Spirobranchus

Kupriyanova, Elena K., Sun, Yanan, Ten Hove, Harry A., Wong, Eunice & Rouse, Greg W., 2015, Serpulidae (Annelida) of Lizard Island, Great Barrier Reef, Australia, Zootaxa 4019 (1), pp. 275-353 : 325-326

Genus Spirobranchus de Blainville, 1818

Type-species. Serpula gigantea Pallas, 1766

Diagnosis. (from ten Hove & Kupriyanova 2009). Tube colour white, blue, pink or salmon, inside and/or outside. Tube typically (sub)triangular in cross-section, with median keel, rarely (sub)circular. Granular overlay absent. Operculum with inverse conical to rather shallow ampulla, covered by calcified endplate, with or without group of spines, sometimes branching. Peduncle broad, thickly triangular in cross-section, with distal lateral wings; inserted at base of branchial crown just left of medial line (formed between first and second normal dorsal radiole on left side). Pseudoperculum absent. Operculum rarely lacking. Radioles may be arranged in a clear spiral of up to 8 whorls, but in most small species as well as in Spirobranchus tetraceros arranged in a circle. Up to 50–60 pairs of radioles in larger species. Inter-radiolar membrane present. Branchial eyes may be present; stylodes absent. Mouth palps present. Seven thoracic chaetigerous segments. Collar trilobed (exceptionally pentalobed). Tonguelets present. Thoracic membranes forming ventral apron across anterior abdominal segment. Collar chaetae bayonetlike, with numerous hairlike processes on its basal portion ( Spirobranchus chaetae ), and limbate. Apomatus chaetae absent. All uncini saw-shaped (9–25 teeth), incidentally with 2 teeth above peg; anterior peg blunt, clearly gouged underneath. Ventral ends of thoracic uncinigerous tori widely separated anteriorly, gradually approaching one another towards the end of thorax, thus leaving a triangular depression. Abdominal chaetae true trumpet-shaped, abruptly bent distally, with two rows of denticles separated by a hollow groove and forming long lateral spine. Achaetous anterior abdominal zone absent. Chaetae becoming increasingly longer posteriorly, but posterior capillary chaetae absent. Posterior glandular pad absent.

Remarks. The larger representatives of this genus, with spiralised branchiae, are spectacularly colourful and generally known as Christmas tree worms. They figure in many guides to reef animals, even in a travel guide ( Finlay et al. 1998: 80). However, not all animals reported under this name are indeed Spirobranchus giganteus sensu latissimo as defined in Fiege & ten Hove (1999 fig. 4), there are quite a few mix-ups with Protula bispiralis and vice versa, even with phoronids. Members of the genus have confusing synonymies, the infraspecific variability of its main diagnostic character, the operculum, resulted in many mistaken identifications. Small specimens are even more difficult to identify, the opercula of juveniles of large sized species such as members of the Sp. giganteus -complex may resemble full grown opercula of small sized species (e.g., ten Hove & Ben-Eliahu 2005, fig. 6). Longitudinal rows of foramina, characteristic for species as Sp. cf. polytrema ( Imajima 1977 fig. 8j) may be present in juvenile tubes of larger sized species, but disappear with increasing size (ten Hove, unpubl.).