Scalibregma Rathke 1843

Genus Scalibregma Rathke, 1843

Type Species: Scalibregma inflatum Rathke, 1843.

Synonym: Oligobranchus Sars, 1846. Fide Hartman 1959.

Diagnosis. Body elongate, arenicoliform. Prostomium T-shaped with lateral horns. Peristomium achaetous, surrounding prostomium dorsally and forming upper and lower lips of mouth ventrally. Parapodia of posterior segments with dorsal and ventral cirri; interramal papilla present; postsetal lamellae absent. Branchiae present in anterior segments. Setae include capillaries, lyrate setae, and sometimes inconspicuous blunt, pointed, or bifurcated spinous setae anterior to capillaries of setigers 1 or 1‒2, representing homologues of lyrate setae; large conspicuous acicular spines absent. Pygidium with long anal cirri.

Remarks. Until recently, Scalibregma inflatum was considered to be cosmopolitan in its distribution. Mackie (1991), however, demonstrated sufficient variability in European populations to define an additional, closely related species, S. celticum Mackie, 1991. Among other observations, Mackie (1991) discovered that short slender spines were present anterior to the capillaries of a few anterior noto- and neuropodia anterior to the setigers where lyrate setae occurred. Prior to this study Scalibregma had been defined as lacking any type of spinous seta. The spinous setae discovered by Mackie were not the large, curved acicular spines that have been reported for species of Asclerocheilus, Oligobregma, Parasclerocheilus Sclerobregma, and Sclerocheilus but were instead inconspicuous companions of the capillaries. For S. inflatum Mackie (1991) found that some of these setae were forked or split on their tips. This observation plus their position in the setal fascicles suggested that they were homologous to the lyrate setae of following segments. Mackie further suggested that the larger recurved spines of other genera were homologous with capillaries.

Mackie (1991) redescribed Scalibregma inflatum based on specimens from the type locality in Norway as well as from Sweden, Scotland, Wales, and Ireland. The second species, S. celticum, was from Scotland, Wales, and France and differed in that the small spinous setae of setigers 1‒2 were blunt-tipped instead of bifurcate. Additionally, eyes were present instead of absent and there were differences in the form of the peristomium, size and distribution of the epidermal pads above the notopodia, and in the number and arrangement of the pygidial cirri. S. celticum was subsequently reported from the Mediterranean by Çinar (2005) and Lomiri et al. (2012).

Mackie (1991) also re-examined Sclerobregma stenocerum Bertelsen & Weston, 1980, from shelf depths along the southeastern United States and found that the anterior acicular spines reported for the species by Bertelsen & Weston (1980) were of the small, inconspicuous kind found in Scalibregma species instead of the large, curved acicular spines found on other species of the Sclerobregma. S. stenocerum was therefore transferred by Mackie (1991) to Scalibregma. Mackie also examined the holotype of S. branchiatum Hartman, 1965, the type-species of Sclerobregma from deep water in the western North Atlantic and found short spinous setae anterior to the larger acicular spines of setigers 1 and 2. A similar situation exists in Cryptosclerocheilus baffinensis Blake, 1972, described from deep water in Baffin Bay. This species was reported to have slender, blunt-tipped spines in the noto- and neuropodia of setiger 2; these were replaced by furcate setae from setiger 3 (Blake 1972). A re-examination of prepared slides of these spines confirms that these are the same type of seta reported by Mackie (1991) for the three species of Scalibregma examined by him.

Following the lead of Mackie (1991), Blake (2000) examined specimens from California previously identified as Scalibregma inflatum and described a new species, S. californicum Blake, 2000. He also suggested that specimens from the U.S. Atlantic coast included at least one new species in addition to S. stenocerum. Most recently, Bakken et al. (2014) described S. hanseni Bakken, Oug & Kongsrud, 2014 from deep water off Norway. These authors also focused on the short, spinous setae anterior to normal capillaries in setigers 1‒2 and found similar spines in Pseudoscalibregma parvum (Hansen, 1879). In my own work, numerous species of Scalibregmatidae have been examined and these short spinous setae, considered homologous to the lyrate setae, have been found in other genera including some with large curved acicular spines. I now believe that most species of Scalibregmatidae having lyrate setae will be found to have the same type of short spinous setae in segments anterior to where the lyrate setae begin.

To date, specimens of Scalibregma from Antarctic waters have been identified in several faunal and ecological accounts as S. inflatum (see reference list below). The only original illustrations of Scalibregma from Antarctica appear to be by Knox & Cameron (1998) of the anterior end and a branchiate parapodium from a specimen collected from the Ross Sea in 578 m.