Sarsinebalia Dahl, 1985

McCormack, Edward & Ashelby and David McGrath, Christopher W., 2016, A review of the Leptostraca of the British Isles with discussion of the genus Sarsinebalia Dahl, Nauplius (e 2016006) 24, pp. 1-19 : 9-10

Genus Sarsinebalia Dahl, 1985

Remarks. Dahl (1985) created the genus Sarsinebalia to accommodate Nebalia typhlops , and based it on four characters: 1) a complicated rostrum with subterminal spine; 2) the features of the eye; 3) lack of a comb-row on the exopod of the first pleopod; and 4) a short exopod of the 2nd maxilla. Dahl (1985) goes on to state that these features are also present in an undescribed species from the Red Sea [according to Moreira et al. (2003) this is corrected to north-west Africa in an unpublished manuscript by Dahl] and two further undescribed species from Australia. Moreira et al. (2003) postulate that the north-west African species could be could be identical to their Sarsinebalia urgorrii Moreira, Gestoso and Troncoso, 2003 whilst the identity of the Australian species is unknown as descriptions of these taxa had not appeared at the time of Dahl’s death. To date, five species have been ascribed to Sarsinebalia : S. typhlops , S. urgorrii , Sarsinebalia cristoboi Moreira, Gestoso and Troncoso, 2003 , Sarsinebalia biscayensis Ledoyer, 1998 , and Sarsinebalia kunyensis Ledoyer, 2000 . According to Mauchline and Gage (1983) and Dahl (1985), specimens recorded from New Jersey, U.S.A. by Hessler and Sanders (1965) as Nebalia typhlops occidentalis Hessler and Sanders, 1965 differ in several significant characters and could represent a further species.

Walker-Smith and Poore (2001) considered Sarsinebalia to be a synonym of Nebalia but only included the type species S. typhlops in their analysis. However, Moreira et al. (2003) retained Sarsinebalia as valid as some (but not all) of the characters proposed by Dahl (1985) hold between S. typhlops , S. urgorrii and S. cristoboi . However, their study likewise overlooked S. biscayensis and S. kunyensis . A recent key to worldwide Nebalia species (Song and Min, 2016) also did not adopt the synonymy of Sarsinebalia suggested by Walker-Smith and Poore (2001).

Since Dahl’s (1985) landmark study there have been significant advances in the taxonomy and systematics of the Leptostraca with around 67% of the currently accepted species having been described since this date with further new species continuing to be described (e.g. Koçak and Moreira, 2015; Song and Min, 2016). Combined with the phylogenetic studies of Olesen (1999) and Walker-Smith and Poore (2001), there is now a greater, if still not complete, understanding of variation in the traditionally used diagnostic characters across the Leptostraca . Many of Dahl’s diagnostic characters for Sarsinebalia no longer stand up to scrutiny and now appear to be more indicative of species- rather than genus-level differences. These are discussed in turn here.

1) Complicated rostrum with subterminal spine. All species of Nebalia have a rostral keel (Walker-Smith and Poore, 2001) so in this respect the rostrum of Sarsinebalia species is no more complex. The subterminal spine is present in Sarsinebalia and the undescribed Nebalia sp. B of Walker-Smith and Poore (2001) as well as the less closely related genera of the Paranebaliidae .Additionally, S. biscayensis has a reduced spine (see Ledoyer, 1998), and some mature males of S. typhlops are also noted by Dahl (1985) as having a reduced spine.

2) Features of the eye. Of the five nominal species, only S. typhlops (and possibly the undescribed species of Dahl, 1985) has the ‘squarish’ eye shape described by Dahl (1985). The eyes of S. urgorrii and S. cristoboi are of a similar but not identical shape, whilst S.biscayensis has long slender eyes (see Ledoyer, 1998) and S. kunyensis appears to have rounded eyes (see Ledoyer, 2000). Eye shape is exceptionally variable in other Nebalia (even as far as being bi-lobed – see Walker-Smith and Poore, 2001) so a ‘squarish’ eye seems not to be too unusual and certainly within the range of variation covered by other Nebalia . In addition, Hessler (1984) illustrated significant developmental changes in the shape and armature of the eye of Dahlella caldariensis Hessler, 1984 . Pigment is absent in S. biscayensis , S. kunyensis and S. typhlops but present in the S. urgorrii and S. cristoboi (but also seems to fade after long-term storage in alcohol, in S. urgorrii at least). As a general rule within the Crustacea, there is a tendency towards unpigmented eyes in deeper water species which may explain its absence in S. biscayensis , S. kunyensis and S. typhlops which are found deeper than S. urgorrii and S. cristoboi . Ommatidia are absent in S. typhlops and S. biscayensis but present in the other three species (also absent in unrelated Speonebalia Bowman, Yager and Iliffe, 1985 , Nebaliella Thiele, 1904 , and Dahlella Hessler, 1984 ).

3) Lack of a comb-row on the exopod of the first pleopod. A comb-row is absent in S. typhlops , S. urgorrii and S. cristoboi but present in both S. biscayensis and S. kunyensis . The length of the comb-row appears to be diagnostic (at least partially so) at a species level in Nebalia (see Walker-Smith and Poore, 2001) and the complete absence of a comb-row could just represent the extreme of this variation.

4) A short exopod of the 2nd maxilla. Only S. typhlops and S. biscayensis have an unusually short exopod on maxilla 2, whereas the other species have an exopod longer than the first segment of the endopod.In S. kunyensis and S. biscayensis the division between the two endopod segments is indistinct but the length of the exopod relative to the overall endopod can be used.

Based on this, the only character that is consistent between all 5 species of Sarsinebalia is the presence of a subterminal rostral spine. As already mentioned this spine occurs elsewhere in the Paranebaliidae and in Walker-Smith and Poore’s (2001) Nebalia sp. B and so is not unique to Sarsinebalia . A formal reappraisal of Sarsinebalia is outside of the scope of the current study and should await examination of material of the currently included species as it is conceivable that other, as yet un-investigated, characters may unite all or some of the species currently assigned to the genus. Molecular methods may also help resolve the status of the genus. Until such time we continue to use Sarsinebalia here in accordance with Moreira et al. (2003).