Gnathia spongicola Barnard, 1920

Gnathia spongicola Barnard, 1920 View in CoL

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5

Gnathia spongicola Barnard, 1920: 332–334, pl. XV, fig. 9. View in CoL

Material examined.

Lectotype [designated here]. South Africa • 1 ♂ ( 4.9 mm); Table Mountain ; 33°3.348'S, 18°1.686'E; depth 347 m; 3 April 1902; SS Pieter Fauer; trawl; hexactinellid sponges ( SAMC A 099274 ) GoogleMaps .

Paralectotype. South Africa • 3 ♂♂ ( 4.4–4.5 mm); same data as lectotype ( SAM A 4147 ) GoogleMaps • 8 ♂♂ ( 3.9–5.6 mm); Cape Point ; 34°34.314'S, 18°14.316'E; depth 247 m; 27 February 1902; SS Pieter Fauer; trawl; hexactinellid sponges ( SAM A 4148 ) GoogleMaps • 1 ♂ (damaged); offshore of Lion’s Head ; depth 238 m; 28 May 1900; SS Pieter Fauer; dredge sampling; hexactinellid sponges ( SAM A 4149 ) .

Other material. South Africa • 1 ♂ (damaged); Still Bay ; 35°22.002'S, 22°31.002'E; depth 200 m; 20 June 1972; identified by Kensley ( SAM A 14603 ) GoogleMaps .

Redescription of adult male.

Body (Fig. 2 A View Figure 2 ) 2.5 times as long as greatest width, widest at pereonite 2 and pereonite 3; dorsal surfaces smooth, sparsely setose. Cephalosome (Figs 2 B View Figure 2 , 5 A View Figure 5 ) 0.5 times as long as wide, lateral margins slightly concave anteriorly, posterior margin straight; dorsal surface with sparse granules, or tubercles around eyes; dorsal sulcus wide, deep, short; translucent region absent; para-ocular ornamentation with several tubercles and setae, posterior median tubercle present. Frontolateral processes present. Frontal margin slightly produced, median point excavated. External scissura present, narrow, shallow. Mediofrontal process present, weak, bifid, without ventral notch, with fine setae. Superior frontolateral process (Fig. 5 B View Figure 5 ) present, single, strong, equally apically bifid, with 8 pairs of long simple setae. Inferior frontolateral process absent. Mesioventral margin straight; setose; anterior tip not dorsally visible. Supraocular lobe pronounced, pointed, accessory supraocular lobe not pronounced. Eyes present, round, 0.4 times as long as cephalosome length, bulbous, standing out from head surface, ommatidia arranged in rows.

Pereon lateral margins narrowing posteriorly, without setae. Pereonite 1 not fused dorsally with cephalosome; dorsolateral margins fully obscured by cephalosome. Pereonite 2 wider than pereonite 1. Pereonite 4 without anterior constriction, median groove absent. Areae laterales present on pereonite 5; dorsal sulcus obscured by pereonite 6. Pereonite 6 with weak lobi laterales; lobuii weak, globular. Pereonite 7 short, narrow, and overlapping pleonite 1. Pleon covered in pectinate scales and epimera not dorsally visible on all pleonites. Pleonite lateral margins with 3 pairs of simple setae, with 1 pair of simple setae medially.

Pleotelson (Fig. 2 F View Figure 2 ) 1.1 times as long as anterior width, covered in pectinate scales; lateral margins smooth, anterolateral margins weakly concave, with 2 pairs of submarginal setae; posterolateral margin distally weakly concave, with 1 pair of submarginal setae; mid-dorsal surface with 1 pair of sub-median setae, apex with 2 setae.

Antennula (Fig. 2 C View Figure 2 ) shorter than antenna. Peduncle article 1 without tubercles, article 2 0.8 times as long as article 1; article 3 1.9 times as long as article 2; article 3 4 times as long as wide. Flagellum as long as article 3, with 5 articles; articles 3 and 4 with 1 aesthetasc, and 1 simple seta; article 5 terminating with 1 aesthetasc, and 4 simple setae. Antenna (Fig. 2 D View Figure 2 ) peduncle with 4 articles; article 3 3.4 times as long as wide, 2.2 times as long as article 2, with 1 penicillate seta, and 5 simple setae; article 4 0.8 times as long as article 3, with 2 penicillate setae, 2.9 times as long as wide, and with 10 simple setae. Flagellum 0.9 times as long as article 4, 0.8 times as long as article 3, with 7 articles, terminating with 5 simple setae.

Mandibl e (Fig. 2 E View Figure 2 ) 1.4 times as long as width, 0.7 times as long as length of cephalosome, triangular, strongly curved distally; apex 21.3 % total length; mandibular seta present. Carina present, smooth, along proximal half. Incisor elevated, standing clear of surface, distal denticulation present. Blade present, dentate, straight, along 78.7 % of margin. Internal lobe absent. Dorsal lobe absent. Basal neck short. Erisma and lamina dentata absent.

Pylopod (Fig. 3 A View Figure 3 ) article 1 1.6 times as long as wide, with two distinct areolae, without distolateral lobe, posterior and lateral margins forming rounded curve, lateral margin with 34 large plumose setae, mesial margin with continuous scale-setae, 5 simple setae present on the surface, distal margin with 13 simple setae; article 2 1.4 times as long as wide, with 25 simple setae; article 3 minute (Fig. 3 B View Figure 3 ) and fused to article 2, with 4 setae.

Maxilliped (Figs 3 C View Figure 3 , 5 D View Figure 5 ) 5 - articled; article 1 lateral margin with continuous marginal scale-setae; article 2 lateral margin with 5 plumose setae; article 3 lateral margin with 6 plumose setae; article 4 lateral margin with 5 plumose setae; article 5 with 8 plumose setae and 4–6 simple setae; endite extending to mid-margin of article 3.

Pereopods 2–6 (Fig. 4 A – E View Figure 4 ) randomly covered in pectinate scales; propodus distal robust seta as long as proximal robust seta; inferior margins with prominent tubercles. Pereopod 2 (Fig. 4 A View Figure 4 ) with tubercles on inferior margin of ischium to carpus; basis 2.5 times as long as greatest width, superior margin with 6 setae, inferior margin with 15 setae; ischium 0.6 times as long as basis, 1.9 times as long as wide, superior margin with 4 setae, inferior margin with 8 setae; merus 0.4 times as long as ischium, 0.9 times as long as wide, superior margin with 3 setae and bulbous protrusion; inferior margin with 5 setae; carpus 0.6 times as long as ischium, twice as long as wide, superior margin with 1 seta, inferior margin with 3 setae; propodus 0.7 times as long as ischium, 2.6 times as long as wide, superior margin with 2 simple setae and 1 penicillate seta, inferior margin with 2 simple setae, 2 short setae, and 2 robust setae; dactylus (with unguis) 0.8 times as long as propodus. Pereopods 3 (Fig. 4 B View Figure 4 ) and 4 (Figs 4 C View Figure 4 , 5 E View Figure 5 ) similar to pereopod 2; pereopod 5 (Fig. 4 D View Figure 4 ) similar to pereopod 6 (Fig. 4 E View Figure 4 ). Pereopod 6 with tubercles on basis to carpus; basis 3.2 times as long as greatest width, superior margin with 10 simple setae and 3 penicillate setae, inferior margin with 13 setae; ischium 0.7 times as long as basis, 2.8 times as long as greatest width, superior margin with 4 setae, inferior margin with 9 setae; merus 0.5 times as long as ischium, 1.8 times as long as wide, superior margin with 3 setae, inferior margin with 6 setae, without dense patch of scale-setae; carpus 0.4 times as long as ischium, 1.9 times as long as wide, superior margin with 1 seta, inferior margin with 4 setae; propodus 0.7 as long as ischium, 4.1 times as long as wide, superior margin with 8 setae, inferior margin with 1 simple seta, and 2 robust setae; dactylus (with unguis) 0.6 times as long as propodus.

Penial process (Fig. 5 F View Figure 5 ) 0.5 times as long as basal width, slightly produced lobe.

Pleopod 2 exopod (Fig. 2 G View Figure 2 ) 2.5 times as long as wide, distally narrowly rounded, medial margin weakly oblique, with 9 plumose setae; endopod 2.2 times as long as wide, distally broadly rounded, with 8 plumose setae; appendix masculina absent; peduncle 1.8 times as wide as long, mesial margin with 2 coupling setae, lateral margin with 1 simple seta.

Uropod (Fig. 2 G View Figure 2 ) rami extending beyond pleotelson, apices broadly rounded. Peduncle with 2 dorsal setae. Endopod 3.2 times as long as greatest width, dorsally with 5 setae; lateral margin straight, with 4 simple setae; distomesial margin sinuate, with 7 long plumose setae. Exopod not extending to end of endopod, 4.2 times as long as greatest width; lateral margin straight, 7 simple setae distolaterally; distomesial margin sinuate, with 4 long plumose setae.

Remarks.

Gnathia spongicola can be identified by several key morphological features: a slightly produced frontal margin; a weak and bifid mediofrontal process; single, strong superior frontolateral processes that are equally apically bifid; pointed and pronounced supraocular lobes; mandibles that are strongly curved distally with dentated blades; and a dorsal sulcus on pereonite 5 that is obscured by the overlapping pereonite 6.

Barnard (1920) did not designate a holotype in the original description of G. spongicola but provided detailed observations on the specimens examined. These syntypes are housed at the SAM, and one male specimen from this series has been designated as the lectotype and is herein redescribed. This lectotype designation is crucial to stabilise the taxonomic identity of G. spongicola , especially in relation to specimens previously labelled as G. spongicola or G. spongicola var. minor (see species descriptions below).

Among the six Gnathia species previously recorded from the Temperate Southern African ( TSA) marine realm, G. spongicola most closely resembles Gnathia disjuncta Barnard, 1920 , particularly in the division of pereonite 5 by a triangular pereonite 6. However, G. spongicola can be distinguished from G. disjuncta by its broader dorsal sulcus on the anterior cephalosome (narrow in G. disjuncta ), the presence of 3–5 tubercles around the eye (compared to two large tubercles along the eye margin in G. disjuncta ), and more bulbous eyes (less prominent in G. disjuncta ). Since the original description of G. disjuncta in 1920, the taxonomic standards for gnathiid species description have become more refined, rendering the current description outdated. A redescription of G. disjuncta is therefore recommended. However, it is worth noting that the type material for G. disjuncta is currently missing from its vial ( SAM A 4152 ) in the SAM collection (N. J. Smit personal observation).

Outside the TSA, the division of pereonite 5 by pereonite 6 is uncommon within males of the genus Gnathia . Gnathia arabica Schotte, 1995 , which exhibits partial division of pereonite 5 by pereonite 6 and prominent spines and tubercles on the pereopods, most closely resembles G. spongicola . However, it can be distinguished by differences in mandible shape, extensive pitting on the cephalosome, and the presence of an appendix masculina on pleopod 2. Although from a different genus, Elaphognathia bifurcill ( Holdich & Harrison, 1980) also shows division of pereonite 5 by pereonite 6, indicating that this character is not exclusive to males of the genus Gnathia ( Holdich and Harrison 1980) .