Geophilomorph centipedes and the littoral habitat - Books and ...

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20 A.D. Barber / Terrestrial Arthropod Reviews 4 (2011) 17–39 Figure 1. Strigamia maritima (Leach, 1817 ) male in shingle Seil Island, Scotland. other gastropods ( Littorina saxatalis ) and lumbricid worms were all observed at various times to be fed on by Strigamia maritima . Th e same author also described how Strigamia maritima attacked small Orchestia (or Drosophila if off ered) by tearing the prey to pieces. When attacking larger Orchestia , 1cm or more in length (which it only did if they were damaged or dying) it made a transverse slit and pushed its head and anterior segments inside and the poison claws were seen to be constantly in motion macerating tissue whilst the centipede was involved in what seemed to be external digestion and suctorial feeding. Group feeding, as observed in this species could be advantageous in dealing with prey that would otherwise be invulnerable to them. Alternatively, small specimens could enter barnacles otherwise inaccessible to larger animals and bring about their opening. Lewis suggests that it is possible that pheromones might be involved in this group behaviour. Members of other orders of centipedes such as the scutigeromorphs and lithobiomorphs with their relatively long legs and rapid movement would be able to move from the supralittoral zone into the upper intertidal area at low tide and back again before the tide came in and submerged them or shelter, if necessary, in air fi lled crevices as the scorpion Serradigitus littoralis (Williams, 1980) of Baja California is thought to do (Due and Polis, 1985 ). Maybe some could even adopt a lifestyle similar to that described in the wolf spider Pardosa lapidicina Emerson, 1885 which moves back and forth with the tides (Morse, 1997 ). However, such an option would not be available to the relatively slow moving geophilomorphs which certainly could migrate up
A.D. Barber / Terrestrial Arthropod Reviews 4 (2011) 17–39 21 and down the beach on a seasonal basis as described for Strigamia maritima (Lewis, 1961a) but would not be able to do this twice a day as required by following the tidal cycle; in any case, this would be unlikely to be energy effi cient. If therefore, they were able, because of their morphology and physiology, to take up more or less permanent residence in areas directly exposed to seawater then this would be advantageous in exploiting the littoral resource. Adaptation of geophilomorphs to the littoral habitat A survey of the locations from which seashore geophilomorphs have been recorded includes rock crevices, shingle, under rocks or stones on shingle, sand or mud, under stones etc. on salt marshes, under seaweed or other plant material (e.g Posidonia , Zostera ) or other material and “strand line debris”. Stranded material off ers a rather open habitat and so it is not surprising that it is colonised by a diversity of arthropods including centipedes whilst crevice dwelling off ers great opportunities for the more or less burrowing geophilomorphs with their worm-like bodies and their modes of locomotion. Animals living here need to be able to tolerate (or avoid by migration or survival in air spaces) the eff ect of inundation with its consequential respiratory and osmoregulatory implications. Animals will be immersed in seawater twice daily for a shorter or longer time depending on their location on the shore although not normally facing continuous 24 hour immersion. Th ey will also be in contact with saline substrates (algae, sand, stones, etc.) and will be taking in salt ions in their food. In estuarine conditions there will also be an issue of varying salinity, generally below that of full sea-water. Unfortunately most of the work on the physiology and adaptations of littoral geophilomorphs is rather old and further studies are clearly desirable. Body design Manton ( 1965 ) identifi ed a range of features that adapted geophilomorphs to their burrowing and crevice dwelling life and, although she generalised from studies on a small number of species, her observations do seem to have some relevance. However, it must be borne in mind that there is considerable variation as between diff erent species, genera and families. For instance, the head is more or less oblong rather than tapered in some species (e.g. some Geophilu s spp., Pachymerium ferrugineum ) nor do all show a clear ‘transition’ and members of the Mecistocephalidae are unlike other geophilomorphs in a number of ways. When walking, geophilomorphs proceed relatively slowly although with little lateral undulation, feeling their way forward with their antennae (all are eyeless) and with the capacity for backward movement if required. Th is allows them to explore cre - vices in search of prey or shelter and to retract as necessary and when sheltering their fl exible multi-segmented bodies allow them to coil up and occupy a limited volume ( Figure 2 ).
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Geophilomorph centipedes and the littoral habitat - Books and ...

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