Zootaxa, Taxonomy of Serpulidae (Annelida ... - Magnolia Press

Morphology
The tube
Whereas tubes of the closely related sabellid family are constructed of mucus and muddy or sandy sediments
(e.g., Bonar 1972; with the exception of the calcareous tube in the sabellid Glomerula Nielsen, 1931
(including Calcisabella Perkins, 1991), e.g., Vinn et al. 2008), all serpulids build tubes of crystalline calcium
carbonate and a mucopolysaccharide matrix using calcium glands located on the collar (e.g., Neff 1968, 1971,
Nott & Parkes 1975, Vovelle et al. 1991). Tube additions are molded by the collar folds when the worm is in a
feeding position, at the entrance of the tube. The resulting tube shape depends upon the degree of rotation of
the worm within the tube and upon the morphology of the collar folds themselves (Faouzi 1930, Hanson
1948b, Hedley 1956a, b, 1958).
In spirorbins the tubes are coiled either dextrally or sinistrally in a tight flat spiral (the character that gave
the name to the group) and are usually completely attached to the substrate (Helicosiphon Gravier, 1907 is an
exception having the tube with erect distal end). In serpulins the tube shape is quite variable and coiling, when
present, is irregular (maybe with the exception of Nogrobs grimaldii (de Montfort, 1808), but the tube of this
taxon starts and ends with a straight part). In almost all serpulids the tubes are attached to the substrate by at
least the proximal older parts. The only known exceptions are the free-living Ditrupa (Fig. 1A), and maybe
Bathyditrupa, Nogrobs grimaldii, and Serpula crenata (Ehlers, 1908; possibly including S. sinica Wu & Chen,
1979). Very likely larvae of these taxa settle on a pebble or a shell (as observed for D. arietina by Charles et
al. (2003) and for S. crenata by ten Hove & Ben-Eliahu, unpublished), and break free later. Some serpulids
have tubes attached to the substrate throughout their entire length (e.g., Pomatoceros triqueter (Linnaeus,
1758)) while others have free erect distal parts (e.g., Hyalopomatus spp.). The direction of tube growth is
apparently affected by environmental conditions (e.g., Knight-Jones 1981). Serpulids are able to deal with
high rates of sedimentation by changing the shape and direction of tube growth (e.g., Hartmann-Schröder
1967, 1971). Standing erect tubes are observed in waters with low current and high sedimentation rate; the
most extreme example being that of Serpula israelitica Amoureux, 1976, with up to 10 cm long erect tubes
embedded in sand (ten Hove, 16 June 1982, observation on Van Veen grab sample, CANCAP Expedition VI,
Sta. 111, South of Santa Luzia, 55–62 m, sand). Tubes completely attached to the substrate may be indicative
of water movements (currents, tides) with low rates of sedimentation (Kupriyanova & Badyaev 1998). A high
density of tubes may result in the distal parts growing away from the substrate (e.g., Jackson 1977, Table 3).
Tubes of some taxa, such as Floriprotis (Fig. 1E) and several Spirobranchus spp. (Fig. 1D) may be completely
embedded in scleractinian corals (see review by Martín & Britayev 1998, Ben-Tzvi et al. 2006). These are not
boring organisms, but settle on a dead coral part and become overgrown later.
The importance of tubes in serpulid taxonomy is underestimated and adequate descriptions and figures are
mostly absent in Recent descriptions. In some genera (e.g., Hydroides) the tube morphology is too uniform for
general taxonomic use, but locally some Hydroides species can be recognized in the field by their tubes. In
other genera (such as Filogranula, Pyrgopolon, Pseudovermilia) the tubes provide excellent diagnostic
characters.
Tube shapes. In external cross-section, tubes of many serpulids are circular or sub-circular when a
flattened area of attachment is present. However, in some taxa the tube cross-sections may be notably
triangular (Pomatoceros, Pomatostegus, Placostegus, Pseudovermilia, Fig. 2E) or sub-triangular with one
major longitudinal keel (Laminatubus alvini ten Hove & Zibrowius, 1986). Tubes of Galeolaria having two
major longitudinal keels can be considered as trapezoidal. Bathyditrupa hovei Kupriyanova, 1993b and
Nogrobs grimaldii are unusual in having tubes rectangular in cross-section. Within a single tube changes may
occur from trapezoidal to polyangular (Pyrgopolon differens (Augener, 1922): ten Hove 1973 Pl. IIB) or from
triangular respectively trapezoidal/semicircular to circular (e.g., Pseudovermilia occidentalis (McIntosh,
1885); Hydroides brachyacanthus Rioja, 1941a: ten Hove 1975 Pl. VII g, k; Imajima & ten Hove 1984 fig. 5).
TAXONOMY OF SERPULIDS: STATE OF AFFAIRS
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