Fabricinuda Fitzhugh, 1990
Fabricinuda sp. 1
Voucher specimens. Sea Lion: Stations 1MFC, 1MFA, 49MFA.
Diagnosis. Voucher complete specimen; body length 9mm plus 3mm for branchial crown; width at fourth chaetiger level 0.25mm; body very narrow, cylindrical, thread-like; preserved specimens white to pale yellow. Tube present in some specimens , loose (easily broken down), muddy with some particles incorporated. All specimens with eight thoracic and three abdominal chaetigers ; chaetigers 12 shortest about as wide than long; chaetigers 3-8 much longer than wide, increasing length posteriorly; chaetiger 9 slightly shorter than 8; remaining abdominal chaetigers successively shorter, chaetiger 11 wider than long.
Branchial crown (missing in majority of examined specimens) present in voucher; with three pairs of radioles; distal ends filamentous. Dorsal lips and ventral lips not confirmed under stereomicroscope observation. Vascularized ventral filamentous appendages absent. Branchial hearts present .
Peristomium with 1- 2 pairs of black, crescentic eyes; narrow and long dorsal median lobe; ventral lobe smaller (less than ½ of dorsal lobe), anterior margin of anterior peristomial ring as a low ridge of even height ventrally, markedly notched laterally rounded lobe to either side of dorsal midline, not overlapping the higher middorsal conical lobe .
Collar chaetae - few narrow hooded chaetae; superior thoracic notochaetae elongate, narrowly hooded, around 5-8 per fascicle; inferior thoracic notochaetae of chaetigers 3-8 bearing 3 pseudospatulate chaetae . Thoracic uncini acicular; 7-8 per fascicle arranged in double rows in chaetigers 1-4 in voucher specimen (in other specimens forming a single irregular row), from chaetigers 5 blending into single, if irregular row ; dark yellow to light brown in colour with large secondary tooth oblique to main fang ; apical teeth slender and slightly decreasing in size towards tip of uncinus; small hood present.
Abdominal neuropodia with few very elongate, narrowly hooded chaetae.
Abdominal uncini with about 10 rows of teeth in profile, 4-5 teeth per row; manubrium about the same length as dentate region, slightly expanded proximally; number of uncini per fascicle slightly decreasing posteriorly.
Pygidium conical, longer than chaetiger 11, with pair of black pygidial eyes situated in posterior fourth of pygidium.
Remarks. This is only third species of family Fabriciidae from the Southern Ocean or Magellan region. The other two known species Novofabricia chilensis Hartmann-Shroder, 1962 from Chile and Raficiba barryi Fitzhugh, 2001 from Antarctica belong to different genera because of the structure of anterior ventral collar as well as other characters (see Fitzhugh 2001, Huang et al. 2011 for details). The reduced collar all around combined with the presence of inferior pseudospatulate chaetae in chaetigers 3-7/ 8 place FI specimens into genus Fabricinuda Fitzugh, 1990. However some characters linked to branchial crown such dorsal and ventral lips are currently not confirmed. This is a first record of genus Fabricinuda from the geographic area investigated here and likely represent a new species. Of the known species (see Fitzhugh 1990, Fitzhugh 2002, Lopez and Rodríguez 2008), FI species is similar to Fabricinuda pseudopalpa Fitzhugh, 1990 and F. longilabrum Fitzhugh, 2002 in lacking ventral filamentous appendages. Fabricinuda longilabrum can be further distinguished from FI species by having the anterior peristomial ring distinctly longer than wide and F. pseudopalpa can be distinguished by possessing middorsal lobes which can range from small and lobe-like to elongate and palp-like and the anterior end of the body being light to dark brown. The other five described species of the genus, F. limnicola, F. bikinii (Hartman, 1954), F. trilobata (Fitzhugh, 1983), F. pseudocollaris Fitzhugh, 1990 and F. rosaelenae López & Rodríguez, 2008 can be readily distinguished by having unbranched, vascularized ventral filamentous appendages in their branchial crowns and lack of dorsal lips.
