Megaphorura (formerly Protaphorura) arctica is the largest member of the Onychiurinae in our region. There are about 50 specimens in the NHML collected by Steve Sutton in July 1977 from Seal Cave on Skomer Island, and mounted on slides by Brian Pitkin. The longest specimen is a female of 4.0 mm in length; males reach 3.7 mm.
     Distinctive characters include the complete absence of any trace of a furca, the presence of 11 distal tibiotarsal setae and absence of dorsal pseudocelli (PSO) on the first thoracic segment (see Fjellberg 1998 who placed this species in a new genus Megaphorura). The post-antennal organ has about 30 simple vesicles (Fig. 1) and the empodium of the foot is long and filamentous reaching beyond the end of the claw (Fig. 2). The typical PSO formula is 32/023/33354 although there is some variation (Fig. 3 and 4). Two anal spines are present (Fig. 5) with occasional mutations (Fig. 6). The NHML specimens are in excellent condition and most morphological features are very easy to see (e.g. mouthparts shown in Figs. 7, 8 and 9).
     It would be worth searching for this species among the detritus of bird colonies as this is a typical habitat elsewhere in Northern Europe.

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Fig. 1 (above): Post-antennal organ (PAO) of Megaphorura arctica collected from Seal Cave, Skomer Island in July 1977 by Steve Sutton.

Fig. 2 (above): Foot of second leg of Megaphorura arctica collected from Seal Cave, Skomer Island in July 1977 by Steve Sutton.

Fig. 3 (above): Left side of head of Megaphorura arctica collected from Seal Cave, Skomer Island in July 1977 by Steve Sutton. There are four pseudocelli (1 to 4) adjacent to the post-antennal organ (PAO).

Fig. 4 (above): Right side of head of the same specimen of Megaphorura arctica shown in Fig. 3. There are three pseudocelli (1 to 3) adjacent to the post-antennal organ (PAO).

Fig. 5 (above): Anal spines (*) of Megaphorura arctica collected from Seal Cave, Skomer Island in July 1977 by Steve Sutton.

Fig. 6 (above): Anal spines (1,2) of Megaphorura arctica collected from Seal Cave, Skomer Island in July 1977 by Steve Sutton. Spine 2 bears an additional small spine.

Fig. 7 (above left): Mouthparts of Megaphorura arctica collected from Seal Cave, Skomer Island in July 1977 by Steve Sutton. hpx, hypopharynx; md, tips of mandible; mx, tips of maxillae.
Fig. 8 (above centre): Tip of the mandible.
Fig. 9 (above right): Tip of the maxilla.