Orbinia hartmanae Day 1977

Orbinia hartmanae Day, 1977

Figure 18

Orbinia hartmanae Day, 1977: 233–234, fig. 2j–n.

Material examined. New South Wales: 2.5 km east of Little Bay, 33°58’55”S, 151°16’28”E, 16.05.1972, depth 51 m, coll. Australian Museum Shelf Benthic Survey, AM W.6474, Holotype; east of Malabar, 33°58’34”S, 151°16’52” E, 31.07.1989, depth 60 m, sand, coll. Fisheries Research Institute (NSW), AM W.24304, 6 specimens. Queensland: Middle Banks, Moreton Bay, 27°13’S, 153°19’E, March 1974, depth 10–37 m, coll. W. Stephenson, AM W.7357, Paratype, 1 specimen. Western Australia: Penguin Island, 32°18’S, 115°41’E, 25.01.2000, depth 1 m, sand, coll. M. Costello, AM W.27478, 2 specimens.

Type locality. East of Little Bay, New South Wales.

Description. Small worms, thoracic width up to 1.3 mm (0.9 mm in holotype). Thorax swollen in anterior part, flattened in posterior part, abdomen cylindrical (Fig. 18A). Prostomium sharply conical with long, thin tapering tip (Fig. 18B, C). Thoracic chaetigers numbering 15–21 (Fig. 18A). Branchiae from chaetiger 9–10, triangular with tapering tips, becoming asymmetrical in abdomen (Fig. 18B, C, E, G, I). Thoracic postchaetal notopodial lobes developed from first chaetiger, digitate, increasing in size along thorax; in abdomen becoming narrow foliaceous, shorter than branchiae (Fig. 18B, C, E, G, I, J). Thoracic neuropodia postchaetal lobes as ridges with one papillae (mammiform) on most thoracic chaetigers, in last 4–8 chaetiger becoming bilobed, with two podal papillae (Fig. 18A, B, D, E, H). Subpodal papillae present on posterior thoracic and anterior abdominal chaetigers; in total, about 10–11 chaetigers with subpodal papillae, with up to 10 papillae per segment; their number increasing with size of worm (Fig. 18D, E, F, I, J); 1–3 stomach papillae present on two anterior abdominal chaetigers, in larger worms also in last thoracic chaetiger (Fig. 18D, F). Interramal cirrus well developed in anterior abdominal chaetigers, reaching almost same length as notopodia, also present in posterior thoracic chaetigers as prechaetal lobe (Fig. 18D, E, G, I, J). Abdominal neuropodia bilobed with outer lobes longer than inner lobes (Fig. 18J) or lobes subequal (Fig. 18A, D, G, I). Subpodal flange well developed in anterior abdominal chaetigers forming flange papilla (Fig. 18A, D, E, G, I, J). Notopodial chaetae crenulate capillaries; abdominal notopodia also with forked chaetae present. Thoracic neuropodia bearing 4–5 rows of curved serrated and smooth uncini and few capillaries in posterior row (Fig. 18 B–E, H); abdominal neuropodia bearing flail chaetae with thin aristate tips and few capillaries (Fig. 18K). Abdominal neuropodia supported by two thin non-projecting aciculae (Fig. 18I, J). Pygidium unknown.

Distribution. Australia, Western Australia, Queensland, New South Wales.

Habitat. Subtidal, sand.

Remarks. In the original description (Day 1977), the interramal cirri were absent in Orbinia hartmanae. The present study showed that interramal cirri were present, at least on the anterior abdominal segments and last two thoracic segments as prechaetal lobes.

Orbinia hartmanae belongs to group B according to Sun & Li (2018), owing to the branchiae on the middle or posterior thorax and thoracic neuropodial lobes with 1–3 papillae. Other species of this group that also have a similar number of thoracic chaetigers, interramal cirri, and flail chaetae in the abdominal neuropodia include Orbinia riseri Pettibone, 1957 from Massachusetts, Orbinia oligopapillata López P. Cladera & G. San Martín, 2006 from the Eastern Pacific coast of Panama, and Orbinia orensanzi Blake, 2017 from Argentina.

Orbinia riseri was redescribed by Day (1973). This species is similar to O. hartmanae in having 18–19 thoracic chaetigers, branchiae from chaetiger 8–10, and the presence of flail chaetae (not mentioned in the original description). However, it differs from O. hartmanae owing to the higher number of subpodal and stomach papillae (total number ≤ 9 in the original description, ≤ 18 in Day’s redescription), which form a continuous row nearly reaching the midventral line.

Orbinia oligopapillata is similar to O. hartmanae owing to a number of characteristics. The main differences between the two species from the original description was the presence of interramal cirri in the anterior abdominal segments and prechaetal lobes on the posterior thoracic segments in O. oligopapillata. Additionally, a smaller number of stomach papillae in O. oligopapillata was mentioned as a distinguishing character. However, Day (1977) did not notice a difference between the subpodal and stomach papillae, and the number of segments bearing stomach papillae is similar in both species. A reinvestigation of the type material of O. hartmanae revealed the presence of interramal cirri and prechaetal lobes. Therefore, the differences between these two species are not obvious and a careful study of type and non-type material is required to confirm the validity of O. oligopapillata.

Orbinia orensanzi differs from O. hartmanae owing to the later beginning of the branchiae (from chaetiger 13–18) and presence of interramal cirri only in the thoracic segments.

Two other species of Orbinia from the West Pacific are Orbinia vietnamensis Gallardo, 1968 from South Vietnam and Orbinia dicrochaeta Wu, 1962 from China. O. vietnamensis is similar to O. hartmanae in having 16 thoracic chaetigers and branchiae from chaetiger 10. However, it differs owing to the higher number of subpodal and stomach papillae, smaller number of uncini in the thoracic neuropodia, and absence of flailed chaetae in the abdominal neuropodia. O. dicrochaeta has 24–27 thoracic chaetigers, subuluncini in the thoracic neuropodia, and lacks flail chaetae.