Gnathia pipinde, Smit & Hadfield, 2022

Smit, Nico J. & Hadfield, Kerry A., 2022, Gnathia pipinde sp. nov. (Crustacea, Isopoda, Gnathiidae), a temporary parasite of the pufferfish, Amblyrhynchotes honckenii, from temperate southern Africa, ZooKeys 1129, pp. 1-19 : 1

Gnathia pipinde sp. nov.

Figs 1 , 2 , 3 , 4 , 5 , 6

Material examined.

Holotype. South Africa • 1 ♂ (4.6 mm TL, dissected); De Hoop Nature Reserve (34°28'44"S, 20°30'38"E); October 1999; leg. N.J. Smit; from Amblyrhynchotes honckenii (NMB P 899) . Paratypes. South Africa • 1 ♂ used for SEM (5.1 mm TL), 11 praniza larvae (P3) (3.8-4.6 mm TL), 1 P 3 larva for SEM (4.2 mm TL); same info as holotype (NMB P 900) • 2 praniza larvae (P3) (3.8, 4.3 mm TL); Chintsa (32°50'01"S, 28°06'58"E); October 2020; leg. K.A. Hadfield; from Amblyrhynchotes honckenii (NMB P 901).

Description of male adult.

(Figs 1 - 4 ). Body 2.8 times as long as greatest width, widest at pereonite 5; dorsal surfaces punctate, sparsely setose. Cephalosome quadrate, 0.8 as long as wide, lateral margins subparallel, posterior margin concave; dorsal surface with sensory pits and sparse granules; dorsal sulcus narrow, deep, short; paraocular ornamentation weakly developed, posteromedian tubercle present. processes present. Frontal margin straight, median point with processes. External scissura present, narrow, shallow. Mediofrontal process present, strong, bifid, without fine setae. Superior frontolateral process present, single, strong, conical, with 6 pairs of long simple setae. Inferior frontolateral process absent. Supraocular lobe pronounced, pointed; accessory supraocular lobe not pronounced. Eyes present, elongate, 0.4 as long as cephalosome length, contiguous with head surface, ommatidia arranged in rows.

Pereon lateral margins subparallel, with few setose setae; anteriorly smooth. Pereonite 1 partially fused dorsally with cephalosome; dorsolateral margins partly obscured by cephalosome. Pereonite 2 wider than pereonite 1. Pereonite 4 with prominent anterior constriction separating it from pereonite 3, median groove present. Areae laterales present on pereonite 5. Pereonite 6 with weak lobi laterales; lobuii absent or weak, conical. Pleon epimera dorsally visible on all pleonites. Pleonite lateral margins with 2 pairs of simple setae, long setose setae randomly distributed on posterior margins. Pleotelson as long as anterior width, covered in pectinate scales; lateral margins finely serrate, anterolateral margins concave, with 3 submarginal setae; posterolateral margin weakly convex, with 2 submarginal setae; mid-dorsal surface with 2 submedian setae, apex with 2 setae.

Antennula shorter than antenna; peduncle article 1 with 2 penicillate setae; article 2 0.8 times as long as article 1, with 2 penicillate setae; article 3 2.1 times as long as article 2, 3.8 times as long as wide. Antennula flagellum 0.8 times as long as article 3, with 5 articles; article 1 with 2 plumose setae; article 3 with 1 aesthetasc seta; article 4 with 1 aesthetasc seta, and 2 simple setae; article 5 terminating with 1 aesthetasc seta, and 3 simple setae. Antenna peduncle article 1 covered in pectinate scales and marginal setae; article 3 2.9 times as long as wide, twice as long as article 2, with 1 penicillate seta, and 12-14 simple setae and 1 penicillate seta; article 4 1.3 times as long as article 3, 3.7 times as long as wide, with 2 penicillate setae, and with 40-50 simple setae; flagellum as long as article 4, with 7 articles, terminating with 4 simple setae.

Mandible 0.6 as long as width of cephalosome, rectangular, strongly curved, distally; apex cylindrical, 22% total length, distally raised in lateral view; mandibular seta present. Carina present, smooth. Incisor knob-like. Blade present, dentate, straight, dentate along 100% of margin, with tufts of setae along distal margin. Basal neck short; sensory pits with short simple hair-like setae distributed randomly on dorsal surface of blade. Pseudoblade, internal lobe and dorsal lobe absent; erisma present; lamina dentata absent.

Maxilliped 5-articled, mesial border with short simple hair-like setae; article 1 lateral margin with continuous marginal short setae, endite extending to distal margin of article 2, without coupling setae; article 2 lateral margin with 5 plumose setae; article 3 lateral margin with 7 plumose setae; article 4 lateral margin with 6 plumose setae; article 5 with 7 plumose setae and 5 simple setae.

Pylopod article 1 with three distinct areolae, 1.6 as long as wide, without distolateral lobe; posterior and lateral margins forming rounded curve; lateral margin with 38 large plumose setae; mesial margin with scale-setae on distal part only, 2 simple setae and 1 penicillate seta; distal margin with 6 simple setae; article 2 1.3 as long as wide; with 8 simple setae; article 3 minute, with 4 simple setae.

Pereopods 2-6 with long simple setae and randomly covered in pectinate scales (only illustrated on pereopod 2); inferior margins with weak tubercles. Pereopod 2 with tubercles on merus and carpus; basis 2.9 times as long as greatest width, superior margin with 19 setae, inferior margin with 12 setae; ischium 0.7 times as long as basis, 2.5 as long as wide, superior margin with 6 simple setae and 1 long setose seta, inferior margin with 17 setae; merus 0.5 as long as ischium, 1.5 as long as wide, superior margin with bulbous protrusion and 4 setae, inferior margin with tubercles and 7 setae; carpus 0.5 as long as ischium, 1.8 as long as wide, superior margin with 2 setae (1 setose), inferior margin with tubercles and 5 setae (1 serrate seta); propodus 0.7 times as long as ischium, 2.5 times as long as wide, superior margin with 3 simple setae and 1 penicillate seta, inferior margin with 2 simple setae and 2 robust setae; dactylus 0.7 as long as propodus, terminates in sharp posterior pointing unguis. Pereopods 3 and 4 similar to pereopod 2. Pereopod 5 similar to pereopod 6. Pereopod 6 with tubercles on merus and carpus; basis 3 times as long as greatest width, superior margin with 14 setae, and 1 penicillate seta, inferior margin with 11 setae; ischium 0.9 as long as basis, 3.2 as long as greatest width, superior margin with 12 setae, inferior margin with 8 setae; merus 0.5 as long as ischium, 1.8 times as long as wide, superior margin with 6 setae, inferior margin with 4 setae, without dense patch of scale-setae; carpus 0.5 as long as ischium, 2.2 times as long as wide, superior margin with 3 setae, inferior margin with 4 setae; propodus 0.6 as long as ischium, 3.8 times as long as wide, superior margin with 5 setae, inferior margin with 5 setae, and 2 robust setae; dactylus 0.6 as long as propodus.

Penes produced, more than a third length of pereon; penial processes 6.5 times as long as basal width, anterior end ending in sac-like extension dorsal to opening.

Pleopod 2 exopod 1.7 as long as wide, distally broadly rounded, with 9 plumose setae; endopod 1.8 as long as wide, distally broadly rounded, with 8 plumose setae; appendix masculina absent; peduncle 0.8 times as wide as long, mesial margin with 2 coupling setae, lateral margin with 1 simple seta.

Uropod rami extending beyond pleotelson, apices narrowly rounded. Peduncle with 1 dorsal seta. Uropod endopod 2.4 as long as greatest width, dorsally with 4 setae; lateral margin straight, lateral margin with 6 simple setae; proximomesial margin weakly convex, with 6 long plumose setae. Uropod exopod not extending to end of endopod, 3.3 times as long as greatest width; lateral margin weakly sinuate, with 17 simple setae; proximomesial margin straight, distally convex, with 3 long plumose setae.

Description of praniza 3 larva.

(Figs 4 - 6 ). Body 3.5 times as long as greatest width; dorsal surfaces sparsely punctate, sparsely setose. Cephalosome 0.7 times as long as wide; posterior margin slightly concave; lateral margins convex; dorsal surface with few sensory pits and no setae; anterior margin straight with lateral concave excavations to accommodate first articles of antennae. Labrum prominent, 0.4 times as long as cephalosome, semicircular with apical processes, anterior margin concave. Eyes well developed, oval-shaped; almost as long as cephalosome; one eye 0.3 as wide as cephalosome, bulbous, standing out from head surface; ommatidia arranged in rows; eye colour black.

Pereon elongate, 2.3 times as long as wide, smooth, with no setae or sensory pits. Pereonite 1 partially fused dorsally with cephalosome; dorsally visible; dorsolateral margins partly obscured by cephalosome. Pereonite 2 and 3 similar in size and shape. Pereonite 4 triangular, 2.1 times as wide as long, 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, lateral shields at leg attachment. Pereonite 6 rectangular, posterior margin slightly concave, lateral shields at leg attachment. Pereonite 7 dorsally visible; posterior margin rounded, overlapping pleonite 1. Pleon with all 5 pleonites dorsally visible; pleon and pleotelson 0.4 times as long as pereon. Pleonite 5 almost twice the length of the other articles. Pleotelson 1.3 times as long as anterior width, covered in pectinate scales; lateral margins finely serrate; anterolateral margins concave, without submarginal setae; posterolateral margin weakly convex, with 2 submarginal setae; mid-dorsal surface with 2 submedian setae, apex with 2 setae.

Antennula shorter than antenna; peduncle with short hair-like setae on anterior borders of all three articles; article 2 with 3 setae, as long as article 1; article 3 with 2 setae (1 penicillate), 2.3 times as long as article 2, 2.9 times as long as wide. Antennula flagellum 1.1 times as long as article 3, with 4 articles; article 1 with 2-3 setae; article 2 with 1 aesthetasc seta and 1 simple seta, 0.6 times as long as flagellum; article 3 with 1 aesthetasc seta; article 4 terminating with 1 aesthetasc seta and 3 simple setae. Antenna with rows of long simple setae on anterior margins of all 4 peduncle articles; peduncle article 3 2.3 times as long as wide, 2 times as long as article 2, with 4 simple setae; article 4 twice as long as article 3, 4.2 times as long as wide, with 6 simple setae; flagellum 1.1 times as long as article 4, with 7 articles, terminating with 3 or 4 simple setae.

Mandible stout, distal margin styliform with 16 teeth on mesial margin (3 smaller at tip of mandible), conical and posteriorly directed, increasing in size from anterior to posterior.

Paragnaths elongate, gutter-like, terminates in sharp point, no teeth.

Maxillula long, slender, 6-8 small teeth on distal inner margin, lateral border with marginal setae proximally.

Maxilliped cylindrical with elongated base, endite extending to distal margin of palp article 2, with 1 long simple seta and coupling seta. Maxilliped palp 3-articled; article 1 with 6 teeth mesially, lateral margin with setae; article 3 with 5-7 simple setae.

Gnathopod smaller than pereopods, with 7 articles, carpus reduced, few simple setae on articles 1-5, 1 robust seta on article 2.

Pereopods 2-6 with long simple setae, pectinate scales covering inner margins of propodus and carpus, and outer margins of merus. Pereopod 2 with tubercles on carpus; basis 2.6 times as long as greatest width, superior margin with 5 setae, inferior margin with 2 setae; ischium 0.7 times as long as basis, twice as long as wide, superior margin with 2 setae, inferior margin with 1 seta; merus 0.5 as long as ischium, 1.3 as long as wide, superior margin with bulbous protrusion, with 3 setae (2 serrate) and pectinate scales, inferior margin with 2 setae; carpus 0.5 as long as ischium, 1.6 as long as wide, superior margin with no setae, inferior margin with 4 setae (1 serrate) and pectinate scales; propodus 0.7 times as long as ischium, 2.3 times as long as wide, superior margin with 2 setae (1 penicillate), inferior margin with 1 simple seta, 2 robust setae and pectinate scales; dactylus 0.9 as long as propodus, with 5 setae, terminates in sharp posterior pointing unguis. Pereopods 3 and 4 similar to pereopod 2 (differ in setation). Pereopod 5 similar to pereopod 6. Pereopod 6 with tubercles on carpus; basis 3.3 times as long as greatest width, superior margin with 12 setae, inferior margin with 3 setae; ischium 0.7 as long as basis, 2.5 as long as greatest width, superior margin with 4 setae (1 penicillate, 2 setose), inferior margin with 2 setae; merus 0.6 as long as ischium, 1.4 times as long as wide, superior margin with bulbous protrusion and 3 setae (2 serrate), inferior margin with 2 setae, with dense patches of pectinate scales; carpus 0.6 as long as ischium, 2.2 times as long as wide, superior margin with 2 setae, inferior margin with 3 setae (1 serrate) and pectinate scales; propodus 0.8 as long as ischium, 3.6 times as long as wide, superior margin with 9 setae, inferior margin with 1 seta, 2 robust setae, and pectinate scales; dactylus 0.6 as long as propodus, with 4 setae, terminates in sharp posterior pointing unguis.

Pleopod 1 exopod 1.9 as long as wide, distally broadly rounded, with 8 plumose setae; endopod 1.8 as long as wide, distally narrowly rounded, with 7 plumose setae; peduncle 0.8 times as wide as long, mesial margin with 2 coupling setae, lateral margin with 1 simple seta.

Uropod rami extending to pleotelson apex, apices narrowly rounded, fringes with short simple setae. Peduncle with 2 dorsal setae. Uropod endopod 1.9 as long as greatest width, dorsally with 3 setae; lateral margin straight, lateral margin with 3 simple setae; proximomesial margin weakly convex, with 6 long plumose setae. Uropod exopod not extending to end of endopod, 3 times as long as greatest width; lateral margin weakly convex, with 5 simple setae; proximomesial margin straight, distally concave, with 4 long plumose setae.

Etymology.

The Xhosa word " Gnathia pipinde " was chosen, because “pipi” means penis and the post “nde” means long in the language of this southern African tribe and thus referring to the most distinct characteristic of this species. Pronounced as pie-pie-n-dê. The species epithet is a noun in apposition.

Distribution.

South coast of South Africa (Western and Eastern Cape Provinces).

Hosts.

Amblyrhynchotes honckenii (Bloch, 1785).

Remarks.

Gnathia pipinde sp. nov. can be identified by the straight frontal margin; presence of conical superior frontolateral process; a strong and bifid mediofrontal processes; pronounced and pointed supraocular lobes; mandible strongly curved with a dentate blade; and the claviform penes produced more than a third the length of the pereon.

When compared to the other known South African gnathiid species, the shape and size of the frontal process of G. pipinde are very similar to those of G. africana Barnard 1914 (see Smit et al. 1999) and G. nkulu Smit & Van As, 2002 (see Smit and Van As 2002). This species can, however, easily be distinguished from the other South African congeners by the shape and size of its elongated penes, narrowing at the distal end with a sac-like extension.

There are currently 134 species of Gnathia known to science ( Boyko et al. 2008 onwards). To the authors’ knowledge there are nine other Gnathia species with elongate penes that differ from each other in shape in size, namely: Gnathia camuripenis Tanaka, 2004; Gnathia cooki Müller, 1989; Gnathia dentata (G.O. Sars, 1872); Gnathia falcipenis Holdich & Harrison, 1980; Gnathia fallax Monod, 1926; Gnathia inopinata Monod, 1926; Gnathia limicola Ota & Tanaka; 2007; Gnathia phallonajopsis Monod, 1925; and Gnathia somalia Kensley, Schotte & Poore, 2009. Of these, only three resemble that of G. pipinde sp. nov. These are G. falcipenis from the Great Barrier Reef, Australia; G. cooki from Morea, Society Islands in the tropical Pacific; and G. camuripenis from southern Japan and the Philippines ( Shodipo et al. 2021). According to Holdich and Harrison (1980), the mediofrontal processes of G. falcipenis is conical and, thus, distinctly different from the bifid mediofrontal processes of G. pipinde sp. nov. The superior frontolateral process and shape of the pleotelson of G. cooki described by Müller (1989) are very similar to those of G. pipinde sp. nov. However, in the South African species there are six long simple setae on each superior frontolateral processes and the inferior frontolateral process are absent, whereas in the species from the Pacific there are only three long simple setae and the inferior frontolateral process are present. In addition, G. pipinde sp. nov. differs in the number of antenna flagellum articles (seven instead of six), and the number of plumose setae on the distal four articles of the maxillipeds (in the order of 5-7-6-7 instead of 5-6-5-7 as in G. cooki ). The males of G. camuripenis can easily be distinguished from G. pipinde sp. nov. in its rounded mediofrontal processes without a ventral notch and large bifid internal lobe present on the mandibles ( Tanaka 2004).

The larvae of G. pipinde sp. nov. can be distinguished from the described larvae of the South African species, G. africana and G. pantherina Smit & Basson, 2002, by the presence of 16 teeth on the mandible ( G. africana with nine or 10 and G. pantherina with eight). The shape of the pleotelson of G. pipinde (posterior two-thirds convex) also differs from that of G. africana (lateral margins straight) and G. pantherina (anterior half of lateral margins slightly concave).

This species is host-specific to Amblyrhynchotes honckenii and only occurs on the temperate south coast of South Africa (with low intensity and rare infections), despite the wide distribution of the host fish (temperate south coast to subtropical east coast of South Africa). The specific locality preference is also observed with another parasitic isopod on this host fish, Cinusa tetrodontis Schioedte & Meinert, 1884. Hadfield et al. (2010) reported this species from A. honckenii , also only from the temperate south coast of South Africa. This specific area seems to be a parasite diversity hotspot within the TSA realm and could still yield other unknown parasites with further research. Information on the nine known gnathiid species from the TSA is summarised in Table 1 , along with a key to these species.

Figures

Figure 1. Gnathia pipinde sp. nov. (NMB P 899), male holotype (4.6 mm TL) A habitus dorsal view B dorsal view of frontal border and mandibles C lateral view of cephalosome D antenna and antennula E pleotelson and uropod F pylopod G pleopod 2 H maxilliped. Scale bars: 200 μm.

Figure 2. Gnathia pipinde sp. nov. (NMB P 899), male holotype (4.6 mm TL) A-E pereopods 2 - 6, respectively. Scale bar: 200 μm.

Figure 3. Gnathia pipinde sp. nov. (NMB P 900), male scanning electron microscope images. A Dorsal view of cephalosome and pereon B ventral view of cephalosome and pereon C dorsal view of mandible D anterodorsal view of cephalosome E ventral view of penes F ventral view of anterior end of penes. Scale bars: 250 μm (A, B); 100 μm (C - E); 10 μm (F).

Figure 4. Gnathia pipinde sp. nov. (NMB P 901), praniza larva (4.1 mm TL) A habitus dorsal view B dorsal cephalosome C pleopod 1 D antenna and antennula E pleotelson and uropod F mandible G paragnath H maxillula I maxilliped J gnathopod. Scale bars: 200 μm (A-E); 50 μm (F-J).

Figure 5. Gnathia pipinde sp. nov. (NMB P 901), praniza larva (4.1 mm TL) A-E pereopods 2 - 6, respectively. Scale bar: 200 μm.

Figure 6. Gnathia pipinde sp. nov. (NMB P 901), praniza larva scanning electron microscope images A anterolateral view of labrum, cephalosome, and antennae B dorsal view of cephalosome C ventral view of cephalosome D ventral view of antenna and antennula E dorsal view of the pleotelson and uropods F lateral view of mandible (m), paragnath (p), and maxillula (ml). Scale bars: 100 μm (A-E); 10 μm (F).