Argulus angelae, Souza & Porto & Malta, 2019

Argulus angelae sp. nov.

Material examined. – Holotype: adult female ( INPA-CR 2209 ) from the body surface of Triportheus albus Cope, 1872 , in liquid medium, from Catalão floodplain lakes complex 03°10'04" S 59°54'45" W, between the Negro and Solimões rivers, State of Amazonas, Brazil GoogleMaps . – Paratypes: Schizodon fasciatus Spix & Agassiz, 1829 (4♀♀ and 2 ƋƋ) ( INPA-CR 2214 , 2222 ) ; Potamorhina latior (Spix & Agassiz, 1829) (2 ♀♀ and 2 ƋƋ) ( INPA-CR 2223 ) ; Rhytiodus microlepis Kner, 1858 (6 ♀♀ and 10ƋƋ) ( INPA-CR 2211 ) ; Psectrogaster rutiloides (Kner, 1858) (1 ♀) ( INPA-CR 2213 ) ; Potamorhina altamazonica (Cope, 1878) (1♀) ( INPA-CR 2215 ) ; Leporinus friderici (Bloch, 1794) (1♀) ( INPA-CR 2216 ) ; Semaprochilodus insignis (Jardine, 1841) (1 ♀ and 2 ƋƋ) ( INPA-CR 2210 ) ; Rhaphiodon oulpinus Spix & Agassiz, 1829 (1 ♀) ( INPA-CR 2212 ) ; Steindachnerina elegans (Steindachner, 1875) (3 ♀♀) ( INPA-CR 2220 ) , Hemiodus sp. (1 ♀) ( INPA-CR 2219 ) , in liquid medium.

Female (Figs 2-12, 18-20)

Total length (tl) 1.6-3.4 (2.9) mm (Figs 2-3). Body elongated. Milk-white coloured dorsal surface with light yellow markings. Carapace longer than wide. Carapace length (cl) 1.1-2.2 (1.8) mm, total length/ carapace length (tl/cl) ratio 1.5-1.7 (1.6). Carapace lateral lobes cover sympods and a third of endopods and exopods on the first pair of legs and the anterior half of the sympods on the second pair.Antero-lateral depressions pronounced and deep, forming a distinct frontal region (Figs 2-3) delimited by the rectangular side grooves. Edge of suction cups visible in dorsal view. Well-defined interocular ribs. Large paired compound eyes in anterior third of the body (Fig. 2). Nauplius eye located on dorsal surface near the centre of carapace. Ventral surface of anterior frontal region armed with numerous similar-sized, sharply pointed, regularly arranged spines beyond anterior margin of larger posterior respiratory area (Fig. 3). Lateral lobes broadly rounded, extending posteriorly to cover base of 2 nd pair of legs (Figs 2-3), separated by large sinus with more than 1 / 3 the length of the carapace. Carapace length/width (cl/w) ratio 0.9- 1.2 (1.1). Respiratory areas consist of smaller ovoid, anterior “area” to larger, posterior ovoid “area” (Figs 3, 11). These are vaguely defined to visible on the ventral surface of the lobes, somewhat obscured in dorsal view.

Thorax (pereon) (Figs 2-3) distended with eggs and indistinctly 4-segmented ventral surface.Dorsal surface displaying three longitudinal pigmented bands, the two lateral ones formed by small circular melanophores and the central one without pigments. On the first somite, a row of dark brown pigments occurs perpendicularly to the body axis, extending across the carapace’ s lobes, shown as Y-shaped patterns.

Abdomen (pleon) length (Figs 2-3) (al) 0.4- 0.9 (0.7), posterior lobes taper to straight sharp points, separated by a sinus, encompassing nearly 55 % of total abdomen length, longer than wide, bearing small homogeneously distributed spines on the ventral and dorsal surface all-over. Total length/abdomen length (tl/al) ratio 3.5-4.2 (3.9). Abdomen (pleon) width (aw) 0.2-0.7 (0.4). Total length/abdomen width (tl/aw) ratio 1.3-2.3 (1.8). Abdomen longer than wide, posterior lobes tapering to a point from behind anal sinus. Paired spermathecae rounded, situated in fused part of abdomen.

First antenna (antennule) (Fig. 8) very small, hooks short, approaching each other at midline. First antenna (Fig. 8) comprising 2 sections: stout proximal section; slender distal section; both 2-segmented. First segment with large, pointed posterior spine; 2 nd segment with a small hook-like anterior spine, a small hook-like terminal spine and a small hook-like medial spine. 3 rd segment bearing single seta, terminal segment displaying group of apical spines.

Second antenna (Fig. 8) 4-segmented:1 st segment bearing pectinate scales, slight projection on posterior margin; 2 nd and 3 rd with number of pectinate setae; 4 th terminating in group of small apical spines. Pair of small post-antennal spines occur on ventral surface of cephalothorax (Fig. 3).

First maxilla (maxillula) transformed to large suction cups, supporting rods with 4-7 sclerites (Fig. 9). Rod elements similar in form; rim of suction cups with a fringe of simple setae in the anterolateral part. Second maxilla (Fig. 12) consist of 5 segments: basal plate ornamented with 3 posteriorly directed sharp teeth and long antero-lateral process; 2 nd segment with a spine distally; 3 rd and 4 th segment very short; 5 th with 3 small terminal claws.

Retractile pre-oral spine, without scales, located midway between maxillary suckers. Mouth tube of moderate length, usually not reaching thoracic ac-

2 3

Figs 2-3. Female of Argulus angelae sp. nov. 2. Dorsal view. 3. Ventral view. Scale bars = 1 mm.

cessory spines, bearing a pair of simple spines on its anterior margin. Denticulate mandibles visible within mouth tube denticles single row (Fig. 10).

Pair of accessory spines located between maxillae and pair of thoracic spines posterior the maxillae (Fig. 3). First to fourth pair of thoracopods biramous and of near equal size; sympods 2-segmented (precoxa, coxa, basis, exopod and endopod), exopods and endopods with plumose setae. First and second pair of legs (Figs 4, 7) with a dorsal flagellum on the second segment and ornamented with plumose setae.

Third (Fig. 6) and fourth pair (Fig. 7) of thoracopods with the first, second and third segment covered with spines; first segment with pronounced natatory lobe (coxopodite expansion), with rounded margins and posterior tip (tapered end) having seven feathery setae; second segment displaying five plumose setae on the posterior margin.

Male ( Figs 13-17 View Fig , 21-22 View Fig )

Total length (tl) 2.2-3.1 (2.7) mm, about 8 % less than the female ( Fig. 14 View Fig ). Dorsal surface of milk-white colour with light yellow markings, but with a rather lighter and dense coloration than in females. Carapace heart-shaped, slightly wider than long. Carapace length (cl) 0.7-1.6 (1.4) mm. Carapace total length/length ratio (tl/lc) 1.8-3.1 (2.0).

Frontal region ( Fig. 13 View Fig ) better defined than female’ s and well defined by antero-lateral depressions and a posterior cephalic sulcus. Lateral lobes broadly rounded ( Fig. 13 View Fig ), separated by large X-shaped sinus nearly half as long as the carapace, and similar to that in females. Dorsal carapace markings similar to that of female, but less dense. Respiratory areas (Fig. 11) are moderately defined and partly visible from dorsal aspect of the lobes.

Thorax (pereon) ( Fig. 13 View Fig ) smaller, narrower and less prominent than the female’ s and displays four well-defined somites. Dorsal surface with three longitudinal pigment bands: the two lateral ones

10

11 12 Fig. 4-12. Female of Argulus angelae sp. nov. 4-7. Legs; scale bar = 0.1 mm. 8. Antenna 1, 2 and antennule. 9. First maxilla; scale bar = 0.1 mm. 10. Retractile pre-oral spine and mouth tube; scale bar = 0.1 mm. 11. Respiratory area; scale bar = 1.0 mm. 12. Second maxilla; scale bar = 0.2 mm.

being formed by melanophores and the central one without patches, but less evident than the female’ s.

Abdomen (pleon) ( Fig. 13 View Fig ) oval and slightly longer than wide, total length/abdomen length ratio (tl/al) 2.4-3.3 (3.0). Abdomen width (aw) 0.2-0.4 (0.3). Abdomen length/width (al/aw) ratio 2.3-4.0 (2.9). Pair of well-defined testis in similar shape than the abdomen, occupying nearly 90 % of the abdominal area. Abdominal lobes extending towards anal sinus, lanceolate at the extremities. Well-defined posterior abdomen sinus, 42 % of the total length of the abdomen. On both sides of the midline of the abdomen there are melanophores forming small dark spots.

First to 4 th pair of biramous limbs (swimming legs, thoracic legs, thoracopods, pereopods) of nearly equal size; sympods 2-segmented (precoxa, coxa, basis, exopod and endopod), exopods and endopods with plumose setae ( Figs 14-17 View Fig ). First and 2 nd thoracic legs provided with flagella, arising from dorso-proximal region of exopod ( Figs 14-15 View Fig ).

Sexually dimorphic characters present in 2 nd, 3 rd and 4 th legs. Sexual modifications of the 2 nd leg consists of five flag-like protrusions ( Fig. 15 View Fig ), adorned with scales. Third leg with two rounded flag-like protrusions ( Fig. 16 View Fig ). Fourth leg with peg process on anterior side modified at the tip opposite to the cup-shaped elevation (accessory structure of couplings). Modifications of the fourth pair of male legs include an anterior projection with a median aperture covering the gonopore. Natatory lobes are triangular in shape with four sections of plumose arrows. Area of attachment: body surface, base of the fins, gills and buccal cavities.

Etymology. The specific name is a tribute to Dra. Angela Maria Bezerra Varella, for all the years dedicated to the studies in fish parasitology in the Amazon, a great researcher and advisor of the postgraduate course in freshwater biology and inner fishing of the National Research Institute of Amazonia. The name of the species derives from the researcher’ s first name: Angela – angelae .