Galathowenia arafurensis, Capa & Parapar & Hutchings, 2012

Capa, Maria, Parapar, Julio & Hutchings, Pat, 2012, Phylogeny of Oweniidae (Polychaeta) based on morphological data and taxonomic revision of Australian fauna, Zoological Journal of the Linnean Society 166 (2), pp. 236-278 : 248-252

GALATHOWENIA ARAFURENSIS SP. NOV.

FIGURES 5 , 6 , TABLES 1, 3

Holotype: Northern Territory, Arafura Sea , NTM W21072 , 9°23′6″S, 134°10.37″E, 88 m.

Paratypes: Northern Territory, Arafura Sea , NTM W21073, 9 °50′118″S, 134°17′762″E, 83 m (one spec.) ; AM W34017, 9°47′59″S, 135°22′00″E, in foraminifera and dead mollusc shells bottom, 92 m, 1.v.2005 (one spec. on a SEM pin) ; AM W34019, 9°22′52″S, 133°39′53″E, bioturbated soft bottom with detritus, 112 m, 13.v.2005 (one spec.) ; AM W34020, 9°01′50″S, 133°15′01″E, bioturbated soft bottom with detritus, 233 m, 20.v.2005 (one spec.) .

Description of holotype: Body cylindrical, 28 mm long, 0.6 mm wide, with 31 segments. Head elongated, truncated anteriorly ( Figs 5A–D , 6A–D ), with terminal mouth extending midventrally as a short slit ( Figs 5D , 6B ) and a pair of ventrolateral brownish eyespots ( Fig. 5C, D ). Ventral pharyngeal organ observed ( Fig. 6E ). A groove present between first and second segments except for a short dorsal portion ( Figs 5C, D , 6B–D ). Anterior three segments uniramous, each with notochaetae only and second slightly longer than first and third (RLUS = 1:1.5:1). Oesophageal commissures evident as a white ventral longitudinal band with Y shape in anterior segments ( Fig. 5D ). Anterior biramous segments five to six times longer than wide. Second biramous chaetiger (segment 5) about 1.5 times longer than first biramous (segment 4); segment 8 the longest, being about four times longer than segment 4. Capillary notochaetae of each fascicle decreasing in length ventrally ( Fig. 6F ), with proximal third smooth and distal end ornamented with scales. Acicular chaetae absent. Neurochaetae present from chaetiger 4, arranged on long and broad ventral tori ( Fig. 6G ) with uncini arranged in 12–16 irregular transverse rows; each uncinus provided with two curved teeth nearly equal in size, arranged in a slight oblique row ( Fig. 6H ). Pygidium with seven short digitiform lobes ( Fig. 5E–G ) surrounding two papillae, located at both sides of the anus opening in the middle of the pygidium ( Fig. 5F, G ). Tube made out of shell fragments and sponge spicules overlapping like roof tiles ( Fig. 5H ). Colour in alcohol brownish or pale yellow, anterior body region with brown-red pigmented areas ( Fig. 5A–D ).

Variation: Only the holotype and one paratype (NTM W21073) are complete. Remaining specimens of similar width (0.6–0.8 mm) and pigmentation pattern. Some slight variation was observed on the relative length of the uniramous segments ( Figs 5B vs. 6B). The pygidium of the paratype is also provided with seven digitiform lobes but this number could vary within the species as it does in other Galathowenia species (see below and Table 3). Incomplete specimens show filamentous prolongations of the tegument associated with the broken posterior ends ( Fig. 5I ). We interpreted them as ‘regeneration processes’ and they have also been found in other oweniids (see also for Myriowenia sp. below).

Ecological notes: The specimens were found only in the Arafura Sea ( Fig. 14 ), in soft bottoms composed of foraminifera, dead molluscs, and detritus at depths between 92– 233 m.

Etymology: This species is named after the Arafura Sea where the type specimens were collected.

*Even though no type material was studied, it is probable that this species was described from incomplete specimens lacking the head and first segment (see also note† for evidence in other species) and therefore the longest segment is not the third but the fourth (second biramous).

†Although in the original description it was reported that the third segment is the longest, it has been demonstrated that specimens described were incomplete ( Parapar, 2001: 408) and that it corresponds to segment 4.

‡According to Parapar (2001).

§The author mentions a darker anterior region but does not indicate any particular pigment pattern.

RLUS, relative length of uniramous segments.

Remarks: Galathowenia arafurensis sp. nov. shares with some other species of Galathowenia the presence of a pygidium provided with multiple lobes. These species are Galathowenia pygidialis (Hartman, 1960) from the Eastern Tropical Pacific, Galathowenia scotiae ( Hartman, 1978) from Antarctica, Galathowenia fragilis Nilsen & Holthe, 1985 with boreal distribution, and Galathowenia joinvillensis (Hartmann- Schröder & Rosenfeldt, 1989), also from Antarctica. Galathowenia arafurensis sp. nov. differs from G. pygidialis in the arrangement of uncinal teeth, as G. pygidialis is the only species of the genus that has a side by side arrangement whereas in the rest of the species, including the one described herein, they are oblique. Galathowenia joinvillensis differs from the new species and others in the genus in the presence of only two uniramous segments instead of three. In addition, G. arafurensis sp. nov. is distinguished from this species and G. fragilis and G. scotiae by the presence of eyes, a pigmented anterior end and the presence of an unusual elongated segment 8, measuring around 20 times the length of the uniramous ones, three features absent in the three previously described species. The differences between G. arafurensis sp. nov. and other Australian species of Galathowenia described in the present study include the body size (more robust and broader in G. arafurensis ), shape of the pygidium, the relative length of the anterior segments (RLUS), and pigment pattern of the anterior end. A species described from Indonesia, Myriochele eurystoma Caullery, 1944 , that clearly belongs to the genus Galathowenia because of the shape of the prostomium, presence of ventral slit, and a groove between the head and the first segment and also between the first and the second one ( Caullery, 1944: fig. 42A–D; Gibbs, 1971: fig. 15A), seems to share some features with G. arafurensis sp. nov. Nevertheless, the animals described were incomplete, lacking the pygidium, and the description is too poor for a complete comparison with the Australian material. This material was unavailable for study but a future comparison between the two species would be of interest.

Figures

Figure 5. Galathowenia arafurensis sp. nov. AM W34017. A, anterior end, dorsal view. B, detail of head and anterior end, dorsal view. C, anterior end, lateral view. D, anterior end, ventral view. E, posterior end, ventral view. F, posterior end, showing anus and multilobed pygidium. G, posterior end, dorsal view. H, tube. I, posterior end of a fragment in regeneration, side view. Abbreviations: b1-b3, biramous segment 1 to 3; gh-1, groove between head and segment 1; g1-2, groove between segment 1 and 2; oec, oesophageal commissures; u1-u3, uniramous segments 1 to 3; arrows: regeneration appendices. Scale bars: A–D, H, I = 200 Mm; E–G = 100 Mm.

Figure 6. A–H, Galathowenia arafurensis sp. nov. A, anterior segments, lateral view. B, anterior end, ventral view. C, anterior end, lateral view. D, anterior end, dorsal view. E, mouth. F, anterior capillary chaetae. G, neuropodial uncini field, segment 5. H, uncini, same segment, oblique view. I–P, Galathowenia sp. I, anterior segments, dorsal view. J, anterior end, ventral view. K, anterior end, dorsal view. L, detail of groove between segment 1 and 2, ventral view. M, detail of lateral flap, segment 5. N, detail of lateral flap, segment 6. O, neuropodial uncinal field, segment 6. P, uncini, segment 6, oblique view. Abbreviations: b1-b3, biramous segment 1 to 3; gh-1, groove between head and segment 1; g1-2, groove between segment 1 and 2; u1-u3, uniramous segments 1 to 3; vph, ventral pharyngeal organ. Registration numbers: A–H, AM W34017: I–P, AM W37065. Scale bars: A = 200 Mm, B–E = 100 Mm; F, G, N = 10 Mm; H = 2 Mm; I, K = 100 Mm, J, L, M = 20 Mm; O = 2 Mm; P = 1 Mm.

Figure 14. Distribution of Australian oweniids except for members of genus Owenia.