Pseudione serejoae, Brito & Cardoso & Boyko, 2018

Brito, Ayrton, Cardoso, Irene Azevedo & Boyko, Christopher B., 2018, A new species of Pseudione Kossmann, 1881 (Crustacea, Isopoda, Bopyridae) parasitizing the squat lobster Munida microphthalma A. Milne-Edwards, 1880 in the Southwestern Atlantic, Zootaxa 4377 (3), pp. 444-450 : 445-449

Pseudione serejoae n. sp.

Figs 1 , 2

Material examined. Holotype, Oceanprof II, Sta. #4-2, 22°24.419´S, 39°55.556´W, 1127 m, 29 August 2003, mature female (7.2 mm TL), MNRJ 28676, infesting right branchial chamber of female Munida microphthalma A. Milne-Edwards, 1880 (30.9 mm CL).

Paratypes: allotype mature male (4.6 mm TL), subadult male (2.0 mm TL), found with holotype in right branchial chamber, MNRJ 28678; mature female (6.1 mm TL), mature male (2.2 mm TL), subadult male (1.0 mm TL) and cryptoniscus larva (0.5 mm TL), infesting left branchial chamber of same host as holotype, MNRJ 28679; Habitats, Sta. #12, 22°13´29.221"S, 39°53´6.807"W, 978 m, 6 April 2008, mature female (9.3 mm TL), mature male (1.3 mm TL), infesting right branchial chamber of male M. microphthalma (14.0 mm CL), mature female (9.4 mm TL), mature male (1.0 mm TL), infesting right branchial chamber of female M. microphthalma (14.6 mm CL), mature female (11.0 mm TL), cryptoniscus larva (0.3 mm TL), infesting right branchial chamber of female M. microphthalma (16 mm CL), MNRJ 28680; Habitats, Sta. #13, 21°40´40.489"S, 39°57´57.119"W, 989 m, 9 April 2008, mature female (4.9 mm TL), mature male (1.0 mm TL), infesting left branchial chamber of male M. microphthalma (8.9 mm CL), MNRJ 28681; Habitats, Sta. #14, 21°6´33.085"S, 40°8´37.904"W, 990 m, 9 April 2008, mature female (8.4 mm TL), infesting left branchial chamber of female M. microphthalma (14.0 mm TL), mature female (7.0 mm TL), mature male (1.0 mm TL), infesting right branchial chamber of male M. microphthalma (13.6 mm CL), MNRJ 28682; Habitats, Sta. #62, 23°9´51.124"S, 40°50´21.622"W, 1244 m, 29 April 2008, mature female (7.3 mm TL), infesting right branchial chamber of female M. microphthalma (13.7 mm CL), MNRJ 28681; Oceanprof I, Sta. #11, 22o11.929´S, 39o49.123´W, 1334 m, 13 February 2003, mature female (4.6 mm TL), subadult male (0.4 mm TL) infesting left branchial chamber of female M. microphthalma (10.3 mm CL), mature female (6.2 mm TL), subadult male (0.5 mm TL), infesting right branchial chamber of male M. microphthalma (10.7 mm CL), mature female (6.7 mm TL), male (1.4 mm TL), two cryptoniscus larvae (0.1 mm TL), infesting right branchial chamber of male M. microphthalma (11 mm CL), MNRJ 28682; Oceanprof I, Sta. #16, 22o15.790´S, 39o53.145´W, 1071m, 13 February 2003, mature female (9.1 mm TL), cryptoniscus larva (0.1 mm TL) infesting right branchial chamber of female M. microphthalma (13.3 mm CL), mature female (1.5 mm TL), infesting left branchial chamber of female M. microphthalma (10.9 mm CL), MNRJ 28683; Oceanprof II, Sta. #1-1, 22o41.863´S, 40o07.185´W, 1318 m, 24 August 2003, mature female (7.5 mm TL), mature male (1.9 mm TL), two cryptoniscus larvae (0.1 mm TL), infesting left branchial chamber of male M. microphthalma (15.3 mm CL), mature female (TL 5.8 mm), subadult male (0.6 mm TL), infesting left branchial chamber of male M. microphthalma (12.3 mm CL), mature female (6.4 mm TL); subadult male (0.6 mm TL), infesting left branchial chamber of male M. microphthalma (15.3 mm CL), MNRJ 28684; Oceanprof II, Sta. #5, 22o27.099´S, 39o54.618´W, 1325 m, 25 August 2003, mature female (7.9 mm TL), mature male (1.3 mm TL), two cryptoniscus larvae (0.2 mm TL), infesting left branchial chamber of male M. microphthalma (13.6 mm CL), mature female (6.8 mm TL), subadult male (0.7 mm TL) infesting right branchial chamber of female M. microphthalma (11.4 mm CL), MNRJ28685; Oceanprof II, Sta. #8-1, 22o49.186´S, 40o16.804´W, 1305 m, 28 August 2003, mature female (5.9 mm TL), subadult male (0.4 mm TL), infesting left branchial chamber of female M. microphthalma (9.4 mm CL), MNRJ28686; Oceanprof II, Sta. #12-1, 22o12.059´S, 39o47.175´W, 1532 m, coll. 24 August 2003, mature female (6.5 mm TL), mature male (0.7 mm TL) infesting right branchial chamber of male M. microphthalma (17 mm CL), MNRJ28687; Oceanprof II, Sta. #16, 22o16.304´S, 39o53.360´W, 1059 m, 22 August 2003, mature female (6 mm TL), subadult male (0.4 mm TL), infesting left branchial chamber of female M. microphthalma (10.3 mm CL), MNRJ28688.

Etymology. Named in honor of the eminent Brazilian carcinologist Cristiana Silveira Serejo (Museu Nacional/ UFRJ) who has contributed much to the knowledge of peracarid diversity.

Description. Female holotype ( Fig. 1 ): body length 7.5 mm, maximal width 5.6 mm at pereomere 3, head length 2.0 mm, head width, including lamina, 2.3 mm, pleon length 2.1 mm; pereon weakly dextral. All body regions and pereomeres distinctly segmented. No pigmentation apparent.

Head immersed in first pereomere with narrow anterior lamina raised and recurved along distal margin, eyes absent ( Fig. 1A, B ).

Antennae and antennules with five and three articles each, respectively; all segments with fine scales ( Fig. 1C, D ).

Barbula with three projections, outer two pairs longer, curved in toward median and with few low lobes on surface; inner projection shorter and stub-like ( Fig. 1E ).

Maxilliped without palp, proximal lobe subquadrate, distal lobe subtriangular with rounded margins ( Fig. 1F, G ).

First oostegite proximal lobe ovate; distal lobe inner margin concave and outer margin convex, internal ridge with sinuous margin bearing few low lobes, no fine digitiform projections ( Fig. 1H, I ).

Pereon of seven pereomeres, broadest across pereomere 3, gradually tapering anteriorly and posteriorly, not markedly elongate ( Fig. 1A, B ). Dorsolateral bosses on pereomeres 1–4 on both sides, weakly formed tergal projections on pereomeres 2–4 on right side and pereomere 1 on left side. Coxal plates on pereomeres 1–4 irregularly shaped, highly crenulated with sharp projections, no two coxal plates of same exact shape; covered with minute scales. Oostegites completely enclosing brood pouch; last oostegite with posterior margin setose ( Fig. 1B ).

Pereopods 3–7 of subequal in size; pereopods 1 and 2 slightly smaller and shorter; bases of pereopods with relatively smooth projections dorsally, increasing in size gradually from pereopods 5 to 7 ( Fig. 1K ). First pereopods surrounding head region; large gaps between all pereopods ( Fig. 1B ). All pereopods with fine scales on articles.

Pleon with five distinct pleomeres plus pleotelson. Pleomeres 1–5 each with extended lanceolate, distally subacute, biramous pleopods, margins weakly crenulated, uniramous lateral plates similar in size and shape to pleopods; pleopods slightly reduced in size anterior to posterior; pleotelson rounded, with pair of large, broad, lanceolate, distally subacute, uniramous uropods, margins weakly crenulated, similar in size and shape to pleopods.

Male allotype ( Fig. 2 ): body length 4.6 mm, maximal width 2.0 mm (pereomeres 3–5), head length 0.5 mm, head width 1.2 mm, pleon length 1.3 mm.

Head sub-ovate, distinct from first segment of pereon ( Fig. 2A ); eyes absent. Antennule of three articles ( Fig. 2C ), antenna of five articles ( Fig. 2D ), extending posterolaterally from head, not visible in dorsal view.

Pereomeres 3–5 broadest, tapering anteriorly and posteriorly. All pereomeres directed laterally, distolateral margins subtriangular with rounded dorsally produced lobes medial to tapered margins ( Fig. 2A, B ).

Pereopods 1–3 subequal in size and shape, without dorsal projections on bases; 4–7 subequal in size and shape, each with carpus relatively longer compared to pereopods 1–3 ( Fig. 2A, E, F ); all articles distinctly separated.

Pleon with five segments plus pleotelson; segments tapering posteriorly, pleomeres directed laterally, posterior margins slightly convex ( Fig. 2A, B ). All pleomeres distinctly segmented, moderately produced laterally, markedly narrower than pereomeres, distolateral margins tapered, angular ( Fig. 2A, B ). Five pairs of tuberculiform subcircular pleopods ( Fig. 2A ).

Pleotelson short, slightly convex distally; uropods absent.

Type locality. 22°24.419´S, 39°55.556´W, Campos Basin , Brazil, southwestern Atlantic Ocean, 1127 m.

Distribution. Campos Basin, Rio de Janeiro, southwestern Atlantic Ocean.

Remarks. Specimens of Pseudione serejoae n. sp. were found parasitizing 21 specimens of Munida microphthalma , an unusually large number of hosts for a type series. The host of the holotype and allotype also contained a subadult male in the same branchial chamber and a female plus a male, a subadult male, and a cryptoniscus larva in the opposite chamber; this is remarkable in terms of the number of parasites (7) being born by the single host. Pseudione serejoae n. sp. shows no preference male or female hosts or for occupying the right or left host branchial chambers.

Pseudione serejoae n. sp. is most similar to P. fibriata Richardson, 1910 and P. minimocrenulata Nierstrasz & Brender à Brandis, 1931. All three species belong to a larger group of species (the Pseudione “crénéles” group sensu Bourdon (1976)) having a wide and crenulated frontal lamina and coxal plates with irregular pointed projections. All three species have a frontal lamina that extends laterally on the head and a pleon that is relatively short compared to the pereon. Pseudione serejoae n. sp. can be distinguished by from these other two most similar species by several characters of the females. These characters are best known for P. mininomocrenulata which has been reported three times and is well described (Nierstrasz & Brender à Brandis 1931; Bourdon 1976; Kazmi & Boyko 2005); in contrast, P. fibriata is known only from the types and has never been fully described ( Richardson 1910). Pseudione serejoae n. sp. has a frontal lamina that is directed medially at the posterior margins, giving the head a “pinched” appearance; P. fibriata and P. minimocrenulata do not have the frontal lamina directed medially at the posterolateral corners. Pseudione serejoae n. sp. has a narrow median region on the pereomeres that is much more strongly concave on the posterior margin than the lateral portions of the posterior margin of the pereomeres; P. fibriata and P. minimocrenulata have an even convex shape on the posterior margins of the pereomeres. Pseudione serejoae n. sp. has relatively smooth lateral margins on pereomeres 5–7; P. fibriata has strong projections on these pereomeres while P. minimocrenulata has a single nipple-like projection on each of these pereomeres. Pseudione serejoae n. sp. has the projections of the barbula relatively smooth with a few low lobes; P. minimocrenulata has numerous fine digitations on these projections (those of P. fibriata are unknown). Pseudione serejoae n. sp. has the inner ridge of the first oostegite with only a few very low lobes; P. minimocrenulata has numerous thin extensions on the inner ridge (the condition in P. fibriata is unknown).

The males of Pseudione serejoae n. sp. and P. minimocrenulata are similar in that both species have the pereomeres and pleomeres as tapered, pointed lateral projections (but see below) but differ in that the male of P. serejoae n. sp. has rounded lobes raised above the lateral margins of all pereomeres, slightly medial to the tapered lateral projections; these are lacking in P. minimocrenulata . The posterior margin of the pleotelson of the male of P. serejoae n. sp. is less convex than that of P. minimocrenulata . It should be noted that the shape of the lateral margins of the pereomeres and pleomeres of P. minimocrenulata males are not the same in all records for this species. Both Nierstrasz & Brender à Brandis (1931) and Kazmi & Boyko (2005) illustrate them as being pointed, while Bourdon (1976) illustrated them as rounded (the typical state for most Pseudione species). The mature male of P. fibriata is unknown as only a subadult male (misidentified as a microniscus stage) was illustrated by Richardson (1910); it was not described.

Figures

FIGURE 2. Pseudione serejoae n. sp., male. A, allotype, dorsal view. B, allotype, ventral view. C, antennule. D, antenna. E, left pereopod 1. F, left pereopod 7.

FIGURE1. Pseudione serejoaen. sp., female.A, holotype, dorsalview.B, holotype,ventral view.C, antennule.D, antenna.E, barbula, right side. F, maxilliped, external view. G, maxilliped, internal view. H, oostegite I, external view. I, oostegite I, internal view. J, left pereopod 1. K, left pereopod 7.