Scalibregma sp. 2  

Scalibregma  Rathke, 1843

Scalibregma sp. 2

Voucher: TOROA: station T5FB.

Diagnosis.  A medium sized species, body elongate, arenicoliform, expanded in anterior half then tapering to narrow abdominal region; voucher specimen incomplete, 9mm long and 1mm wide at its widest part for 22 chaetigers. Colour light yellow, without orange cast (common in other Scalibregma species); without pigmentation; upon staining, Shirla stain retained ventrally to neuropodia of chaetiger 4 as a patch of pink to reddish dots; similar staining retained in dorsal and ventral cirri of narrow abdominal region.

Body surface with the annulation formed by rows of quadrate cells, these moderately developed, rather faint; cells rectangular and very narrow (much longer than wide); segments tri- to quadriannulate. Ventral midline from chaetiger 2 with group of four large epidermal pads per segment in anterior segments merging into a single pad in middle and posterior segments, forming ridge line within mid-ventral groove; mid-ventral groove and ridge line continuing posteriorly.

Prostomium anteriorly somewhat dome shaped with distinct lateral processes or horns; posterior margin of prostomium visible dorsally; eyes absent. Peristomium achaetous, not concealing posterior margin of prostomium; without distinct segmentation, integument best described as wrinkled, particularly ventrally. Mouth with a row of about 10 narrow lobes forming upper lip, lower lip at level of chaetiger 1, integument wrinkled without obvious lobes .

Arborescent (=dendritically) branched branchiae present on chaetigers 2‒5 posterior to notochaetae. Parapodia biramous, reduced, inconspicuous anteriorly becoming larger and more conspicuous in middle and posterior chaetigers. Dorsal and ventral cirri develop from about chaetiger 11; dorsal cirri round to oval, somewhat inflated, ventral cirri similar; without pigmentation, with yellowish glands present (these turn pink to reddish upon staining with Shirla-stain). Interramal papillae small, in anterior chaetigers, becoming larger by mid body.

All chaetigers with noto- and neuropodial fascicles of slender capillaries; in anterior region arranged into 2 rows, with chaetae of posterior row longest; capillaries of middle and posterior chaetigers arranged in 1‒2 rows.  Chaetiger 1 with additional anterior row of very short, slender chaetae, at least 6 observed in the voucher specimen; these include pointed aristate spinous chaetae, some subdistally slightly enlarged; few appear to be furcate, tips likely broken off; further clarifications with the help of SEM may be needed. Lyrate chaetae present from chaetiger 2; each lyrate chaetae with distinctly unequal tines with the longer tine tapering to very slender filamentous tip. Pygidium uknown.

Remarks. The cosmopolitan status of Scalibregma inflatum (Ashworth, 1902) from Northern Europe  has been questioned and upon careful examination, similar, but distinct species were recently discovered (e.g. Mackie, 1991; Blake, 2000; Baken et al., 2014). Upon revision of Southern Ocean material, a new species Scalibragma australis has been described by Blake (2015). Falkland Islands collection also revealed a diversity of Scalibregma species, with at least 3 species new to science present. Scalibregma sp. 2 differs from the known species as well as from Scalibregma sp. 1 and Scalibregma sp. 3. These differences are summarised in table below, with the conspicuous shape of prostomium being an easy to observe character. Additional observation with the help of SEM will be necessary to fully diagnose this species.

Comparison of selected characters among six known species of Scalibregma and Falkland Island specimen (modified from Blake, 2015).