Pseudorhabdosynochus exoticus, Sigura & Justine, 2008

Sigura, Aude & Justine, Jean-Lou, 2008, Monogeneans of the speckled blue grouper, Epinephelus cyanopodus (Perciformes, Serranidae), from off New Caledonia, with a description of four new species of Pseudorhabdosynochus and one new species of Laticola (Monogenea: Diplectanidae), and evidence of monogenean faunal changes according to the size of fish, Zootaxa 1695, pp. 1-44 : 22-24

Pseudorhabdosynochus exoticus n. sp.

( Figs 10–11)

Type host: Epinephelus cyanopodus Richardson (Serranidae) .

Type locality: Lagoon off Nouméa, New Caledonia.

Site: Between secondary gill lamellae.

Type specimens: Holotype, JNC1660 A35, Passe de Dumbéa , off Nouméa, New Caledonia (22°20’S, 166°15’E, 25.xi.2005).

Material examined: 226 specimens including 63 ‘carmine’ (c) and 17 ‘picrate’ (p).

Material deposited: Holotype (c) and 154 paratypes (24 c, 123 uc, 17 p), MNHN, JNC546 , 1625 , 1626 , 1660 , 1661 ; paratypes, BMNH 2007.11.23.8–9 (2 c), 2007.11.23.10–11 (2 uc); USNPC 100404 (2 c), 100405 (2 uc); SAMA AHC 29299–300 (2 c), 29301–2 (2 uc); HCIP M-460 (2 c, 2 uc); SZU 2007112104-1–2 (2 c), 2007112104-3–4 (2 uc).

Prevalence: 76 % (13/17) in all fish (Table 2); 100% (12/12) in large fish with ‘specific’ fauna ( Table 10).

Intensity: See Table 2; maximum calculated intensity 144; this species represented 15% of the total number of monogeneans.

Etymology: From Greek exotikos, ‘from the outside, alien, foreign’ to mark the strange structure of this species.

Description. Body length h 470, c 500±82 (395–800, n = 32), width h 280, c 289±37 (200–370, n = 32). Tegument scaly; tegumental scales located only on both sides of squamodisc and a narrow band above it, on ventral and dorsal sides; total number of tegumental scales c. 80 per side. Anterior region with 3 pairs of head organs and 2 pairs of eye-spots; distance between outer margins of anterior eye-spot pair h 32, c 34 (26–38, n = 11), of posterior eye-spot pair h 34, c 37±6.4 (29–60, n = 27); eyes of anterior pair often disaggregated.

Haptor differentiated from rest of body, less wide than body, width h 180, c 188±9 (170–215, n = 31), provided with 2 similar squamodiscs, 2 pairs of lateral hamuli, 3 bars and 14 marginal hooklets.

Squamodiscs round in shape, made up of rows of rodlets; central rows forming closed circles; rodlets progressively thinner from centre to periphery; rodlets adjacent in all rows except last row; last row with very thin, separated rodlets; ventral and dorsal squamodiscs similar; rodlets in all rows except first and last row bear anteriorly directed spur (‘éperon’); rodlets at both extremities of row devoid of spurs; ventral squamodisc length h 60, c 60±5.2 (49–69, n = 29), width h 53, c 53±2.1 (51–62, n = 29), with h 12, generally 12 (9–14, n = 29) rows of rodlets and 2 closed oval; total number of rodlets h 103, mean 101 (90–110, n = 7, individual variations in Table 6); dorsal squamodisc, length h 59, c 60±4.7 (52–69, n = 28), width h 54, c 52±1.6 (49–56, n = 28), with h 13, generally 12 (10–13, n = 28) rows of rodlets and 1–2 closed ovals; total number of rodlets h 102, mean 95 (83–105, n = 9, individual variations in Table 6). Structure and measurements of squamodiscs remarkably constant among specimens.

Ventral hamulus with thick handle and distinct guard, outer length h 45, c 45±1.4 (41–49, n = 63), p 49±1.8 (45–53, n = 32), inner length h 43, c 42±1.8 (36–45, n = 63), p 45±1.5 (41–47, n = 32). Dorsal hamulus with indistinct guard, outer length h 43, c 42±1.3 (39–45, n = 64), p 43±1.6, (37–45, n = 32), inner length h 24, c 24±1.2 (20–27, n = 64), p 24±1.1 (21–26, n = 32). Dorsal (lateral) bars straight, with flattened medial extremity and cylindrical lateral extremity with posteriorly directed hook, length h 59, c 61±2.6 (54–69, n = 64), p 66±4.8 (61–90, n = 32), maximum width h 13, c 14±2.9 (10–19, n = 56), p 19±2.4 (14–24, n = 31). Ventral bar flat, bow-shaped, with constricted median portion and elongate extremities, length h 76, c 79±4.4 (68–90, n = 31), p 81 (67–93, n = 16), maximum width h 12, c 13±1.2 (10–15, n = 31), p 15 (13–17, n = 16); groove visible on its ventral side.

Pharynx subspherical, length h 46, c 43±4.0 (35–51, n = 32), width h 38, c 39±3.6 (34–50, n = 32). Oesophagus apparently absent, such that intestinal bifurcation immediately follows pharynx. Caeca simple, terminate blindly at level of posterior margin of vitelline field.

Testis small, subspherical, intercaecal, length h 21, c 40 (21–60, n = 10), width h 48, c 81 (26–126, n = 10); testis lateral to ovary or, if very small, posterior to ovary. Vas deferens emerges from antero-sinistral part of testis, enlarges into seminal vesicle; seminal vesicle in middle region of body, transforms into duct; duct transforms into small bulb, followed by second small bulb; duct enlarges then connects with quadriloculate organ. Prostatic reservoir very small, connects with quadriloculate organ. Quadriloculate organ with extremely thick wall, fourth (posterior) chamber slightly more sclerotised than 3 anterior chambers; fourth chamber ends in tubular structure (homologous to the cone of other species, but not conical in this case); short cylinder, probably homologous to tube of other species, at extremity of ‘cone’, with complex internal structure ( Fig. 10C); no filament. Inner length of quadriloculate organ h 41, c 39±1.8 (36–43, n = 32), p 58 (50–65, n = 16); ‘cone’ length h 16, c 16±0.9 (14–18, n = 32), p 16 (15–18, n = 16); ‘tube’ length h 5, c 5±0.4 (4–5, n = 32), p 4 (3–6, n = 16); ‘tube’ diameter at extremity h 5, c 4±0.4 (3–5, n = 32), p 5 (4–6, n = 16).

* Holotype, drawn in Figs. 11J, K. c, closed row; i, incomplete row.

Ovary subequatorial, intercaecal, pre-testicular, encircles right caecum. Ovary width h 105, c 97±14 (74– 124, n = 30). Oviduct passes medially to form oötype, surrounded by Mehlis’ gland; oötype short, opens into uterus. Uterus dextral. Unsclerotised vagina inconspicuous. Duct from sclerotised vagina to oötype inconspicuous. Vitelline fields extend posteriorly from posterior to pharyngeal level in 2 lateral bands, widely confluent in post-testicular region and terminate anterior to peduncle. Bilateral connections from vitelline fields to oötype inconspicuous. Egg in utero elongate, 75 x 38 (n = 1).

Sclerotised vagina (nomenclature of parts according to Justine 2007a inapplicable, see Figure 12) sinistral, a complex sclerotised structure; aspect changes according to specimen and orientation ( Figure 11). Sclerotised vagina comprises a discoid structure with a dorsal central dome, and a dorsal structure with variable shape, often showing up to three small cavities. In perfectly polar view of the disc, the dome appears to be surrounded by a ring of c. 18 lobes ( Fig. 10D). Homologies with the usual structure found in Pseudorhabdosynochus unknown, but the duct from the sclerotised vagina to the ootype connects at the level of the dorsal structure, which thus is probably homologous to the secondary chamber of other species. Diameter of sclerotised vagina h 15, c 16±1.3 (13–18, n = 32), p 18 (14–20, n = 16) Orientation of sclerotised vagina: disc generally in semi-polar view, sometimes in ‘lateral’ view ( Figs 11C, D, G, H); dorsal structure generally posterior.

Differential diagnosis. P. exoticus has unique characters that differentiate it from all other species of Pseudorhabdosynochus :

— the sclerotised vagina has an aberrant structure, in which the usual parts (trumpet, chambers, canals) cannot be recognized.

— the quadriloculate organ has a very special distal (posterior) extremity, in which the usual organization of cone and tube cannot be recognized.

— the lateral bars of the haptor have a hook on the outer extremity, in contrast to many species of Pseudorhabdosynochus that have a cylindrical median extremity.

The only other species of Pseudorhabdosynochus in which the sclerotized vagina does not show the usual pattern is P. guitoe Justine, 2007 from E. maculatus off New Caledonia, but the structure is completely different. In addition, the quadriloculate organ of P. guitoe , as in P. exoticus , has a very thick wall and no real cone, but its structure is different at the distal extremity.

The general disk-shape of the sclerotised vagina of P. exoticus bears some resemblance with that of Laticola dae Justine, 2007 and L. cyanus ; homologies are uncertain and an interpretation in term of phylogenetic relationships or of polarization of characters is certainly premature, but at least these striking resemblances suggest that similar genes, present in a common ancestor of Laticola spp. and Pseudorhabdosynochus spp. , are expressed in the three species.

P. exoticus , although showing the distinctive characters of Pseudorhabdosynochus , particularly the quadriloculate organ, is clearly an aberrant species, differing from all other species of the genus.

Remarks on the rodlet spurs. The rodlets of the squamodiscs of P. exoticus bear anteriorly directed spurs. These spurs are sometimes mentioned for diplectanids. Euzet & Oliver (1965) provided a figure and a detailed description of spurs (‘éperons’) on the squamodiscs of Echinoplectanum echinophallus ( Euzet & Oliver, 1965) Justine & Euzet, 2006 . Spurs were also found in Ec. plectropomi ( Young, 1969) Justine &Euzet, 2006 , but not in five other species of Echinoplectanum Justine & Euzet, 2006 . Diplectanum uitoe Justine, 2007 from E. maculatus also has spurs, but they are absent in the eight species of Pseudorhabdosynochus described from the same fish ( Justine 2007a). Among five species of Pseudorhabdosynochus described from E. costae (Steindachner) , only two have spurs ( P. dolicocolpos Neifar & Euzet, 2007 and P. sosia Neifar & Euzet, 2007 ) ( Neifar & Euzet 2007). A detailed examination with the focus set on the surface of the rodlets is necessary to ascertain the presence of absence of the spurs in a squamodisc. The previous examples of several species described by the same authors show that the presence of the spurs is highly variable within members of Echinoplectanum , Diplectanum and Pseudorhabdosynochus . Presence of spurs has probably no significance for the differentiation of genera but can be considered an additional character for the differentiation of certain species.