Leucothoe angraensis, Senna & Andrade & Ramos & Skinner, 2021

Senna, André R., Andrade, Luiz F., Ramos, Brenda S. & Skinner, Luis F., 2021, A new ascidian-dwelling species of Leucothoe Leach, 1814 (Amphipoda: Leucothoidae) from Ilha Grande Bay, Rio de Janeiro state, Brazil, Journal of Natural History 55 (21 - 22), pp. 1441-1460 : 1444-1455

Leucothoe angraensis sp. nov.

( Figures 2–7 )

Material examined

Holotype: female, 6.1 mm, dissected and drawn, 23°03 ʹ 10.5”S, 44°14 ʹ 37.6”W, 0–6 m depth, in Phallusia nigra, Ponta Leste, Angra dos Reis municipality, Ilha Grande Bay , Rio de Janeiro state, Brazil, 21/V/2015, B. S. Ramos and L. F. Skinner col. ( UERJ 1350 ).

Paratypes: 1 male, 7.5 mm, dissected and drawn, same collection data ( UERJ 1351 ); 1 female, 4.1 mm, habitus drawn, same collection data ( UERJ 1352 ); 1 female, 7.4 mm, dissected, same collection data ( UERJ 1353 ); 6 specimens, same collection data ( UERJ 1354 ); 3 specimens, same collection data ( MZUSP 41126 ) .

Diagnosis

Ventral cephalic keel, anterior margin produced and round. Mandibular palp, second article with 14 slender setae. Maxilla 2, inner plate, inner margin with 10 slender setae, apical margin with one stout and one slender seta, distolateral region and outer margin setulose; outer plate, apical margin with three stout setae, distal region and outer margin setulose. Female gnathopod 1, coxa with one anteroventral facial seta; dactylus reaching 0.35 × the length of propodus. Male gnathopod 1, coxa without facial setae; dactylus reaching 0.35 × the length of propodus. Female gnathopod 2, basis anterior margin with three medium slender setae, without anterodistal tubercle; carpus apically smooth; propodus with one mediofacial setal row above midline, reaching 0.4 × of propodus length, lateral face without setal row, a submarginal row of slender setae reaching 0.6 × of propodus length, palm convex with two major and two small distal tubercles near dactylus articulation; dactylus reaching half the length of propodus. Male gnathopod 2, basis anterior margin with 14 small and medium slender setae, bearing an anterodistal tubercle; carpus apically smooth, distally truncate; propodus with one mediofacial setal row above midline, reaching 0.4 × of propodus length, lateral face without setal row, without submarginal row of slender setae, palm convex with one major and two small distal tubercles near dactylus articulation, plus one major tubercle about half the length of the dactylus; dactylus reaching 0.6 × the length of propodus. Epimeral plate 1 with anteroventral row of four slender setae. Epimeral plate 2, posteroventral corner produced and acute. Epimeral plate 3, posterior margin with two distal small stout setae, posteroventral corner weakly produced and subacute. Telson, lateral margin with two proximal small slender setae, apex round, with two subapical small slender setae.

Description

Based on female holotype (UERJ 1350). Body dorsally smooth and naked. Head about as deep as long. Rostrum slightly produced downwards, subacute. Lateral cephalic lobe rounded. Ventral cephalic keel, anterior margin produced and round, anteroventral margin sinuous, ventrally cusped. Eyes oval. Antennae subequal in length, about a quarter of habitus length. Antenna 1, peduncle, first article 3.3 × longer than wide, dorsal margin naked, ventral margin with one proximal plumose seta, some sparse small slender setae, ventrodistal corner with a tuft of one simple and three plumose slender setae; second article 4.5 × longer than wide, slightly shorter than first article, dorsal and ventral margins moderately setose; third article small, 1.8 × longer than wide, about 0.3 × the length of second article, scarcely setose; flagellum 8-articulate, about 0.4 × the length of peduncle, articles 1–5 bearing an esthetasc at the distodorsal corner each; accessory flagellum 1-articulate, apically setose. Antenna 2, peduncle, first and second articles small, without setae; third article about 0.7 × the length of first and second articles combined; fourth article slender, about 6.5 × longer than wide, dorsal and ventral margins moderately setose, with some sparse plumose slender setae; fifth article slender, about 8.3 × longer than wide, about 0.8 × the length of fourth article, scarcely setose; flagellum 5-articulate, about 0.1 × the length of peduncle. Mandibles slightly asymmetric. Left mandible, molar absent, accessory setal row with 15 multi-cuspidate curved setae, lacinia mobilis strong, apically multi-cuspidate, incisor multi-cuspidate; palp 3-articulate, first article about 1.7 × longer than wide, naked, second article slightly elongate, about 4 × longer than wide and 3.5 × longer than first article, bearing 14 slender setae, third article, slender, about 0.4 × the length of second article, slightly curved ventrally, with two subapical slender setae. Right mandible like the left one, accessory setal row with 16 multi-cuspidate curved setae, lacinia mobilis feeble; peduncle, second article bearing 15 slender setae. Maxilla 1, inner plate small, rounded, bearing one apical slender seta; outer plate sub-rectangular, inner margin with five distal slender setae and one small stout seta, apical margin with nine multi-cuspidate stout setae; palp 2-articulate, second article slender, with four apical slender setae. Maxilla 2, inner plate about 1.8 × longer than wide and 1.8 × wider than outer plate, inner margin with 10 slender setae, apical margin with one stout and one slender seta, distolateral region and outer margin setulose; outer plate slightly longer than inner plate, apical margin with three stout setae, distal region and outer margin setulose. Maxilliped, inner plate distal margin truncate with v-shaped indentation and three small stout setae, outer margin with a row of small slender setae; outer plate, inner margin smooth and setose, reaching 0.4 × the length of palp article 1, bearing an apical bifid stout seta, distolateral corner with a row of five plumose setae; palp 4-articulate, first article about 1.2 × longer than wide, inner margin with simple setae, outer margin with plumose setae, second article slightly longer than first, inner margin convex and setose, third article facially setulose in its distal half, fourth article slender, curved, subequal in length to third article, distally acute, nail present.

Coxae 1–4 subequal in length, slightly overlapping. Gnathopod 1, coxa subtrapezoidal, slightly longer than wide, anteroventrally produced and round, with one anteroventral facial seta, anteroventral and ventral margins bearing small slender setae; basis about 3.3 × longer than wide, anterior margin with five proximal small slender setae; ischium and merus naked; carpus elongate, palmar margin minutely serrate, with small setae, apex curved upwards; propodus straight, margin minutely serrate, with small setae, bearing a blunt stout seta near dactylus articulation; dactylus smooth, reaching 0.35 × the length of propodus. Gnathopod 2, coxa subquadrate, anteroventral and ventral margins bearing small slender setae; basis about 2.8 × longer than wide, anterior margin with three medium slender setae; ischium and merus small, both with setae posteroventrally; carpus expanded and setose, about 0.6 × the length of propodus, apically smooth; propodus enlarged, slightly longer than basis, ischium, and merus combined, about twice longer than wide, with one mediofacial setal row above midline, reaching 0.4 × of propodus length, lateral face without setal row, with a submarginal row of slender setae, subparallel to palm, reaching 0.6 × the length of propodus, anterior margin smooth, distal margin subtruncate, anterodistal corner with a small row of long setae, posterior margin smooth, palm convex with two major and two small distal tubercles near dactylus articulation, bearing couples of small setae spread on its entire length; dactylus smooth and curved, reaching half the length of propodus. Pereopod 3, coxa 1.5 × longer than wide, anteroventral and ventral margins bearing small slender setae; basis slender, 5.7 × longer than wide, anterior margin bearing small slender setae, posterior margin with two long slender setae; ischium naked; merus and carpus slender, with small setae in the anterodistal and posterodistal corners, combined reaching 0.7 × the length of basis, merus about 1.3 × longer than carpus; propodus slender, slightly longer than carpus, posterior margin bearing three small stout setae; dactylus smooth and curved. Pereopod 4 similar to pereopod 3, coxa slightly longer than wide, margins smooth, posteroventral lobe subacutely produced, posterodorsal margin slightly concave; basis, posterior margin without setae. Pereopod 5, coxa about 1.5 × wider than long, bilobated, posteroventral lobe with two marginal slender setae, slightly more produced than anteroventral lobe; basis broadly expanded, about 1.3 × longer than wide, anterior margin bearing small stout setae spread on its entire length, posterior margin smooth, posteroventral lobe weakly produced; ischium slightly longer than wide; merus about 2.9 × longer than wide, posteroventral corner slightly produced; carpus and propodus slender, combined subequal in length to basis, about 1.7 × longer than merus, anterior margin bearing small stout setae, propodus about 1.7 × longer than carpus; dactylus smooth and curved. Pereopod 6, coxa about 1.5 × wider than long, bilobated, posteroventral lobe with five marginal slender setae, slightly more produced than anteroventral lobe, posterior margin with six small slender setae; basis broadly expanded, about 1.3 × longer than wide, anterior margin bearing small stout setae spread on its entire length, posterior margin smooth, posteroventral lobe weakly produced; ischium slightly longer than wide; merus about 3.7 × longer than wide, posteroventral corner slightly produced; carpus and propodus slender, combined about 1.2 × longer than basis, about 1.6 × longer than merus, anterior margin bearing small stout setae, propodus about 1.5 × longer than carpus; dactylus smooth and curved. Pereopod 7, coxa small, subrectangular, about 1.4 × wider than long, posterior margin with three small slender setae; basis broadly expanded, about 1.3 × longer than wide, anterior margin bearing small stout setae spread on its entire length, posterior margin continuously setulose, posteroventral lobe weakly produced; ischium slightly longer than wide; merus about 4 × longer than wide, posteroventral corner slightly produced; carpus and propodus slender, combined slightly longer than basis, about 1.6 × longer than merus, anterior margin bearing small stout setae, propodus about 1.8 × longer than carpus; dactylus smooth and curved.

Epimeral plate 1, ventral margin with an anterior row of four slender setae, posterior margin naked and slightly concave, posteroventral corner weakly produced and round, bearing a small slender seta. Epimeral plate 2, ventral margin with four small stout setae irregularly spread, posterior margin naked and concave, posteroventral corner produced and acute. Epimeral plate 3, ventral margin with two anterior small stout setae, posterior margin not sinuous, with two distal small stout setae, posteroventral corner weakly produced and subacute. Uropod 1, peduncle slender, about 5.5 × longer than wide, dorsal margin bearing small stout setae spread on its entire length; rami slender, apically acute and slightly curved upwards, dorsal margin bearing small stout setae spread on entire length; outer ramus slightly shorter than peduncle; inner ramus subequal in length to peduncle. Uropod 2, peduncle about 4 × longer than wide, dorsal margin with three stout setae; rami lanceolate, with sparse stout setae, margins minutely setulose; outer ramus about 0.75 × the length of peduncle; inner ramus about 1.5 × longer than outer ramus. Uropod 3, peduncle about 4.6 × longer than wide, dorsal margin with three stout setae; rami lanceolate, with sparse stout setae, margins minutely setulose; outer ramus slightly shorter than peduncle; inner ramus subequal in length to outer ramus. Telson entire, 2.8 × longer than wide, lateral margin with two proximal small slender setae, apex round, with two subapical small slender setae.

Sexual dimorphism

Based on male paratype (UERJ 1351). Gnathopod 1, coxa subtrapezoidal, slightly longer than wide, anteroventrally produced and subtriangular, anteroventral facial seta absent, anterior margin concave, naked, ventral margin bearing small slender setae, posterior margin concave, naked; basis about 3.3 × longer than wide, anterior margin with four proximal small slender setae; ischium and merus naked; carpus elongate, palmar margin minutely serrate, with small setae, apex curved upwards; propodus straight, margin minutely serrate, with small setae, bearing four distal stout setae; dactylus smooth, reaching 0.35 × the length of propodus. Gnathopod 2, more robust than in female; coxa subquadrate, slightly wider than long, anterior margin convex, anteroventral and ventral margins bearing small slender setae; basis about 2.6 × longer than wide, anterior margin with 14 small to medium setae spread on its entire length, bearing an anterodistal tubercle; ischium and merus small, merus with setae posteroventrally; carpus expanded and setose, about half the length of propodus, apically smooth, distally truncate; propodus enlarged, subequal in length to basis, ischium, and merus combined, about twice longer than wide, with one mediofacial setal row above midline, reaching 0.4 × of propodus length, lateral face without setal row, without facial row of setae, anterior margin smooth, distal margin subtruncate, anterodistal corner with a small row of long setae, posterior margin smooth, palm convex with one major and two small distal tubercles near dactylus articulation, plus one major tubercle about half the length of the dactylus; dactylus smooth and curved, reaching 0.6 × the length of propodus.

Etymology

The specific epithet is given in reference to the provenance of the type material, the municipality of Angra dos Reis, Rio de Janeiro state, Brazil .

Remarks

The most morphologically similar species to L. angraensis sp. nov. is L. wuriti Thomas & Klebba, 2007 , with type locality from Belize, since both share the following characters: head anterior margin rounded, eyes present, mandibular palp article 2 with 11–20 setae (14–15 in L. angraensis sp. nov., 18 in L. wuriti ); gnathopod 1, coxa anterodistal margin subtriangular, basis posterior margin naked, propodus palm without large triangular spines, dactylus reaching greater than 0.2 × propodus length (0.35 × in L. angraensis sp. nov., 0.36 × in L. wuriti ); gnathopod 2, basis posterior margin smooth, carpus apically smooth, 0.6 × propodus length, propodus distal margin subtruncate; pereopods 5–7 basis broadly expanded; and epimeral plate 3, posterior margin not sinuous, with posteroventral corner weakly produced. However, L. angraensis sp. nov. differs from L. wuriti in the following characters (those of L. wuriti in parenthesis): Ventral cephalic keel anterior margin produced and round (straight, vertical); gnathopod 1, carpus, distal and proximal margins naked and smooth (with slender and stout setae, respectively); gnathopod 2 basis with anterodistal tubercle (without anterodistal tubercle), carpus distally truncate (subacute), propodus mediofacial setal row reaching 0.4 × of propodus length (reaching 0.92 ×), dactylus reaching 0.6 × the length of propodus (almost 0.8 ×); pereopod 5, basis, posterior margin smooth (bearing three distal setae); pereopod 6, basis, posterior margin oblique to the anterior margin, angle at half-length (almost parallel to the anterior margin, angle at two-thirds of the length); and telson, lateral margin with two proximal small slender setae (naked), apex round (tridentate).

According to White (2011b), L. spinicarpa , is the most frequently cited species of Leucothoidae , with a supposed cosmopolitan distribution and bathymetrical range from the intertidal to 3,600 m depth, which contradicts the typically highly specific habitat requirements of leucothoid amphipods. The authors claim that this suggests that different species have been misidentified as L. spinicarpa . This species, originally described from Denmark, but with a neotype determined by Crowe (2006) based on material from Norway. Leucothoe angraensis sp. nov. can be easily distinguished from L. spinicarpa in the following characters (those of L. spinicarpa in parenthesis): antenna 1, about a quarter of habitus length (one-third), flagellum 8-articulate (16-articulate), accessory flagellum 1-articulate (absent); gnathopod 2, basis bearing an anterodistal tubercle (without tubercle), carpus apically smooth (apically dentate), propodus mediofacial setal row reaching 0.4 × of propodus length (reaching about two-thirds), palm with one major and two small distal tubercles near dactylus articulation, plus one major tubercle about half the length of the dactylus (with small projections); pereopods 5–7, basis broadly expanded (narrowly expanded); epimeral plate 3, posterior margin not sinuous (sinuous); and telson, apex round (bifid).

Regarding the species of Leucothoe currently known from Brazilian waters, all of them can be differentiated from L. angraensis sp. nov. by a series of characters. Leucothoe basilobata Serejo, 1998 is easily distinguished from the others, including L. angraensis sp. nov. by the presence of a well-developed anterodistal lobe in basis of male gnathopod 2, which gives the name to the species. Besides that, it differs from the new species by the following (characters in L. angraensis sp. nov. in parenthesis): mandible, incisor almost smooth (about 10 cusps), the second article of palp bearing two setae (14/15 setae); gnathopod 2, carpus subacute, ending in a long stout seta (truncate, smooth), palm with four blunt spines which increase in size in direction of the dactylus insertion (with one major and two small distal tubercles near dactylus articulation, plus one major tubercle about half the length of the dactylus); telson, apex minutely excavate (round).

Leucothoe cheiriserra Serejo, 1998 is another species easily differentiated from L. angraensis sp. nov. by the gnathopod 1 with strong spines in two rows on the posterior margin of propodus and dactylus small, about 9% (female) to 13% (male) of propodus length. Additionally, L. cheiriserra presents gnathopod 2 with carpus subacute, ending in a long stout seta, and telson apex minutely excavate, like L. basilobata , while L. angraensis sp. nov. has propodus of gnathopod 1 with margin minutely serrate, small setae, and four distal stout setae, dactylus reaching 0.35 × the of propodus length, gnathopod 2 with carpus apically truncate and smooth, and telson, apex round.

Leucothoe kensleyi Thomas & Klebba, 2006 , whose type locality is Ft. Lauderdale, Florida, USA, is also easily recognised as dissimilar to the new Brazilian species by ( L. angraensis sp. nov. in parenthesis): lateral cephalic lobe acute (round); mandible, palp second article with three setae (14/15 setae); gnathopod 2, basis without anterodistal tubercle (bearing anterodistal tubercle), palm smooth (with one major and two small distal tubercles near dactylus articulation, plus one major tubercle about half the length of the dactylus); pereopod 4, coxa with anteroventral corner sharp, ventral margin serrate (anteroventral corner round, ventral margin smooth); telson, apex tridentate (round).

Leucothoe laurensi Thomas & Ortiz, 1995 was originally described from Cuba, Ascension Island and from the Florida Keys to the Carolinas ( Thomas and Ortiz 1995) and, after that, was recorded from the Brazilian states of Pernambuco and Bahia by Serejo (1998). This species can be distinguished from all the other species of Leucothoe known from Brazilian waters, including the new species described herein, because it is the only one presenting: gnathopod 1 with carpal spur thick, with a long lateral slender seta; and gnathopod 2, carpus with apical rounded cusps, anterodistal corner of propodus projected as a bladelike process and inner margin of dactylus minutely serrate. On the other hand, this species shares with L. angraensis sp. nov. the truncate apex of carpus of gnathopod 2.

Leucothoe leptosa Serejo, 1998 differs from the new species by the following ( L. angraensis sp. nov. in parenthesis): antenna 1, peduncle article 3 enlarged distally (ordinary); coxae 3–4 ventral margin crenulate (smooth); gnathopod 2 carpus apically dentate (apically smooth); pereopods 3–4, propodus, posterodistal corner with three stout setae (one stout seta); epimeral plate 1 naked (with anteroventral row of setae); and telson, apex acute (round).

Leucothoe lihue J.L. Barnard, 1970 can also be easily distinguished from all the other species from Brazil by its exclusive gnathopod 1 of stout form, with dactylus very short. Additionally, L. lihue shares with L. angraensis sp. nov. the gnathopod 2 with an anterodistal tubercle present in the basis and male carpus apically smooth, distally truncate, but differs from the latest by some other characters ( L. angraensis sp. nov. in parenthesis): head, lateral cephalic lobe truncate and angulate (round); mandible, palp second article with two setae (14/15 setae), third article shorter than first (longer than); coxae 5, 6 with facial setae (without); pereopods 5–7, basis narrowly expanded (broadly expanded).

Leucothoe occidentalis Reid, 1951 has type locality from Tropical West Africa, about 9° 30 ʹ N 14– 15°W, was described by Reid (1951) as L. spinicarpa var. occidentalis , rediagnosed by Krapp-Schickel and Menioui (2005), and previously recorded from Brazil by; Serejo (1998) as L. spinicarpa . It resembles L. angraensis sp. nov. in many characters, but can be distinguished from that by the following ( L. angraensis sp. nov. in parenthesis): mandible, second article of palp bearing six setae (14/15 setae); gnathopod 1, coxa with ventral margin naked (bearing small slender setae); male gnathopod 2, palm with all projections near dactylus articulation (projections more developed, the most proximal one about half the length of the dactylus; pereopods 6–7, basis with posterior margin finely crenulate, without setae (smooth, continuously setulose); epimeral plate 2, posteroventral corner weakly produced (strongly produced); epimeral plate 3, posteroventral corner not produced (weakly produced).

Leucothoe oxumae Alves, Neves & Johnsson, 2020 differs from the latest by presenting ( L. angraensis sp. nov. in parenthesis): mandible, incisor 5-cuspidate (about 10 cusps), the second article of palp bearing ten setae (14/15 setae), lacinia mobilis asymmetrical in shape, but similar in size (left strong, right feeble); maxilla 2, outer and inner plates, lateral margin naked (setulose); gnathopod 1, coxa with margins naked; male gnathopod 2, basis without anterodistal tubercle (bearing anterodistal tubercle); epimeral plate 1 naked (with anteroventral row of setae); epimeral plate 2, posteroventral corner rounded, not produced (produced and acute); and epimeral plate 3, posteroventral corner produced and rounded (weakly produced and subacute).

Finally, Leucothoe urospinosa Serejo, 1998 differs from L. angraensis sp. nov. by the following ( L. angraensis sp. nov. in parenthesis): Lateral cephalic lobe bevelled (round); mandible, palp second article with three setae (14/15 setae), third article shorter than first (longer than); gnathopod 1, coxa subquadrate, with corners slightly dentate (subtrapezoidal, anteroventrally produced and subtriangular); gnathopod 2, carpus subacute, ending in a long stout seta (truncate, smooth) pereopod 4, coxa with posteroventral margin oblique (posteroventral lobe subacutely produced, posterodorsal margin slightly concave); epimeral plate 3, posterior margin sinuous, posteroventral corner round (not sinuous, weakly produced and subacute); uropods 1 and 3, outer ramus greatly shorter than inner ramus (rami subequal in length); telson bearing a couple of dorsal plumose setae (dorsal setae absent).

Biology

The ascidians have their bodies wrapped in a tunic and their anatomy forms three main cavities: internal cavity of the branchial sac, outer cavity of the mantle, and peribranchial cavity. The presence of L. angraensis sp. nov. in P. nigra was observed in all cavities of the ascidians, but with much less frequency in the outer cavity of the mantle than in the other cavities.

Other macroinvertebrates were also found in the ascidian cavities, such as polychaetes and nematodes. Individuals of the new species were found in all 10 collected specimens of P. nigra , even when these other organisms were present. The individuals were found sometimes alone in each tunicate, in pairs, or even in groups.

More studies are needed with a wide number of ascidians species along the entire Ilha Grande Bay and vicinities, in order to determine the real distribution of the new species and whether it has a species-specific association with P. nigra or if it can be found on other biological substrates.

Type locality

Ponta Leste (23°03 ʹ 10.5”S 44°14 ʹ 37.6”W), Angra dos Reis municipality, Ilha Grande Bay , Rio de Janeiro state, Brazil .

Geographical distribution

Known only from its type locality ( Figure 8 ).

Figures

Figure 2. Leucothoe angraensis sp. nov. Female paratype (UERJ 1352): Habitus. Scale bar: 1.0 mm.

Figure 3. Leucothoe angraensis sp. nov. Female holotype (UERJ 1350): (a) Antenna 1; (b) Antenna 2; (c) Head in lateral view; (d) Head in dorsal view; (e) Left mandible; (f) Right mandible; (g) Maxilla 1; (h) Maxilla 2; (i) Maxilliped. Scale bars: 0.5 mm for C–D; 0.4 mm for A; 0.1 for G–H; 0.2 mm for the remaining.

Figure 4. Leucothoe angraensis sp. nov. Female holotype (UERJ 1350): (a–b) Gnathopods 1–2, medial view. Scale bars: 0.2 mm for A; 0.5 mm for B.

Figure 5. Leucothoe angraensis sp. nov. Female holotype (UERJ 1350): (a–e) Pereopods 3–7. Scale bars: 0.5 mm.

Figure 6. Leucothoe angraensis sp. nov. Female holotype (UERJ 1350): (a–c) Epimeral plates 1–3; (D–F) Uropods 1–3; (G) Telson. Scale bars: 0.5 mm for A–C; 0.2 mm for the remaining.

Figure 7. Leucothoe angraensis sp. nov. Male paratype (UERJ 1351): (a–b) Gnathopods 1–2, medial view. Scale bars: 0.5 mm.

Figure 8. Known distribution of Leucothoe angraensis sp. nov.: Ponta Leste, Angra dos Reis,Ilha Grande Bay, Brazil.