Gnathia bermudensis, Hadfield, Kerry A., Schizas, Nikolaos V., Chatterjee, Tapas & Smit, Nico J., 2019

Hadfield, Kerry A., Schizas, Nikolaos V., Chatterjee, Tapas & Smit, Nico J., 2019, Gnathia bermudensis (Crustacea, Isopoda, Gnathiidae), a new species from the mesophotic reefs of Bermuda, with a key to Gnathia from the Greater Caribbean biogeographic region, ZooKeys 891, pp. 1-16 : 1

Gnathia bermudensis sp. nov. Figures 2 , 3 , 4

Material examined.

Holotype. Bermuda • 1 ♂ (2.2 mm TL); Plantagenet Bank (31°56.55'N, 65°09.29'W); 56 m; 12 Aug 2016; Diver 2, from sediment; Sample ID BEX 2016-449 (BAMZ 2016-338-147).

Paratypes. Bermuda • 3 ♂♂ (1.9-2.1 mm TL) (one dissected), 1 ♂ used for SEM (1.8 mm TL), 1 ♀ (1.6 mm TL); same info as holotype (BAMZ 2016-338-148).

Other material.

Bermuda • 4 ♂♂ (1.8-1.9 mm TL) (one dissected); Spittal (32°19.119'N, 64°39.437'W); 45 m; 3 Aug 2016; sediment from Montastraea cavernosa (Linnaeus, 1767) corals, Divers 39; Sample ID BEX 2016-227, Parent BEX2016-225 (sediment from several Montastraea cavernosa colonies) (BAMZ 2016-338-149) • 1 ♂ (2.0 mm TL); NNE (32°28.59'N, 64°34.46'W); 90 m; 4 Aug 2016; Event Divers; Sample ID BEX 2016-250, Parent BEX2016-248 (BAMZ 2016-338-150) • 1 zuphea (Z1) (0.45 mm TL); NNE (32°28.59'N, 64°34.46'W); 4 Aug 2016; algae substrate; Sample ID BEX 2016-251 • 1 ♂ used for SEM (1.7 mm TL); Spittal (32°19.119'N, 64°39.437'W); from rhodolith collected between 82-152 m; 7 Aug 2016; Dive 22, Nomad 1 (a Triton Submersible); Sample ID BEX 2016-299, Parent BEX2016-0265 • 1 ♂ (2.0 mm TL), 1 ♀ (1.9 mm TL), 1 zuphea (0.8 mm TL); Tiger 4 (32°11.17'N, 64°58.36'W); 7 Aug 2016; Divers 12, from sediment; Sample ID BEX 2016-304, Parent BEX2016-0282 (rhodolith with red encrusting sponge,> 40 m) (BAMZ 2016-338-151) • 2 ♂♂ (1.9-2.0 mm TL); Spittal (32°19.119'N, 64°39.437'W); 77 m; 11 Aug 2016; wash from rhodolith; Sample ID BEX 2016-428 • 1 ♂ (2.0 mm TL), 1 praniza (P3) (2.3 mm TL), 1 zuphea (Z1) (0.5 mm TL); Spittal (32°19.119'N, 64°39.437'W); 77 m; 11 Aug 2016; Diver 30; Sample ID BEX 2016-430 • 4 zuphea (Z1) (0.5 mm TL); Plantagenet Bank (31°56.55'N, 65°09.29'W); 56 m; 12 Aug 2016; Divers 2; Sample ID BEX 2016-450 • 2 ♂♂ (1.7-1.9 mm TL) (one used for SEM); Plantagenet Bank (31°56.55'N, 65°09.29'W); 56 m; 12 Aug 2016; Divers 6; Sample ID BEX 2016-451. All samples were collected by GUE technical divers except Sample ID BEX 2016-299, Parent BEX2016-0265, which was collected by a Triton Submersible.

Description of male.

Body 2.3 times as long as greatest width, widest at pereonite 3; dorsal surfaces sparsely punctate, sparsely setose. Cephalosome quadrate, 0.7 as long as wide, lateral margins sub-parallel; dorsal surface with sparse granules; dorsal sulcus narrow, shallow, short; translucent region absent; paraocular ornamentation strongly developed, posteromedian tubercle present. Frontolateral present. Frontal margin slightly produced. External scissura present, wide, shallow. process present, weak, bifid, without fine setae. Supraocular lobe pronounced, pointed; accessory supraocular lobe not pronounced. Superior frontolateral process present, single, strong, conical, with two long simple setae. Inferior frontolateral process absent. Mesioventral margin concave. Eyes present, elongate, 0.3 times as long as cephalosome length, bulbous, standing out from head surface, ommatidia arranged in rows, eye colour black.

Pereon lateral margins subparallel, with few setae; anteriorly with sparse fine granules. Pereonite 1 not fused dorsally with cephalosome; dorsolateral margins fully obscured by cephalosome. Pereonite 2 wider than pereonite 1. Areae laterales present on pereonite 5. Pereonite 6 without lobi laterales; lobuii weak, globular. Pleon covered in pectinate scales, epimera not dorsally visible on all pleonites. Pleonite 1 lateral margins with one pair of simple setae, with one pair of simple setae medially. Pleotelson as long as anterior width, covered in pectinate scales. Pleotelson lateral margins finely serrate, anterolateral margins weakly convex, with two submarginal setae; posterolateral margin distally weakly concave, with two submarginal setae; apex with two setae.

Antennula peduncle article 2 0.8 times as long as article 1; article 3 1.9 times as long as article 2, 2.7 times as long as wide; flagellum 1.1 times as long as article 3, with five articles; article 3 with one aesthetasc seta and one simple seta; article 4 with one aesthetasc seta and one simple seta; article 5 terminating with one aesthetasc seta and three simple setae. Antenna peduncle article 4 2.5 times as long as wide, twice as long as article 3, and four simple setae; article 5 1.3 times as long as article 4, 2.8 times as long as wide, inferior margin with three penicillate setae, with six simple setae; flagellum 1.5 times as long as article 5, with seven articles.

Mandible 0.4 as long as width of cephalosome, triangular, weakly curved, evenly; apex 42% total length; mandibular seta present. Incisor dentate. Blade present, dentate, weakly convex, dentate along 100% of margin. Pseudoblade absent; internal lobe absent; dorsal lobe absent; basal neck short; erisma present.

Maxilliped 5-articled; article 1 lateral margin with continuous marginal scale-setae; article 2 lateral margin with four plumose setae; article 3 lateral margin with six plumose setae; article 4 lateral margin with four plumose setae; article 5 with eight plumose setae; endite extending to mid-margin of article 3; without coupling setae.

Pylopod first article 1.5 as long as wide, without distolateral lobe; posterior and lateral margins forming rounded curve; lateral margin with 23 large plumose setae; mesial margin with continuous scale-setae; distal margin with three simple setae; second article 1.1 as long as wide.

Pereopods 2-6 with long simple setae and randomly covered in pectinate scales; pereopod 2 with tubercles on carpus and basis to ischium. Pereopod 2 basis 2.8 times as long as greatest width, superior margin with five setae, inferior margin with two setae; ischium 0.6 times as long as basis, 2.6 as long as wide, superior margin with one seta, inferior margin with three setae; merus 0.5 as long as ischium, 1.5 as long as wide, superior margin with two setae, inferior margin with four setae; carpus 0.6 as long as ischium, 1.9 as long as wide, superior margin without setae, inferior margin with two setae; propodus 0.8 times as long as ischium, 2.8 times as long as wide, superior and inferior margins without setae, and two robust setae; dactylus 0.7 as long as propodus. Pereopods 3 and 4 similar to pereopod 2. Pereopod 5 similar to pereopod 6. Pereopod 6 with tubercles on merus and carpus; basis 3.1 times as long as greatest width, superior margin with two setae, inferior margin with two setae; ischium 0.7 as long as basis, 2.7 as long as greatest width, superior margin with three setae, inferior margin with four setae; merus 0.6 as long as ischium, 2.1 times as long as wide, superior margin with three setae, inferior margin with two setae; carpus 0.6 as long as ischium, 1.7 times as long as wide, superior margin and inferior margin with one seta; propodus 0.9 as long as ischium, 3.8 times as long as wide, superior margin with three setae, inferior margin with one seta, and two robust setae; dactylus 0.6 as long as propodus.

Penes opening flush with surface of sternite 7.

Pleopod 2 exopod 1.9 as long as wide, distally broadly rounded, with eight plumose setae; endopod 1.9 as long as wide, distally broadly rounded, with eight plumose setae; appendix masculina absent; peduncle 1.5 times as wide as long, mesial margin with two coupling setae, lateral margin with one simple seta.

Uropod rami extending beyond pleotelson, apices narrowly rounded. Uropod endopod 2.4 as long as greatest width, dorsally with five setae; lateral margin straight; proximomesial margin weakly convex, with seven long plumose setae. Uropod exopod not extending to end of endopod, 2.9 times as long as greatest width; lateral margin straight, with two simple setae; proximomesial margin straight, distally convex, mesiodistal margin with seven long plumose setae.

Etymology.

The epithet bermudensis is for the country Bermuda, being the first Gnathia record from this island nation.

Distribution.

Bermuda.

Hosts.

Not known.

Remarks.

Gnathia bermudensis sp. nov. may be identified by the produced frontal margin; presence of two superior frontolateral processes; a weak and bifid mediofrontal process; and pronounced and pointed supraocular lobes. The uropod rami extend past the posterior point of the pleotelson; pereonite 1 is not dorsally fused with the cephalosome; large eyes (0.3 as long as cephalosome length); and a weakly curved, dentate mandible.

This species is from a moderate depth of 56-90 m and was collected from several habitat types (algae, loose gravel, rhodoliths, sediment associated with scleractinian corals, muddy sand, and sponges) encompassing the mesophotic reef ecosystems of Bermuda. The Mesophotic Coral Ecosystems (MCEs) of Bermuda represent the most northern coral reef systems of the Atlantic; they are visually dominated by scleractinian corals at the upper depth limits, which are replaced gradually at greater depths by rhodoliths, macroalgae beds and fossilised reefs ( Goodbody-Gringley et al. 2019). The new gnathiid species has been found on the mesophotic slopes of the main seamount (i.e., the main island of Bermuda) and the smaller seamount Plantagenet ( Figure 1 ); therefore, it is expected to be found throughout the deeper reefs of Bermuda. Only four other species of Gnathia have been collected from greater depths in this region.

Gnathia bermudensis sp. nov. is most similar to G. beethoveni Paul & Menzies, 1971, G. calsi Müller, 1993, G. johanna Monod, 1926, G. magdalenensis Müller, 1988, and G. virginalis Monod, 1926 from the region. The frontal margin of G. beethoveni differs from Gnathia bermudensis in having less pronounced supraocular lobes, four frontolateral processes, a shallow median notch, and the cephalosome is lacking dorsal tubercles. Gnathia calsi also has a deeply notched mediofrontal process with two lobes (and setae), and well developed but angular supraocular lobes, not seen in Gnathia bermudensis sp. nov. Gnathia johanna is narrower than Gnathia bermudensis sp. nov., with less pronounced supraocular lobes and a single convex mediofrontal process (with setae) between the superior frontolateral processes. Gnathia magdalenensis and G. virginalis differ from Gnathia bermudensis sp. nov. in having slightly pointed supraocular lobes, a single pointed mediofrontal process with setae, and a longer cephalosome that is fused with pereonite 1.

Although adult females and zuphea juveniles were collected with the males, they cannot be confidently linked to this species without molecular or ecological data. More collections and rearing of the gnathiid isopods would need to be made in the future for more information and validation of these different life stages, as well as to determine the hosts of the juvenile stages.

Figures

Figure 1. Map of collection sites around Bermuda. Data overlay GEBCO _ 2014 Grid which provides 30 arc-second global grid of elevations. Depth contours in meters.

Figure 2. Gnathia bermudensis sp. nov. (BAMZ 2016 - 338 - 147), male holotype (2.2 mm TL) A dorsal view B dorsal view of cephalosome C dorsal view of pleotelson and uropods D dorsal view of mandible E antenna F antennula G pylopod H maxilliped. Scale bars: 100 μm.

Figure 3. Gnathia bermudensis sp. nov. (BAMZ 2016 - 338 - 147), male holotype (2.2 mm TL) A pleopod 2 B-F pereopods 2 - 6, respectively. Scale bar: 100 μm.

Figure 4. Gnathia bermudensis sp. nov. (BAMZ 2016 - 338 - 148), male paratype (1.8 mm TL) Scanning Electron Microscope (SEM) images. A dorsal view B frontal margin and mandibles C ventral view of cephalosome D maxilliped E dorsal view of pleotelson and uropods. Scale bars: 100 μm.