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Orbiniidae Family Orbiniidae (orbiniid)
Scolecida (Annelida: Polychaeta)
About Family Orbiniidae polychaetes in New Zealand.  
How to recognise the family: Long, slender, sand-dwelling unselective deposit feeders which are without head appendages. A combination of characters define an orbiniid, but perhaps most characteristic at first glance are the short straps of the dorsally displaced, pointed gill pairs which are present on most segments, except for a diagnostic number of anterior segments. The internal chitinous aciculae found in parapodial lobes are unusual outside of Eunicida and Phyllodocida families. Most orbiniids have sharply conical prostomia but in Naineris and Proscoloplos it is blunt. Anterior orbiniid segments have parapodia which are lateral, characteristic chaetae which include notochaetal capillaries with cusp-like irregularities along the edge (crenulate), and usually serried ranks of thicker neurochaetal angled hooks or spines which may also be ridged or crenulate. There is often a line of post-chaetal papillae in addition to post-chaetal lobes. Anteriorly the body is usually somewhat flattened rather than round, often appearing cigar-shaped from above. More posteriorly the body cross-section becomes uniformly U-shaped, with the neuropodia displaced to the top outer edge and different chaetae present which are longer, more slender, with crenulate capillaries and forked chaetae. The two body zones are usually called thorax and abdomen, and the number of thoracic segments is important taxonomically but this may be hard to determine when the transition is gradual. The pygidium is a crenulated open collar with one or two pairs of short ventral cirri. Adult size: To more than 100 mm long but less than 2 mm in width.
How to recognise the New Zealand genera: Scoloplos species lack numerous papilla and are rather nondescript, Orbinia and Phylo have "stomach" (= ventral) papillae. Phylo species in addition have dark projecting spines like harpoons present in anterior chaetigers.
Quick pick shore species: The common New Zealand shore orbiniids are mostly readily recognised. Scoloplos cylindrifer Ehlers, 1904 (formerly in Haploscoplos) has two-lobed gills from around chaetiger 18. Scoloplos ohlini (Ehlers, 1900) has single-lobed gills from around chaetiger six. Orbinia papillosa (Ehlers, 1907) has numerous papillae behind the chaetae and extending across the ventral surface of some segments. The spined Phylo species differ in thorax length with Phylo novazealandiae Day, 1977 having 15 thoracic chaetigers, while Phylo felix Kinberg, 1866 has 16 or more. An undescribed small species belonging to Proscoloplos, which has neurochaetal hooks, a rounded prostomium and the first segment behind the mouth without chaetae, is an addition to the known New Zealand orbiniids as reviewed in 1977.
Possible misidentifications: None
Distributions, lifestyle, and habitat: Orbiniids occur throughout New Zealand. Most of the species occur from mid-intertidal levels to shallow subtidal on semi-protected shores. Few species occur in deeper water.In intertidal sand diggings orbiniids are noticeable as ragged threads stretched between clods. They are difficult to collect intact because of their sheer length and thinness. Scoloplos species, especially Scoloplos cylindrifer, and also Orbinia papillosa are common in intertidal sands. Phylo and Scoloplos species occur mostly subtidally. A small orange Proscoloplos species occurs in coralline algal turf on rocky shores.
Abundance: Common.
Taxonomic note: The family used to be known as the Ariciidae. Despite the importance of the 'thorax/abdomen' division in orbiniids it is not defined by one character alone. Hartman (Hartman 1957) defines the thorax as more depressed and with 'differing' parapodia, and defines the abdomen as having more dorsal, more slender neuropodia, with (presumably) fewer chaetae ('restricted fascicles'). She does not refer to chaetal types. Thus, unless the criteria are stated, it is difficult to know what basis has been used in a description. Indeed, there is no inherent reason why different characters shouldn't transition at different segments. Thus better to state segmental occurrences of each character separately.
References: (Blake 1996a: p1-26, f1.1-8), (Day 1977: p217-246, f1-3), (Ehlers 1904: p45-46, P6.16-19), (Ehlers 1907: p16-20, f7-14), (Estcourt 1967: p72), (Hartman 1957: p262, P23), (Morton & Miller 1973: p470 as Ariciidae).
(Full citations at Family pages literature cited list.)

Species in the guide: Rock Species: None for this family.
Sand Species: Orbinia papillosa | Scoloplos cylindrifer | Scoloplos ohlini
Shell Species: None for this family.

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Last modified by G. Read, 25/07/2004    (dd/mm/yy)