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"Hippothoa distans MacGillivray



Text Figures 3, 35


Hippothoa distans MacGillivray, p. Hincks, 1881, p. 14; MacGillivray, 1889, p. 321-322, pl. 187, figs. 10-13; Waters, 1904, p. 54-55 (in part). pl. 3, fig. 8d; Brown, 1952, p. 202-204, fig. 142. Hippothoa divaricata, MacGillivray, 1889, P. 320-321, p1. 187, figs. 8-9.


Lectotype (designated by Brown, 1952): National Museum of Victoria, Melbourne, Australia No. 64171. Specimen described: BM 1897.5.1.788, Port Phillip Heads, Victoria, Australia.


Description: The colony is hyaline and varies from loosely coherent to uniserial. Basal wall calcification is nearly absent. Autozooid apertures are oval with a U-shaped sinus. Female zooids are the same size as the autozooids; ovicell lacks pores. Female apertures have a proximal, broad U-shaped sinus. Males are closely associated with the autozooids and are small, round, with a centrally located round aperture.


Measurements (BM 1897.5.1.788): autoz l .294mm, autoz w .168mm, a apert 1.035mm, a apert w .041 mm, female 1.301 mm, female w .154mm, f apert 1.042 mm, f apert w .042mm, ovic 1.154mm, ovic w .154mm.


Discussion: The autozooid is convex with a faint longitudinal midrib that maximally is moderately developed, but may be indistinct. The autozooidal aperture is unique as there is a notch on either side of the shallow U-shaped sinus (text Fig. 35,A). The female zooid may also have a poorly developed longitudinal midrib; the aperture has a shallow, broad U-shaped sinus with denticles occasionally present. An umbo is frequently developed in the middle of the ovicell.


Male zooids are not common and are difficult to recognize because of their small size.


Hippothoa distans was first described by MacGillivray (1869). Based on this description, it is difficult to distinguish it from other uniserial and loosely coherent Australian species. An identifying character may be the `short, obtuse, conical process" on the ovicell. Hincks (1881) indicated that the species was abundant in the Bass Straight, thereby increasing the probability that the species I am interpreting as H. distans, is that intended by MacGillivray.


Since Hincks (1881) synonymized Hippothoa distans with H. flagellum, there has been a conflict concerning the nomenclature. MacGillivray (1889) illustrated Hippothoa distans and, although the autozooidal aperture is not well defined, the female aperture is like most of the British Museum material designated as types by Brown (1952). Waters (1904) appears to have included both H. distans and H. aruensis n. sp. in his concept. The enlarged aperture of figure 8d (Waters, 1904, p 1-3) belongs to H. distans; the apertural shape and the rounded, flattened area in the center, identifies the female as H. aruensis. Waters (1904) was the first to illustrate the uniserial males, describing them as two short processes. Numerous other authors, using the name H. distans, have either confused H. distans with the lndo-Pacific species H. aruensis or have used the name to refer to northern hemisphere forms which are referable to either H. divaricata or H. flagellum.


Brown (1952) attempted to settle the identity problem of Hippothoa distans. He was not successful for several reaons. One reason was that one of his designated specimens at the British Museum (1897.5.1.788) was incrusted by two species, H. distans and H. watersi n. sp. Another reason was that Brown (1952) synonymized H. distans MacGillivray and H. flagellum Manzoni which both Gautier (1961) and Cook (1968) questioned. Gautier (1961) not only believed that Brown (1952) had figured H. divaricata instead of H. distans, but also questioned the validity of the latter name. As stated above, there was no illustration to accompany MacGillivray's insufficient description. Gautier (1961) considered H. distans and H. flagellum synonymous, with the latter having priority. Cook (1968) followed Gautier's use of the name H. flagellum, but for different reasons. She was not necessarily of the opinion that H. flagellum and H. distans were synonymous, but believed that the type material needed to be redescribed. Until that time, H. flagellum was the best alternative. Another reason was that her West African material strongly resembled the Plymouth specimens of H. flagellum.


Continuing the use of the name Hippothoa distans appears to be justified. Although Brown did not clearly define his species, all specimens designated by him, except BM 1897.5.1.788 composed of H. distans and H. watersi, are assignable to H. distans. His illustration (fig. 142) indicates the slightly flared proximal portion of the aperture and the notches on either side of the sinus. These are two important definitive characters for the species.


Occurrence: Recent. Southwest Australia, Tasmania." (Morris, 1980: 26-7)


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© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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