Cyamus monodontis Lütken, 1870

Iwasa-Arai, Tammy, Carvalho, Vitor Luz & Serejo, Cristiana Silveira, 2017, 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, Journal of Natural History (J. Nat. Hist.) 51 (37 - 38), pp. 2225-2245 : 2228-2231

Cyamus monodontis Lütken, 1870

( Figures 1 and 2 )

Cyamus monodontis Lütken, 1870: 279 . – Lütken 1873: 282. – Leung 1967: 285, fig. 4c. – Lincoln and Hurley 1974b: 68. – Leung 1976: 160. – Berzin and Vlasova 1982: 157, 158. – Margolis and Arai 1989: 12. – Haney 1999: 124–128, figs 47–49. – Martin and Heyning 1999: 28.

Cyamus (Cyamus) monodontis – Margolis et al. 2000: 71–74, fig. 4.

Material examined (host Monodon monoceros )

Lectotype. One male, 9.4 mm, Greenland, ZMUC-CRU-8685 . Paralectotypes: four males, 8.5– 9.3 mm, Greenland, ZMUC CRU- 467. Allotype: one female, 7.2 mm, Thule , Greenland, ZMUC CRU-8686 . Other non-type material: one female, 5.4 mm, Greenland, ZMUC CRU-7641 ; three males, 5.2–7.2 mm, 3 females, 7.1–7.8 mm, Thule, Greenland, ZMUC CRU-8570 .

Hosts

Monodon monoceros , Delphinapterus leucas (Pallas) .

Diagnosis

Pereonite 2 without knoblike process on the posterior margin. Lateral gills stout, uniramous; male accessory gills asymmetrically bilobed, anterior lobe shortest, female accessory gills oval. Pereonite 5 smooth, male pereonites 6 and 7 with two pairs of acute ventral processes, female P6 with three pairs and P7 with one pair of acute ventral processes.

Redescription

Lectotype, male, 9.4 mm, ZMUC CRU-8685. Body compact and dorso-ventrally depressed. 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 squared process on posterolateral margin. Pereonites 3 and 4 shorter in length than pereonites 1, 2 and 5–7, subequal in width to pereonite 5, with terminal posterior projections, without pereopods, each bearing one pair of gills and one accessory gill. Pereonite 5 smooth. Pereonites 6 and 7 each bearing two pairs of acute ventral processes (ventral spines), the first pair antero-directed, the second, latero-directed. Pereonite 7 triangular. Penes large, stout ( Figure 1 ).

Antenna 1 long, with 4 articles, terminal article narrow and long, bearing apical tuft of setae, and brush-like setal groupings on the internal margin of terminal article; other articles sparsely setose. Antenna 2 with 4 articles, with setae on terminal article; article 3 the longest. 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; inner margin setose; inner lobes partially fused, rounded distally. Left mandible with palp absent; incisor five-toothed; lacinia mobilis five-toothed; spine row short, with three setae; molar process absent. Right mandible with palp absent; right incisor five-toothed; lacinia mobilis multituberculate with two teeth; spine row of three setae; molar process absent; submolar setae lacking. Maxilla 1 with seven denticulate setae on outer lobe; palp 1 onearticulate, with long setae. Maxilla 2 with distomedial expansion of inner lobe bearing two setae. Maxillipeds with inner plate lacking setae; outer plate with 3–4 setae, palp 4- articulated, sparsely setose ( Figure 2 ).

Gnathopod 1 approximately one-fourth size of gnathopod 2, coxa not fused with pereon, anterior margin of propodus with elongate expansion. Gnathopod 2 coxa not fused with pereon; ventral face of basi-ischium with blunt process on anterolateral corner, large blunt expansion located proximally of process; carpus and propodus fused; proximal process of interior margin of propodus oval, propodus with subacute palmar tooth, subequal in length to proximal process, dactylus large and unornamented, reaching propodus’ oval proximal process. Pereopods 3 and 4 absent. Pereonites 3 and 4 bearing stout, uniramous and outwardly directed lateral gill; lateral gill cylindrical, 3.5 times longer than wide. Pereonites 3 and 4 bearing bilobed medial (accessory) gill; accessory gill much shorter than lateral gill, also arising as coxal epipod. Accessory gill lobes asymmetrical, posterior lobe the longest. Pereopods 5–7 coxae not fused with pereon. Basi-ischium with large, acute process, distally directed, located distally on antero-ventral face. 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 1 ).

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.

Female, 7.2 mm, ZMUC CRU-8686 – Pereonites 3 and 4 broader than those of male, subequal in width to pereonites 5 and 6, bearing triangular oostegite. Margins of oostegites lined with short, simple setae. Pereonites 3 and 4 bearing small round accessory gills, posterior margin smooth. Pereonite 5 without ventral acute processes, genital valves present; medial margin of genital valve well rounded, bearing cluster of short setae. Pereonite 6 bearing three pairs of ventral acute processes, forwardly, laterally and backwardly directed, pereonite 7 with one pair of ventral acute processes, laterally directed; pleon lacking pleopods.

Remarks

The syntype series of Cyamus monodontis was available from the Zoologisk Museum, University of Copenhagen, which made it possible for us to designate a lectotype and paralectotypes, and provide a redescription using modern standards. Cyamus monodontis was described originally as an ectoparasite of Monodon monoceros from Greenland ( Lütken, 1870). Its body shape is similar to that of Cyamus nodosus , which co-occurs on Monodon monoceros , and to that of Cyamus ceti ( Linnaeus, 1758) , ectoparasite of bowhead whales Balaena mysticetus Linnaeus, 1758 and gray whales Eschrichtius robustus (Lilljeborg) . Lateral gills of C. monodontis are more similar to those of C. nodosus , while its accessory gills are more similar to those of C. ceti , which are asymmetrically bilobed. Cyamus monodontis differs from them by the spination on the ventral face of pereonites 5–7 and the absence of knob-like processes on the posterior margin of pereonite 2.

Despite C. monodontis being recorded for both M. monoceros and D. leucas , all the examined material was collected from a single host species, M. monoceros . Delphinapterus leucas was recorded by Margolis (1954) and Grüner (1975) as host, but it seems that the majority of the available material in collections is from M. monoceros ( Margolis 1954; Lincoln and Hurley 1974b; Haney 1999). A description of C. monodontis specimens from D. leucas is available in Margolis et al. (2000).

Figures

Figure 1. Cyamus monodontis Lütken, 1870. Lectotype, male, 9.4 mm, ZMUC CRU-8685. AG: accessory gill; Gn: gnathopod; LG: lateral gill. Scale bars = 1 mm.

Figure 2. Cyamus monodontis Lütken, 1870. Lectotype, male, 9.4 mm, ZMUC CRU-8685. 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.