Elthusa raynaudii (Milne Edwards, 1840)

van der Wal, Serita, Smit, Nico J. & Hadfield, Kerry A., 2019, Review of the fish parasitic genus Elthusa Schioedte & Meinert, 1884 (Crustacea, Isopoda, Cymothoidae) from South Africa, including the description of three new species, ZooKeys 841, pp. 1-37 : 1

Elthusa raynaudii (Milne Edwards, 1840) Figures 1, 2, 3, Table 1

Livoneca Raynaudii : Milne Edwards 1840: 262; Krauss 1843: 66; Bleeker 1857: 30; Schioedte and Meinert 1884: 367, pl. 12, figs 9-13; Thielemann 1910: 42; Hale 1926: 215-217, figs 10 a–j.

Cymothoa Novae-Zealandia: White 1847: 110 (nomen nudum).

Lironeca novae-zealandia : Miers 1874: 228; 1876: 106, pl. III, fig. 2; 1881: 64, 67.

Lironeca laticauda : Miers 1877: 677, pl. 69, fig. 5; Ellis 1981: 124.

Livoneca Raynaudi .- Gerstaecker 1882: 259.

Livoneca Novae Zelandiae.- Gerstaecker 1882: 263.

Lironeca Stewarti: Filhol 1885: 450, pl. 4, fig. 6.

Lironeca neo-zelanica .- Thomson and Chilton 1886: 154.

Livoneca raynaudii .- Whitelegge 1902: 236; Chilton 1909: 606; 1911: 309; 1912: 135; Stebbing 1910: 125; Young 1926: 283; Hale 1926: 215, fig. 10; 1929: 261, figs 253, 259; 1940: 303; Barnard 1940: 491; 1955: 6; Hurley 1961: 268; Hewitt and Hine 1972: 108; Sivertsen and Holthuis 1980: 34; Beumer et al. 1982: 33.

Livoneca epimerias : Richardson 1909: 88, fig. 13; Kussakin 1979: 301, figs 69, 170.

Livoneca raynaudi .- Nierstrasz 1915: 97; 1931: 145; Barnard 1920: 358; Pillai 1954: 16.

Livoneca laticauda .- Nierstrasz 1931: 143.

Lironeca raynaudii .-Brian and Dartevelle 1949: 176; Avdeev 1975: 250; 1978: 281; Trilles 1976: 778, pl. 1, fig. 4; Poore 1981: 341.

Lironeca raynaudi .- Menzies 1962: 115, fig. 36 A–B; Kensley 1978: 80, fig. 33B; Moreira and Sadowsky 1978: 111.

Lironeca magna : Mañé-Garzón 1979: 18, figs 1-5.

Elthusa raynaudii .- Bruce 1990: 263; Bruce et al. 2002: 177; Williams et al. 2010: 99-101.

Elthusa raynaudi .- Ghani 2003: 218.

Type material.

Type material held at the Museum national d’Histoire naturelle, Paris (syntypes MNHN-IU-2016-9885; MNHN-IU-2016-9884).

Type locality.

Cape of Good Hope, South Africa.

Type host.

Unknown.

Material examined

(all from South Africa). Syntype. SOUTH AFRICA • 1 ♀ (ovigerous, 26.7 mm TL, 14.1 mm W); south coast of South Africa, Cape of Good Hope; MNHN-IU-2016-9885. Other material. SOUTH AFRICA • 1 ♀ (ovigerous, 26.0 mm TL, 14.0 mm W); Indian Ocean, south coast of South Africa, RV Africana (fish sorting table); 34°38'S, 25°38'E; April 2003; coll. Nico J. Smit; dissected; in the collection of the authors at NWU • 1 ♀ (ovigerous, 26.0 mm TL, 15.0 mm W); Atlantic Ocean, RV Dr Fridtjof Nansen trawl (Station NAN401T062); January 2007; coll. L Atkinson; SAMC-A47881 • 1 ♀ (ovigerous, 20.0 mm TL, 12.0 mm W); Atlantic Ocean, RV Dr Fridtjof Nansen (fish sorting table); 32°17'S, 16°54'E; 269 m; February 2010; coll. KA Hadfield; dissected; SAMC-A089957.

Description

(ovigerous ♀). Figs 1-3. Body ovoid, slightly twisted to the left, 1.7 times as long as greatest width; dorsal surfaces smooth and polished in appearance, widest at pereonite 5, most narrow at pereonite 1; pereonite lateral margins mostly posteriorly ovate, medially indented. Cephalon 0.9 times longer than wide, visible in dorsal view, sub-truncate with blunt anterior margin. Frontal margin thickened, ventrally folded. Eyes oval with distinct margins; one eye 0.2 times width of cephalon, 0.4 times length of cephalon. Pereonite 1 smooth; anterior border medially straight, curved laterally; anterolateral angle narrowly rounded, extending to the medial region of eyes. Posterior margins of pereonites smooth, slightly curved laterally. Coxae 2-3 wide, with posteroventral angles rounded; coxae 4-7 with rounded point, not extending past pereonite posterior margin. Pereonites 2-5 subequal, becoming more progressively rounded posteriorly; pereonites 6 and 7 slightly narrower. Pleon 0.4 times as long as total body length, with pleonite 1 largely concealed by pereonite 7, slightly visible in dorsal view; pleonites posterior margin mostly concave. Pleonite 2 partially overlapped by pereonite 7. Pleonites 3-5 similar in form to pleonite 2; pleonites subequal in length, with posterolateral angles narrowly rounded, posterior margin straight. Pleotelson 0.6 times as long as anterior width, dorsal surface smooth; lateral margins weakly convex; posterior margin evenly rounded.

Antennula shorter than antenna, consisting of eight articles; antennula peduncle articles I and II distinct and articulated, extending to anterior of pereonite 1. Antenna consists of eleven articles, extending to middle of pereonite 1.

Pereopod 1 basis 1.6 times as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin without bulbous protrusion; carpus with rounded proximal margin; propodus 1.4 times as long as wide; dactylus slender, 1.6 times as long as propodus, 2.9 times as long as basal width. All pereopods without robust or simple setae. Pereopod 7 basis with carina, 2.5 times as long as greatest width; ischium without protrusions, 0.5 times as long as basis; merus 0.7 times as long as wide, 0.4 times as long as ischium; carpus without bulbous protrusion, 0.7 times as long as wide, 0.3 times as long as ischium; propodus 0.8 times as long as wide, 0.3 times as long as ischium; dactylus slender, 2.3 times as long as propodus, 3.5 times as long as basal width.

Pleopods simple, exopod larger than endopod. Pleopod 1 exopod 1.3 times as long as wide, lateral margin weakly convex, distally narrowly rounded, mesial margin straight; peduncle 2.3 times as wide as long.

Uropod more than half the length of pleotelson; peduncle 0.5 times longer than rami, lateral margin without setae; rami not extending beyond pleotelson, apices broadly rounded. Endopod apically rounded, 2.7 times as long as greatest width, terminating without setae. Exopod extending to end of endopod, 2.2 times as long as greatest width, apically rounded, terminating without setae.

Variations. Intra-specific variations can cause difficulty in identification and should be taken into consideration. One of the more obvious variations is the overall body shape of examined individuals, as seen from the dorsal view. While the syntype ( MNHN–IU–2016– 9885) has weakly convex, symmetrical lateral margins, specimen SAMC-A089957 is not as symmetrical, with the right margin being strongly convex and that of the left margin, weakly convex. The latter specimen therefore appears to be less symmetrical. Bruce (1990) mentioned this occasional asymmetrical body shape as an observed variation, as a result of slightly twisted individuals. The body shape of the South African specimen (SAMC-A089957) accords to the shape of individuals illustrated and described by Bruce (1990). In addition, the widest part of this species may vary between pereonite 4 and pereonite 5. This variation may also cause individual body shapes to appear dissimilar. The anterior margin of the cephalon of the syntype ( MNHN–IU–2016– 9885) appears to be rounded rather than subtruncate. The posterior margin of pleonite 5 can be roughly straight (AM G2181 from Bruce 1990), have a slight medial point, or be weakly concave ( Bruce 1990, present study). Although Bruce (1990) described the uropods as being short, most measure more than half the length of the pleotelson.

Size. Ovigerous females 20.0-26.7 mm TL, 14.0-15.0 mm W. Other material: ovigerous females 22.0-67.0 mm TL (average 30.83 mm TL) ( Bruce 1990).

Distribution.

Records listed from west to east. North Pacific Ocean: Bering Sea ( Kensley 1976). South America: Punta Quillaipe ( Menzies 1962) and Chile ( Nierstrasz 1931); Uruguay ( Mañé-Garzón 1979). South Atlantic Ocean: Saint Helena and Tristan da Cunha ( Sivertsen and Holthuis 1980). South Africa: Table Bay ( Barnard 1920); Cape of Good Hope ( Milne Edwards 1840); Durban ( Barnard 1955). India: Travancore ( Pillai 1954). Southern Indian Ocean: Amsterdam Island ( Kensley 1976). Australia: southern and south-eastern Australia ( Schioedte and Meinert 1884, Hale 1926, Bruce 1990, Whitelegge 1901). Japan: Yokohama ( Schioedte and Meinert 1884). New Zealand ( Filhol 1885, Chilton 1909, Nierstrasz 1915, Hurley 1961, Bruce 1990).

Hosts.

Elthusa raynaudii has been recorded from various fish hosts of multiple orders and families. These hosts are: Chelidonichthys kumu (Cuvier, 1829) (see Avdeev 1978); Chorisochismus dentex (Pallas, 1769) (see Barnard 1920); Cyttus australis (Richardson, 1843) (see Avdeev 1978, 1984, Bruce 1990); Cyttus novaezelandiae (Arthur, 1885) (see Avdeev 1978, 1984); Cyttus traversi Hutton, 1872, previously Cyttoidops mccullochi (Whitley, 1947) (see Avdeev 1984, Bruce 1990); Genypterus blacodes (Bloch and Schneider, 1801) (see Hewitt and Hine 1972); Gnathanacanthus goetzeei Bleeker, 1855 (see Bruce 1990); Hyporhamphus intermedius (Cantor, 1842) (see Powell 1959, Stephenson 1969); Latris lineata (Forster, 1801) (see Kensley 1976); Meuschenia freycineti (Quoy and Gaimard, 1824) (see Bruce 1990); Mustelus antarcticus Günther, 1870 (see Hewitt and Hine 1972); Nemadactylus monodactylus (Carmichael, 1819), previously Acantholatris monodactylus (Carmichael, 1819) (see Sivertsen and Holthuis 1980); Nematalosa nasus (Bloch, 1795) (see Ghani 2003); Notacanthus sexspinis Richardson, 1846 (see Avdeev 1978, 1984); Notothenia microlepidota Hutton, 1875, previously Notothenia colbecki (see Chilton 1909, Hewitt and Hine 1972, Avdeev 1978, 1984); Notolabrus tetricus (Richardson, 1840), previously Pseudolabrus tetricus (see Bruce 1990); Paranotothenia magellanica (Forster, 1801), previously Notothenia macrocephala (see Avdeev 1978); Ilisha melastoma (Bloch and Schneider, 1801) previously Pellona brachysoma (see Pillai 1954); Pelotretis flavilatus Waite, 1911 (see Chilton 1911); Pseudophycis bachus (Forster, 1801), previously Physiculus bachus (see Hewitt and Hine 1972); Physiculus sp. (see Bruce 1990); Pseudophycis barbata Günther, 1863, previously Physiculus barbatus ( Günther, 1863) (see Bruce 1990); Pseudolabrus miles (Schneider and Forster, 1801) (see Poore 1981, Bruce 1990); Pseudophycis bachus (Forster, 1801) (see Chilton 1911, Bruce 1990); Rexea solandri (Cuvier, 1832) (see Bruce 1990); Rhombosolea sp. (see Hewitt and Hine 1972); Sardinops sagax (Jenyns, 1842), previously Clupea neopilchardus Steindachner, 1879 (see Chilton 1911); Scorpaena cardinalis Solander and Richardson, 1842 (see Poore 1981); Sebastes capensis (Gmelin, 1789), previously Sebastichthys capensis (Gmelin, 1789) (see Sivertsen and Holthuis 1980); Stolephorus commersonnii Lacepède, 1803 (see Pillai 1954); Thyrsites atun (Euphrasen, 1791) (see Sivertsen and Holthuis 1980); Zenopsis nebulosa (Temminck and Schlegel, 1845), previously Zenopsis nebulosus (see Bruce 1990); Zeus faber Linnaeus, 1758 (see Hale 1926, Avdeev 1984). Unidentified by scientific names: banded perch ( Serranidae ), flathead ( Platycephalidae ) (see Bruce 1990).

Remarks.

Elthusa raynaudii can be distinguished by the cephalon having a narrowly truncate rostrum; pereonite 1 with anterior margin straight; pleonites subequal in shape and width; and broadly rounded uropod apices that extend to more than half the length of the pleotelson.

Originally described in 1840, from the Cape of Good Hope in South Africa, from an unknown host, Elthusa raynaudii has been recorded numerous times from a wide range of localities within the Indo-Pacific region. It is the only species of Elthusa that has been described from sub-Saharan Africa. It has been recorded from an unknown host from the Cape of Good Hope (see Milne Edwards 1840); from the rocksucker, Chorisochismus dentex (Pallas, 1769) near Cape Town (Table Bay) (see Barnard 1920); from a wrasse in Durban (see Barnard 1955); as well as from the striped trumpeter, Latris lineata (Forster, 1801) (see Kensley 1976).

Elthusa sigani Bruce, 1990, which is only known from its type locality in Queensland, Australia, seems to be most similar to E. raynaudii . Elthusa sigani can be distinguished from E. raynaudii by having an evenly concave pereonite 1 anterior margin; a flat, straight cephalon anterior margin; and coxae 7 that extend past the posterior margin of pereonite 7. In addition, E. sigani is a much smaller species in overall body length range (9.0-13.0 mm), compared to E. raynaudii (20.0-26.7 mm).