N An annotated checklist of the family Cymothoidae ( Isopoda : Cymothooidea ) infesting marine fishes from Malaysian waters , with new host and geographical records

A checklist of parasitic cymothoids from Malaysian waters is presented based on available literature and material collected from 2010 to 2020. Most of the collected specimens were recorded from waters of Terengganu, east coast of Peninsular Malaysia (facing South China Sea), whereas literature records were represented from Sarawak, along the Miri coast of northwest Borneo. The checklist comprises 18 species under 10 genera, seven of which are new records from Malaysia, which includes Anilocra nemipteri Bruce, 1987; Ceratothoa barracuda Martin, Bruce and Nowak, 2015; Ceratothoa carinata (Bianconi, 1869); Cymothoa epimerica Avdeev, 1979; Elthusa sigani Bruce, 1990; Joryma engraulidis (Barnard, 1936) and Renocila richardsonae Williams and Bunkley-Williams, 1992. Eight new host records are based on collected specimens: Anilocra nemipteri was dorsally attached on Nemipterus nemurus (Bleeker 1857), Nemipterus nematophorus (Bleeker 1854), Nemipterus tambuloides (Bleeker 1853), and Nemipterus thosaporni Russell 1991 (family Nemipteridae); Ceratothoa carinata was found in the buccal cavity of Decapterus macrosoma Bleeker 1851 (family Carangidae); Cymothoa eremita (Brunnich, 1783) was attached in the buccal cavity of Nemipterus tambuloides and Nemipterus furcosus (Valenciennes 1830); Elthusa sigani was found attached on Pterois russelli Bennett 1831 (family Scorpaenidae); and Renocila richardsonae was attached on the caudal fin of Upeneus japonicus (Houttuyn 1782) (family Mullidae). All cymothoid species listed here are known to have a Central Indo Pacific distribution, with some ranging as far as the western Indian Ocean. The cymothoid-host association is here listed from 28 fish families, with the most common reported from Carangidae (pompanos, jack mackerels, runners, scads), Engraulidae (anchovies) and Leiognathidae (ponyfishes, slipmouths). This paper is the first comprehensive treatment to update both verified literature data and deposited specimens, with a key for the family Cymothoidae in Malaysian waters.


Introduction
Cymothoid isopods are parasitic crustaceans that can severely affect harvested fishes in both fisheries and aquaculture and cause global economic losses (Nowak et al. 2020). Attributing to the fact that cymothoids are ubiquitous in freshwater, brackish and predominantly marine waters, these parasites can be found on commercial and non-commercial fishes. To date, 380 verified species under 46 genera (excluding nomen dubium and taxon inquirendum) have been recorded and listed on the World Register for Marine Species (Boyko et al. 2008 onwards), with increasing evidence of cymothoids displaying high host and site-specificity. Although there is no clear evidence on host morphological or behavioral influences towards cymothoidhost preferences , it has been postulated that some cymothoids are inclined to select hosts of similar ecological or ecosystem preferences between varying latitudes, with increased specificity within the tropics (Brusca 1981). In addition, the nature and distribution of the host may predispose cymothoid geographical occurrence. Hence, some cymothoids such as Glossobius auritus Bovallius, 1885 and Glossobius impressus (Say, 1818) may display extensive geographical occurrence (Martin et al. 2015b), while others such as Cinusa tetrodontis Schioedte & Meinert, 1884 have only been recorded in waters from South Africa (Hadfield et al. 2010).
Though there has been significant development on cymothoid taxonomic research worldwide, regional documentation has been inconsistent and sporadic in certain areas. A map of the marine cymothoid distribution by Smit et al. (2014) showed skewed results, with the highest diversity represented within the tropical regions of the Central Indo-Pacific realm, followed by the Western Indo-Pacific and Tropical Atlantic realm. While the highest cymothoids biodiversity are centred on the tropics, the low account of recorded species from the temperate regions and other tropical realms (e.g. Eastern Indo-Pacific and Tropical Eastern Hadfield et al. 2010Hadfield et al. , 2013Hadfield et al. , 2014Hadfield et al. , 2015Hadfield et al. , 2016Van der Wal et al. 2019); Bruce for Australia and neighboring islands (e.g. Bruce 1987aBruce , b, c, 1990Bruce , 2007; and more recently the works of Aneesh, Rameshkumar and Ravichandran for cymothoids of Indian waters (Aneesh at al. 2015(Aneesh at al. , 2016(Aneesh at al. , 2019a(Aneesh at al. -d, 2020a(Aneesh at al. , b, 2021aRameshkumar et al. 2012Rameshkumar et al. , 2013aRavichandran et al. 2010aRavichandran et al. , b, 2019.
Notwithstanding the point that the Central Indo-Pacific has the highest cymothoid diversity records worldwide, Malaysia accounts for little contribution towards this data.
Strategically located at the Indo-Malaysian triangle (Wallace et al. 2003), its waters are exposed to a plethora of ecosystems (rocky and sandy intertidal shores, mangroves, sea grass, coral reefs). Despite the lack of consistent and adequate sampling, the isopod fauna can be expected to increase in due course with the aid of more human resources and expertise. Minimal cymothoid records specific to the Malaysian region are attributed to records from Lanchester (1902) during his Skeat Expedition to Peninsular Malaysia and Anand  for cymothoids off the coast of Miri in Borneo. Unfortunately, the type specimen for Cymothoa pulchrum Lanchester, 1902 could not be located (see Martin et al. 2016) and material examined by Anand  were not deposited in any established museums or repository, and one could only rely on their published photographs and have been noted to have misidentification in their record. Bruce and Wong (2015) have strongly indicated that there have been few historic accounts for isopods from South East Asia. Ergo, despite being far from comprehensive, the authors hope that this list will serve as an initial effort for verifying and locating examined material for cymothoid specimens from Malaysian waters.
Type material. Female holotype (NMV 112947). For a list of paratypes and other material examined refer to Bruce (1987a).
It is evident that Anilocra nemipteri is host specific to the families Nemipteridae and Pomacentridae. Bruce (1987a)
According to Aneesh et al. 2019b, Anandkumar et al.'s (2017 figure of Joryma brachysoma (Pillai, 1964) from the host Netuma bilineata in Sarawak, Malaysia is a misidentification and refers to Catoessa gruneri based on its morphological characteristics. Papua (Trilles 1979). Based on the known host association and its distribution, Ceratothoa barracuda is likely to have an Indo-Pacific distribution: from East Africa and Southeast Asia to Japan and south of New Caledonia (Froese and Pauly 2019).
Remarks. Ceratothoa barracuda is here reported as a new locality record for Malaysian waters. The species is easily identified by the elongate body; subtriangular cephalon, subacute anterolateral projections on pereonite 1, pleotelson with a convex posterior margin, and pereopods 5-7 basis each with strong carinae and enlarged ischium (Martin et al. 2015a).
Ceratothoa barracuda is most likened to Ceratothoa carinata, but C. carinata has a pleotelson with a strongly concave posterior margin, an enlarged ischium and basis only present on pereopod 7, and the articles distal to article 4 of the antennula are narrower than those of C.
Remarks. Ceratothoa carinata is here reported as a new locality record for Malaysian waters.
Diagnostic characteristics of this species includes a medial ridge extending longitudinally along the dorsal pereon surface; laterally depressed and wider than long pleotelson; an enlarged carinate ischium and enlarged bulbous protrusion on the merus of pereonite 7; uropods reaching the distal edge of the pleotelson; and a concave pleotelson posterior margin (Martin et al. 2015a).Ceratothoa trigonocephala (Leach, 1818) and Ceratothoa trillesi (Avdeev, 1979b) are similar species to Ceratothoa carinata, but the former two have a narrow pleonite 1, shorter pleotelson with a generally convex posterior margin, a smooth and convex dorsum, and pereopod 7 lacks an enlarged ischium.Bianconi (1869)   Host. Host specimens for this study were not recorded by the SEAFDEC expedition crew, but Remarks. Cymothoa epimerica is here reported as a new locality record for Malaysian waters.
The species has an ovoid body; subtriangular cephalon deeply immersed in pereonite 1; pereonite 1 anterolateral margins deeply curved towards cephalon; pereopods 5-7 superior proximal margin with acute carinae and dorsallyvisible; and coxae 6 and 7 posteroventral margins acute and dorsally visible (Martin et al. 2016). Our female specimens are very much similar to the illustrations and photographs provided by Martin et al. (2016), with the distinctively visible pereonite 1 margins and acute coxae 6 and 7 posteroventral margins, which is not as prominent in Cymothoa eremita or Cymothoa pulchrum.
Cymothoa epimerica from Seychelles (SMF-76) and the Red Sea (SMF-567 and SMF-572) without host association or illustrations has been documented by Trilles (2008) and briefly mentioned the similarities of Cymothoa epimerica and Cymothoa curta. C. epimerica and C.
Remarks. Cymothoa eremita is here reported as a new locality record for Malaysian waters.
This species is instantly identified by the subtruncate cephalon; pereonite 1 anterolateral margins extending nearly half the length of cephalon; pleon as wide as pereon; uropods not extending to pleotelson posterior margin; bulbous protrusion on pereopod 7 ischium; and small horn-like structures on the posterolateral margins of pereonite 1. (Hadfield et al. 2013).
The cymothoid has been reported from the family Carangidae (Caranx sp., see Monod 1924) but until enough evidence is available, this record is considerably uncertain.
Distribution. Known from the central and western Indo-Pacific region: Malaysia (Lanchester Lanka (Monod 1924); Vietnam (Monod 1934;Trilles 1975); Japan (Shiino 1951;Saito et al. 2000;Nagasawa and Uyeno 2012); Australia (Avdeev 1978b); French Polynesia and Fiji (Galzin and Trilles 1979) Remarks. Cymothoa pulchrum has ananteriorly subtruncate cephalon; wide and subtruncate pereonite 1 anterolateral margins nearly reaching rostrum; pleon partially overlapped by Cymothoapulchrum was not available in their catalogue. In the event the type material is not available, designation of a neotype specimen is not necessary, as the species has been thoroughly described and easily distinguishable from its other Cymothoa relatives. In addition, host association and geographical distribution has been well documented for the species as to not pose any threat to its nomenclatural stability and universality.
Type material. Female holotype held at the Queensland Museum (QM W13080). For paratype details see Bruce (1990).
Material examined (New record). Distribution. Only known from Moreton Bay, Australia (Bruce 1990), and the South China Sea, Peninsular Malaysia (present material).
Remarks. Elthusa sigani is here reported as a new locality record for Malaysian waters. Our specimen agrees with the illustrations by Bruce (1990), in which the species is characterised by the even body, broad rostrum, antennule and antenna subequal in length, antennules separate, dorsally visible coxae (particularly coxae 5-7), rounded uropods not exceeding pleotelson posterior margin, and wide pleon. The only variation noted in our specimen is that it is not as twisted as Bruce's (1990) female specimen. Though the specimen can be confused with Elthusa raynaudii (Milne-Edwards, 1840) by the similar coxal and pleon morphology (see Bruce 1990), it can be easily distinguished from Elthusa sigani by the difference in body size (>20 mm vs<13 mm), pereopods 5-7 morphology (proximal carina with a boss vs smooth carina) and body surface (harder exterior vs softer exterior).
This species is different from other species within the genus by the dorsally conspicuous cephalon reaching beyond pereonite 1 expansion, unilateral and non-bilobed expansion of pereonite 1, and the broadly rounded pleotelson (Aneesh et al. 2019a). Kazmi's et al. (2002) figure of J. engraulidis from the host Sardillella sp. is confound to J. hilsae, but can be differentiated by the cephalon prominent dorsally and moving to the margin of pereonite 1 expansion (vs, pereonite 1 anterolateral expansion bilateral and slightly bilobed, pleonites are not overlapped, pleotelson loosely rounded, uropods rami equal mandibular palp 3-segmented ).
The species was formerly referred to as Agarna engraulidis Barnard, 1936 but was later transferred to Livoneca engraulidis by Pillai (1964) and lastly to the genus Joryma by Bowman and Tareen (1983), but both the latter authors were apprehensive in addressing the species position in their generic diagnosis. Other than Barnard's (1936) minimal description and figure, the type had to be located to resolve the genus conundrum and to redescribed the specimen to modern standards. Aneesh's (2019a) attempt to locate the type specimen was futile, but was fortunate to designate a newly collected specimen as a neotype (similar to Barnard'  Remarks. Lobothorax typus is easily diagnosed from the anterolateral margins of pereonite 1 projecting forward beyond the anterior margin of the cephalon, a weak dorsal median ridge that runs along pereonites 1 to 7, and pereonites 5 to 7 abruptly shorter than pereonite 4 (Yu and Bruce 2006  Nerocila arres and Nerocila sigani were described by Bowman and Tareen (1983) and accepted as valid by Bruce (1987b) and . Bruce and Harrisson-Nelson (1988) later synonymized the two species stating that the five distinguishing characteristics listed by Bowman and Tareen (1983) are highly variable or not reliable as a diagnostic characteristic. Trilles et al. (2013) later redescribed and illustrated both Nerocila arres and Nerocila siganiof which the former conforms holotype of Bowman and Tareen (1983) and is reinstated as valid.
Though both Nerocila arresand Nerocila serra is similar in the shape of the pereonites, pleotelson, dactyls of pereopods 1, 2, 4, and 5; it differs from the latter in the uropodal endopod
Type material. The specimen at the MNHN (Is. 508) is in a sad state of affairs (Bruce 1987b Kong (Bal and Joshi 1959;Bruce 1988;Printrakoon and Purivirojkul 2011;Trilles et al. 2013;Rameshkumar et al. 2014c;Anand Kumar et al. 2017;Ravichandran et al. 2019). Though the sample size of the entire three hosts collected was less than 25 per species, the prevalence and mean intensity were low (<17% and 1.3 respectively).
Type material. Holotype was held at the British Museum of Natural History (BMNH 1849: 86). Presented by I. Ward, according to Ellis (1981) and figured by Bruce (1987b).
Distribution. Recorded from the Central Indo Pacific region and the Indian Ocean (Miers 1880;Ellis 1981;Bruce 1987b;Rameshkumar et al. 2011;Anand Kumar et al. 2015.
Remarks. Nerocila longispina has a body twice as long as wide, widest at pereonites 6 and 7; narrowly rounded or slender medial point cephalon anterior margin; longer pointed processes on coxae 2-7; wider than long and smoothly rounded pleotelson; uropod rami extending beyond posterior margin of pleotelson; exopod slightly longer than endopod; a notch on medial margin and very coarsely serrated lateral margin of the uropod endopod (Ravichandran et al. 2019).
Remarks. Nerocila siganiis identified the body widest at pereonites 5 and 6; anteriorly broad and rounded cephalon; absence of swelling in pereopod dactyls; pointed posteroventral corners of all pereonites; long and pointed coxae processes; coxae 6 and 7 distinctly longer than posteroventral processes of respective pereonites; smoothly rounded pleotelson and absent of medial lobe; subequal dactyl spines on pereopods 1-5; exopod slightly longer than endopod; endopod with a deep notch on medial margin and serrate lateral margin (Bowman andTareen 1983, Trilles et al. 2013). China ; Philippines (Schioedte and Meinert 1884;Yamauchi et al. 2005; Cruz-Lacierda and Nagasawa 2017); Australia (Avdeev 1978b;Bruce 1990). Norileca indica resides at the gills of its host, attaching to the ventral part of the host's branchial cavity. The cephalon faces the anterior end of the host, and its ventral side is directed outwards, opposite the branchial operculum (Bruce 1990;Neeraja et al. 2014;Behera et al. 2016). Generally, the mancae, and immature males do not exhibit the strong body twist until its adult phase, and the position of the body asymmetry depends on the settlement of the cymothoid within the body cavity. The adult will be twisted to the right when it occupies the left branchial cavity and vice versa (Nagasawa and Petchsupa 2009;Neeraja et al. 2014). Kottarathil et al., (2019)  We agree with Van der Wal et al. (2017) that both Yamauchi's et al. (2005) and Behera's et al. (2016) host association record is considered false, since Norileca indica is a gill-attaching and does not reside in the stomach of dolphinfish, and to date, the species has not been recorded on

Remarks. Norileca indica
Nemipterus randalli and could refer to another species.
Type material. The female holotype is deposited in the National Museum of Natural History (USNM 231173). For details of paratypes refer to Williams and Bunkley-Williams (1992) Type locality. Sulada Island, Philippines (see Williams and Bunkley-Williams, 1992 (Williams and Bunkley-Williams, 1992).
Remarks. Renocila richardsonae is here reported as a new locality record for Malaysian waters. This species differs from other members of the genus by the distinct protrusion of pereopods 1 and 2 basis and 1 to 6 ischium. For a detailed key to the species of Renocila refer to Williams and Bunkley-Williams (1992).
The specimens collected from Sarawak had a prevalence of 6% and a mean intensity of one isopod per fish. The species was observed attached towards the caudal peduncle of its host (similar to that reported in Williams and Bunkley-Williams, 1992), with slightly severe musculature lesion due to the strong holdfast of the cymothoid's pereopods.

Discussion
Eighteen species of cymothoids were found in Malaysian waters with a total of 76 cymothoidhost species correlations from 29 families identified in the greater Indo-Pacific region (refer to  Brusca (1978Brusca ( , 1981

Cymothoid implication towards aquaculture
Cymothoids are economically significant parasites as they are known to infect a wide range of fishes (be it wild or commercially important species) with a range of health implications (Nowak et al. 2020 anteriorly), antennae 1 and 2 subequal (vs 2 longer than 1), pereopods 6 and 7 with carina on basis (vs pereopods without carina on basis), pleonites 2-5 subequal in width (vs 5 narrower than 2-4), and uropods extending beyond pleotelson (vs reaching mid-length of pleotelson) (see Trilles et al. 2012).

Conclusion
The availability of collected samples from various field trips and expeditions, as well as donations from researchers of different organisations (see 'acknowledgment') allowed for a better understanding of cymothoids in Malaysian waters. Though far from having a comprehensive list based on the minimal specimens obtainable and literary records, it was crucial because comparison of ample specimens from different locations and host associations enabled a better understanding of commonly occurring cymothoids and cymothoid hostassociation, geographical distribution. Prevalence and mean intensity of cymothoids on both wild or aquaculture fish populations can pose a challenge for sampling since it is not consistently recorded seasonally for all species, and therefore unpredictable to target which host species has a higher tendency of being parasitised often. These are areas worthy of future investigation (particular cymothoids of low host specificity), particularly for stakeholders investing in the fisheries, aquaculture, and food safety industry.