Palp growth, regeneration, and longevity of the obligate hermit crab symbiont Dipolydora commensalis (Annelida: Spionidae)

Abstract

Abstract. The polychaete Dipolydora commensalis is an obligate symbiont of hermit crabs and produces a burrow along the columella of the gastropod shells they inhabit. Adults of D. commensalis have short palps that they use to feed on particles dropped or brought in by the respiratory currents of hosts. To determine whether hermit crabs influence palp length, specimens of D. commensalis were isolated in glass capillary tubes and the growth of palps was measured over a 3‐week period. Palp length was also measured in worms isolated in gastropod shells with or without hermit crabs for 2 weeks. In addition, to determine whether adults of D. commensalis have regeneration capabilities like those of free‐living relatives, worms were cut at the fifth or 15th setiger and then monitored for 35 d. Worms extracted from shells and placed into capillary tubes had initial palp lengths of 1.0±0.4 mm (n=17); after isolation, palps were 40% longer (1.4±0.4 mm, n=17). Worms in gastropod shells with hermit crabs had an average palp length of 0.9±0.4 mm (n=31), whereas worms in shells without hermit crabs had palps that were 33% longer (1.2±0.5 mm, n=40). Adults of D. commensalis are capable of regeneration; 35 d after ablation at setigers 5 or 15, the average number of anterior setigers regenerated was 5 (n=15) and 9±1.3 (n=13), respectively. The average number of posterior setigers regenerated from the 15 setiger anterior fragments was 11±6 (n=10). The findings suggest that the palps (and sometimes anterior ends) of the worms are exposed during feeding and are cut during movement of the hermit crab. In the laboratory worms can live for >4 years, considerably longer than the functional life span of most gastropod shells inhabited by hermit crabs.

Morphology, feeding and behaviour of British Magelona (Annelida: Magelonidae), with discussions on the form and function of abdominal lateral pouches

“…Animals kept in capillary tubes within the aerated tank lasted about 4 days only. This was in marked contrast to the success others have had in maintaining various Spionida for long periods of time (over 4 years) in capillary tubes within petri dishes (Williams, 2002;Dualan and Williams, 2011). This dependence on sediment was recorded by McIntosh (1911), "sand is very necessary for the existence of this form, for though the animals survive a considerable period in captivity in vessels filled with pure sea-water, they thrive much longer amongst fine sand, with a few inches of water over it".…”

Anterior regeneration in the polychaeteMarenzelleria viridis(Annelida: Spionidae)

“… Although regeneration of the anterior end is not known in this species, it readily regenerates feeding appendages (palps), as has been documented in other spionids (e.g., Dualan & Williams ; Hentschel & Harper ). …”

“…The blastema elongates and internal differentiation (neuronal and muscular regeneration) occurs, followed by the appearance of segments and segmental structures (Gibson & Harvey ; Gibson & Paterson ; Lindsay et al. , ; Dualan & Williams ; David & Williams ,b; Weidhase et al. ).…”

Cell proliferation dynamics in regeneration of the operculum head appendage in the annelid Pomatoceros lamarckii

“…Members of the third “superphylum,” the Lophotrochozoa, also sport a great variety of appendages, many of which are capable of regeneration. These include the arms, siphons, and sensory tentacles of molluscs (Lange, ; Chase and Kamil, ; Pekkarinen, ; Bobkova et al, ), and the diverse anterior appendages of annelid worms (Bubel et al, , ; Lindsay et al, ; Dualan and Williams, ). Such appendages play an important ecological role.…”

“…Also, regeneration may place a burden on the animal through, for example, the cost of re‐growing the missing structure, impairment of activities such as feeding and reproduction during regeneration, and increasing predation risk (Maginnis, ). Ecophysiological aspects of appendage regeneration have been studied in a number of lophotrochozoan species (De Vlas, ; Tomiyama and Ito, ; Berke et al, ; Dualan and Williams, ; Hoso, ; Nuñez et al, ). However, the mechanisms underlying lophotrochozoan appendage regeneration have thus far received much less attention.…”