Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva, 2022

Sousa, Francisco Diogo R., Elmoor-Loureiro, Lourdes Maria A., Freiry, Raquel Fontoura, Álvarez-Silva, Juan Pablo, Stenert, Cristina, Maltchik, Leonardo, Lopes, Paloma M. & Bozelli, Reinaldo Luiz, 2022, A new species of Acantholeberis (Crustacea, Branchiopoda) suggests an ancient geographic distribution of the genus in South America, European Journal of Taxonomy 821, pp. 40-56 : 43-51

Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov.

urn:lsid:zoobank.org:act:D49FF844-884C-4015-B691-D9F4CB67F961

Figs 2–7

Differential diagnosis

Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov. differs from the Andean A. smirnovi Paggi & Herrera-Martinez, 2020 in the relatively straight ventral margin of the head, with a truncated protuberance near the labrum. The differences in the limbs between the two species pertain to the proportion of several setae; however, the main differences might be found when observing the exopodite setae and the scrapers of the inner portion of the second limb ( Fig. 3E, G ), with scraper 6 markedly longer than scrapers 5 and 7. Seta 3 on the exopodite of the third limb in A. accolismaris sp. nov. is about 0.8 times as long as seta 4, whereas in A. smirnovi it is about 0.6 as long. The lateral and ventral surface of the postabdominal claw of A. accolismaris sp. nov. is completely covered by short and thin spines while these spines in A. smirnovi are relatively long and organized in three ventral groups. We observed that the lengths of the branches of the antenna in A. accolismaris sp. nov. are markedly different (the endopodite is about 0.8 times as long as the exopodite) while in A. smirnovi they are of similar length; however, this difference might represent a variable morphological trait. The morphological description of A. curvirostris in the literature is very ambiguous; however, scrapers 5 and 6 on the second limb are of similar length. Furthermore, the length of seta 6 of the exopodite on the third limb is shorter than half the length of seta 7 ( Dumont & Silva-Briano 1998; Hudec 2010). These proportions are different in A. accolismaris sp. nov.

Etymology

The specific name refers to geographic distribution of the new species and comes from Latin words ‘ accola ’ (‘who lives nearby’) and ‘ marae ’ (‘sea’).

Material examined

Holotype BRAZIL • adult parthenogenetic ♀, undissected in a tube with 92% ethanol; Rio Grande do Sul, Tavares, Planície Costeira; 31°30′40″ S, 51°16′02″ W; wetland; MZUSP42444 .

Paratypes BRAZIL • 18 adult parthenogenetic ♀♀; same collection data as for holotype; Oct. 2016; Raquel Fontoura Freiry leg.; FDRS0696 , EL03499 • 50 ♀♀, mostly juveniles; Rio de Janeiro, Macaé, Restinga de Jurubatiba ; 22°14′53.1″ S, 41°35′1.2″ W; Feb. 2010; pond; Paloma Marinho Lopes leg.; EL02092 , FDRS0697 .

Type locality

A wetland in the Planície Costeira, Tavares, Rio Grande do Sul, Brazil (31°30′40″ S, 51°16′02″ W).

Description (adult parthenogenetic females)

GENERAL HABITUS ( Figs 2A–E , 5A–B ). Body elongated, sub-rectangular in lateral view, oblong in ventral and dorsal views, length 0.7–1.5 mm, height/length ratio about 0.45–0.75; posterodorsal and posteroventral angles prominent. Dorsal margin regularly arched and interrupted by a shallow cervical sinus. Ventral margin clearly arched in anterior part, posterior part slightly curved inwards giving a straight aspect in lateral view. Posterior margin concave near posterodorsal angle. In dorsal and ventral views body not laterally compressed, without lateral projection.

CARAPACE ( Figs 2A–G , 6A–H ). Brownish; dorsal and ventral margins smooth; ventral margin with thick rim (more evident towards anterior part of carapace). Setae on ventral margin organized in three groups: first one set with 8–10 outwardly directed setae and 40–50 plumose and ventrally directed setae ( Figs 2A, D, F–G , 6G–H ); second one set of short naked setae ( Fig. 6C ); third one armed with long setae bearing protuberances armed with spinulae at the basis ( Fig. 6E ). Setae on posterior margin organized in two groups: first one has up to eight long setae with slightly curved proximal part and basis armed with spinulae ( Fig. 6D ), second one armed with setae decreasing in length towards posterodorsal angle and bases armed with spinulae ( Fig. 6F ).

CEPHALIC STRUCTURES ( Figs 2 , 5 ). Head ( Figs 2A–E , 5A–B ). Elongated, triangular, about 0.4 times as long as body. Dorsal margin smooth and slightly arched, a shallow cervical sinus present. Ventral margin with two inflated parts, the first one slight and positioned near base of antennule, the second one relatively robust, sometimes folded or truncated and positioned above labrum; marginal line between inflated parts straight. Ocellus markedly smaller than compound eye. Dorsal organ shorter than compound eye, rounded, with fine ring, positioned near cervical sinus ( Fig. 2I ). Rostrum not developed. Labrum ( Fig. 2A, H ) with a long horn armed with five rows of minute setulae. Antennule ( Figs 2J–K , 5C–H ). Slightly shorter than head length and dilated in distal part. Ventrolateral basal sensory seta about 0.2 times length of antennular body. Antennular body armed with up to eleven transverse rows of spinules, distal part armed with several teeth surrounding insertion of aesthetascs; inner face with teeth organized in up to eight groups ( Figs 2K , 5C–F ). Nine aesthetascs with forked apex, four of them markedly longer than others. Antenna ( Figs 2L–P , 5I–O ). Coxal region folded; basal segment robust, covered with transverse rows of fine spines and spinules, apical spine of similar length to spine of second segment of exopodite, sensory setae about two times as long as first segment of exopodite ( Figs 2M , 5J–K ). Branches markedly different in length, with cylindrical segments covered with rows of spinules; endopodite about 0.8 times as long as exopodite. Exopodite with four segments: first segment shorter than rest, armed with robust spines laterally ( Figs 2M , 5J ); second segment elongated, spine about middle length of segment itself; third segment without apical setae; fourth segment elongated with spine and three apical bisegmented setae armed with lateral spines and long setulae, spine about 0.5 times as long as segment itself. Endopodite with three segments: first segment armed with exceptionally long sclerotized and bisegmented seta which bears, on proximal part, thin lateral spines, distal part armed with 10–13 robust spines reducing in size distally ( Figs 2N , 5N ); second segment with long (but shorter than seta on first segment) and bisegmented seta which bears, on proximal part, short setulae, distal part with short and fine spines and setulae ( Fig. 5O ); third segment with spine and three apical bisegmented setae ( Figs 2O–P , 5L–M ), spine about 0.5 times as long as segment itself. Antennal formula: spines 0101/001, setae 0003/113. Maxilla ( Figs 2Q–R , 5P–Q ). Well developed, with three setulated setae and one short stout protuberance resembling crown-like seta.

THORACIC LIMBS ( Figs 3 , 7 ). Six pairs of thoracic limbs. Limb I ( Figs 3A–D , 7A–C ). Accessory seta plumose, ODL armed with two apical setae; first seta short and naked, about 0.2 times as long as second seta; second seta bisegmented, armed with short spinule on distal part, markedly long, about 2.6 times as long as accessory seta. IDL (en4) with two rows of short setulae on posterior surface and three apical setae; first seta about two times as short as second seta; second seta bisegmented and armed with short setulae on distal part about, 1.8 times as short as third seta; third seta bisegmented, markedly long and armed with short setulae on distal part. Endite 3 armed with a anterior seta (1), three posterior setae (a–c) which bears short setulae and a stiff seta, setae (a–b) similar in length and slightly longer than seta (c), stiff setae denticulated, shorter than setae (a–c). Endite 2 armed with three posterior setae (d–f) and a denticulated stiff seta, setae (d–f) bisegmented with proximal part armed with short spinulae, distal part plumose. Endite 1 with three posterior setae (g–i) and a denticulated stiff seta; setae (g–i) bisegmented and armed with short spinulae. Two ejector hooks of different lengths armed with short spinulae on distal part. Gnathobase with four setulated setae. Limb II ( Figs 3E–G , 7D–G ). Exopodite elongated, armed with three setae (a–c); setae (a) and (c) of similar length; seta (b) about 1.8 times as long as others. Inner lobe with eight bisegmented scrapers and nine setulated soft setae; scrapers 1–4 armed with short and fine spinulae on distal part, scrapers 5 and 6 armed with thin denticles, scraper 6 armed with short spines, scraper 8 armed with up to five thick denticles; scraper 6 markedly longer than scrapers 5, 7 and 8 which are similar in length. Gnathobase with naked proximal portion, distal portion armed with five elements; filter comb with eight setulated setae. Limb III ( Figs 3H–K , 7H–K ). Epipodite with short finger-like projection. Exopodite rectangular about 2.4 times as high as wide, with five distal (1–5) and three plumose lateral setae (6–8); seta 1 slightly shorter than seta 8; seta 3 about 0.8 times as long as seta 4; seta 4 about 0.7 times as long as exopodite; seta 6 about 0.4 times as long as seta 7; seta 8 about 0.7 times as long as exopodite. Distal endite armed with one posterior and three anterior setae (1–3) and two elements ( Fig. 7H–J ); setae 1 with spinulae on distal part, about 1.8 times as long as setae 2–3 which are setulated on distal part and have similar length. Basal endite with four setae (4–7) increasing in length distally, seta 7 markedly longer than seta 6. Eight long and setulated posterior setae increasing in length towards gnathobase (a–h). Gnathobase armed with four elements (1’–4’), bottle-shaped sensillum on proximal part (1’), distal part with element of sharp apex (2’) and two naked elements (3’–4’). Filter comb with nine setae. Limb IV ( Figs 3L–M , 7L–N ). Exopodite subquadrangular with portion between distal and lateral setae densely setulated; five distal (1–5) and three lateral setae (6–8); seta 1 geniculated and unilaterally armed with short spinulae, about two times as long as seta 2; seta 5 about 0.6 times as long as seta 1 and about 1.8 times as long as seta 4; lateral setae plumose, seta 8 longer than setae 7 and 6. Distal endite with four setae (1–4), seta 1 scraper-like and with thin spine at distal portion, flaming-torch-like setae (3–4) armed with long setulae, seta 3 is shorter than setae 2 and 4. Basal endite armed with five setulated setae increasing in length towards gnathobase (a–e). Gnathobase thick, with three elements and curved setulated seta; filter plate with eight setae. Limb V ( Figs 3N–O , 7O–P ). Pre-epipodite rounded and densely setulated, epipodite oval with short projection. Exopodite wide and lobed, armed with five (1–5) distal and two (6–7) lateral plumose setae; setae 1–2 of similar length and longer than seta 3; seta 4 slightly longer than seta 5; setae 6 and 7 of similar length. Inner lobe wide and densely setulated, armed with two long setae (1–2) and element; seta 2 armed with up 9 stiff setae followed by setulae, about 0.6 times as long as seta 1; setae 2 setulated. Gnathobasic filter plate with eight long setae. Limb VI ( Figs 3P , 7Q ). Epipodite with short projection. Limb as elongated lobe, unilaterally setulated, with curved apex and wide base.

POSTABDMOMINAL STRUCTURES. Abdomen ( Figs 4A , 6I ). Elongated regularly arched, armed with up to ten rows of setulae of similar length, about 0.6 times as long as postabdomen. Postabdomen ( Figs 4A–B , 6I ). In frontal view clearly trilobed and massive. In lateral view wide, height/length ratio about 0.7. Ventral margin slightly straight and armed with up to five rows of short setulae. Dorsal margin separated in anal and preanal parts; preanal margin armed with up to twenty-four groups organized in 2–3 long setulae; anal margin about 0.3 of preanal margin length, armed with 10–12 groups of setulae. Postabdominal setae longer than postabdomen length, bisegmented, proximal part of distal segment folded and densely setulated ( Fig. 4D ). Postabdominal claws ( Figs 4A–B , 6I ). About 0.4 times as long as postabdomen, with lateral and ventral surfaces completely covered with short and thin spines, pecten armed with thin spines. Basal spines ( Figs 4C , 6K ). Cluster with two robust spines of variable length inserted laterally on postabdominal claws.

Ephippial females and males

Not studied.

Distribution and biology

So far Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov. is distributed in shallow water bodies on the Brazilian coast ( Fig. 1 ). It was found in temporary ponds in Rio de Janeiro and Rio Grande do Sul States. This is an acidophilic species living in water bodies with a pH between 4.2 and 5.1, at altitudes between 4 and 15 m a.s.l., preferentially associated with macrophytes.

Figures

Fig. 2. Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov., parthenogenetic female from the Planície Costeira, Rio Grande do Sul (FDRS0696). A. Habitus, holotype. B–C. Lateral view, shape variation of carapace. D. Ventral view. E. Dorsal view. F. Outwardly directed setae. G. Plumose and ventrally directed setae. H. Horn-like outgrowth anterior to labrum. I. Dorsal organ. J. Antennule. K. Idem, inner surface. L. Antenna. M. Idem, first segment of exopodite, distal outer spine and inner sensory seta on basal segment. N. Idem, lateral seta of first segment of endopodite, armature detail. O–P. Morphology of apical setae of endopodite and exopodite. Q. Maxilla. R. Idem, short crown-like seta.

Fig. 3. Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov., parthenogenetic female from the Planície Costeira, Rio Grande do Sul (FDRS0696). A. First limb. B. Idem, endites and stiff setae. C. Idem, morphology of stiff setae of endites. D. Inner distal lobe and outer distal lobe. E. Second limb. F. Idem, gnathobase. G. Idem, comparative system of proportion of scrapers, white circles representA. smirnovi Paggi & Herrera-Martinez, 2020 and black circles representA. accolismaris sp. nov. H. Third limb.I–J. Idem, distal endite, arrow indicating the posterior seta.K. Idem, ganathobase. L. Fourth limb. M. Idem, seta 1 of distal endite. N. Fifth limb. O. Idem, inner lobe. P. Sixth limb.

Fig. 4. Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov., parthenogenetic female from the Planície Costeira, Rio Grande do Sul. A. Lateral view of postabdomen. B. Apical view of postabdomen. C. Basal spines variation. D. Detail of postabdominal setae showing difference between proximal and distal segment.

Fig. 5. Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov., parthenogenetic femalefrom Jurubatiba National Park.A. Habitus.B. Head.C.Antennule.D–H.Antennule ornamentation (arrows show teeth organized in groups). I. Antenna. J–K. Antenna in lateral view, showing its base and first exopodite segment. L–O. Antennal setae. P–Q. Maxilla (arrow shows the short crown-like seta). Scale bars: A–B, I = 100 µm; C–H, J–Q = 10 µm.

Fig. 6. Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov., parthenogenetic female from Jurubatiba National Park. A. Valve. B–F. Close view of selected regions of valve margin, as defined in subfigure A (arrows indicate some fine details). G–H. Carapace ventral view. I. Postabdomen. J. Postabdominal claw. K. Basal spines of the claw (arrow). Scale bars: A, G, I = 100 µm; B–F, H, J–K = 10 µm.

Fig. 7. Acantholeberis accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov., parthenogenetic female from Jurubatiba National Park.A–C. First limb.A. Stiff seta on first endite. B. Stiff setae on second and third endites. C. Setae d–f on endite 2. D–G. Second limb. D. Partial view of the endite. E. Scraper 8. F–G. Gnathobase, arrow shows the position of fourth element. H–K. Third limb. H–I. Exopodite. J–K. Distal endite, arrows indicate the sensilla. L–N. Fourth limb. L. General view. M. Exopodite. N. Endite and gnathobase. O–P. Fifth limb. Q. Sixth limb. Scale bars: 10 µm.

Fig. 1. Geographic distribution of species of Acantholeberis Lilljeborg, 1853 in South America. Black triangles represent previous records of A. smirnovi Paggi & Herrera-Martinez, 2020 (Paggi & Herrera- Martinez 2020). Asterisks show records of A. accolismaris Sousa, Elmoor-Loureiro & Álvarez-Silva sp. nov.