Mothocya xenobranchia Bruce, 1986

Hadfield, Kerry A., Sikkel, Paul C. & Smit, Nico J., 2014, 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, ZooKeys 439, pp. 109-125 : 111

Taxon classification Animalia Isopoda Cymothoidae

Mothocya xenobranchia Bruce, 1986 Figs 1-2

Mothocya xenobranchia Bruce, 1986: 1116-1119, figs. 13-14. - Trilles 1994: 203. - Bunkley-Williams et al. 1998: 29. - Bunkley-Williams et al. 2006: 178. - Schotte et al. 2009: 983.

Material examined.

♀ (15.0 mm TL; 10.0 mm W), ♂ (9.0 mm TL; 4.0 mm W) collected from Lameshur Bay, 18°18'59"N, 64°43'25"W, St. John Island, US Virgin Islands, from the gills of the Atlantic needlefish (34 mm TL), Strongylura marina , 18 May 2013, coll. Nico J. Smit (AMNH_IZC 00197448).

Ovigerous female.

Body moderately twisted, 1.4 times as long as greatest width, strongly arched longitudinally, widest at pereonite 3, most narrow at pereonite 1, lateral margins slightly convex. Cephalon 0.7 times longer than wide, visible from dorsal view, subtriangular. Eyes oval with distinct margins, 0.2 times width of cephalon, 0.4 times length of cephalon. Coxae 2-3 narrow; 4-7 large, rounded and produced, slightly produced past pereonite margin. Pereonites 1-4 increasing in length and width; 5-7 decreasing in length and width; becoming more progressively rounded posteriorly. Pleon with pleonite 1 largely concealed by pereonite 7; pleonites posterior margin smooth, mostly concave; pleonites 2-5 partially overlapped by pereonite 7; pleonite 5 posterior margin straight. Pleotelson 0.6 times as long as anterior width, dorsal surface smooth, anterolateral margin recessed, lateral margins widen slightly then curve inwards, posterior margin broadly truncate, without median point.

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.

Molar process present, mandible palp without setae. Maxillula with 4 terminal robust setae. Maxilla lateral lobe with 2 recurved robust setae; mesial lobe with 2 large recurved robust setae. Maxilliped weakly segmented, palp article 2 with no simple setae, article 3 with 4 recurved robust setae and no 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.

Pleopod 1 exopod as long as wide, lateral margin strongly convex, distally broadly rounded, mesial margin strongly convex; endopod 1.2 times as long as wide, lateral margin weakly convex, distally narrowly rounded, mesial margin straight, peduncle 0.7 times as wide as long. Pleopods 2-5 similar in structure to pleopod 1. Large medial lobes present and increasing in size from pleopods 1 to 5. Peduncle lobes increasing in size from pleopods 2 to 5.

Uropod longer than pleotelson; peduncle 0.7 times longer than exopod, lateral margin without setae; rami extending beyond pleotelson, marginal setae absent, apices broadly rounded. Endopod apically slightly pointed, 3.6 times as long as greatest width, lateral margin weakly convex, mesial margin weakly convex, terminating without setae. Exopod extending beyond endopod, 1.9 times longer than endopod, 3.8 times as long as greatest width, apically rounded, lateral margin straight, mesial margin straight, terminating without setae.

Type material.

Holotype (16.2 mm TL) from the gill cavity of Tylosurus crocodilis crocodilis from Bahia Mochima, Venezuela (USNM 216274); Paratypes (USNM 216275-216278) ( Bruce 1986; not examined).

Distribution.

Off the coast of Florida, Florida Keys (USA); Cumaná, Venezuela ( Bruce 1986, Bunkley-Williams et al. 1998, Schotte et al. 2009); and St. John Island, US Virgin Islands (present study).

Hosts.

Known from the hound needlefish, Tylosurus crocodilis crocodilis ( Péron & Lesueur, 1821) ( Bruce 1986, Bunkley-Williams et al. 1998, Schotte et al. 2009) and Strongylura marina (Walbaum, 1792) (previously unconfirmed but verified in the present study). There is also another unconfirmed record from Strongylura notata notata (Poey, 1860) in Florida ( Bruce 1986).

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 Mothocya 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 Mothocya xenobranchia in that Mothocya 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 Mothocya 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, Mothocya 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 Mothocya xenobranchia and thus there is no overlap of this isopod species on its host species in the Caribbean.

This record of Mothocya 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.