New records of fish parasitic isopods of the gill-attaching genus Mothocya Costa, in Hope, 1851 from the Virgin Islands, Caribbean, with description of a new species

Abstract Two species of Mothocya Costa, in Hope, 1851 are reported from the Virgin Islands. Mothocya xenobranchia Bruce, 1986 was collected from St. John Island from the gills of the Atlantic needlefish, Strongylura marina, which is a new locality record and also confirms a previously uncertain host identity. Mothocya bertlucy sp. n. is described from St. Thomas, St John and Guana Islands, from the gills of the redlip blenny, Ophioblennius macclurei, the first record of a blenny as host for any Mothocya. The distinguishing characters of Mothocya bertlucy sp. n. include its small size (< 9 mm) and eyes, the slender pleotelson with a narrowly rounded caudomedial point, extended uropod peduncle and uropods which do not extend past the pleotelson posterior margin, and the narrow pleon which is only slightly overlapped by pereonite 7.


Introduction
Cymothoid isopods are one of the most recognisable groups of isopods to fisherman and anglers . These large (> 6 mm) aquatic parasites are commonly found on the external surface, inside the buccal cavity, or in the branchial cavity of their fish host. Cymothoids removed from the gills are often asymmetrical in body shape, twisted slightly due to the shape of the gill arches and operculum in the branchial cavity (Kensley and Schotte 1989).
In some cases, these parasites cause gill and branchial filament damage (Kroger andGuthrie 1972, Colorni et al. 1997). Williams and Williams (1978) commented on the discolouration and considerable erosion of the gill filaments and opercular flap in some fish they studied. Rokicki (1982) noted atrophy of the gill filaments which automatically affects the fish's development; and Colorni et al. (1997) reported on deformed and calcified gill rakers as well as gill filaments which were dystrophic and fused together with total obliteration of both primary and secondary lamellae.
One of these gill-attaching cymothoid genera is Mothocya Costa, in Hope, 1851. Historically the systematics and biology of this genus had not been considered problematic, but Bruce (1986) showed that Irona Schioedte & Meinert, 1884 and Mothocya were synonymous and that many of the species were misidentified, which had led to the misrepresentation of their hosts and distributions. Bruce (1986) comprehensively reviewed Mothocya and corrected many of these errors, revising seven species and describing 18 new species. Since then, another four species have been described (WoRMS 2014), making a total of 29 valid Mothocya species in the world .
There are six known species of Mothocya in the Caribbean Sea. These are M. argenosa Bruce, 1986 (Bermuda; Florida and Georgia, USA; Cuba; and the British Virgin Islands); M. bermudensis Bruce, 1986 (Bermuda; Haiti; Saint Barthélemy, Leeward Islands); M. bohlkeorum Williams & Williams, 1982 (Florida, USA;Bahamas;Saint Eustatius, Leeward Islands;and Puerto Rico); M. nana (Schioedte & Meinert, 1884) (Florida, Georgia and Maryland USA; Saint Barthélemy, Leeward Islands; and Panama), M. omidaptria Bruce, 1986 (Brazil and West Indies), and M. xenobranchia Bruce, 1986 (Florida, USA;and Venezuela). To date there are no known species recorded from the US Virgin Islands and only one species known from the British Virgin Islands (M. argenosa). The new species described here increases the number of species known from the Caribbean to seven.

Methods
Collections were made from the Virgin Islands, specifically St. John, and St. Thomas, US Virgin Islands, and Guana Island, British Virgin Islands, in the Caribbean Sea during 2013 as part of a study on blood parasites of Caribbean reef fishes. Atlantic needlefish (Strongylura marina) were collected near the surface at night by snorkelers using hand nets, while redlip blennies (Ophioblennius macclurei) were collected by hand nets during the day from reef habitat in shallow bays by snorkelers or divers. Isopods were removed from the gills of their infected hosts using forceps, preserved in 70% ethanol, and processed according to techniques described in Hadfield et al. (2010Hadfield et al. ( , 2011. Species descriptions were prepared in DELTA (Descriptive Language for Taxonomy, see Coleman et al. 2010) using a general Cymothoidae character set (as in Hadfield et al. 2013Hadfield et al. , 2014. Ratios and measurements were rounded off to one decimal place and were made using maximum values of the specific measured article. Classification follows Brandt and Poore (2003). Host nomenclature and distribution are from FishBase (Froese and Pauly 2014).
Abbreviations. AMNH -American Museum of Natural History, New York, NY, USA; TL -total length; USNM -National Museum of Natural History, Smithsonian Institution, Washington, DC, USA; W -width.
Remarks. Female Mothocya are often twisted to one side due to the confines of the gill chamber. Mothocya can be identified by the asymmetrical body shape, antennula longer than the antenna, a maxilliped with an oostegite lobe and the brood pouch from coxae 2-4 and 6. Males are smaller and not twisted, with appendix masculina on pleopod 2.
A detailed diagnosis of Mothocya was given by Bruce (1986), including female and male characters as well as additional characters for the genus. The current diagnosis is a shortened and updated version with more information on the main defining characters such as the body, pleopod and uropod morphology. These important characteristics are very useful in species identifications, as is the host species with some Mothocya species being host species or host genus specific. Bruce (1986) synonymised Irona with Mothocya, with many of the Irona species actually being junior synonyms for Mothocya species. The validity of the genus Irona was considered uncertain for many years (Monod 1923, 1971, Trilles 1968) after Schioedte and Meinert (1884) described it as well as redescribing Mothocya in the same paper. Bruce (1986) described 18 new species of Mothocya in his review, nine of which had synonymies from earlier misidentifications. Many species appear very similar in general appearance, with the antennulae, antennae, mouthparts and pereopods uniform across species and thus not very informative at species level (Bruce 1986).
When looking at individual characters, Mothocya can be distinguished from other gill-inhabiting genera. Elthusa Schioedte & Meinert, 1884 is similar to Mothocya and can be distinguished by the antennula being shorter than the antenna (longer in Mothocya), maxilliped article 3 is slender with setae (robust and without setae in Mothocya), and the pereopod dactyli are relatively short whereas they are long and robust in Mothocya (Bruce 1990). Ichthyoxenus Herklots, 1870, differs from Mothocya with the antennula being shorter than the antenna, having a strongly ovate and vaulted body, as well as a narrow pleon and short and rounded coxae.

Mothocya xenobranchia Bruce, 1986
Antennula comprised of 7 articles; articles 1 and 2 distinct and articulated; article 2 0.8 times as long as article 1; article 3 as long as wide, 0.5 times as long as combined lengths of articles 1 and 2; last article terminating in 4-7 short simple setae. Antenna comprised of 7 articles; article 3 1.2 times as long as article 2, 2.1 times as long as wide; article 4 2.3 times as long as wide, 0.9 times as long as article 3; article 5 0.7 times as long as article 4, 1.7 times as long as wide; last article terminating in 6-7 short simple setae.
Pereopod 1 basis 1.2 times as long as greatest width; ischium 0.9 times as long as basis; merus proximal margin with slight bulbous protrusion; carpus with straight proximal margin; propodus 1.3 times as long as wide; dactylus slender, 1.1 times as long as propodus, 2.3 times as long as basal width. Pereopod 7 basis 1.9 times as long as greatest width; ischium 0.9 as long as basis, without protrusions; merus proximal margin without bulbous protrusion, 0.5 as long as ischium, 0.9 times as long as wide; carpus 0.9 as long as ischium, without bulbous protrusion, 1.1 times as long as wide; propodus 0.8 as long as ischium, 1.7 times as long as wide; dactylus slender, 0.9 as long as propodus, 2.4 times as long as basal width. Pereopod 7 with small indentations on the inner side of the ischium, merus and carpus.
Remarks. Mothocya xenobranchia is known from Belonidae fish hosts and distinguished by the broad body which is arched in lateral view, the invaginations on the inner portion of pereopod 7, antenna with seven articles, and the shape of the pleotelson which is tapered anteriorly, then widens before bluntly rounding off.
When comparing M. xenobranchia from the present study to the description given by Bruce (1986) there are a few minor differences but these are within the normal range of species variation. Variations include a different length to width ratio of the body and size of the eyes on the cephalon, more pronounced rostrum in the holotype, different number of setae on maxilla, but these characteristics given by Bruce (1986) are averages based on many specimens and can be variable depending on the specimen. In his remarks on the species, Bruce (1986) states the antenna can have seven or eight articles too and thus even this difference can be accounted for.
The other Caribbean species differ from M. xenobranchia in that M. bermudensis is smaller overall, with smaller eyes and less produced coxae; Mothocya argenosa has larger eyes, a larger and rounder pleotelson and smaller coxae; and M. nana has a narrower body shape and is not arched longitudinally. Mothocya bohlkeorum has a narrow strongly produced rostrum; antennula and antenna bases closer together; larger and rounder coxae; and less developed proximomedial and peduncle lobes on the pleopods. Lastly, M. omidaptria has much longer uropods, is not arched in lateral view, acute coxae on pereonite 7, and a narrowly produced rostrum. Furthermore, these species all have different hosts to M. xenobranchia and thus there is no overlap of this isopod species on its host species in the Caribbean.
This record of M. xenobranchia in the US Virgin Islands is a new locality record and also confirms the previously uncertain host record of Strongylura marina (Bruce 1986). The locality record conforms to the distribution of this species within the western Atlantic. Likewise, the host record is also from a Belonidae species and thus conforms to the host preference of this species. Paratypes. ♀ dissected (7.0 mm TL; 3.5 mm W), three immature ♂♂, one dissected (5.5-6.0 mm TL; 2.0-2.5 mm W), collected from Brewers Bay, 18°20'24"N,  Ovigerous female holotype. Body oval and moderately twisted, 1.9 times as long as greatest width, widest at pereonite 3, most narrow at pereonite 1, lateral margins slightly convex. Cephalon 0.7 times longer than wide, visible from dorsal view. Eyes oval with distinct margins, 0.2 times width of cephalon, 0.4 times length of cephalon. Pereonite 1 smooth, anterolateral angle rounded. Posterior margins of pereonites smooth and slightly curved laterally. Coxae narrow with rounded point, shorter or same length as pereonite. Pereonites 1-3 increasing in length and width; 4-7 decreasing in length and width, becoming progressively rounded posteriorly. Pleon with pleonite 1 largely concealed by pereonite 7, visible in dorsal view; pleonites posterior margin smooth, mostly concave; pleonite 2 partially overlapped by pereonite 7; pleonite 5 posterior margin slightly concave. Pleotelson 0.6 times as long as anterior width, dorsal surface smooth, lateral margins weakly concave, posterior margin converging to blunt caudomedial point.

Mothocya bertlucy
Antennula comprised of 8 articles; articles 1 and 2 distinct and articulated with plumose setae; article 2 0.9 times as long as article 1; article 3 1.2 times as long as wide, 0.5 times as long as combined lengths of articles 1 and 2 with plumose seta; short simple  setae present on last four articles, last article terminating in 4-8 short simple setae. Antenna comprised of 9 articles; article 3 1.3 times as long as article 2, 1.3 times as long as wide; article 4 1.4 times as long as wide, 1.1 times as long as article 3; article 5 as long as article 4, 1.4 times as long as wide; short simple setae on last three articles, last article terminating in 6-7 short simple setae.
Pereopods without robust or simple setae. Pereopod 1 basis 1.8 times as long as greatest width; ischium 0.6 times as long as basis; merus proximal margin without bulbous protrusion; carpus with straight proximal margin; propodus 1.4 times as long as wide; dactylus slender, 1.3 times as long as propodus, 2.6 times as long as basal width. Pereopod 2 propodus 1.3 as long as wide; dactylus 1.3 as long as propodus. Pereopod 7 basis 1.7 times as long as greatest width; ischium 0.7 as long as basis, without protrusions; merus proximal margin with slight bulbous protrusion, 0.4 as long as ischium, 0.6 times as long as wide; carpus 0.9 as long as ischium, without bulbous protrusion, 0.6 times as long as wide; propodus 0.9 as long as ischium, 1.3 times as long as wide; dactylus slender, 1.7 as long as propodus, 2.7 times as long as basal width.
Uropod more than half the length of pleotelson, peduncle 1.2 times longer than rami, peduncle lateral margin without setae; rami not extending beyond pleotelson, marginal setae absent, apices broadly rounded. Endopod apically rounded, 2.8 times as long as greatest width, lateral margin straight, mesial margin straight, terminating without setae. Exopod extending beyond endopod, 1.7 times longer than endopod, 4.2 times as long as greatest width, apically rounded, lateral margin straight, mesial margin straight, terminating without setae.
Male. Males similar to females but smaller. Body more oval and not twisted, 2.1 times as long as wide. Maxilliped article three with three recurved robust setae. Maxilla with one recurved robust seta on the medial lobe and two on the lateral lobe. Penis set close together, medially united. Pleopod 2 appendix masculina basally swollen, 0.8 times as long as endopod, distally bluntly rounded. Pleotelson triangular converging to a sharp caudal point. Uropods extend past posterior margin of pleotelson and endopod is longer, exopod 1.5 times as long as endopod.
The species most similar to Mothocya bertlucy sp. n. is M. rosea Bruce, 1986 found on the Mexican and Californian coasts. In comparison to M. bertlucy, M. rosea has more produced proximomedial lobes on pleopods 3-5, larger eyes, broad truncate pleotelson, and four setae on the maxilliped article 3.
The three small Mothocya species from atherinids (M. argenosa; M. epimerica; and M. waminda Bruce, 1986) were all compared to the current species. Mothocya argenosa from the western Atlantic measures 5.6-9.8 mm, but has larger eyes, longer uropods, the pleotelson is more rounded and the posterolateral margins of pereonite 7 are acute. Mothocya epimerica from the Mediterranean has a more pointed rostrum, rounded pleotelson, larger eyes and four setae on the maxilliped. Mothocya waminda from the Indo-Pacific has an appendix masculina on pereopod 2 in the female and longer uropods.
Mothocya bertlucy sp. n. differs from all the other known Caribbean species in that M. bohlkeorum has much larger and more produced coxae and a larger truncate pleotelson; M. nana has a wider pleotelson, truncate rostrum and larger coxae; M. bermudensis has an antennula with only seven articles, large eyes and an arched body; and M. omidaptria has longer uropods extending past the pleotelson, a strongly produced rostrum and acute coxae as well as posterolateral angles of pereonite 7. This is the first account of a Mothocya species from the US Virgin Islands and is also the first record on a blenny, which helps establish its status as a new species as Bruce (1986) commented that "host identity may be useful in making a Mothocya identification."