Malawidopsis, Jacobs & Martens, 2022

Jacobs, Bram & Martens, Koen, 2022, An endemic species flock of Cypridopsinae (Crustacea, Ostracoda) from the ancient Lake Malawi (Africa), with the description of a new genus and three new species, Zootaxa 5100 (3), pp. 301-348 : 307-309

Genus Malawidopsis gen. nov.

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Type species: Malawidopsis stellae gen. et sp. nov. (here designated)

Other species included. M. cunningtoni ( Sars, 1910) comb. nov., M. fulleborni ( Daday, 1910) comb. nov., M. antoniae gen. et sp. nov., M. ruwaydae gen. et sp. nov., and at least 12 other new species, briefly (but not formally) described below.

Diagnosis. Cp elongated, with RV widely overlapping LV on all sides, even partially along the dorsal margin. External valve ornamentation variable, from fairly smooth, to heavily reticulate or set with pustules, in some species set with stiff and stout setae.

Valves elongated, subtriangular or sub-rectangular, with greatest height situated well in front of the middle; calcified inner lamellae wide. LV without inner lists; some species with parts of a (mostly posteroventral) submarginal selvage. RV with one conspicuous, well-inwardly displaced inner list anteriorly and ventrally, most species also posteriorly; some species with submarginal anterior selvage. A2 with natatory setae long, extending beyond the tips of the end claws; seta g on terminal segment missing; this limb with sexual dimorphism as normal for the family. MdCox slender, alpha-seta on palp minute, both beta and gamma-setae stout and hirsute. Mx 1 with second palp-segment rectangular and elongate, length c 3–5x the basal width. Rpp larger than Lpp. Walking leg ( T2 ) stout, with seta d2 of medium length, seta d1 missing. T3 a cleaning leg with a distal pincer; penultimate segment fused, carrying an additional dorsal seta F, slightly distal of the middle. CR absent in males, in females reduced to typical cypridopsine type with ramus, one short lateral and one long distal seta; ramus elongate and with parallel sides, length c 4x basal width. Hp with lobe ls protruding well beyond lobe ms; the former of variable shape; postlabyrinthal spermiduct with one additional coil. Zenkers’ organ with 13–15 spinous whorls.

Differential diagnosis. The nine other described genera in the Plesiocypridopsini trib. nov. all have a frontal RV>LV overlap, as in the new genus.

The moss-dwelling genus Bryocypris has strong posterior selvages in both valves, and strong anterior and posterior inner lists in the RV. The A2 has short natatory setae, a long alpha seta on the Md-palp and a CR with a short and triangular base (see Martens 1989)

Kapcypridopsis , originally described from the Western Cape in South Africa by McKenzie (1977), has a RV without an anterior inner list and an A2 with short natatory setae. The alpha seta on the Md-palp is longer than then beta seta, the second palp segment on the Mx1 is rectangular but short (length is c 1.5 times the width), while the CR is small and triangular and the lateral seta is missing .

Klieopsis , described by Martens et al. (1991) for Cypridopsis horai (Klie, 1927) from India, has a RV with strong anterior and posterior selvages, and the posterior selvage is reinforced with posterior septae. The natatory setae on the A2 are short, and claws G2 and Gm are reduced to setae, the second palp segment on the Mx1 is rectangular but short (length is c 1.5 times the width), but the CR has an elongated base (length is c 3 times the basal width) with parallel sides.

Martenscypridopsis , described by Karanovic & Pesce (2000) from Algeria, is one of two cypridopsine genera where the CR has fully disappeared in both sexes (the other being Pseudocypridopsis Karanovic, 1999 in Cypridopsini ). The Cp of Martenscypridopsis shows an anterior RV>LV overlap in dorsal view, but a reversed LV>RV overlap caudally. The RV has no anterior inner list and the second palp segment on the Mx1 is rectangular, but relatively short (length is c twice the width).

Sarscypridopsis , also described by McKenzie (1977), is the most speciose cypridopsine genus in southern Africa. Its species have a rectangular, but relatively short, second palp segment on the Mx1 (length is c twice the basal width), an alpha seta on the Md-palp which is longer than the beta seta and a CR with a short and triangular base.

The enigmatic genus Tanganyikacypridopsis is endemic to Lake Tanganyika and also has an anterior RV>LV overlap in dorsal view, but a reversed LV>RV overlap caudally. The species in this genus have a characteristic posterior selvage on the LV and a prominent anterior and posterior inner list on the RV. The A1 has a stout Rome organ, quite unusual for a cypridopsine group, the alpha seta on the Md-palp is as long as the beta seta, the second palp segment of the Mx1 is rectangular but short (length is c 1.5 times basal width) and the CR has a short triangular base.

The genus Siamopsis Savatenalinton, 2017 is characterized by the presence of an internal postero-dorsal “plate” on the LV, which is absent in Malawidopsis gen. nov.

The genus Thermopsis , described from North America by Külköylüoglu et al. (2003), has no anterior inner lists on either valve, only postero-ventral “double folded” inner lists, the natatory setae on the A2 are short, while the base of the CR is short and triangular. Most characteristic is the large hyper-developed claw on the terminal Md-palp segment, which is also fused with this segment, i.e., no longer articulating. The second palp segment of the Mx1 is almost as long as it is wide, and slightly spatulate, indicating that this genus might rather belong in the Potamocypridini .

It can be deduced from their comparative morphologies that the new genus described here is closely related to Plesiocypridopsis . The two genera share at least the shape and length of the second palp segment of the Mx1 palp (length = c 4 x basal width in Plesiocypridopsis ) and the elongated base (length is c 4 times the basal width) of the CR, with almost parallel sides. Main differences in Plesiocypridopsis are the absence of the anterior inner list on the RV, the alpha seta on the Md-palp, which is larger and of different shape than in the new genus, while the left prehensile palp (the largest) has an extra apical fold in the first segment in Plesiocypridopsis .

In addition, Austrocypridopsis , an enigmatic genus described from the subantarctic Campbell Island off New Zealand ( McKenzie 1982), is presently lodged in the Cypridopsini ( Table 2 ), but the actual anterior valve overlap is uncertain (“right valve slightly larger than left valve” ( McKenzie 1982: 768, this overlap was not illustrated). Because of the uncertain position of Austrocypridopsis , we provide the following differential diagnostic: this genus has a long seta d 1 (twice as long as seta d 2) on the T2, which is unusual for a cypridopsine genus. In addition, Austrocypridopsis has short natatory setae of the A2 and a CR with an elongated, but triangular base.

None of the above genera have an extra dorsal seta (F) on the penultimate segment of the T3, but as this seta is so small that it is easily missed if one is not directly looking for it, its taxonomic value must be investigated in other genera.

Remarks. As far as can be deduced from the present information, the new genus is speciose, with at least 17 species (including ‘ Cypridopsis’ cunningtoni Sars, 1910 and ‘Potamocypris’ fuelleborni Daday, 1910 ) apparently being endemic to Lake Malawi. Blome et al. (2014) reported on two further new cypridopsine species most likely belonging to the present genus from their samples from the South East Arm of Lake Malawi. We here formally describe three species from our Usipa-collections, the others are briefly illustrated and described, but are left in open nomenclature.