Hippomonavella ramosae, Garciâa Goâmez, 2000

Garciâa Goâmez, C. M. Loâpez De La Cuadra J. C., 2000, The Cheilostomate Bryozoa (Bryozoa: Cheilostomatida) collected by the Spanish`AntaÂrtida 8611 ’ Expedition to the Scotia Arc and South Shetland Islands, Journal of Natural History 34, pp. 755-772 : 765-769

Hippomonavella ramosae n. sp.

(®gures 16, 17)

Material

HOLOTYPE:`AntaÂrtida 8611’ st. no. 47. Shag Rocks. One incomplete colony on a little rock, with ovicells. MNCN 25.03 /1903.

Other material examined for comparison

Hippomonavella praeclara (MacGillivray) : Fyansford Formation ( Balcombian , Middle Miocene ) at Fossil Beach , Mornington , Port Phillip Bay, Victoria ( Australia). National Museum of Victoria: NMV P142987 and NMV P142988 . Pieces of bilaminar colonies .

Hippomonavella pellucidula (Calvet) ,`AntaÂrtida 8611’ st. no. 133, South Georgia. Small pieces of a broken colony, lacking ovicells.

Description

Colony encrusting, unilaminar. Autozooids polygonal elongate, rectangular or hexagonal. Zooidal dimensions are given in table 4. Frontal wall umbonuloid, rugose, perforated by marginal pores. Ori®ce longer than wide, distally semicircular and proximally quadrate, with pointed lateroproximal condyles. Peristome very low, with two lateral lips. The distal part of the peristome is formed by the frontal wall of the succeeding zooid. Ovicell hyperstomial, perforated by pseudopores, partially immersed in the distal zooid, with its margins overgrown by later calci®cation. One suboral central avicularium on each autozooid, small and elliptical, proximally orientated. Interzooidal communication by basal pore chambers.

Discussion

Hippomonavell a ramosae is the second Antarctic representative of Hippomonavella Canu and Bassler , a genus formerly known in the Southern Ocean by H. pellucidula (Calvet) (®gures 18±20), only found in South Georgia ( Calvet, 1904; Hayward and Ryland, 1991; Hayward, 1995). Hippomonavella ramosae is externally distinguished from H. pellucidula by the proximally quadrate ori®ce, median avicularia, rugose frontal wall and basal pore chambers (®gure 16), while H. pellucidula has a circular ori®ce, usually lateral avicularia, smooth frontal wall and mural pore chambers (®gure 18), thus being externally more similar to the type species H. praeclara (MacGillivray) (®gure 21). Hippomonavell a ramosae is similar to H. ¯exuosa Gordon ( Gordon, 1989), from New Zealand, which has similar ori®ce, zooidal shape and central suboral avicularia, although they may be distinguished because H. ¯exuosa has two oral spines and a longer avicularium than H. ramosae . Examination of the inner side of the frontal wall of both Antarctic species and also the type species H. praeclara shows that they have umbonuloid frontal walls. However, H. ramosae and H. praeclara display a typical form in which the umbonuloid component of the wall occupies most of the inner surface (®gures 17, 22). In contrast, H. pellucidula , which is externally more similar to H. praeclara than to H. ramosae , has a very small umbonuloid component (approximately one-seventh of the total length) (®gures 19, 20). This may be understood following the model proposed by Gordon and Voigt (1996) for the origin of the umbonuloid and lepralioid types of frontal wall, in which lepralioid ascophorans would derive from umbonuloids by the reduction of the umbonuloid component and the subsequent formation of a true ascus. In this case, H. praeclara and H. ramosae represent an early umbonuloid stage while H. pellucidula , although still umbonuloid, has a more evolved, almost lepralioid, frontal wall.

In recent works, the genus Hippomonavella is included in the family Smittinidae Levinsen ( Gordon, 1989; Hayward, 1995). After Gordon (1994), the families Smittinidae Levinsen and Bitectiporidae MacGillivray constitute the superfamily Smittinoidea Levinsen , the diagnosis of which, updated by Gordon (1994) includes as a diagnostic feature`Zooids with a lepralioid ascus’, which would imply that Hippomonavella could not belong to the Smittinoidea . Nevertheless, Gordon and Voigt (1996) consider that the lepralioid frontal wall may be derived from an ancestral umbonuloid shield. Thus, whether the wall is umbonuloid or lepralioid is not a reliable character at the family and higher levels, as species with one or the other type of frontal wall may be closely related. Hippomonavella , with a hippoporine ori®ce [ Gordon (1994) proposes the replacement of the descriptor`hippoporinid ori®ce’ by`hippoporine ori®ce’], and lacking a lyrula, is better accommodated in the Bitectiporidae than in the Smittinidae . The similarity of the inner side of the ori®ce and frontal wall of Bitectipora lineata MacGillivray , ®gured by Gordon (1994, ®gure 1c), and Hippomonavella pellucidula is very remarkable, despite the pseudopores present in B. lineata but absent in H. pellucidula .

Etymology: ramosae refers to Ana Ramos, member of the`AntaÂrtida 8611’ expedition and Chief Researcher of the Spanish BENTART projects, in recognition of her contribution to Spanish research in Antarctica.