Arcturopsis giardi (Bonnier, 1896)

King, Rachael A. & Poore, Gary C. B., 2001, Diagnosis of Arcturopsis Koehler, 1911 and redescription of A. giardi (Bonnier, 1896) (Crustacea, Isopoda, Arcturidae), Zoosystema 23 (3), pp. 467-477 : 470-476

Arcturopsis giardi (Bonnier, 1896)

( Figs 1-4 )

Astacilla giardi Bonnier, 1896: 581-587 , pl. 31, figs 3; 4.

Arcturopsis giardi – Koehler 1911: 19-20, fig. 10.

TYPE MATERIAL. — Queries to the Muséum national d’Histoire naturelle, Paris and to the Zoological Museums in Hamburg and Berlin failed to reveal the whereabouts of the 16 specimens (nine females, four adult males and three others) collected by the Caudan in the Bay of Biscay. A neotype is selected here.

MATERIAL EXAMINED. — Capbreton Canyon. NE Atlantic Ocean, Bay of Biscay , 43°38.00’N, 1°51.79’W, 923 m, RV Côte d´Aquitaine, epibenthic sled, stn Capbreton, 7. VII.1988, J. C. Sorbe, neotype, 1 8.4 mm (88/ DI19, MNHN-Is5689) ; 1, 20.8 mm (MNHN-Is5690); 3 juvenile 13.5 mm, 15 mm, 7.4 mm and 1 juvenile 6.5 mm (MNHN- Is5691, Is5695); 2 mancas 4.9 mm, 3 mm; 1

21.5 mm, 4 juvenile, 12.5 mm, 12 mm, 8.5 mm, 6 mm, 1, 8 mm, 1 juvenile, 6.6 mm and 2 mancas, 5 mm, 3 mm ( NMV J44925 - J44931 ).

DESCRIPTION

Female

Body geniculate, cylindrical. Anterolateral margins of head rounded, small rostral point evident. Fusion of head and pereonite 1 indicated by a dorsolateral groove incised laterally. Lateral margin of pereonite 1 extended anteriorly overlapping and fusing with margin of head. Fused head with a tubercle central and anterior to eyes, two tubercles posterior to eyes and one tubercle on dorsal posterior margin of pereonite 1. Pereonite 2 with small lateral tubercles, lateral margins extended. Pereonite 3 wider than pereonite 2, with lateral tubercles, lateral margins extended. Pereonite 4 about six times as long as pereonite 3, dorsally wider than pereonite 3 anteriorly, tapering posteriorly, with anterior lateral expansions, anterior half dorsally elevated, with rounded tubercle on dorsal posterior margin, and with two smaller tubercles anteriorly. Pereonites 5 to 7 progressively shorter, with paired tubercles dorsally, with lateral expansions visible dorsally. Pleotelson with evidence of three fused pleonites, its total length similar to combined lengths of pereonites 5 to 7; in dorsal view pleotelson lateral margin rounded, with small anterior lateral wings and truncate apex.

Eyes round, dorsolateral. Antenna 1 extending to just beyond end of second peduncular article of antenna 2; flagellum slender with lateral and distal aesthetascs. Antenna 2 slender, more than half as long as body; flagellum of two articles plus straight claw; flagellum lower margin with or rarely without row of simple spines along full length (see Remarks).

Mouthparts concealed by lateral expansion of head and pereonite 1. Left mandible molar with finely toothed molar bearing proximal seta; lacinia mobilis 4-toothed; incisor irregularly 3- toothed. Right mandible with smooth molar; spine row of 4; 3-toothed incisor. Maxilla 1 inner lobe with three terminal setae; outer lobe with nine distal robust setae. Maxilla 2 inner lobe with 13 plumose setae, middle lobe with four setae, outer lobe with two setae. Maxillipedal endite with four mesial setae; palp articles 2 and 3 with mesial setal rows, article 4 with mesial and lateral setal rows, article 5 with distal setae.

Pereopod 1 included within margin of head; propodus as long as carpus, mesially setose; dactylus less than half length of propodus, bearing unguis, longer than dactylus. Pereopods 2 to 4 carpus to propodus with paired rows each of about 9 to 11 long setae; dactylus absent; flexion between carpus and propodus present. Pereopods 5 to 7 progressively shorter; dactylus smooth, secondary unguis much smaller than primary.

Uropodal exopod oblique, not reaching midpoint of endopod, with three unequal distal setae.

Oostegites present on maxilliped and pereopods 1 to 4; maxillipedal oostegite rounded; oostegite 1 strap-like and extending posteriorly; oostegites 2 and 3 more or less triangular, thin; oostegite 4 chitinised, with transverse suture delimiting posterior lobe.

Male

Body approximately 2.5 times as long as that of female, extremely geniculate and cylindrical. Anterolateral lobes of head rounded, rostrum small. Head and pereonite 1 fused and with similar ornamentation to female. Pereonite 2 with slight tuberculation, small extension of lateral margins. Pereonite 3 with slight dorsal tuberculation, larger than pereonite 2, small extension of lateral margins; with midventral structure projecting more than three times depth of pereonite 3, extending forward and curving to project posteriorly, with two lateral projections and one large posterior projection. Pereonite 4 about 18 times longer than pereonite 3, in dorsal and lateral view constricted for anterior third and widening posteriorly. Pereonites 5 to 7 progressively smaller, smoother than in female but with some tuberculation, lateral margins extended. Pleotelson with evidence of three fused pleonites plus pleotelson, as long as pereonites 5 to 7. Pleotelson more elongate in dorsal view than female, with anterior lateral wings and truncate end. Eyes round, dorsolateral. Antennae 1 and 2, mouthparts, pereopods and uropods as in female. Penial plate divided anteriorly. Pleopod 1 exopod with a lateral finely setose notch, with three plumose setae of equal length on posterior face. Pleopod 2 appendix masculina basally as wide as endopod, exceeding endopod by one-third its length, tapering to two barbed filaments.

DEVELOPMENTAL STAGES

Manca 1 ( Fig. 5A )

Sexes undifferentiated, pereopod 7 absent.

Manca 2 ( Fig. 5B )

Sexes undifferentiated, pereopod 7 visible as a bud on the ventral surface of pereonite 7.

Juvenile female ( Fig. 5C )

Pereopod 7 well-developed, pereonite 4 anteriorly widened dorsally, oostegites not fully developed although rudimentary ventral marsupium formed.

Brooding female ( Fig. 1A, B )

Oostegites fully developed and ventral marsupium fully formed; marsupium with eggs, embryos or mancas.

Juvenile males, stage 1 ( Fig. 5D )

Pereopod 7 well-developed, midventral appendage on pereonite 3 visible as a bud, penial plate not evident, appendix masculina not present.

Juvenile males, stage 2 ( Fig. 5E )

Midventral appendage on pereonite 3 developed and visible laterally between the pereopods, penial plate not evident, pleopod 2 bearing simple cylindrical appendix masculina.

Copulatory males ( Fig. 1C, D )

Midventral appendage on pereonite 3 fully developed with tridentate apex curved backwards, penial plate fully developed, appendix masculina fully developed.

REMARKS

Bonnier’s type material of A. giardi cannot be found but his published description is detailed and we are satisfied that the new material belongs to this species. The female drawn here in detail has no spines on the lower margin of the first two articles of the flagellum of antenna 2 but in all the other specimens in the sample examined (male and female) spines occurred ( Fig. 2B, C ).

Arcturopsis giardi differs from the other two species of the genus in many ways. In A. giardi pereonite 4 of the female is not as triangular in dorsal view as in A. senegalensis but more elongate and there are no lateral tuberculations as in A. rudis . A. giardi females are not as ornamented as females of the other two species. The flagellum of antenna 2 is of two articles and not three as in the other two species. The pleotelson of the A. giardi female is more rounded laterally. The males of A. giardi also seem to be more elongate, especially pereonite 4, than the males of the other two species. The morphology of the midventral appendage seems to be species specific with those of A. senegalensis and A. rudis not tridentate.

Comments on A. rudis and A. senegalensis are based on Koehler’s (1911) original descriptions and illustrations as no specimens could be found for new observations. The male type specimen of A. rudis is most likely to be a juvenile as the midventral appendage does not look to be fully formed; pleopods 1 and 2 were not figured.

Figures

FIG. 1. — Arcturopsis giardi (Bonnier, 1896); A, B, habitus (MNHN-Is5689); C, D, habitus (MNHN-Is5690); E, midventral appendage (lateral view); F, midventral appendage (ventral view); G, ovigerous (ventral view). Scale bars: 1.0 mm.

FIG. 2.—Arcturopsis giardi (Bonnier, 1896); A, B, D-H, (MNHN-Is5689); A, antenna 1; B, antenna 2; C, antenna 2 flagellum with scales (NMV J44931); D, maxilliped (left); E, left and right mandible; F maxilla 1 (left); G, maxilla 2 (left); H, uropod. Scale bars: A-C, H, 0.25 mm; D-G, 0.5 mm.

FIG. 3. — Arcturopsis giardi (Bonnier, 1896), (MNHN-Is5689); A, pereopod 1; B, pereopod 2; C, pereopod 3; D, pereopod 4; E, pereopod 5; F, pereopod 6; G, pereopod 7. Scale bar: 0.5 mm.

FIG. 4. — Arcturopsis giardi (Bonnier, 1896); A-C, (MNHN-Is5690); A, pleopod 1; B, penes (dorsal and ventral views); C, pleopod 2 with appendix masculina; D, pleopod 2 of juvenile with rudimentary appendix masculina (NMV J44928). Scale bars: A, C, D, 0.5 mm; B, 0.2 mm.

FIG. 5. — Arcturopsis giardi (Bonnier, 1896); A, manca 1; B, manca 2; C, juvenile female; D, juvenile male stage 1; E, juvenile male stage 2. Scale bar: 1.0 mm.