Leucon (Leucon) assimilis, Sars, 1887

Mühlenhardt-Siegel, Ute, 2011, New and known species of the family Leuconidae (Cumacea, Peracarida) from Antarctic deep-sea basins 3117, Zootaxa 3117 (1), pp. 1-68 : 21-23

L. (Leucon) assimilis Sars, 1887

Previous records. described for the Kerguelen (232 m), rediscovered by Hale (1937) and Ledoyer (1977) around the Kerguelen; Weddell Sea ( Ledoyer, 1993, 185– 820 m; Petrescu & Wittmann, 2003, 240– 630 m); Falkland Islands, Tierra del Fuego, Magellan Strait ( Petrescu, 1994, 75– 432 m), Ross Sea ( Rehm et al., 2007, no depth data); Prydz Bay several stations (unpublished data).

Diagnosis. Dorsomedian line serrate with a gap in the serration close to the posterior margin of the carapace; frontal area with three to four teeth on each side along the ventral margin.

New records. ( Figures 14–15 )

In the ANDEEP samples are specimens of Leucon (L.) assimilis : with three to four teeth laterally along lower margin of frontal lobe; dorsomedian line serrate, with a small interruption close to the posterior margin of the carapace; very long first antenna ( Figures 14–15 ).

L. assimilis complex: Without lateral teeth: W Weddell Sea: ANDEEP III #133: 2 specimens;

with one lateral tooth: Peninsula: ANT XIX #131 : 1 specimen ;

with three lateral teeth (as in L. assimilis ): Peninsula: ANT XIX #114 : 1 very young manca; ANT XIX #129 : 1 specimen ; W Weddell Sea: ANDEEP III #121: 2 specimens; ANDEEP III #151: 2 specimens; E Weddell Sea: ANDEEP III #80: 4 specimens;

Leucon (L.) cf. assimilis : lateral teeth present, but dorsomedian serration of carapace not reaching the posterior margin.

With only two lateral teeth at frontal lobe: E Weddell Sea: ANT XV #145: 1 specimen;

with four lateral teeth, L. (L.) cf. assimilis : Peninsula: ANDEEP III #153: 1 specimen; W Weddell Sea: ANT XIX #133 : 1 specimen ; ANT XIX #137 : 1 male ; ANDEEP III #151 (1178 m); E Weddell Sea: ANT XV #89: 2 specimens; ANDEEP III #74: 1 specimen; Lazarev Sea: ANDEEP III #59 (4651 m), 1 adult male (damaged);

with four to five lateral teeth, L. (L.) cf. assimilis: S Sandwich Trench : ANT XIX #140 : 5 specimens , ZMH: K 42938 .

Remarks. The specimens from the Antarctic expeditions with three or more lateral teeth on the lower margin of the frontal area are regarded as one species. The number of teeth is four in males and mostly three in females. The number of dorsomedian teeth ranges between 16+ 2 in subadult males to 17+6 or 19+ 3 in females. Adult males have less dorsomedian teeth than females. Many specimens do have three shallow teeth above the antennal notch along the basis of the pseudorostrum. Larger specimens of both sexes may have two to four teeth in the antennal notch. The basal article of the exopodite of the maxilliped 3 very often bears a tooth (in one specimen from the western Weddell Sea there are eight teeth). The number of teeth at the exopodite of the pereiopod 1 can vary: zero (Peninsula) to six (Weddell Sea W+E). The tooth at the ischium is present in the specimens from the western Weddell Sea or missing in the specimens from the Peninsula and the eastern Weddell Sea. The length proportions in the uropods are not really constant in the Antarctic material, but the differences are not distinct enough to justify the erection of new species.

Leucon assimilis may indeed be a indicating a complex of cryptic species. This problem could not be solved exclusively by morphological methods and warrants the use of molecular genetic methods.

Figures

FIGURE 14. Leucon (L.) assimilis Sars, 1887, SEM photos, habitus (above left), anterior region (above right and below left), A1 in higher magnification (below right).

FIGURE 15. Leucon (L.) assimilis Sars, 1887, SEM photos, details of ocular lobe (above left) and uropods.