Gnathia masca Farquharson & Smit, sp. nov.
Creators: name: Farquharson, Charon
name: Smit, Nico J.
name: Grutter, Alexandra S.
name: Davies, Angela J.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Gnathiidae
Gnathia
Gnathia masca

description: Gnathia masca Farquharson & Smit sp. nov.
Material examined. Holotype. Male, 2.6 mm, 24 November 2005, Coconut Beach, (14.68185ºS, 145.44825ºE), Museum of Tropical Queensland (W31156). Paratypes. 12 males, 4 females, 10 larvae, 24 November 2005, Coconut Beach, (14.68185ºS, 145.44825ºE), Museum of Tropical Queensland (W31157). Other material. 4 males, 4 females, 12 larvae, 26 November 2005, Coconut Beach, (14.68185ºS, 145.44825ºE), Museum of Tropical Queensland (W31158).
Hosts. From 16S mtDNA sequences of blood meals from pranizae of this species it was evident that they had fed on the following fishes, Arothron stellatus (Bloch & Schneider, 1801), Arothron hispidus (Linnaeus, 1758), Epinephelus malabaricus (Bloch & Schneider, 1801), Lethrinus ornatus Valenciennes, 1830 and L. lentjan (Lacepède, 1802) (see Jones et al. 2007).
Diagnosis. Eyes large, 0.3 times length of cephalosome. Frontal border produced with conical superior frontolateral processes and an inferior conical medio-frontal process. Mandible 0.6 times length of cephalosome with 5 or 6 processes on dentate blade. Distinct internal lobe with 6 or 7 crenulations and a single large distal process. Appendix masculina curved, 0.6 times endopod length with tapering tip.
Male description (Figs 1–3, 10)
Description. Body 3.1 times as long as wide (Fig. 1 A). Cephalosome (Fig. 1 A, B) rectangular, 1.3 times as wide as long, dorsal sulcus shallow, extending half length of cephalosome, lateral margins slightly concave and posterior margin concave, with central area convex. Eyes less than one-third of cephalosome (Fig. 1 B). Many wartlike tubercles distributed dorsally and laterally of eyes, as well as on dorsal surface of cephalosome. Cuticular extensions distributed randomly over dorsal and lateral surface of cephalosome. Median tubercle prominent with wart-like tubercles on the central area (Fig. 1 B). Frontal border (Fig. 1 B) slightly produced. Superior fronto-lateral processes conical, with 3 long, simple setae on each process, inferior medio-frontal process conical. Pereon (Fig. 1 A) with numerous short, cuticular extensions and few long simple setae on anterior, lateral and posterior margins of all pereonites. Pereonite 1 dorsally visible. Pereonite 2 and 3 of similar size, widest part of the body, almost as wide as pereonite 5, lateral margins pointing anteriorly. Pereonite 4 with prominent anterior constriction. Pereonites 5 and 6 both at least twice as long as other pereonites. Pereonite 6 with posterior margin concave, with lobi laterales, no lobuii.
Pleonites (Fig. 1 A), pleon and pleotelson less than third of total body length, epimera dorsally visible on all pleonites. Few simple setae and pectinate scales on lateral and dorsal surface of all pleonites.
Antenna 1 (Fig. 1 C) article 1 of peduncle with 3 plumose setae distally, second article with 1 plumose seta and 4 to 5 simple setae distally, third article with 6 to 7 long simple setae distally, all three articles randomly covered with very short hair-like simple setae and pectinate scales. Flagellum with 5 articles, about 1.3 times as long as article 3 of peduncle, article 3 with 1 long aesthetasc seta and 1 simple seta, article 4 with one aesthetasc seta, article 5 terminating in one aesthetasc and three simple setae.
Antenna 2 (Fig. 1 D) peduncle article 3 with single plumose seta mid-laterally and 7 or 8 long simple setae distally, article 4 with 4 simple setae mid-laterally and 14 or 15 simple setae distally, all 5 articles randomly covered with pectinate scales, flagellum with 7 articles, flagellum about 1.2 times as long as peduncle article 4.
Mandible (Fig. 1 A, B, E) 2.5 times as long as wide, about two-thirds length of cephalosome, narrow basal neck, curved inwards with 5 or 6 processes on dentate blade. Distinct internal lobe dorsally on blade with 6 or 7 crenulations and large distal process, a tussle of setae between each crenulation. Slight incisor present, single long simple mandibular seta extending out of the carina. Cuticular extensions and sensory pits distributed randomly on the dorsal surface of the dentate blade as well as internal lobe.
Maxilliped (Fig. 2 A) 5-articled, proximal article largest with single lateral endite just reaching article 3. Lateral margin of proximal article densely setose with short, simple setae. Distal 4 articles bearing plumose setae on the lateral margins in order of 3-7-5-8, mesial borders with short, simple setae. Palp 2.6 times as long as wide.
Pylopod (Fig. 2 B) three-articled, article 1 greatly enlarged, convex mesial border fringed with 28–32 long PMS, short, simple lateral and proximal setae; 5 long simple setae distally on posterior surface and 4 simple setae near lateral border. Article 1 with 3 areolas increasing in size proximally. Article 2 oval, 1.3 times as long as wide, margins setose, 4 long simple setae distally on posterior surface. Article 3 minute, with fringing simple setae.
Pereopods (Fig. 3 A–E) 2–6 similar in shape. Numerous long setae on basis of all pereopods; pereopod 3 basis with single plumose seta anteriorly (Fig. 3 B), pereopods 4 and 6 with single posterior plumose seta each on basis. Pereopod 6 with single robust seta on posterior bulbous protrusion of merus (Fig. 3 E). Carpus of pereopod 2 with single serrate seta dorso-distally and pereopod 6 carpus with 3 serrate setae anteriorly. All pereopods with pectinate scales randomly over surface.
Pleopod 2 (Fig. 1 F) endopod longer and wider than exopod, both endopod and exopod with 8 PMS, lateral margins of endopod and exopod covered with short simple setae. Appendix masculina curved, 0.6 times endopod length, with tapering tip.
Pleotelson (Fig. 1 G) wider than long, lateral margins slightly convex, dorsal surface with two pairs of long simple setae, many pectinate scales on dorsal surface.
Uropodal (Fig. 1 G) endopod extending beyond apex of pleotelson, exopod reaching apex. Endopod 2.2 as long as greatest width, with 7 long PMS. Exopod 3.1 as long as greatest width with 5 or 6 PMS; pectinate scales on lateral margins of endopod and exopod. Uropodal basis with single simple seta, covered with pectinate scales.
Penis small with 2 contiguous papillae, wider than long.
Pigmentation (Fig. 10 A) on cephalosome orange–brown in live specimens, stretching between eyes. Similar pigmentation present on rest of body. Eyes distinct orange-brown colour.
Adult female (Figs 4–6, 10)
Description. Body (Fig. 4 A) length of paratypes 2.4–2.9 mm. Body about 2.2 times as long as wide (Fig. 4 A). Cephalosome (Fig. 4 A, B) rectangular, lateral margins slightly convex, short and broadened, 1.8 times as wide as long. Eyes one-third length of cephalosome. Short hair-like simple setae distributed randomly over the dorsal, ventral and lateral surfaces of the cephalosome. Two long, simple setae dorsally next to each eye. Frontal border (Fig. 4 B) broadly rounded, produced, slightly concave anteriorly, with 2 simple setae on mid-dorsal area. Pereon (Fig. 4 A) swollen, covered with numerous long simple setae and pectinated scales on lateral and dorsal surface, sutures between pereonite 5 and 7. Pereonite 4 and 5 with areae laterales at leg attachment. Pereonite 6 with lobi laterales. Most setae on lateral and anterior margins of pereonites. Pleon (Fig. 4 A) and pleotelson less than a quarter of the total length; epimera not distinct. Simple setae and pectinate scales randomly distributed on lateral and dorsal surface of pleonites.
Antenna 1 (fig. 4c) short, few short, simple setae on distal end of article 1 and 2, and 4 to 5 simple setae distally on third article. Flagellum with four articles, about 1.4 times as long as article 3 of peduncle, article 2 and 3 with single aesthetasc seta each, article 4 terminating in single aesthetasc seta and 3 long, simple setae.
Antenna 2 (Fig. 1 D) peduncle article 2, 3 and 4 with few simple setae on the distal end, article 3 and 4 with one plumose seta each on the distal end. Flagellum with 7 articles, about 1.2 times as long as peduncle article 4. Peduncle articles of both antennae covered with very short, simple hair-like setae and pectinate scales.
Maxilliped endite short, not reaching article 2 of palp. Palp bearing plumose setae on lateral margins in order of 3-6-5-7 (Fig. 5 A). Article 4 of palp with 2 simple setae distally. Coxa with attached oostegite as broad, but longer than the palp. Mesial borders of basis, oostegite and the palp densely setose.
Pylopod (Fig. 5 B) article 1 broad, robust, curved anteriorly, with 3 simple setae mid-ventrally, article 3 with 5 to 6 long simple setae distally. Oval-shaped oostegite, 2.3 times as long as wide, covers mouthparts ventrally, not surpassing frontal border. Posterior surface and lateral borders of all articles and oostegite covered with pectinate scales.
Pereopods (Fig. 6 A–E) 2–6 similar in shape. Pereopod 2 with single plumose setae anteriorly on basis; pereopods 3 to 6 without plumose setae on basis. Pereopods 3 and 6 (Fig. 6 B, E) with robust setae posteriorly on bulbous protrusion of merus, not plumose setae as on pereopod 2; pereopod 4 and 5 (Fig. 6 C, D) with simple setae on bulbous protrusion. Carpus of pereopod 3 to 6 without serrate setae. Dorsal and ventral surface of all pereopods randomly covered with pectinate scales.
Pleopod (Fig. 4 E) endopod and exopod both fringed distally with 7 to 9 PMS. Retinacula present on sympodite, with a single simple seta on the opposite lateral margin. Lateral margins of endopod and exopod covered with pectinate scales.
Pleotelson (Fig. 4 F) wider than long, lateral margins slightly concave, dorsal surface with 3 pairs of simple setae and pectinate scales on dorsal surface, distal apex with 2 long, simple setae.
Uropodal (Fig. 4 F) endopod stretching beyond apex of pleotelson, exopod reaching apex, both with 7 PMS and covered with pectinate scales. Uropodal basis with single simple seta and covered with pectinate scales.
Pigmentation (Fig. 10 B) in live specimens with similar orange-brown pigmentation to male on cephalosome dorsal to eyes. Similar pigmentation also on dorsal surface of pereonites, distinctly visible on pereonites 5 and 6.
Third stage praniza (P3) (Figs 7–10)
Description. Body (Fig. 7 A) length of paratypes 2.6–2.8 mm. Body about 3.4 times as long as wide. Cephalosome (Fig. 7 A) almost as wide as long, posterior margin straight, slightly wider than anterior margin, lateral margins slightly convex. Eyes well-developed, almost same length as cephalosome. Medio-anterior margin of cephalosome straight with lateral concave excavations to accommodate first articles of antennae. Tubercles and setae absent. Labrum (Fig. 7 B) prominent, more than half as long as cephalosome, semicircular with apical process, anterior margin concave and truncated posterior margin. Ventral parts of labrum gutter-like with central groove, covers mandibles dorsally and laterally. Pereon (Fig. 7 A) wider than cephalosome, 2.3 times as long as wide. Pereonite 1 dorsally visible. Pereonite 2 and 3 similar in size and shape. Pereonite 4 twice as wide as long, lateral sides tapering towards rounded posterior margin, posterior margin stretching over pereonite 5, lateral shields at leg attachment. Pereonite 5 consists of elastic membrane fully expanded in praniza stage with blood meal, bulbous shields present on lateral sides at leg attachment. Pereonite 6 rectangular, with posterior margin slightly concave, lateral shields at leg attachment. Pereonite 7 dorsally visible, small with rounded posterior margin, overlapping first pleonite. Pleon (Fig. 7 A) and pleotelson about a quarter of the total length, few simple setae on lateral sides of pleonites, 1 short, simple seta in middle of each pleonite’s dorsal surface, few pectinate scales distributed mid-dorsally on each pleonite.
Antenna 1 (Fig. 7 C) peduncle article 1 with 2 simple setae, article 2 with 5 simple setae distally and article 3 with 2 simple setae. Flagellum with six articles, about 1.5 times as long as peduncle article 3. Article 1 with 2 to 3 short simple setae mid-dorsally, few setae on article 2 and 3, article 4 and 5 with a single aesthetasc seta each, article 6 terminating in 4 simple setae.
Antenna 2 (Fig. 7 D) peduncle article 1 and 2 with few simple setae, article 3 with 5 to 6 distal setae and article 4 with 4 to 5 distal setae and 2 plumose setae. Flagellum with seven articles, about 1.5 times as long as peduncle article 4, few simple setae at distal end of each article, article 7 terminating with 5 simple setae.
Mandible (Fig. 8 A) stout, swollen at base, distal margin styliform with 7 large, triangular teeth, directed backwardly and 2 small teeth at tip.
Paragnaths (Fig. 8 E) elongated, gutter-like, terminates in sharp point.
Maxillule (Fig. 8 D) long, slender, swollen at the base, 5–6 small teeth on distal inner margin.
Maxilliped (Fig. 8 C) palp with 3 articles, first article with 3 to 4 small teeth, second article with 5 to 6 simple setae and article 3 terminating in sharp point, with simple seta mid-laterally.
Gnathopod (Fig. 8 B) with seven articles, few simple setae on all articles, 1 tooth-shaped tubercle on lateral margin of second article. Dactylus strongly hooked.
Pereopods (Fig. 9 A–E) 2–6 similar in shape. Pereopod 3 and 4 without plumose setae on posterior margin of basis and pereopods 5 and 6 (Fig. 9 D, E) each have 2 plumose setae on the posterior margin. Pereopod 6 with single robust serrate seta on the posterior margin of ischium. Pereopods 4, 5 and 6 without a short serrate seta on posterior margin of carpus. All articles of all pereopods covered with pectinate scales.
Pleopod 1(Fig. 7 E) endopod and exopod, with 8 or 9 PMS, pectinate scales on all margins.
Pleotelson (Fig. 7 F) longer than wide, anterior and posterior part of lateral margin slightly concave, mid-anterior parts slightly convex. Pair of simple setae on posterior dorsal surface, distal apex terminating in 2 simple setae. Anterio-dorsal surface covered in pectinate scales.
Uropodal (Fig. 7 F) endopod extending to approximately same length as apex of pleotelson, exopod not reaching apex. Both endopod and exopod with 7 PMS. Few pectinate scales on lateral dorsal areas of endopod and exopod. Uropodal basis with one simple seta and anterior-dorsal surface covered with few pectinate scales.
Pigmentation (Fig. 10 C) of live specimens with orange-brown pigmentation on margins of cephalosome and on posterior margins of pereonites 5 and 6. Eyes also distinct orange-brown in colour.
Etymology. The species name is derived from the Latin for a mask, or masked, in. reference to the band of orange-brown pigmentation that stretches between the eyes of the adult males.
Remarks. Gnathia masca sp. nov. is distinguished from all other Australian Gnathia by the combination of a distinct dentate internal lobe with 6 to 7 crenulations and a single large distal process, and prominent conical medio-frontal process. Several other Great Barrier Reef (GBR) Gnathia have internal lobes (e.g. G. falcipenis Holdich & Harrison, 1980, G. cornuta Holdich & Harrison, 1980, G. aureamaculosa and G. g r u t t e r a e) but lack the distinct crenulations and large distal process of Gnathia masca sp. nov. The present species is furthermore most similar to G. camponotus Cohen & Poore, 1994 in mandibular morphology but the medio-frontal process of G. camponotus is much further anterioirly produced than that of the species described here. These species can further be separated based on the shape of their cephalosomes and setation of the maxillipeds.
Very few description of Gnathia females and juveniles are available for comparison, however, Gnathia masca sp. nov. females can easily be distinguished from the known GBR Gnathia females (e.g. G. aureamaculosa, G. grutterae, G. trimaculata) by the shape of the pylopod, pleotelson and setation of the cephalosome. Similarly juvenile Gnathia masca sp. nov. can be distinguished from the above species’ juveniles by its very characteristic shaped cephalosome and pleotelson and unique shape and number of teeth on the mandible. More comprehensive comparisons between the females and juveniles of Gnathia species and the establishing of what really constitute unique characteristics will only be possible when more are described.
Distribution. From fringing reefs off Lizard Island, Great Barrier Reef, Australia.
description: Published as part of Farquharson, Charon, Smit, Nico J., Grutter, Alexandra S. & Davies, Angela J., 2012, Gnathia masca sp. nov. (Crustacea, Isopoda, Gnathiidae) from Lizard Island, Great Barrier Reef, Australia, pp. 22-36 in Zootaxa 3233 on pages 23-35, DOI: 10.5281/zenodo.212948