland in the whale's ventral cervical region. C. magna male and female tails were found intertwined within the glandular lumen, and eggs were observed within its presumed secretion, illuminating the transmission path out of the host. The cephalic ends of these worms were often meters away (curvilinearly), embedded deeply within epaxial muscle. A single worm's complete, tortuous 312 cm course, from the gland to its termination in the contralateral epaxial muscle, is described for the first time. This study also provides the first scanning electron micrographs of C. magna, which illustrate taxonomically important features of the heads and tails of both male and female worms.
Habitat use pattern of the giant parasitic nematode Crassicauda magna within the pygmy sperm whale Kogia breviceps.