Scalibregmatidae Malmgren, 1867

Wiklund, Helena, Neal, Lenka, Glover, Adrian G., Drennan, Regan, Muriel Rabone, & Dahlgren, Thomas G., 2019, Abyssal fauna of polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean: Annelida: Capitellidae, Opheliidae, Scalibregmatidae, and Travisiidae, ZooKeys 883, pp. 1-82 : 1

Scalibregmatidae Malmgren, 1867

Notes.

The family Scalibregmatidae was established by Malmgren (1867) to accommodate annelids with rugose appearance of the cuticle and either elongate (arenicoliform) or maggot-shaped body form, with often anteriorly inflated bodies such as Scalibregma inflatum Rathke, 1843 and Polyphysia crassa ( Ørsted, 1843). Currently, there are over 50 valid scalibregmatid species ( Read and Fauchald 2018a) but see also discussion about Travisia .

The characters used to differentiate genera are the prostomial shape, presence and development of branchiae, presence of spines in anterior notopodia (and sometimes also in neuropodia), presence and development of branchiae and development of dorsal and ventral cirri, particularly in posterior part of the body (e.g. Blake 1981, 2000c). However, these characters are considered problematic due to their overlap between genera ( Blake 2000c). Additionally, characters such as the form of the prostomium and presence of branchiae depend on the stage of ontogeny ( Blake 2015). Recently, Blake (2015) reported previously overlooked characters that he considers species specific such as development of ventral part of the peristomium into complex upper and lower lips surrounding the mouth; form of short, spinous chaetae anterior to capillaries in parapodia preceding lyrate chaetae and development of internal glands within parapodia. Blake (2015) also concluded that small specimens cannot be reliably referred to a species or genus without a growth sequence and previously described species should be re-examined for characters such as presence of spinous chaetae in anterior parapodia and development of internal glands.

Although Scalibregmatidae range from the intertidal to the deep sea, most species occur below 1000 m ( Blake 2015). Four scalibregmatid species were encountered in the UKSR-collected material. Three of these are assigned to the genus Oligobregma Kudenov & Blake, 1978, while one species could not be assigned to a genus based on morphology due to its poor condition. Generic assignment of ABYSSLINE species to Oligobregma is based on the presence of the following characters: elongate arenicoliform body, prostomium with prominent frontal horns, absence of branchiae, presence of spines in anterior chaetigers and presence of well-developed dorsal and ventral cirri in posterior chaetigers.

The diagnosis of Oligobregma presented here is amended from that given by Blake (2017), mainly to take into account a more posterior appearance of furcate chaetae, which Blake (2017) considered to appear prior to chaetigers 2-4.

Diagnosis.

Body elongate and arenicoliform. Prostomium T-shaped with two prominent frontal horns. Eyes present or absent, nuchal organs present. Peristomium achaetous, surrounding prostomium dorsally and forming upper and lower lips of mouth ventrally. Branchiae absent. Parapodia well developed, with dorsal and ventral cirri on posterior chaetigers; interramal papillae present or absent. Large acicular spines present on anterior chaetigers. Capillaries present in all parapodia; lyrate chaeta present. Some species with short, slender, blunt or pointed spinous chaetae anterior to capillaries of chaetigers 1, 2 or 3, representing homologues of lyrate chaetae. Pygidium with anal cirri.