(Fig. 3)
Amphion de Reynaudii Milne Edwards 1832: 336 –340, pl. 12, Figs. 1 –10. Amphion Reynaudii Milne Edwards 1837: 489, pl. 28, figs. 8, 9.
Amphion reynaudii Dohrn 1870: 607 -626, Figs. 1 –10.— Heegaard 1969: 01–82, Figs. 1 –158. Amphion provocatoris Bate 1888: 913 –918, pl. 148.
Amphion armata Koeppel 1902: 295.
Amphionides valdiviae Zimmer 1904: 226.— Gurney 1960: 83. Amphionides reynaudii Williamson 1973: 36 –49, Figs. 1 –4.— Fransen 2010: 83 –95, Figs. 62.1–62.6.— Kutschera et al. 2012:916 -930; Figs. 1 –7.
Material examined. Brazil, Fernando de Noronha Archipelago. CARECOS Project. St FN-BG, 3°51'23.28”S 32°27'18”W; 0–0.6 m, WP2, 300-µm mesh size, Mysis VI (MOUFPE 15.719). Camadas Finas I Project. St FN-99, 03°46’25’’S 032°22’77”W; 0–150 m, bongo, 300-µm mesh size, 5 Mysis (II, VI, VII, X, XII) (MOUFPE 15.711). St FN-100, 03°46’47”S 032°21’12”W; 0-150m, bongo, 500-µm mesh size, 2 Mysis (II, VII) (MOUFPE 15.713). St FN-90, 03°47’22” S 032° 22’29” W; 0–150 m, bongo, 300-µm mesh size, Mysis II, VIII, X (MOUFPE 15.714). St FN-91, 03°45’12”S 032°19’84”W; 0–150 m, bongo, 500-µm mesh size, 2 Mysis (IV, VIII) (MOUFPE 15.715). St FN-106, 03°54’32”S 032° 27’08”W; 7.6–22.8 cm, Hyponeuston, 500-µm mesh size, Mysis IV (MOUFPE 15.716). St FN-98, 03°46’58”S 032°21’17”W; 0–150 m, bongo, 500-µm mesh size, Mysis IV (MOUFPE 15.717). St FN- 107, 03°54’50”S 032°28’08”W; 0–7.6 cm, Epineuston, 500-µm mesh size, Mysis VI (MOUFPE 15.718). St FN- 91, 03°45’12” S 032° 20’24” W; 7.6–22.8 cm, Hyponeuston, 500-µm mesh size, Mysis IX (MOUFPE 15.720). St FN-93, 03°45’18” S 032°19’94’’ W; 0–150m, bongo, 500-µm mesh size, Mysis X (MOUFPE 15.721). St. Peter and St. Paul’s Archipelago and Rocas Atoll. Camadas Finas I Project. St RA-66, 03°47’02” S 033° 56’45” W; 7.6– 22.8 cm, Hyponeuston, 500-µm mesh size, Mysis XI (MOUFPE 15.722). St SPSP-73, 00°55’00” N 029° 20’05” W; 0–7.6 cm, Epineuston, 500-µm mesh size, Mysis II (MOUFPE 15.712).
Diagnosis for the larvae. Body long and laterally compressed; long, diaphanous and delicate carapace, anterior margin with a pair of orbital spines, and a pair of simple antennal spines; with anterior dorsal organ, short rostrum; large eyes, eye-stalk with ellipsoid form and possess ommatidia, each with crystalline cone cells; short abdomen with six segments, bearing a lateral process on the first abdominal segment in stages II-XII; pleopods absent in stages II-IX; the first pair of thoracic appendages develops into functional maxillipeds; the second and third maxillipeds develop into locomotory organs with long exopodial swimming fans. In later larval stages the second and the third maxillipeds can only be distinguished from the thoracopods by their enervation and position, all these appendages are known as thoracopods; the first stage (sensu Fransen 2010) starts with two antennae, mandible, maxillula, maxilla, and three thoracopods, in the second stage, the fourth thoracopod starts to develop as a little bud. In the successive Mysis stages the other thoracopods develop; telson with rounded posterior border in early stages to pointed posterior border in later stages. Uropods vestigial in the second stage, present in all other stages, always forming a tail fan together with the telson (modified from Heegard 1969; Fransen 2010; Kutschera et al. 2012).
Geographic distribution. eastern North Atlantic: Canaries, Cape Verde; western North Atlantic: Bermudas, Caribben; eastern South Atlantic: west Africa; Northern Indian Ocean: Arabian Sea, Error Seamount, Bay of Bengal; western Indian Ocean: Saya-de-Malya, Seyshelles, Madagascar, Mauritius islands, Mozambique slopes; eastern North Pacific: Colombia; eastern South Pacific: Chile from Caldera to Easter Island; Desventuradas, Juan Fernándes, Salas and Gómez and San Felix islands; western North Pacific: Japan; Philippines; Northeastern Australia; central North Pacific: Hawaii (Heegaard 1969; Williamson 1973; Vereshchaka 1995; Lindley & Hernandes 1999; Rivera et al. 2004; Landeira et al. 2010).
New records. St. Peter and St’. Paul Archipelago, Fernando de Noronha Archipelago and Rocas Atoll.
Remarks. This study is the first record of this species for these oceanic islands and also the first record in neuston samples. Nine larval stages were registered in this study, based on the stage classification of Heegaard (1969). Among the three specimens classified as Mysis X in this study, one specimen is probably an intermediary stage between Mysis X and XI sensu Heegaard (1969), because of the different size and development of the last thoracopods (Fig. 3 i, Table 1). The existence of this intermediary stage was first hypothesized by Kutschera et al. (2012), although it was not found in their study.
Several specimens found in this study differ in size from those analyzed by Heegaard (1969) and Kutschera et al. (2012).
The Mysis IV sensu Heegaard (1969), which corresponds to stage 1 sensu Kutschera et al. (2012) was caught as three individuals with 2.23 to 2.41 mm CL and 5.81 to 6.23 mm TL (Table 1). The Mysis IV found in Heegaard (1969) was of similar size, with CL = 2.2 mm and TL = 6.0 mm (CL = 2.2 to 2.3 mm and TL = 6.1 to 6.2 mm in Kutschera et al. 2012). One specimens classified as Mysis IV in this study was considerably smaller, with a TL = 5.81 mm (the same size of the Mysis III in Heegaard 1969), but with a similar morphology of the Mysis IV, because of the well-developed first pereiopod, telson and uropods (Fig. 3 b).
In this study, two specimens were found as Mysis VIII with very different sizes, with 3.69 mm and 4.60 mm CL and 8.30 mm and 9.42 mm TL. One of those Mysis VIII was considerably smaller than expected, but showed a morphology that was similar to a Mysis VIII, because of the poorly developed first pereiopod (Fig. 3 f, Table 1). The Mysis VIII in Heegaard (1969) showed CL = 4.5 mm and TL = 9.0 mm, similar to the larger specimen in this study. Kutschera et al. 2012 also found a considerable size range for their stage 4 (i.e., Mysis VIII), with CL = 3.8 to 4.2 mm and TL = 9.0 to 9.1 mm.
The Mysis X presented in this study showed a TL = 6.52 to 7.88 mm and CL = 13.03 to 15.65 mm; for three specimens measured (Table 1); the larvae recorded by Heegaard (1969) presented a TL = 7.0 mm and CL = 13.0 mm and the larvae recorded by Kutschera et al. 2012 as stage 6 presented a TL = 7.9 mm and CL = 13.0 - 15.5 mm. The specimens with 14.95 and 15.65 mm recorded in the present study were larger than the Mysis X described by Heegaard (1969). However, it did not present any characteristics (e.g. no present pleopod development) of the Mysis XI (Fig. 3 i). The present study records Mysis XI and XII with TL = 15.4 and 21.17, respectively, which were also smaller than the larvae described by Heegaard (1969). Probably, the specimens recorded in this study may be the hypothetical phase between Mysis XI and XII suggested by Kutschera et al. (2012).
Heegaard (1969) described thirteen different larval stages from the Indian Ocean Expedition. In contrast, Williamson (1973) analyzed the same samples studied by Heegaard (1969) and suggested that the stages XII and XIII were a female and a male specimens, respectively, and that they were not successive larval stages, as suggested by Heegaard (1969). Kutschera et al. (2012) have drawn the same conclusion as Williamson (1973). In the present study, one Mysis XII was found, with the characteristics of a female (Fig. 3 l), which should have no eighth thoracopods and a uniramous first pleopod (Williamson 1973; Fransen 2010). In fact, the sexual differentiation starts in Mysis IX. Later stages may be separated into females and males based on the lengths of the flagella and the thickness of the antennular peduncle (Williamson 1973; Fransen 2010), but, in this study, sexual differentiations were not verified for Mysis IX, X and XI.
Distribution of Amphionides reynaudii. In this study, larvae of A. reynaudii were found around all three island ecosystems. Also, the specimens were caught with three different gears (neuston, bongo and WP-2 nets). Their densities and frequencies were extremely low. In the neuston net, density varied from 0.1 ind. 100 m -3 (Epineuston FN and SPSP, Hyponeuston AR) to 33 ind. 100 m -³ (Hyponeuston FN). The initial larval stages were found in the neuston net (Mysis II and IV) (Table I). The only exception was one Mysis X larva found off AR. The larvae were found mainly during the night, except at SPSP.
Densities and frequencies of A. reynaudii larvae in the bongo nets around FN varied from 2.0 ind. 100 m - 3 in the 500-µm mesh to 2.4 ind. 100 m - 3 in the 300-µm mesh. All larval stages were found in the bongo net, and all specimens were registered during the night. In the subsurface WP-2 net hauls, only one specimen (Mysis VI, Table 1) was caught, in the nearshore area of FN, during the day.