Scoloplos simplex ( Hutchings 1974 )

Zhadan, Anna, 2020, Review of Orbiniidae (Annelida, Sedentaria) from Australia, Zootaxa 4860 (4), pp. 451-502 : 460-464

Scoloplos simplex ( Hutchings 1974)

Figures 5 , 6

Haploscoloplos simplex Hutchings, 1974:118 , fig. 2a–d.

Scoloplos (Scoloplos) simplex: Day 1977: 228–229 ; Hutchings & Rainer 1979: 761–762.

Scoloplos (Scoloplos) difficilis Day 1977: 229–230 , fig. 2a–e.

Scoloplos simplex: Brown 1979: 762 , fig. 1a–d.

Material examined. New South Wales: entrance to the Wallis Lake, 32°17’S, 152°29’E, December 1970, sandy, fast flowing water, coll. P. Dixon, O’Gower, AM W.5246, Holotype; Towlers Bay , Pittwater, 33°37’ 30”S, 151°17’E, 19.12.1980, intertidal, sand, coll. D. Dexter, AM W.195999, 21 specimens; Careel Bay , Pittwater, 33°37’S, 151°19’E, 08.04.1996, intertidal, Zostera , coll. P.A. Hutchings, AM W.23424, 3 specimens. Tasmania: near George Town , Tamar estuary, 41°06’S, 146°49’E, February 1984, mud and sand, coll. D. Henderson, AM W.198694, 11 specimens.

Comparative material examined. Queensland, Jackson Creek, mouth of Moreton Bay , 27°21’S, 153°06’E, 12.07.1973, sand flats, coll. P.A. Hutchings, C. Wallace, AM W.6038, Holotype of S. difficilis .

Type locality. Wallis Lake , New South Wales .

Description. Holotype complete, with thoracic width 2.3 mm, other specimens 0.5– 3 mm wide. Thoracic chaetiger numbering 16 in holotype, 12–16 in other specimens. Thorax cylindrical, occasionally slightly flattened or swollen anteriorly ( Figs 5A, E, F , 6A, C, F ). Branchiae from chaetiger 9–16, as small papillae; in abdomen bran- chiae rapidly increasing in size, becoming longer, narrow triangular ( Figs 5 B–D, H, 6D, F, J). Thoracic notopodial postchaetal lobes absent or very small on anterior chaetigers, then increasing in size, becoming triangular in shape and-digitiform in posterior thoracic segments ( Fig. 6 B–E, G). Thoracic neuropodial postchaetal lobes absent on anterior chaetigers, then arising as small, papilliform to triangular lobes, slightly increasing in size along thorax, all simple ( Fig. 6 B–E, G). Abdominal notopodial lobes narrow, from foliaceous to digitate, longer than branchiae ( Figs 5C, D, G, H , 6B, I, J ). Abdominal neuropodia bilobed, with smaller outer lobe; in posterior segments with subpodal notch and narrow subpodal flange ( Figs 5 B–D, G, H, 6B, I, J). Thoracic notochaetae all crenulate capillaries; thoracic neurochaetae divided into upper and lower fascicles; 2–3 rows of crenulate capillaries in both fascicles and slender slightly curved finely serrated uncini forming anterior row in upper fascicle ( Fig. 6G, H ). Abdominal chaetae all thin capillaries, forked chaetae not found. Pygidium with two short cirri, anus terminal ( Fig. 5D ).

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

Habitat. Intertidal and upper subtidal, sand, muddy sand, seagrass.

Remarks. Scoloplos simplex was originally described as a part of the genus Haploscoloplos Monro, 1933 ,

although the presence of uncini in the thoracic neuropodia was noted ( Hutchings 1974). Day (1977) transferred this species to the genus Scoloplos , and described a similar species, Scoloplos difficilis Day, 1977 from Queensland. The only difference between these two species was the starting-point of the branchiae segment (9–11 in S. simplex vs 14–15 in S. difficilis ). Hutchings & Rainer (1979) synonymised S. difficilis with S. simplex as the branchiae in the holotype of S. difficilis were found on chaetiger 11. In addition, they noticed the presence of flail chaetae in the abdominal parapodia in larger specimens of both species. The flail chaetae have not been found in the present study because only chaetae of small specimens were investigated. Scoloplos simplex and S. difficilis have overlapping distribution and same habitat, occurring intertidally and subtidally in sheltered estuarine area. A re-investigation of the holotypes of both species showed that in the holotype of S. simplex the branchiae were found on chaetiger 15 ( Fig. 5A, B ), whereas the holotype of S. difficilis was poorly preserved, so the position of the first branchia was difficult to determine, but presumably the branchiae start on chaetiger 10 ( Fig. 5E, F ). Examination of the holotype of S. difficilis reveals that the branchiae occur earlier than in S. simplex , which is the reverse of what Day (1977) states. The present study confirmed the synonymy of these two species as the starting segment of branchiae varies from chaetiger 9 to 16 even within one sample. Therefore, it cannot be used as evidence for species recognition. Moreover, the few first pairs of branchia are so small that they can only be seen in well-preserved species and with the help of staining.

Figures

FIGURE 5. Scoloplos simplex, A–D: AM W.5246 holotype, methylene blue staining; E–H:AM W.6038 holotype of S. difficilis, methylene blue staining; A. Thorax, dorsal view; B. Thorax-abdomen transition, dorso-lateral view; C. abdomen, dorsal view; D. Posterior end of the body with pygidium, dorso-lateral view; E. Thorax, dorsal view; F. Same, lateral view; G. Thorax-abdomen transition, dorso-lateral view; H. Abdomen, dorsal view. Arrows indicate the appearing of the first branchia.

FIGURE 6. Scoloplos simplex, A–F: AM W.195999, stereomicroscope, methylene blue staining; G–J: AM W.198694, compound microscope. A. General lateral view; B. Thorax-abdomen transition, lateral view; C. Thorax, lateral view; D. Thoraxabdomen transition, lateral view; E. Anterior end, lateral view; F. Thorax, dorsal view; arrow indicates first branchia; G. Parapodium of chaetiger 2; H. Close up of neuropodia of chaetiger 2; I. Parapodium of chaetiger 27; J. Posterior parapodium. br, branchia; cc, crenulated capillaries; ne, neuropodium; no, notopodium; u, uncini.