Orbaspina, Valentine & Brock, 2003

Valentine, James L. & Brock, Glenn A., 2003, A New Siphonotretid Brachiopod from the Silurian of Central-Western New South Wales, Australia, Records of the Australian Museum 55 (2), pp. 231-244 : 236-237

Family Siphonotretidae Kutorga, 1848

Genera included. Siphonotreta de Verneuil, 1845 ; Acanthambonia Cooper, 1956 ; Alichovia Goryanskij, 1969 ; Celdobolus Havlíěek, 1982 ; Cyrbasiotreta Williams & Curry, 1985 ; Eosiphonotreta Havlíěek, 1982 ; Gorchakovia Popov & Khazanovitch (in Popov et al., 1989); Helmersenia Pander (in von Helmersen, 1861); Karnotreta Williams & Curry, 1985 ; Mesotreta Kutorga, 1848 ; Multispinula Rowell, 1962 ; Nushbiella Popov (in Kolobova & Popov, 1986);? Quasithambonia Bednarczyk & Biernat, 1978 ; Schizambon Walcott, 1884 ; Siphonobolus Havlíěek, 1982 ; Siphonotretella Popov & Holmer, 1994 ; Orbaspina n.gen., described herein.

Discussion. Walcott (1912) included the Obolellidae , comprising the genera Obolella , Botsfordia , Schizopholis and Quebecia , in the superfamily Siphonotretacea regarding these taxa as “primitive” siphonotretids. Despite comprising a mixed assemblage of calcareous and phosphatic taxa this group remained essentially unchallenged until the reviews of Goryanskij (in Sarytcheva, 1960) and Rowell (1962, 1965). Each of these genera lack hollow spines, except for Schizopholis , which belongs to the Acrothelidae , a group characterized by the presence of hollow spines developed on the larval shell of both valves. Schindewolf (1955) rejected Walcott’s (1912) taxonomic assignment for Schizopholis , reassigning the genus to a new family and superfamily, Schizopholididae and Schizopholidacea, respectively. Holmer & Popov (2000) have since synonymized Schizopholidacea withAcrothelidae. Rowell (1962: 146) synonymized Quebecia with Yorkia , believing it to show “all the essential characters of Yorkia .” Goryanskij (in Sarytcheva, 1960) also included the calcareous obolids within the Siphonotretida , but these were regarded by Rowell (1962) to constitute a separate superfamily on the basis of their calcitic shell structure. Botsfordia was reassigned by Schindewolf (1955) to a new family, Botsfordiidae .

In addition to Siphonotreta and Schizambon, Walcott (1908, 1912 ) assigned a second group of calcareous and phosphatic taxa consisting of Dearbornia , Trematobolus and Keyserlingia , to the Siphonotretidae . Walcott (1912: 80) described Dearbornia clarki Walcott as “one of the simple or rudimentary forms of the Siphonotretidae ”. Bell (1941: 219) reassigned D. clarki to Acrothele on the basis of its organophosphatic shell composition and “a morphology congeneric with Acrothele .” Trematobolus , while superficially resembling Schizambon , lacks hollow spines and has a calcareous composition that led Rowell (1962) to reassign this genus to the Obolellidae . Keyserlingia now resides within the acrotretid family Ceratretidae (Holmer & Popov, 2000) .

As discussed by Brock (1998), Walcott (1897, 1912) also assigned the yorkiids to the Siphonotretidae . However, the calcareous shell composition, rudimentary articulation structures and lack of hollow spines in the yorkiids led Rowell (1962) to relocate them into a new family, the Yorkiidae , within the Obolelloidea.As their placement here was also uncomfortable, Rowell (1965) relocated them a second time to the Kutorginoidea, a classification that has since been accepted by most other workers (see Brock, 1998: 611).

Cooper (1956) assigned Acanthambonia , residing within a new subfamily, Acanthamboniinae, to the obolids. Despite being a somewhat uncomfortable placement, it was followed by Wright (1963), Rowell (1965), Cocks (1978) and Williams & Curry (1985). Goryanskij (1969), while maintaining Cooper’s (1956) taxonomic placement of Acanthambonia , questioned this assignment and highlighted a number of common features shared between Acanthambonia and Helmersenia (including tubular hollow spines). This led Havlíěek (1982) and subsequent workers (e.g., Popov & Nõlvak, 1987; Holmer, 1989; Schallreuter, 1999) to reassign Acanthamboniinae to the siphonotretids.

Rowell (1962, 1965), Havlíěek (1982) and Harper et al. (1993) placed Dysoristus and Ferrobolus within the Siphonotretidae . However, the lack of hollow spines, baculate shell structure and pitted larval shell microornament in both genera (Popov & Ushatinskaya, 1992; Popov & Holmer, 1994), indicates their affinities lie more closely with the Lingulida (Holmer & Popov, 2000) , particularly the zhanatellids ( Popov & Holmer, 1994).

The poorly known genus Craniotreta , from the Middle Cambrian west Taurus Mountains of Turkey, was described by Termier & Monod (1978) as a siphonotretid. However, the acrotretid-like shell structure, apical process, muscle scars and lack of hollow spines indicate the affinities of Craniotreta do not lie with the siphonotretids. Holmer & Popov (2000) have speculated that Craniotreta may be synonymous with the acrotretid Linnarssonia .