Macrothrix sarsi, Kotov, 2007

Kotov, Alexey A., 2007, Revision of the hirsuticornis-like species of Macrothrix Baird, 1843 (Cladocera: Anomopoda: Macrothricidae) from Subantarctic and temperate regions of the southern hemisphere, Journal of Natural History 41 (41 - 44), pp. 2569-2620 : 2597-2600

publication ID	https://doi.org/ 10.1080/00222930701689937
persistent identifier	https://treatment.plazi.org/id/03E32C46-B155-FFB3-FE3C-FBBDDAA21298
treatment provided by	Felipe
scientific name	Macrothrix sarsi
status	sp. nov.

Treatment

Macrothrix sarsi View in CoL sp. nov.

( Figures 13G, H View Figure 13 , 14–16 View Figure 14 View Figure 15 View Figure 16 )

Macrothrix propinqua Sars 1909 View in CoL in Sars 1916, p 325 –326, Plate 36, Figures 2, 2a–c View Figure 2 ; Seaman et al. 1999, p 104.

Not Macrothrix propinqua Sars 1909, p 5 View in CoL –15, Plate 1.

Etymology

The species is named after George Ossian Sars, a famous Norwegian carcinologist and one of the greatest investigators of the Cladocera , whose material is used for the species description.

Type locality

A water body ‘‘ Cape of Good Hope V’’, Western Cape Province, Republic of South Africa. Sars (1916) wrote that the sample was taken ‘‘in the neighbourhood of Bergvliet’ ’.

Type material

Holotype: a parthenogenetic female in 90% alcohol, tube GOS F18493a. Label of holotype: ‘‘ Macrothrix sarsi n.sp., Cape of Good Hope , parth. fem., HOLOTYPE’ ’. Paratypes: 78 parth. ♀♀ from type locality, GOS F18493b (tube); one dissected parth. ♀ from type locality, GOS F18493c–h (six slides); nine parth. ♀♀ from type locality, GOS F9304 (slide); eight parth. ♀♀ from ‘‘ Cape of Good Hope II’’, GOS F9303 (slide); 11 parth. ♀♀ from ‘‘ Cape of Good Hope’ ’, GOS F11171 (slide) .

Diagnosis

Adult parthenogenetic female. In lateral view body subovoid, cervical depression very shallow, dorsal margin not breached by a ‘‘step’’ in posterior boundary of head ( Figure 14A View Figure 14 ), dorsal margin of valves with a minute serration ( Figure 14D View Figure 14 ), posterodorsal angle as rounded triangle, lies somewhat ventrally to middle of body height. In anterior view, body compressed laterally and supplied with a sharp dorsal keel. No dome above eye. Ocellus small. Dorsal organ small. Labrum with a slightly projected apex bearing two tubercles. Setae on ventral margin of valve as in other species ( Figures 14E–G View Figure 14 ).

Postabdomen subovoid, with rounded distal extremity, without ‘‘heel’’ basally, distinct reticulation on sides ( Figure 14H View Figure 14 ), its ventral margin straight, with few series of fine spinules; first series consists of specially long elements ( Figure 14I, J View Figure 14 ). Dorsal margin distinctly bilobed; preanal margin with transversal series of minute setules, anal margin with groups of thicker setules. Postabdominal seta longer than postabdomen, with distal segment somewhat shorter than basal one and densely armed with long setules; basal segment with numerous, short setules. On external side of postabdominal claw, a series of three to four thin denticles.

Antenna I markedly widened distally, slightly curved, without a subapical external angulation; sensory seta located externally very far (three or even more antennular diameters at base) from antenna I joint; on anterior face five transverse rows of spinules, but no reticulation ( Figure 14K, L View Figure 14 ). Nine relatively long aesthetascs, two of them significantly larger than the rest. Antenna II with distal burrowing spine on basal segment markedly longer than proximal segment of exopod ( Figure 15A View Figure 15 ). Length of all apical swimming setae subequal, armature as in other species ( Figure 15D–G View Figure 15 ). Lateral seta on proximal endopod segment larger than other setae, lacking robust denticles in middle ( Figure 15B, C View Figure 15 ). A spine on second segment of exopod short, less than half length of next segment. On posterior side of segments 1–3 of exopod there are no additional denticles, but sometimes there are several small spinules.

Limb I with apical seta of outer distal lobe having distal segment unilaterally armed with robust setules ( Figure 16A, B View Figure 16 ), inner-distal lobe with three bisegmented setae of different size, smallest seta setulated only on its middle portion, anterior setae as represented in Figure 16 View Figure 16 CE, posterior setae d–e with bulbs at tips ( Figure 16F View Figure 16 ), ejector hooks of subequal size ( Figure 16G, H View Figure 16 ). On limb II, scrapers 1–2 with delicate feathering, scrapers 3–7 with thicker denticles of size characteristic for the genus; a solitary posterior seta present near gnathobase ( Figure 16J, K View Figure 16 ), filter plate II with four setae, without a small rudiment of fifth seta. On limb III epipodite with five setae; seta 1 as long as 3, armed with fine setules distally; smooth setulated projections proximally to seta 3 and between setae 2 and 3 ( Figure 16L View Figure 16 ), on inner-distal limb portion, seta 1 with fine setules distally, seta a with fine setules basally and strong spinules distally, seta b slightly longer than a, but markedly longer than c ( Figure 16M View Figure 16 ), basal endite normally with four soft setae ( Figure 16L View Figure 16 ). Limb IV with exopodite bearing a distal group of three bilaterally feathered setae of somewhat different size ( Figure 16N View Figure 16 ); on inner-distal portion of the limb seta 1 with strong setules basally and five to six denticles distally; posteriorly on limb inner margin a row of five long setae ( Figure 16O View Figure 16 ). On limb V there are three setae at inner margin, seta 1 with distalmost extremity as a naked whip ( Figure 16P View Figure 16 ).

Atypical adult. A single atypical adult had two setae on exopodite II ( Figure 16J View Figure 16 ) and five setae on basal endite III ( Figure 16M View Figure 16 ).

Juvenile female. In contrast to adult, body more elongated and quadrangular ( Figure 14M View Figure 14 ), with posterior border of dorsal head margin elevated above valves; posterior margin of valve almost straight, postero-dorsal angle at level of dorsal margin, ventral margin of valve strongly convex; antenna I relatively longer; antennae II and swimming antennal setae longer, rows of setules on antenna I and II weakly developed.

Ephippial female, male. Unknown.

Size. Parthenogenetic females 0.45–0.86 mm; up to 0.93 mm according to Sars (1916).

Taxonomic notes. Sars (1916) determined this population from the Cape of Good Hope as belonging to his species M. propinqua Sars, 1909 . The latter is here considered as a junior synonym of M. oviformis . At the same time, the South African populations, misidentified as ‘‘ M. propinqua ’’ by Sars (1916), belong to another species, named here M. sarsi sp. nov.

The description of Sars (1916) contains few characters helpful for distinguishing the species of hirsuticornis -like forms as some of the ‘‘differences’’ are doubtful in terms of recent understanding of Macrothrix systematics. For example, Sars (1916) mentioned a large epipodite on limb V, but its size is too variable in other species of Macrothrix (Kotov et al. 2004) to be a good taxonomic character. The present opinion is based predominantly on a study of Sars’ material instead of his description.

Distribution. Macrothrix sarsi sp. nov. is present only in the Cape of Good Hope region of the Republic of South Africa. Some species of Macrothrix (i.e. M. spinosa , M. odiosa , and M. capensis ) are common in South African water bodies. In contrast, M. sarsi is apparently a rare species, it was not found by Smirnov (2007a), who examined in detail some 290 samples from South Africa. Clarke and Rayner’s (1999) report of ‘‘ M. propinqua ’’ from Namibia must be confirmed.