Prenda arvensis, Francisco Diogo R. Sousa, Lourdes M. A. Elmoor-Loureiro & Sandro Santos, 2016

Francisco Diogo R. Sousa, Lourdes M. A. Elmoor-Loureiro & Sandro Santos, 2016, New findings of Hexalona-branch representatives in Brazil, with a description of Prenda gen. nov. (Crustacea: Anomopoda: Aloninae), Journal of Natural History 50 (43), pp. 1-42 : 34-37

Prenda arvensis gen. nov. and sp. nov.

( Figures 9 – 11 )

Type locality

A temporary pond located in a high-altitude field (aproximadately 1200 m), Bom Jesus, Rio Grande do Sul, Brazil (28°36 ʹ 57 ʺ S, 50°22 ʹ 11 ʺ W).

Material type

Holotype: Dissected parthenogenetic female on the slide deposited at the Museum of Zoology of the State University of Bahia under accession number UFBA2168 . The label of the holotype is: ‘ Prenda arvensis gen. nov. and sp. nov., 1 parth. ♀ from a temporary pond, Bom Jesus , Rio Grande do Sul, Brazil. Holotype ’.

Paratypes: Four parthenogenetic females from temporary pond located in highaltitude field, Bom Jesus, Rio Grande do Sul, Brazil (28°36 ʹ 57 ʺ S, 50°22 ʹ 11 ʺ W). Material collected by MSc. Raquel Freiry and Dr. Leonardo Maltchik on 17 June 2014 and leg by Dr. Cristina Stenert. Slides containing dissected specimens deposited at Laboratório de Biodiversidade Aquática, Universidade Católica de Brasília ( CLLA 216-219).

Etymology

The name arvensis comes from the Latin word arvum (field). This name is related to the habitat of new species, which is associated with a temporary pond located in a highaltitude field in Rio Grande do Sul state.

Diagnosis

As for the genus.

Description

Parthenogenetic females. Habitus ( Figure 9 A). In a lateral view, the carapace is oval, maximum height at middle of body, body height/length ratio about 0.63, not laterally compressed. Dorsal margin convex. Dorsal keel absent.

Head ( Figure 9 A, D – E). Ocellus and eye of different size. Head shield not studied. Rostrum short, in lateral view projected towards the ventral margin of carapace. Two connected main pores of similar size, connection relatively wide; PP about 0.5 IP; lateral head pores tiny, located at level between main head IP. Labrum ( Figures 9 F, 11O). Anterior margin armed with large notch; posterior margin with two clusters of setulae; apex rounded.

Carapace ( Figure 9 A – C). Covered with fine longitudinal lines; ventral margin almost straight, with 36 plumose setae per valve, posterior setae long. Posterior margin almost straight, armed with internal spinulae not arranged in groups, projected beyond the margin in the posteroventral corner; distalmost spinulae short.

Antennule ( Figure 9 G). Not exceeding the length of rostrum, about 2 times longer than wide; three rows of short setulae on the antennular body. Antennular sensory seta slender, about 3 times smaller than the antennular body, inserted in two-thirds of antennule length counting from the base. Nine aesthetascs of different length projecting beyond the tip of rostrum; aesthetascs very short, about 2.5 times shorter than length of the antennular body.

Antenna ( Figure 9 H). Coxal setae not studied. Basal segment thick, armed with a short spine and spinulae. Antennal formula: spines 001/101, setae 113/003. Median segment of exopod and endopod shorter than apical segments. Seta on first segment of exopod thin, not exceeding the length of branches of the antenna. Seta on second segment of exopod bisegmented, similar in length to shorter apical seta. Spine on first segment of endopod short, exceeding half the length, but not reaching the end of second segment. Apical spines of the endopod and exopod slightly longer than length of apical segments of antenna. Apical seta bisegmented and setulated. All segments bear spinulae at terminal portion; setulae on second segment of exopod long.

Abdomen about 1.7 times shorter than thorax, armed with three rows of abdominal setae.

Postabdomen ( Figures 9 I – J, 11P). About 2.8 times as long as wide, ventral slightly rounded, with two rows of spinulae on dorsal margin. Preanal and postanal angles evident; preanal margin longer than anal and postanal margin. Anal margin strongly concave, with 3 – 4 groups of denticles. Postanal margin slightly concave, truncated, with prominent distal angle. Eight to 10 lateral fascicles armed with poorly developed setulae. Seven robust merged marginal denticles increasing in length towards distal portion, distalmost denticles bear spinulae on the anterior margin. Postabdominal seta not studied. Postabdominal claw ( Figure 9 I – K). Implanted at the projected short basis from the postabdomen, similar to length of anal margin, uniformly curved, with 3 – 4 short spinulae on the base; pecten armed with one row of inner and outer spinulae; outer row with spinulae of similar length; distal spinulae on inner row longer than others. Basal spine ( Figure 9 I – K) short, of similar length to claw at its base, without spinulae or setulae.

Mandibles not studied. Maxilla ( Figure 10 A). Armed with two setulated setae. Six pairs of limbs.

Limb I ( Figures 10 B – D, 11Q). Epipod oval with long projection. ODL with a seta armed with slight and short setulae from distal part, shorter than length of IDL setae; accessory seta not studied. IDL (en4) with two groups of spinulae on its face, three setae present; seta 1 relatively developed, about 3.5 times shorter than setae 2 – 3, naked; setae 2 and 3 similar in length, bisegmented and armed with short and slight setulae. Endite 3 with four setae; posterior setae (a – b) longer than anterior seta 1, which is slender. Endite 2 with two rows of spinulae; three posterior setae present (d – f), setae (e – f) similar in length, both setae have thick spinulae on the lateral face; endite armed with a minute element inserted near to base of the seta (d); seta (d) setulated and exceeding half the length of setae (e – f). Endite 1 with three posterior setae (g – i); seta (g) and (h) bisegmented and densely setulated in distal part, of similar length; seta (i) rudimentary. Ejector hooks of different length and armed with short denticles. Ventral face of the limb with nine groups of setulae organised in clusters, decreasing in length towards the distal portion. Gnathobase elongated; setulae were not observed on the gnathobase.

Limb II ( Figure 10 E – F). Exopod elongated, with one row of setulae; one seta setulated at distal portion present, about 2 times shorter than exopod itself. Inner limb portion armed with eight scrapers decreasing in length towards the gnathobase; scraper 5 – 4 of similar length; scrapers 1 – 5 armed with fine spinulae; scrapers 6 – 8 armed with fine spines. Proximal portion of the gnathobase short, apex armed with setulae; distal portion armed with four elements, first as a short sensillum, second as element with distal portion acute and slightly geniculated, third element armed with denticles, fourth element short and obtuse. Filter comb with seven setae; first seta short and densely setulated; other setae long and slightly setulated (setulae on the setae not showed).

Limb III ( Figures 10 G – I, 11R). Epipod not studied. Exopod subquadrangular, with five distal and two lateral setae. Seventh seta setulated and about 1.5 times longer than sixth seta; sixth seta setulated. Fifth seta long, armed with short setulae, about 1.5 times longer than second seta. Third and fourth setae setulated and similar in length. Second seta about 1.6 times longer than first seta, armed unilaterally with short spinulae. First seta naked, shorter than midlength of second seta. Distal endite armed with three setae (1 – 3), two scraper-like of similar length (1 – 2); third seta curved and armed with many setulae bilaterally implanted (3); four plumose posterior setae similar in length (a – d). Basal endite with four soft anterior setae increasing in length towards the gnathobase, one sensillum present. Gnathobase armed with four elements, the first being a cylindrical sensillum, the second a short geniculated seta, the third elongated and not acute, the fourth element with tip acute, naked. Filter comb with seven setae (setulae not showed on the figures).

Limb IV ( Figures 10 J – L, 11R). Pre-epipod rounded and densely setulated. Epipod oval with a long projection. Exopod subquadrangular with six setae; setae 3 – 6 plumose; seta 4 slightly longer than setae 5 – 6; third seta long, similar in length to second seta; first seta slightly shorter than second seta, naked. Distal endite with four setae (1 – 4), one scraperlike (1), three flaming torch-like (3 – 4); the first flaming torch relatively robust, with long setulae (2). Basal endite with three soft setae of similar length. Gnathobase armed with one globular sensillum and one setulated seta implanted on a robust base. Filter plate with five setulated setae (setulae not showed on the figures).

Limb V ( Figures 10 M – N, 11R). Pre-epipod rounded and densely setulated, epipod oval with long projection. Exopod divided into two lobes, incursion between lobes relatively shallow; four plumose setae present; setae 2 – 4 similar in length; first seta about 2 times shorter than other setae. Internal lobe wide, oval and with long setulae; two setulated setae on the inner face of the lobe, first seta longer than length of the lobe; filter plate armed with three naked setae and one element.

Limb VI ( Figures 10 O, 11R). A short and wide lobe, relatively rounded, about 1.3 times longer than width of lobe; apical margin of the lobe with long setulae; only one lateral margin totally setulated.

Male. Unknown.

Ephipial female. Unknown.

Size. Up to 0.37 mm.

Geographical distribution. Prenda arvensis gen. nov. and sp. nov. seems to have a reduced geographic distribution, restricted to altitude fields. So far, this species has been observed only in the type locality. This is a rare species and we believe it to be endemic. Prenda arvensis gen. nov. and sp. nov. inhabits a temporary pond covered by S phagnum. The water conditions point to an acid environment ( pH below 5).

Figures

Figure 9. Prenda arvensis gen. nov. and sp. nov. from type locality. (A) Habitus; (B) anteroventral corner of carapace; (C) posteroventral corner of carapace; (D – E) head pores; (F) labral keel; (G) antennule; (H) antenna; (I – J) postabdomen; (K) ventral view from terminal claw and basal spines. Scale bars = 50 µm.

Figure 10. Prenda arvensis gen. nov. and sp. nov. from type locality. (A) Maxilla; (B) limb I; (C) idem, third endite; (D) idem – ODL and IDL; (E) limb II; (F) idem, exopod; (G) limb III, exopod; (H – I) idem, endites; (H) distal endite; (I) basal endite; (J) limb IV, exopod; (K – L) idem, endites; (L) filtercomb; (M) limb V; (N) idem, iternal lobe; (O) limb VI. For abbreviations, see Material and methods. Scale bar = 50 µm.

Figure 11. (A – C) Alona cf. guttata: (A) habitus from parthenogenetic female; (B) labral keel; (C) postabdomen. (D – G) Alona elisae sp. nov., holotype: (D) habitus from parthenogenetic female; (E) labral keel; (F) postabdomen; (G) idem, lateral fascicles; (H) habitus from male; (I) male, labral keel and hook; (J) male, postabdomen. (K – N) Alona isabellae sp. nov., holotype: (K) habitus from parthenogenetic female; (L) labral keel; (M) postabdomen; (N) idem, lateral fascicles. (O – R) Prenda arvensis gen. nov. and sp. nov., holotype: (O) labral keel; (P) postabdomen; (Q) limb I; (R) limbs IV, V and VI. For abbreviations, see Material and methods. Scale bars: B, C, E, F, I, J, M, O – R = 25 µm; A, D, H, K = 50 µm.