Magnospina, Sousa, Francisco Diogo R., Elmoor-Loureiro, Lourdes Maria Abdu & Santos, Sandro, 2016

Sousa, Francisco Diogo R., Elmoor-Loureiro, Lourdes Maria Abdu & Santos, Sandro, 2016, Position of the dentifera-group in the Coronatella-branch and its relocation to a new genus: Magnospina gen. n. (Crustacea, Chydoridae, Aloninae), ZooKeys 586, pp. 95-119 : 96-100

Taxon classification Animalia Diplostraca Chydoridae

Magnospina gen. n.

Type species of the genus.

Magnospina dentifera comb. n. = Alona dentifera (Sars, 1901).

Etymology.

The name " Magnospina " is derived from two Latin words, magna = large, long and spina = spine. The generic name refers to the long basal spine on the postabdominal claw.

Description.

Parthenogenetic female.Habitus without dorsal keel, ovoid or with moderate lateral compression, length 0.32-0.48 mm, maximum height before the mid-length of body; body height/length about 1.3-.17. Head Eye and ocellus of subequal or different sizes. Rostrum short from a lateral view, wide from a frontal view, not pointed, rounded or truncated; head shield wide, with the distance between the mandibular articulations higher than length of its posterior portion, with or without ornamentation; head pores absent or presents, in last case three connected main head pores, lateral head pores minute. Labral keel wide, oval and naked, apex not elongated. Carapace ornamentation not evident, slightly punctuated or with narrow longitudinal lines; valves armed with 40-53 setae internally inserted at the ventral margin and differentiated in three groups, setae from the anterior group markedly longer than median and posterior groups; ventral margin with a distinctive rounded angle at 1/3 of the length of the margin. Anteroventral corner of valves rounded; posteroventral corner armed with 1-4 large denticles, broad at their bases, protruding downwards, without setules between them; posterodorsal corner poorly defined. Posterior margin almost straight, armed with inner setules on the carapace which are not arranged in groups. Antennule not exceeding the tip of the rostrum, about 2.5 times as long as it is wide; three or four rows of setules on the antennular body. Antennular sensory seta about 1/2 length of antennular body. Nine aesthetascs of different length present in a distal position not exceeding the length of antennular body. Antenna with formula of antennal setae 003/113, spines 101/001; first segment of endopod and exopod elongated, about two times longer than the others segments; weak setules or spicules on the segments. First exopod segment with a narrow, naked or plumose seta, with length similar or slightly longer than the branches. Spine on the first endopod segment longer than second endopod segment. Apical spines slightly longer than the apical segments or about two times shorter than the apical segment itself. Three plumose apical setae not differentiated in size among themselves. Postabdomen approxamately 1.3-2.5 times as long as wide, narrowing distally. Dorsal margin weakly convex or straight. Preanal angle clearly prominent; preanal, anal and postanal margins of different length; postanal margin about 1.5-1.8 longer than anal margin, armed with 9-13 marginal denticles, of which the most distal (1-4) might be individualized, proximal denticles organized in clusters; 8-10 lateral fascicles with setules relatively weak. Postabdominal claw inserted on the projection of postabdomen, 1.3-1.5 times longer than anal margin; spinules on the ventral margin may be present; pecten of spinules on the internal and external face of claw, median pecten with strong spinules; base of the claw armed with 1-5 long and strong spinules. Basal spine almost straight, remarkably long, longer than 2/3 of the postabdominal claw length, with or without spinules on the dorsal margin. First Maxilla with two setulated setae. Limb I with epipod oval, with a finger-like projection. ODL with bisegmented seta, serrated from middle portion towards the distal portion; accessory seta implanted near the base of the ODL. IDL (en 4) with two robust setae (2-3), seta (1) rudimentary or absent; IDL setae 2-3 thick, armed with thick basal denticles. Endite 3 with four setae, anterior seta (1) shorter or similar in length to posterior setae (a-b); setae (a-b) of similar or different length; a sensillum might be present on the endite. Endite 2 with three posterior long setae (d-f) which differ strongly in length among themselves; seta (d) shorter than the seta (e), setae (e-f) with thick spinules on the lateral face; a sensillum might be present on the endite. Endite 3 armed with three posterior setae (g-i); seta (i) plumose, about 1/2 of the setae (g-h). Ejector hooks relatively short. Ventral face of the limb with six-seven groups of setules organized in clusters. Limb II with exopod elongated, short seta present which might be plumose, about two-three times shorter than exopod itself. Inner portion armed with eight scrapers not specialized and decreasing in length towards distal portion, but with some denticles on the scrapers 6-8; anterior soft setae absent; gnathobase armed with four elements, filter comb armed with seven setae, of which two proximal are shorter than the others. Limb III with pre-epipod rounded and setulated, epipod oval with a short finger-like projection. Exopod with four distal and two lateral setae; fifth and sixth setae differentiated in length, third and fourth setae long; second seta about 1.4-1.7 times longer than first setae. Setae 3-6 clearly plumose. Distal endite armed with three setae and one sensillum, setae 1-2 scraper-like of different length; third seta curved and armed with many bilaterally implanted setules (3); four plumose posterior setae present. Basal endite with four soft anterior setae increasing in length towards the gnathobase, a sensillum might be present. Gnathobase with three elements, filtercomb with seven setae. Limb IV with pre-epipod rounded or rectangular and setulated, epipod oval with a long finger-like projection. Exopod with six marginal setae; first and second setae long, not plumose; third seta plumose, short, about two times shorter than the second seta; fourth seta long and plumose; fifth and sixth setae plumose and with similar lengths; Distal endite with four setae (1-4), one scraper-like (1), three flaming-torch-like (3-4); flaming-torch setae not modified. Basal endite with three slightly setulated soft setae. Gnathobase armed with a setulated seta shorter than the length endite itself, filter comb with five setae. Limb V with pre-epipod rounded or rectangular and setulated, epipod oval with a long finger-like projection. Exopod not divided in lobes, armed with four plumose setae. Setae 2-4 of subequal lengths; first seta about two-three times shorter than the other setae. Internal lobe wide, oval and with long setules apically and laterally implanted; two setulated setae on the inner face which are shorter than the length of lobe itself. Filter comb with one or without seta. Limb VI absent.

Adult male. As for Magnospina dentifera comb. n.

Diagnosis of the genus.

Parthenogenetic female.Habitus ovoid, without dorsal keel. Head with rostrum wide, not pointed; head shield wide with distance between mandibular articulations higher than length of its posterior portion, main head pores absent in adults of Magnospina dentifera comb. n. or with three connected main head pores in Magnospina siamensis comb. n.; lateral head pores absent ( Magnospina detifera comb. n.) or present ( Magnospina siamensis comb. n.). Labral keel wide and naked, apex not elongated. Carapace ornamentation not evident, punctuated or with narrow longitudinal lines; valves armed with 40-53 setae internally inserted at the ventral margin and differentiated in three groups, setae from the anterior group markedly longer than median and posterior groups; ventral margin with a distinctive rounded angle at 1/3 of the margin length; posteroventral corner armed with 1-4 large denticles, broad at their bases, protruding downwards, without setules between them. Antennule not exceeding the tip of the rostrum, nine aesthetascs of different lengths present distally. Antenna with formula of antennal setae 003/113; spines 101/001; basal segments on the exopod and endopod about two times longer than the other segments; weak setules or spicules on the segments. Postabdomen narrowing distally, preanal angle prominent; postanal margin armed with 9-13 marginal denticles which the most distal (1-4) might be individualized, proximal denticles organized in clusters; eight-10 lateral fascicles with weak setules. Postabdominal claw inserted on the projection of postabdomen, longer than anal margin; spinules on the ventral margin may be present; pecten of spinules on the internal and external face of the claw, base of claw armed with 1-5 long and spinules. Basal spine remarkably long, longer than 2/3 of postabdominal claw length, with or without spinules on the dorsal margin (absent in Magnospina siamensis comb. n.). Limb I with endite 1 armed with three setae (g-i); IDL (en 4) with two robust setae (2-3), seta 1 rudimentary ( Magnospina dentifera comb. n.) or absent ( Magnospina siamensis comb. n.); IDL setae 2-3 thick, armed with thick basal denticles. Limb II without soft setae; short seta on the exopod; scrapers not specialized, but with some denticles, especially on scrapers 6-8; gnathobase armed with four elements, filter comb armed with seven setae, of which two proximal are shorter than others. Limb III with six setae on the exopod, third and fourth setae long; distal endite armed with three setae and one sensillum; gnathobase with three elements, filter comb with seven setae. Limb IV relatively short, six setae on the exopod; third seta plumose, short, about two times shorter than the second seta; flaming-torch setae on the distal endite not modified; gnathobase armed with a setulated setae shorter than the length of endite itself, filter comb with five setae. Limb V relatively short, setae 3-4 of exopod subequal in length; filter comb reduced, with one short seta in Magnospina dentifera comb. n. and none in Magnospina siamensis comb. n.. Limb VI absent.

Adult male. Habitus smaller than female (Figure 27). Postabdomen strongly narrowing distally. Postabdominal claw short and ticker than female (Figures 30-31). Basal spine about half-length of postabdominal claw, with tip forked (Figure 31). Limb I with two setae on the IDL (en4), setae armed with denticles; male seta with tip slightly curved; copulatory hook with one projection on the tip (Figures 32-33).

Differential diagnosis.

The synapomorphies of Magnospina gen. n. are (1) basal spines longer than 2/3 of postabdominal claw, (2) presence of 1-4 large denticles, broad at their bases, protruding downwards, without setules between them. Magnospina gen. n. can also be differentiated from the genus Coronatella because it has a distinctive rounded angle at 1/3 of the length of the ventral margin, marginal setae of valves differentiated in three groups, setae from anterior group markedly longer, wide rostrum, postabdomen narrowing distally; the males of Coronatella do not bear two lateral aesthetascs on the antennules. Magnospina gen. n. differs from Anthalona in the presence of a distinctive rounded angle at 1/3 of the length of the ventral margin, sacks underneath lateral head pores (cosmaria) being absent, shape of postabdomen, poorly developed setules of the lateral fascicles, morphology of IDL (which does not have specialized denticles), and armature of limb I; the males of Anthalona also do not bear lateral aesthetascs on the antennules. The new genus differs from Karualona in the morphology of IDL setae, shape of the postabdomen, poorly developed setules of the lateral fascicles, seta on the exopod of limb II (present in Magnospina gen. n. and absent in Karualona ) and endite basal of limb IV armed with three flaming-torch; the antennule of Karualona males bear just one lateral aesthetasc. Magnospina gen. n. is closer to Leberis according to Eliáz-Gutiérrez et al. (2008); however, it is distinguished by the presence of long setae on anterior group of ventral margin of the carapace, in the morphology of setae 2-3 of the IDL (Figures 18-19), presence of seta on exopod of limb II, absence of a dorsal keel (Figures 1-5), and presence of a long basal spine on postabdominal claw of postabdomen (Figures 13-16); males of Leberis also do not bear denticles on the posteroventral corner of valves. Magnospina gen. n. differs from Celsinotum Frey, 1991 in the absence of a dorsal keel, absence of spine-like setae on the posterior portion of valves, presence of relatively long apical (endopod and exopod) and basal (endopod) spines on the segment of the antenna, long basal spine on the postadbominal claw, absence of a rudimentary seta (i) on endite 1 of limb I (in Magnospina gen. n. setae (i) is developed). The new genus differs clearly from Bergamina Elmoor-Loureiro, Santos-Wisniewski & Rocha, 2013 in morphology of postabdomen, presence of denticles on the posteroventral margin of valves and absence of anterior seta between endites 1-2 of limb I (see Elmoor-Loureiro et al. 2013). Magnospina gen. n. differs from Extremalona Sinev & Shiel, 2012 in general morphology, presence of denticles on the posteroventral margin of valves, postabdomen morphology and armature of setae 2-3 of IDL; male of Extremalona also bears six lateral aesthetascs on the antennules. Ovalona Van Damme & Dumont, 2008 has a well-developed seta 1 on the IDL, endite 1 of the limb I without seta (i) and exopod of the limb III armed with seven setae. Magnospina gen. n. does not present any of aforementioned morphological traits to Ovalona . Table 1 shows the main differences and similarities between genera of the Coronatella -branch.