Idanthyrsus australiensis ( Haswell, 1883 )

Hutchings, Pat, Capa, María & Peart, Rachael, 2012, 3306, Zootaxa 3306, pp. 1-60 : 6-13

Idanthyrsus australiensis ( Haswell, 1883)

Figures 1A, B, 2–5, 6A, Table 1

Sabellaria (Hermella) australiensis Haswell, 1883: 634 , pl. 12; figs 7–11.

Sabellaria australiensis .— McIntosh, 1885: 416.

Sabellaria sexhamata .— Collin, 1902: 742; not Grube, 1878: 219.

Sabellaria (Pallasia) pennata . — Augener, 1914: 79; not Peters, 1854.

Pallasia pennata .— Fauvel, 1917: 262. Augener, 1922: 33; 1926: 253; not Peters, 1854: 613.

Idanthyrsus pennatus . — Dakin, Bennett and Pope, 1953: 153; not Peters, 1854: 613.

Idanthyrsus glaessneri . — Kirtley, 1994: 97, fig. 6.7.

Material examined. TYPE?: Sabellaria (Hermella) australiensis Haswell, 1883 , BMNH 1882.2.22.71*, 47 mm in length excluding cauda, 6 mm in width (anteriorly), 47 chaetigers (in 2 parts, anterior fragment with 30 chaetigers and posterior with 17 chaetigers). Queensland: Thursday Island , 10°35'S 142°13'E, 7.8–12.3 m, collected by HMS Alert .

Additional material examined. Queensland: Cape Yorke Peninsula, south of Fly Point , Putta Putta Beach, 10°45'S 142°36'E, 11.vii.1976, 1, AM W26926 , on semi-exposed boulder bank; Thursday Island , 10°35'S 142°13'E, 4, AM W7087 *, 1, AM W26683 (mounted for SEM) , 1, AM W26684 (mounted for SEM) , AM W26851 ; Gladstone, Calliope River , 23°55'S 151°10'E, 1, AM W199314 *; Gladstone Harbour, 23°51'S 151°16'E, 06.xi.1975, 1, QM G10564 ; Gladstone, Calliope River , 23°55'S 151°10'E, 5; Gladstone Harbour, 23°51'S 151°16'E, 06.xi.1975, 3, QM G10565 *; Mary River , 26°23' S 152°45' E, 31.xii.1971, low tide, 1, AM W26928 ; Hervey Bay, Point Vernon , 25°15'S 152°49'E, iv.1972, 1, AM W201700 *; Maroochydore, Alexandra Headland, 26°39'S 153°06'E, 01.iv.1972, 1, AM W26929 ; Caloundra , 26°48'S 153°08'E, viii.1945, 4, QM G4043 , from south beach rocks; 2, QM G4044 ; 1938, 1, QM G212812 ; Moreton Bay, Peel Island, Horseshoe Bay , 27°30'S 153°21'E, 18.xii.1977, 1, QM G212813 *, from under rocks submerged at low tide. New South Wales: Lennox Heads, 28°48'S 153°36'E, 27.iii.1972, 1, AM W26971 ; south of Clarence River mouth, Minnie Water, 29°47'S 153°18'E, 2–3.xi.1963, 3, AM W26895 ; 25.ii.1971, 1, AM W26901 , from shore reef, in crevices, covered in coralline algae, 1, AM W26900 , from shore reef, underneath boulders in rockpools; Wilson Headland, 29°50'S 153°17'E, 12.v.1984, 6, AM W26857 ; off Coffs Harbour, Arrawarra Head , 30°04'S 153°12'E, 14.x.1974, 11, AM W9196 *, cemented together forming small colony; Coffs Harbour, SW face of South Solitary Island , 30°12'S 153°16'E, 19.v.1972, 7.6–10.7 m, 5, AM W26917 ; 17.v.1973, 15.2 m, 3, AM W26916 , from small boulders covered in ascidians; Coffs Harbour, west side of Solitary Island , 30°12'S 153°16'E, 18.v.1972, 1, AM W26923 ; Toowoon Bay, near Tuggerah Lake , 33°22'S 151°30'E, 13.iv.1986, 0.6 m, 3, AM W26858 , from rocks loosely piled, but cemented together, covered in Homosira banksii; off Avalon, 33° 38'S, 151° 20'E, 31.i.1973, 36.6 m, 1, AM W26849 , from reef flat; Long Reef , 33°45'S 151°19'E, 16.xi.1970, 3, AM W4524 * (mounted for SEM) , from on underside of rocks, in sandy, firm tubes; Long Reef, north side of reef, 33°45'S 151°19'E, 23.ii.1971, 1, AM W26902 ; v.1967, 2, MV F78871 *; Port Jackson , 33°50'S 151°16'E, 10.i.1983, intertidal, 1, AM W198478 *; North Head , 33°50'S 151°18'E, 26.v.1972, 28.9 m, 1, AM W6963 *; 13.xii.1972, 28.9 m, 1, AM W26925 ; Maroubra , 33°57'06"S 151°17'37"E, 01.xii.1954, 1, AM W1575 *; Kurnell, Potter Point, 34°03'S 151°13'E, 27.ix.1989, low tide, 4, AM W26863 , from on and under rocks; Port Hacking , near Jibbon Head, 34°05'S 151°10'E, 23 m, 1, AM W16351 *, from reef; north of Wollongong , Bellambi Reef, 34°26'S 150°53'E, 14.xi.1971, 1, AM W26968 , from rock pool, in holdfast of seaweed; Shellharbour, 34°35'S 150°52'E, between tide marks, 5, AM W26903 ; Shellharbour, near bluestone quarry, 34°35'S 150°52'E, 05.ix.1971, 7.6–9.1 m, 3, AM W26974 ; Gerroa, Blackhead , 34°46'S 150°49'E, 25.ix.1982, mid tide, 1, AM W198479 *; north of Broulee , 35°51'S 150°11'E, i.1971, 1, MV F78866 *; near Jervis Bay, Wreck Bay , Cemetry Point, 35°11'S 150°38'E, 27.ii.1976, intertidal, 1, AM W26927 , on coralline algae; Twofold Bay, Murrumbulga Point , 37°05'S 149°54'E, 09.x.1984, intertidal, 1, AM W199879 *, from gravel and algal washings on rock platform; 27.iii.1985, intertidal, 1, AM W199889 *, cryptic fauna and rock platform; 25.vi.1985, subtidal, 2, AM W199880 *, crevice fauna and amongst Diopatra tubes on rock platform; Twofold Bay , Red Point, 37°05'S 149°54'E, 20.v.1995, 1, AM W26907 ; Munganno Point , 37°05'S 149°54'E, 10.x. 1984, 6 m, 10, AM W199892 * from erect bryozoan colony on wharf pile. Victoria: South tip of Mallacoota, Bastion Point, 37°34'S 149°46'E, 1, AM W26525 (mounted for SEM) ; Western Port , Merricks, 38°24'S 145°07'E, 1969, 1, MV F78856 *; Bass Strait, 5 km south of Point Reginald , 38°48'S 143°17'E, xi. 1981, 47 m, 1, MV F78883 *; Western Port , Somers, 38°24'S 145°10'E, 2, MV F78853 *; Flinders Ocean Beach, 38°29'S 145°02'E, 17.xii.1969, 1, MV F78872 *; Venus Bay, west of Eagles Nest , 38°40'S 145°41'E, 01.ii.1966, 1, MV F78868 *; Western Port , near Shoreham, Honeysuckle Point, 38°26'S 145°04'E, 14.xi.1970, 1, MV F78864 *; Flinders, south reef, 38°29'S 145°02'E, 13.xi.1965, 1, MV F78863 *; Airey's Inlet, 38°28'S 144°06'E, 31.i.1967, 1, MV F78869 . South Australia: Sellicks Beach , 35°20'S 138°27'E, 16.iii.1979, 3, AM W198439 *, York Peninsula, Gleeson's Landing , 34°35'S 137°43'E, 27.xi.1985, intertidal, 1, SAM E3093 , from under rocks; 3, SAM E3094 , from under rocks; Aldinga Bay , 35°21'S 138°25'E, 12.x.1977, low tide, 1, AM W14055 *, under rocks. Western Australia: King George Sound, Mistaken Island , 35°04'S 117°56'E, 1.i.1988, 1, AM W26894 , crevice fauna; Cape Naturaliste, Bunker Bay , 33°32'S 115°02'E, 30.i.1972, low tide, 6, WAM V156 , from amongst metamorphic rocks; Bunker Bay , 33°31' 5.48"S 115° 03 25.56'E, 30.i.72, low tide, many, WAM V284 ; 2 km off North Point *, 32°01'S 115°30'E, 11.i. 1991, 30 m, 1, AM W26908 , from reef and coral bommie surrounded by algal beds; Rottnest Island, Strickland Bay , 32°00'S 115°30'E, 20.i.1991, 1, AM W26904 , from reef edge, rock and algae; Sandy Cape, Point Peron, 32°01'S 115°30'E, 1946, 2, AM W26856, 1 , AM W26855 ; 2 km south of Cape Peron, reef west of Groyne , 32°01'S 115°30'E, 26.xii.1983, 3, AM W26862 , from sponges and gorgonaceans from cove on reef; Point Clone, 32°01'S 115°30'E, 29.xi.1945, 1, AM W26854 ; Warnborough Sound, 32°20'S 115°43'E, 21.iii. 1993, 5 m, 1, AM W26909 , from Posidonia sp. beds; Fremantle, South Mole , 32°03'S 115°44'E, 1, AM W26861 ; Cockburn Sound , 32°01'S 115°45'E, 15.ii.1966, 1, WAM V3814 ; Cottesloe Reef, near Groyne , 31°59'S 115°45'E, 29.iii.1973, 2, WAM V311 , from under stones and in dead shells; Cottesloe Beach, 31°59'S 115°45'E, 08.i.1988, intertidal, 2, AM W26864 ; 29.iii.1973, 2, WAM 72–74 , from under stones and in dead shells; Kendrew Island , Dampier Archipelago, 20°29'S 116°32'E, 03.iv. 1987, 10 m, 1, AM W26911 , crevice fauna; Finucane Island , 20°18'S 118°33'E, 20.vi. 1970, AM W26914 ; Roly Rocks, 20°33'S 116°32'E, 03.iv. 1987, 10 m, 1, AM W26910 ; Port Hedland, Finucane Island , 20°18'S 118°33'E, 21.vi.1970, 1, AM W26912 ; Broome, Gantheame Point, 17°59'S 122°11'E, 04.vii.1970, ELWM spring, 2, AM W26859 ; 15.iii.1987, 12– 18 m, 2, NTM W4916 *, from rocky reef; 15.iii.1987, LWS, 1, NTM W4548 *, from rock slabs in silt; Broome, Cable Beach , 17°57'S 122°12'E, 29.ix.1984, LWS, 1, NTM W2280 *, from under stones; 02.xii. 1981, 3 m, 2, MV F78852 ; Riddell Point, Broome , 17°56.30'S 122°12.33'E, 19.viii.1982, 1 WAM 1890 . Northern Territory: Port Essington, Sandy Island , 11°06'S 132°18'E, 02.v. 1982, 14 m, 1, NTM W1122 *, from muddy bottom; 1, NTM W1124 *, from muddy bottom; Port Essington, Burford , 11°29'S 131°57'E, 13.x.1981, 1, NTM W1120 *, from reef flat; Cobourg Peninsula, Burford Island , 11°29'S 131°57'E, 13.x.1981, 1, NTM W25 *; Charles Point, Beagle Gulf, 12˚18.96'S 130˚40.74'E, 23 m, 13.x.1993, NTM W23480 .

Other species examined for comparison. HOLOTYPE of Idanthyrsus glaessneri Kirtley, 1994 , LACM AHF N6277 , sand flat at low tide, Lakes Entrance , Victoria, 37.8°S 147.9° E, coll. B. Dew, 1.3 cm in length, 3.42 mm in width (maximum width of thorax without chaetae).

Description. Type flesh coloured, with dark brown blotches on sides of operculum and anterior end and darkly pigmented cauda. Body compact and robust ( Fig. 1A). Operculum with completely separate lobes, longer than wide ( Figs 1A, 3B), with distal end sloped posteriorly (oblique to longitudinal axis). Fourteen pairs of paleae in outer row, with cylindrical shaft ( Fig. 3A, C), and flat, straight blade, ornamented with alternate, sharp-tipped, similar sized and slightly curved denticles on margins. Inner row with nine pairs of cylindrical and smooth paleae, tapering evenly to acute tip ( Figs 1A, B, 3A, D). Opercular papillae, 14 pairs, peripheral to outer row of paleae on each lobe ( Fig. 3A). Three pairs of nuchal spines with bent tips (hooks) on each side, concave margins smooth, limbation absent ( Figs 1B, 3A). Tentacular filaments, arranged in nine rows ( Fig. 3B). Median ridge and median organ present, extending to dorsal edge of junction of opercular lobes, raised and pigmented (illustrated in non type material, Fig. 2B, C). Numerous eyespots present on both sides of median ridge. Palps about half length of operculum. Segment 1 (chaetiger 1), with neuropodial lobe on either side of U-shaped buccal organ (illustrated in non type material Fig. 2B); capillary neurochaetae present, flattened and with finely denticulated margins ( Fig. 3E). Segment 2 (chaetiger 2) with three pairs of triangular lateral lobes, connecting dorsal branchiae to neuropodia; with similar neurochaetae as those on chaetiger 1. Neuropodia of chaetiger 1 and 2 not vertically aligned, those of chaetiger 2 situated more laterally ( Fig. 1B). Fourty six pairs of dorsal branchiae present from chaetiger 2, continuing along entire length of body but diminishing in size in posterior segments, some represented only by scars ( Fig. 1A). Branchiae conical, with transverse rows of cilia and blunt tips ( Fig. 1A, B). Segments 3–5 (parathoracic) with two types of chaetae arranged transversely, eight, straight, flattened, lanceolate, some with frayed twisted tips, majority represented only by stumps and eight fine, smooth capillaries, inserted between lanceolate chaetae ( Fig. 3F). Segments 3–5 with lancelolate neurochaetae arranged in two tiers of different lengths (longer about twice the length of shorter, as illustrated in non type material Fig. 4I). Notopodial parathoracic chaetae larger and more robust than neuropodial. Abdominal region with 42 chaetigers. Notopodia as transverse tori with uncini, decreasing in number posteriorly. Each uncinus with two vertical rows of teeth, each with about eight teeth ( Fig. 3I). Neuropodia with capillaries becoming longer posteriorly, with thin and flattened blades ornamented with thecal laminar extensions distally forming oblique rows and splayed tips ( Fig. 3G, H). Cauda smooth, about a quarter of abdominal length ( Fig. 1A).

Variation. As the type material and material from the type locality is in relatively poor condition we provide here some supplementary information based on the material from Arrawarra, northern NSW ( Fig. 2A–H). The median ridge and median organ ( Fig. 2C) have a line of eye spots on both sides. The lobes of chaetiger 1 have fine capillary neurochaetae laterally displaced in relationship to those of chaetiger 2 ( Fig. 2E). Chaetiger 2 with three pairs of triangular lateral lobes which connect the branchiae to the neuropodia ( Fig. 2D). The triangular shaped branchiae ( Fig. 2F) continue all along the abdomen. Parathoracic neuropodia were examined under SEM on material from Long Reef, NSW showing two tiers of lanceolate neurochaetae present ( Fig. 4I).

A large number of specimens were examined from several localities, including sexually mature individuals, that vary in length (4–60 mm), width (1–6 mm), number of chaetigers (25–52), number of outer opercular paleae (8–28 pairs), inner opercular paleae (6–17 pairs), opercular papillae (5–16 pairs), nuchal hooks (2–3 pairs), number of rows of tentacular filaments (8–11), number of branchiae (14–46 pairs), number of teeth on abdominal uncini (8–10) and number of abdominal chaetigers (15–49). These variations can be mainly attributed to size of the specimens, with larger animals tending to have more paleae, papillae, uncinial teeth and abdominal chaetigers. As minor differences in structure of paleae and nuchal hooks have been used previously to differentiate species, we illustrate these structures from material collected from Long Reef , Sydney , NSW ( Fig. 4A–M) and from Mallacoota , Victoria ( Fig. 5A–G) the type locality of Idanthyrsus glaessneri Kirtley, 1994 , in addition to material from type locality ( Fig. 3A–I). The outer paleae of specimens examined from each of these three localities vary slightly in terms of length of the denticles on margins, and we suggest that this represents a gradual gradation rather than separate species and represent a difficult character to measure ( Figs 3C, 4C, 5C). Lanceolate parathoracic notochaetae appear to be contractile within parapodia (compare Fig. 4H and Fig. 5E), and we suggest that these parapodia are highly mobile. Neurochaetae of the first two segments are missing from one side on holotype, but on non type material from type locality (eg. AM W26683, AM W26684) they are present on both sides. Abdominal neurochaetae are similar in these three distant localities ( Figs 3G, H, 4J, K, 5F). Divergence of the opercular lobes varies and we suggest this may be a function of size and fixation .

Remarks. The diagnostic characters of I. australiensis are the combination of the absence of a limbation on the nuchal spines, the presence of three lateral lobes on segment 2, and the presence of branchiae on posterior segments. Kirtley (1994) primarily used the shape and thecal development of the outer and inner paleae to distinguish between species, but in most cases intraspecific variation was not considered. We have tried to group this variation observed in some groups regarding the arrangement, shape, relative length and relative numbers of denticles on both sides of outer paleae (Table 1). The structure of the notopodial chaetae of the parathoracic segments also differs between I. australiensis ( Figs 3F, 4H) and I. nesos n. sp. (see this paper), in the former the capillaries imbetween the lanceolate chaetae are thin whereas in the new species the capillaries have a wider distal end, resembling lanceolate chaetae ( Fig. 8F, G). However, for virtually all described species these parathoracic notochaetae are poorly if at all described and comparison cannot be made at this stage, and this is also true for the parathoracic neurochaetae and therefore these characters are not given in Table 1, but we suggest they may provide useful characters to distinguish between species.

Idanthyrsus glaessneri Kirtley, 1994 from Lakes Entrance, Victoria, Australia, was briefly described and only the outer and inner opercular paleae illustrated. In his key to species of Idanthyrsus, Kirtley (1994) separated this species from I. australiensis due to the length of denticles (without sharp tipped denticles in I. glaesneri and sharp in I. australiensis ), ornamentation of the thecae (irregular wavy lines across blade in I. glaesneri ) and overall shape of paleae (strongly bent in I. glaesneri and slightly sigmoidal in I. australiensis ). After examination of the holotype of I. glaesneri , which has been partially dried at some stage, is posteriorly incomplete, and has lost the majority of the outer row of paleae, we would describe the outer opercular paleae as with alternate denticles, slightly curved, with a ratio of 1:1. This together with other diagnostic features (presence of three lateral lobes on segment 2 and the presence of branchiae on posterior segments) appear to fall within the range observed for I. australiensis and we have therefore synonymised the two species.

Examining a large amount of material of I. australiensis from many localities ( Fig. 6A) has allowed us to assess the variability of characters such as the ornamentation of the paleae which Kirtley (1994) had largely relied upon to distinguish species and we have concluded that additional characters such as numbers and distribution of denticles on the outer paleae, number and shape of nuchal spines, numbers of lateral lobes on segment 2 and absence or presence of branchiae in posterior abdominal segments are useful to distinguish between species (see Table 1). In summary, we suggest that I. australiensis exhibits some variation in a suite of characters but no discrete geographical patterns can be detected along the distribution range of this species ( Fig. 6A).

Distribution. Australia wide from NE Queensland to NW Western Australia, except Tasmania ( Fig. 6A).

Habitat. Found from low intertidal to depths of 50 m attached to solid substrate, sometimes occurring as crevice fauna. Specimens typically form small colonies of 6–10 individuals, although specimens from Bunker Bay, in Western Australia, were found in larger colonies, consisting of several hundreds of specimens.