Geoffreya, Kotov & Sinev & Berrios, 2010

Kotov, Alexey A., Sinev, Artem Y. & Berrios, Viviana Lorena, 2010, The Cladocera (Crustacea: Branchiopoda) of six high altitude water bodies in the North Chilean Andes, with discussion of Andean endemism 2430, Zootaxa 2430 (1), pp. 1-66 : 50-51

Geoffreya gen. nov.

Etymology. This genus is also named after Dr Geoffrey Fryer.

Type species. Geoffreya fryeri gen. nov., sp. nov.

Diagnosis. Small-sized alonine. Female with body of Aloninae habitus, rounded, somewhat widening posteriorly, moderately compressed laterally. Head shield of alonine habitus, rostrum short, broadly rounded, posterior extremity broadly rounded, notched. Ocellus larger than eye. Two interconnected main head pores, posterior pore larger than anterior one. Lateral head pores minute. Labrum with a low, wide labral keel, with a cluster of setae on anterior margin. Postero-dorsal angle of valves with about 100 thin setules. Thorax of same length as abdomen. Postabdomen short, of moderate width, somewhat narrowing distally, with broadly rounded dorso-distal angle. Dorsal margin with distal part 1.3 times longer than preanal one, with postanal portion about 1.5 times longer than anal one. Postanal portion weakly convex, anal margin concave. Preanal angle well-defined, postanal angle ill-defined. Postanal margin provided with 7–9 well-developed marginal denticles and 11–14 lateral fascicles of setules, distalmost seta of each fascicle longest, in postanal fascicles 1.5 times longer than marginal denticles. Postabdominal claw of moderate length, slightly shorter than preanal portion of postabdomen. Basal spine very short, about 0.05 of claw length. Antenna I of moderate length, with nine terminal aestetasces, no projection at the base of antennular seta. Antenna of moderate size, antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Antennal spines long, well developed, basal and middle segments of exopodite with clusters of large setules in distal part. Five pairs of thorachic limbs.Limb I without accessory seta, IDL with three setae, IDL seta 1 very small, setae 2 and 3 slender, armed with thin setules. Limb II exopodite without seta, eight scraping setae of similar thicknes, filter plate with six setae. Limb III exopodite with four seta only, lateral setae absent. Limb IV exopodite with four seta only, lateral setae absent, inner portion of limb with a distal scraping setae and three flaming-torch setae. Limb V exopodite with four seta, seta 1 longest, filter plate V consist of a single seta.

Differential diagnosis. Geoffreya gen. nov. could be separated from all other genera of Aloninae by the unique morphology of limbs III and IV, both having only four setae (all of them terminal) on exopodite. Seta 1 longer than setae 2–4 of exopodite V is also never recorded for any genera of Aloninae , usually seta 1 is the shortest among exopodite V setae. Other distinctive features of the genus include only six setae in filter plate II; small size of exopodites III–V in comparison with the limb I; two main head pores of different size; postabdominal claw with very short spine; clusters of hard setules on basal and middle segments of antenna I exopodite; very long setules of lateral fascicles of postabdomen.

Comments. In external morphology, Geoffreya gen. nov. has a typical Alona -like appearance, but thoracic limbs are unique for the subfamily Aloninae . The first, and foremost, peculiarity is the structure of the exopodites III and IV, each having only four setae, while the majority of Aloninae genera have exopodite III with 6 or 7 setae and exopodite IV – with 6 setae ( Kotov 2000a). Reduction of these seta is observed very rarely among alonines: (1) in species of Leydigia exopodite III has from 3 to 7 setae ( Kotov 2009b); (2) in the monotypic genus Spinalona exopodite III has 4 setae, but exopodite IV in both cases has 6 setae ( Kotov & Elías-Gutiérrez 2002). In the genus Kozhowia , exopodite IV has 4 well developed setae and a single rudimentary seta, and unlike in Geoffreya gen. nov., the terminal setae are reduced (see Kotov 2000b). The reduced number of exopodite III–IV setae is also found in the monotypic genus Indialona , the only member of tribe Indialonini Kotov 2000 . However, Geoffreya gen. nov. does not belong to Indialonini , since it has a typical for the Alonini morphology of limbs I–II, in contrast to Indialona with many setae reduced there (see Kotov 2000a). The number of setae in filter plate II of our new genus is also rare for the subfamily: most alonines have seven setae, Geoffreya gen. nov. and Bryospilus ( Chiambeng & Dumont 1999) have six setae; Spinalona posessed only five setae ( Kotov & Elías-Gutiérrez 2002).

Exopodites of limbs III–IV of Geoffreya gen. nov. are especially small in comparison with exopodite V, and the space occupied by limbs is very small in comparison with the most other genera of the subfamily. Such diminution of exopodites, together with shortening of setae, is observed in genera Armatalona (see Sinev 2004a), Bryospilus (see Dumont & Chiambeng 1999), Phreatalona (see Van Damme et al., 2009, Sinev & Kotov, 2000), Monospilus and Graptoleberis (see Alonso 1996), but always in a lesser degree. According to Smirnov (1971), in Monospilus and Graptoleberis with such small exopodites, the exopodite pump is not functioning, and such specific functional-morphological trait seems the case in Geoffreya gen. nov.

Geoffreya gen. nov. demonstrates a set of characters which could be related with its mode of life, namely living in muddy bottom sediments. Such peculiarities are: (1) small eye and large ocellus; (2) body widened posteriorly and compressed laterally; (3) broad, robust postabdomen with well-developed lateral setules; (4) strong antennae with large spines and clusters of strong setules (see Kotov 2006, Van Damme et al. 2005; Van Damme & Dumont 2008b; Kotov 2009b). These characters are characteristic of Leydigia , Leydigiopsis , Alona s. str. (former quadrangularis -group). In its general appearance, Geoffreya gen. nov. is relatively similar to Alona quadrangularis . But Geoffreya gen. nov. lacks very long seta 5 of exopodite III and lacks very large exopodites IV–V, which create strong exopodite pump necessary for life at low oxygen concentration ( Fryer 1968), characteristic of the aforementioned genera. In contrast, the exopodite pump of Geoffreya gen.nov. may be very weak and possibly not functioning. However, the lack of oxygen in muddy bottom sediments is common, but not obligatory: if mud consists mostly of inorganic particles (like clay, ice floor, or salt crystals) and the water body is shallow, well-oxygenated, and wind-stirred, like Lagunillas lake where Geoffreya gen. nov. is found, the favorable conditions can be attained.

The position of Geoffreya gen. nov. within the subfamily is not obvious. The numerous reductions of setae and other parts of the thoracic limbs, found in Geoffreya gen. nov., take place in many non-related genera of Aloninae (reduction of the accessory seta and seta i of limb I, reduction of a terminal setae of exopodite III, reduction of two setae in filter plate III, reduction of limb IV), or very rare and even unique for the alonines (reduction of lateral setae on exopodites III–IV, reduction of a seta number in filter plate II). We can only speculate that the genus may be remotely related to the Coronatella -branch of Aloninae (see Van Damme & Dumont 2008b).