Updates on Cyamidae (Crustacea: Amphipoda): redescriptions of Cyamus monodontis Lütken, 1870 and Cyamus nodosus Lütken, 1861, a new species of Isocyamus, and new host records for Syncyamus ilheusensis Haney, De Almeida and Reis, 2004 Author Iwasa-Arai, Tammy Author Carvalho, Vitor Luz Author Serejo, Cristiana Silveira text Journal of Natural History 2017 J. Nat. Hist. 2017-09-13 51 37 - 38 2225 2245 http://dx.doi.org/10.1080/00222933.2017.1365965 journal article 10.1080/00222933.2017.1365965 1464-5262 4746859 451A4857-9CFC-4C81-AF70-8DFD0D7CEB16 Isocyamus indopacetus Iwasa-Arai and Serejo , sp. nov. ( Figures 5–7 ) Material examined Holotype , male, 9.2 mm , Baie de la Somme ( 22.329°S ; 166.824°E ), New Caledonia , from Indopacetus paci fi cus , C. Garrigue et al. col., November 2013 , MNHN-IU-2014-12863. Diagnosis Maxilliped inner lobes rounded, with distal outer lobes. Gnathopod 2 with proximal palmar expansion and triangular palmar tooth. Accessory gills subtriangular; lateral gills with a pair of spine-like processes at the base. Maxilla 2 with reduced outer lobes. Lower lip with inner lobes fully fused. Pereopod 5–7 basi-ischium with anterolateral acute process distally directed. Etymology The specific epithet refers to the host genus, Indopacetus Moore). Description Holotype , male, 9.2 mm , MNHN-IU-2014-12863. Body compact and dorso-ventrally depressed, dorsal surface smooth. Eyes small and ovoid. Head quadrangular, partially fused with pereonite 1; lateral incision between head and pereonite 1 absent. Pereonite 1 with lateral expansion. Pereonite 2 with typical anterodorsal epaulet-like cuticular infoldings and knob-like process on posterolateral margin ( Figures 5 and 7 (a)). Pereonites 3 and 4 subequal in length to other somites, slightly narrower than pereonite 5, without pereopods, each bearing one pair of sausage-like gills, one subtriangular accessory gill and two accessory spine-like processes arising from each lateral gill ( Figures 5 and 7 (b)). Pereonites 5, 6 and 7 each bearing one pair of acute ventral processes (ventral spines), antero-directed ( Figures 5 and 7 (d)). Pereonite 7 triangular. Penes large, stout. Antenna 1 four-articulate, terminal article narrow and long, bearing a continuous band on the internal margin of terminal article; subterminal article sparsely setose. Antenna 2 three-articulate, with sparse setae. Upper lip with distomedial invagination, producing distally rounded left and right subequal lobes, epistome moderate, not reaching distomedial invagination. Lower lip outer lobes longer than inner lobes; outer lobes broad, triangular; terminal margin heavily setose and inner margin setose; inner lobes fully fused, triangular. Left mandible with palp absent; incisor five-toothed; lacinia mobilis five-toothed; spine row of three setae; molar process absent. Right mandible with palp absent; right incisor six-toothed; lacinia mobilis multituberculate with two teeth; spine row absent; molar process absent; submolar setae lacking. Maxilla 1 with seven denticulate robust setae on outer lobe; palp one-articulate, with long setae, not reaching outer lobe setae. Maxilla 2 with distomedial expansion of inner lobe; outer lobe fused. Maxillipeds with inner plate lacking setae, fused basally, maxillipeds outer plate present, anteriorly directed; palp absent ( Figures 6 and 7 (c)). Figure 5. Isocyamus indopacetus Iwasa-Arai and Serejo sp. nov. Holotype, male, 9.2 mm, MNHN-IU-2014-12863. AG: accessory gill; Gn: gnathopod; LG: lateral gill; P: pereopod. Scale bars = 1 mm. Figure 6. Isocyamus indopacetus Iwasa-Arai and Serejo sp. nov. Holotype, male, 9.2 mm, MNHN-IU- 2014-12863. Ant: antenna; LL: lower lip; lMd: left mandible; rMd; right mandible; Mx: maxilla; Mxp: maxilliped; UL: upper lip. Scale bars: antenna 1 = 1 mm; all others = 100 μm. Gnathopod 1 approximately one-fourth size of gnathopod 2, coxa not fused with pereon, anterior margin of propodus with proximal broad expansion. Gnathopod 2 coxa not fused with pereon; basi-ischium with large triangular expansion on anterior margin; carpus and propodus fused; proximal interior margin of propodus with a small blunt projection, propodus with subacute palmar tooth, larger than proximal expansion, dactylus large and unornamented, reaching propodus’ proximal expansion. Pereopods 3 and 4 absent. Pereonites 3 and 4 bearing stout, uniramous and outwardly directed lateral gill; lateral gill cylindrical, 7.5 times longer than wide. Pereonites 3 and 4 bearing triangular, leaf-shaped medial (accessory) gill; accessory gill subequal in length to lateral gill, also arising as coxal epipod; pair of spine-like process arising from each gill, laterally directed. Coxae of pereopods 5 through 7 not fused with pereon. Basi-ischium with anterolateral acute process on ventral face, distally directed. Anterior margin of ischium uniform, unornamented. Inferior margin of merus uniform. Carpus with anterolateral expansion. Propodus subelliptical, with no teeth or spines. Dactylus acute, angle of recurve dactylus extreme, approximately 90° ( Figure 5 ). Figure 7. Isocyamus indopacetus Iwasa-Arai and Serejo sp. nov. Holotype, male, 9.2 mm, MNHN-IU- 2014-12863. (a) Dorsal view. Triangles indicate epaulet-like cuticular infoldings. (b) Ventral view. Asterisks indicate spine-like processes of gills. AG: accessory gill; LG: lateral gill. (c) Mouthparts. (d) Ventral view. Arrows indicate acute ventral processes of pereonites 5, 6 and 7. Pleon reduced with one pair of pleopods, fused basally and separate distally, with each pleopod ending in a spherical lobe and bearing short setae along its lateral margins. Remarks Until the present study Isocyamus included four species that are ectoparasites of different hosts ( Table 2 ). Isocyamus indopacetus sp. nov. is close to I. deltobranchium in the subtriangular shape of accessory gills, which is an exclusive character of these species. However, I. indopacetus sp. nov. presents two spine-like processes at the base of each lateral gill, whereas I. deltobranchium has only one process per gill ( Figures 5 and 7 (b); Table 3 ). Also, Isocyamus indopacetus sp. nov. exhibits the maxilliped with outer plate, an unique character among other Isocyamus ( Figures 6 and 7 (c)). Nonetheless, while other species of Isocyamus have the dactyl of gnathopod 1 with a combed ridge, it is smooth in I. indopacetus sp. nov. ( Figure 5 ). Table 3. Diagnostic features of Isocyamus .

Spines on	Acute ventral
Maxilliped	Accessory	basis of	Epaulette-like processes at	processes on Pr5/
Species	outer lobe	gills in males	gills	anterodorsal margin of Pr2	Pr6/Pr7
Isocyamus antarcticensis	Absent	Clavate	1	Present	Present
Berzin and Vlasova,
1982
Isocyamus delphinii	Absent	Cylindrical	1	Absent	Present
(Guérin-Meneville,
1836)
Isocyamus deltobranchium	Absent	Subtriangular	1	Present	Present
Sedlak-Weinstein,
1992b
Isocyamus indopacetus	Present	Subtriangular	2	Present	Present
sp. nov.
Isocyamus kogiae Sedlak-	Absent	Leaf-like	1	Present	Absent
Weinstein, 1992a

Longman’ s beaked whale is considered one of the rarest and least well known cetaceans ( Garrigue et al. 2016 ). This is the first record of a whale-louse species parasitising the Longman beaked whale, though Yamada et al. (2012) reported that Indopacetus paci fi cus often carried unidentified whale lice, and highlighted the importance of having more research on external parasites of these beaked whales. Key to species of Isocyamus (modified from Sedlak-Weinstein 1992b ) 1. One pair of ventral acute processes on segments 5–7....................................................... 2 – No ventral processes on segments 5–7........................................................................ I. kogiae 2. Accessory gills in males shorter than lateral gills, subtriangular or clavate, pereonite 2 with anterodorsal epaulet-like cuticular infoldings ........................................................... 3 – Accessory gills in males equal in length to lateral gills, cylindrical, pereonite 2 anterodorsal margin straight .............................................................................................. I. delphinii 3. One spine-like process on basis of lateral gills ...................................................................... 4 – Two spine-like processes on basis of lateral gills ...... ...... I. indopacetus sp. nov. ( Figure 2 ) 4. Accessory gills in males triangular, palm of gnathopod 2 of female with posterior tooth only... ................................................. ................................................. I. deltobranchium – Accessory gills in males clavate, palm of gnathopod 2 of female with anterior and posterior pointed teeth ...................................................................................................... I. antarcticensis