Haploniscus rostratus ( Menzies, 1962 )

Brökeland, Wiebke, 2010, Redescription of Haploniscus rostratus (Menzies, 1962) (Crustacea: Peracarida: Isopoda) with observations on the postmarsupial development, size ranges and distribution, Zootaxa 2521, pp. 1-25 : 2-21

Haploniscus rostratus ( Menzies, 1962)

Synonymy: Antennuloniscus rostratus Menzies, 1962: 109 . Haploniscus rostratus Menzies & Schultz, 1968: 142 .

Holotype: female, length 3.3 mm, pleon width 0.55 mm, deposited in the American Museum of Natural History, catalog #12002. The type specimen could not be located in the museum’s collection.

Type locality: Southeast Atlantic, Cape Basin, south-western flank of the Schmidt-Ott Rise southwest of Capetown, Ve ma -14-29, L.G.O. Biotrawl No. 52, 41°03’S 07°49’E, 4960 m.

Remarks. Although the type specimen could not be examined, the unique habitus and the rostrum of H. rostratus allow an unambiguous identification even based on the rather vague original description given by Menzies. According to the text of this description the type specimen has five flagellar articles in antenna 1.

Menzies defined the peduncle to have two articles, while it has in fact three following the definition by Wägele (1983). Hence it follows that the actual number of flagellar articles in the holotype is four, which is confirmed by Menzies’ illustration (p. 108). This indicates that the holotype is a stage V female.

Diagnosis. Body elongated, rectangular, length at least 3.1 width. Head length 0.6 width, with slight lateral constriction in anterior quarter, frontal margin slightly convex, with large rostral process. Rostrum elongated, length at least 1.5 width, apically with upcurved acute dorsal part and rounded ventral part with small cuticular teeth, near cepahlon with distinct ventral ridge, touching the clypeus. Anterior margins of pereonites 2–5 with acute angles slightly projecting anteriorly, of pereonites 1, 6 and 7 rounded. Posterior margins of pereonites 1–6 with acute angles slightly projecting caudally, of pereonite 6 prolonged into caudally directed processes, of pereonite 7 rounded, resulting in uneven outline of posterior body. Pereonites 2–6 of males and 3–6 of females of subequal width, pereonites 1 and 7 narrower. Distinct lateral constriction between pereonite 7 and pleotelson. Pereonites 5–7 fused with each other and pleotelson. Pleotelson length at least 1.2 width in adult females; lateral margins straight, nearly parallel in males, tapering distally in females; posterior margin concave in adult males, convex in adult females; pleotelson processes extending beyond posterior margin and uropods, length 0.3 pleotelson length in adult males, 0.1 pleotelson length in adult females. Cuticle structured by numerous subcircular depressions. Antenna 1 with four flagellar articles in adults. Antenna 2 article 3 elongated, with well defined dorsal tooth; article 6 with tooth terminally; flagellum inserting subapically, about as long as peduncular articles 5 and 6 together. Pereopods without sensory setae, except for dorsal seta subapically on carpus of pereopod 6, all pereopods with distinct accessory claw, pereopods 2–7 with spinous cuticular combs on carpus propodus joint. Male pleopod 1 length 2.4 width, widest part in basal third, width 2.0 width of narrowest part in apical third, with lateral processes in distal part and oblique spine rows across ventral grooves. Male pleopod 2 endopod short, not extending beyond protopod. Uropods resting in fold between pleotelson process and ventral surface of pleotelson in adult males.

Stages. Nine postmarsupial stages can be distinguished. Three manca stages (I–III), in which the sex is indeterminable, are followed by three stages each in males and females (IV VI).

Description of stage V female (preparatory). Size range: Length: 1.90–3.24 mm, width: 0.53–0.95 mm. Body ( Figs 2 B, D; 4B; 6B) elongated, slightly oval, length 3.5 width. Head length 0.1 body length, 0.6 width. Rostrum 0.9 head length, dorsal margin strongly curved basally and distally. Pereonites 3 6 broadest, pereonite 2 only slightly narrower, pereonite 7 narrowest; processes of pereonite 6 not reaching posterior margin of pereonite 7. Pleotelson length 0.3 body length, 1.4 width, lateral margins tapering slightly distally; pleotelson process length 0.1 pleotelson length.

Antenna 1 (Fig. 8H) length 0.2 body length, peduncular article 1 broadest, length 1.9 width, with 1 simple and 3 broom setae distally; article 2 as long as article 1, length 2.8 width, club-shaped, with 3 simple and 4 broom setae distally; article 3 length 0.3 article 1 length, width 0.6 article 1 width, with 1 simple seta distally. Flagellum with 4 articles; article 1 shortest, with 2 broom setae distally; articles 2–4 of subequal length, about 1.7 article 1 length, article 3 with 1 aesthetasc, article 4 with 1 aesthetasc and 2 long simple setae.

Antenna 2 ( Fig. 7 F) length 0.4 body length, peduncular articles 1 and 2 of subequal length and width, short, article 2 with 1 simple seta; article 3 elongated, length 3.2 article 2 length, 2.5 width, with 2 simple setae, dorsal tooth slightly shorter than article width; article 4 1.3 article 2 length, with 2 simple setae; article 5 length 2.7 article 2 length, 2.9 width, with about 8 simple setae in distal half; article 6 length 2.5 article 2 length, 4.0 width, with 1 long and 2 small broom setae and 2 3 simple setae in distal third, distal tooth length about 0.15 article length. Flagellum total length 1.7 peduncular article 6 length, with 8 articles, decreasing in length and width from proximal to distal, with up to 4 simple setae per article.

Pereopods ( Figs 11 A,B; 12 A C; 13 A, B): Basis of all pereopods with 2 long simple setae dorsally; basis of pereopod 1 with 2 simple setae ventrally, of pereopods 2 and 3 with 1 broom and 2 3 simple setae ventrally, of pereopods 4 6 with 3 broom and 2 simple setae ventrally, of pereopod 7 with 2 simple setae ventrally.

Ischium with 1 2 setae dorsally and ventrally each.

Merus with 2 setae distoventrally and distodorsally each, 1 or 2 of these long, pereopod 1 dorsal seta short and stout, spine-like.

Ventral margins of carpus, propodus and dactylus fringed by comb-like scale rows.

Carpus of pereopod 1 with 4 setae ventrally, of pereopods 2 7 with no more than 3 setae ventrally; distal carpus of pereopods 2 7 with 1 broom seta (broken off on pereopods 2 5) and 1 short simple seta dorsally; carpus of pereopod 6 additionally with one very stout sensory seta inserting between the broom and simple seta; apical combs of peropods 2 7 of different size, outer comb slightly larger, more spinose than inner comb.

Propodus with 3–6 setae ventrally, pereopod 1 with 1 long simple seta distodorsally, pereopod 2 with 1 seta dorsally and 1 long and 1 shorter seta distodorsally, pereopods 3 7 with 1 simple and 1 broom seta distodorsally; with small comb apically.

Dactylus with 2 4 setae near insertion of unguis and large accessory claw, unguis of posterior pereopods shorter in relation to dactylus.

Pleopod 2 ( Fig. 13 D) operculum suboval, length 1.1 width, anterior margin slanted, with central third projecting anteriorly.

Pleopod 3 ( Fig. 11 C) endopod length 1.3 width, outer plumose seta longest. Exopod length 0.6 endopod length, 1.6 width, with 1 simple seta distally.

Pleopod 4 ( Fig. 11 D) endopod length 1.9 width. Exopod length 0.5 endopod length, 2.6 width, plumose seta length about 1.6 exopod length.

Pleopod 5 ( Fig. 11 E) length 2.1 width.

Uropod ( Fig. 2 A) extending beyond posterior margin, not reaching tips of pleotelson processes.

Description of stage VI female (adult). Size range: Length: 2.47–3.19 mm, width: 0.76–1.00 mm.

Body ( Figs 2 A; 4A; 6A) slightly oval, length 3.1 width, ventral surface strongly concave from pereonite 1 to pleonite 1. Rostrum length 0.6 head length, dorsal margin strongly curved basally and distally. Pereonites 3 6 broadest; processes of pereonite 6 not reaching posterior margin of pereonite 7. Pleotelson more tapering than in stage V females, length 1.2 width; ventral surface triangular in lateral view due to depression of ventral body surface anteriorly of operculum.

Antenna 1 (Fig. 8G) like in stage V females.

Antenna 2 ( Fig. 7 D) similar to that of stage V females, article 3 distal tooth with long simple seta (broken off in stage V female); articles 5 and 6 more slender, article 5 length 3.2 width, article 6 length 4.75 width, article 5 with broom seta (broken off in stage V female).

Mandible ( Figs 9 A, D) incisor with 5 cusps; lacinia mobilis of left mandible with 4 teeth; spine row with 2 serrated and 3 setulated spines, spine row of right mandible with 3 serrated and 2 setulated spines. Molar with two opposing rows of irregular teeth, 4 strong setae proximally of outer tooth row, accessory tooth row proximally of inner tooth row and 2 3 setae on molar trunk. Palp slightly longer than mandibular body, article 1 with 1 simple distal seta, article 2 with 3 stout setae distally, article 3 with 6 7 stout setae along inner margin.

Hypopharynx ( Fig. 10 D) length 0.7 width, with several small stout setae distally and numerous fine setae arranged along inner and distal margins of lobes.

Maxilla 1 ( Fig. 10 B) lateral lobe length 2.8 width, distal margin with 11 stout setae, outer margin with rows of setae proximally, inner margin with 2 setae distally, surface with scattered rows of small setae; mesial lobe length 0.8 outer lobe length, 4.1 width, width 0.6 outer lobe width, distal margin with 5 strong setae and 2 simple setae, outer margin with several setae.

Maxilla 2 ( Fig. 10 A) lateral and middle lobes subequal in length and width, length about 5.6 width; mesial lobe width 1.7 middle lobe width, length 1.4 middle lobe length, 4.7 width. Proximal inner margin of mesial lobe with about 9 long, distally setulated setae; distal inner margin with 1 small stout seta and numerous setae, partly setulated distally; distal margin with 1 simple seta, 2 short serrated and 2 longer simple stout setae. Lateral and middle lobe each with 1 small stout seta and 1 short and 2 long stout setae distally. Inner margin of middle endite with several setae, outer margin of lateral endite with numerous setae, partly setulated distally.

Maxilliped ( Fig. 10 C) endite apical margin with 3 small fan setae, 3 small stout setae and several small setae; apical medial margin with 1 larger stout and several simple setae; few setae on dorsal surface, 3 retinaculae. Epipod slightly longer than endite.

Marsupium ( Fig. 4 A; 6A) extending from pereonite 1 to posterior margin of pleonite 1. Oostegites ( Fig. 14 A C) on pereopods 1 4, oostegite of pereonite 1 minute, about as long as basis of pereopod 1, pereopod 2 oostegite length about 0.7 pereopod 2 length, pereopod 3 oostegite length 1.2 pereopod 3 length, pereopod, pereopod 4 oostegite length about 1.1 pereopod 4 length, width 1.5 pereopod 3 oostegite width.

Description of stage IV female (juvenile). Size range: Length: 1.81–2.81 mm, width: 0.42–0.78 mm.

Body ( Figs 2 C; 4C; 6C) rectangular, length 3.5 width. Rostrum length 0.75 head length, dorsal margin strongly curved distally. Pereonites 2–6 of subequal width; pereonite 6 posterior angles extending beyond posterior margin of pereonite 7. Pleotelson tapering only slightly, length 1.65 width, pleotelson process length 0.2 pleotelson length.

Antenna 1 (Fig. 8I) with 3 flagellar articles, articles 2 and 3 with one aesthetasc each.

Haploniscus rostratus ( Menzies, 1962) . Antenna 2 (A–C) and antenna 1 (E–L): A, manca III; B, manca II; C, manca I; D, male VI; E, male V; F, male IV; G, female VI; H, female V; I, female IV; J, manca III, K, manca II; L, manca I. Scale bar 0.1 mm.

Antenna 2 ( Fig. 7 E) similar to that of stage V females (flagellum with 8 articles, damaged in illustrated specimen).

Description of stage VI male (adult). Size range: Length: 2.44–2.78 mm, width; 0.61–0.75 mm. Body ( Figs 3 A; 5A, D, E; 6D) rectangular, length 3.7 width. Rostrum (Fig.) length 1.1 head length, dorsal margin only weakly curved. Pereonites 2–6 broadest; processes of pereonite 6 not reaching posterior margin of pereonite 7. Pleotelson lateral margins nearly parallel, length 1.2 width; pleotelson process length 0.3 pleotelson length.

Antenna 1 (Fig. 8D) flagellum with 4 articles, article 2 with 1 aesthetasc, article 3 with 2 aesthetascs, article 4 with 3 aesthetascs.

Antenna 2 ( Fig. 7 A) article 5 length 2.9 width, article 6 length 3.3 width, slightly more setose than in females; flagellum with 10 articles, slightly stouter than in females, with up to 11 setae per article.

Pleopod 1 ( Fig. 15 C) length 0.6 pleotelson length, 2.4 width; narrowing in distal half, neck (narrowest part) after 0.75 of its length, neck width 0.5 maximum width. Distal quarter with lateral processes not reaching distal margin of pleopod. Distal margins rounded, slightly undulating, with several setae.

Pleopod 2 ( Figs. 15 D; 16A) protopod length 2.1 width, with about 12 long setae along outer margin. Endopod short, almost reaching tip of protopod, length 3.6 width; sperm duct opening in distal half, basal chamber simple with only a few weak folds reaching into the lumen.

Uropods ( Fig. 3 A) lying in dorsal fold between pleotelson process and terminal margin and pleotelson.

Description of stage V male (preparatory). Size range: Length: 1.68–2.61 mm, width: 0.56–0.69 mm.

Body ( Figs 2 F; 3B; 5B; 6E) rectangular, length 3.6 width. Rostrum 0.7 head length, dorsal margin strongly curved, similar to rostrum of stage V female. Pereonites 2–6 broadest; posterior processes of pereonite 6 extending to posterior margin of pereonite 7. Pleotelson lateral margins nearly parallel; pleotelson process length 0.2 pleotelson length.

Antenna 1 (Fig. 8E) flagellum with 4 articles, slightly stouter than in females; article 3 with 1, article 4 with 2 aesthetascs.

Antenna 2 ( Fig. 7 B) article 5 length 3.5 width; article 6 length 3.1 width; flagellum with 10 articles, slightly stouter than in females, with up to 6 setae per article.

Pleopod 1 ( Fig. 15 B) length 0.5 pleotelson length, 2.5 width, neck width 0.6 maximum width. Lateral processes visible, but still fused to the dorsal surface. Distal margins rounded, slightly undulating, with some setae.

Pleopod 2 ( Fig. 15 E) protopod with strong transversal muscles as in stage VI males, endopod article 2 shorter than in stage VI males, reaching exopod; sperm duct developing, but without opening.

Uropods ( Fig. 3 B) lying in dorsal fold between pleotelson process and terminal margin and pleotelson.

Description of stage IV male (juvenile). Size range: Length: 1.93–2.34 mm, width: 0.51–0.68 mm.

Body ( Figs 3 C; 5C; 6F) rectangular, length 3.8 width. Rostrum length 0.7 head length, dorsal margin strongly curved distally. Pereonites 2–6 broadest; processes of pereonite 6 extending beyond posterior margin of pereonite 7. Pleotelson tapering very slightly, length 1.4 width; pleotelson process length 0.2 pleotelson length.

Antenna 1 (Fig. 8F) flagellum with 3 articles, article 3 with 1 aestetasc.

Antenna 2 ( Fig. 7 C) article 5 length 3.0 width, article 6 length 3.6 width, flagellum with 8 articles, with up to 6 setae per article.

Pleopod 1 ( Fig.15 A) developing, length 0.8 operculum length, 1.9 width, strongly vaulted ventrally, separated distally, each tip with 1 seta.

Pleopod 2 ( Fig. 15 F) operculum, length 1.1 width, with fewer setae than in females, no trace of developing separation of left and right pleopod.

Description of manca III. Size range: Length 1.58–1.88 mm, width 0.44–0.53 mm.

Body ( Figs 3 G; 5H; 6G) rectangular, length 3.8 width. Rostrum length 0.9 head length, distodorsal margin strongly curved. Pereonites 2 6 of subequal width; processes of pereonite 6 extending beyond posterior margin of pereonite 7. Pleotelson length 1.6 width; lateral margins nearly parallel; pleotelson process length 0.2 pleotelson length.

Antenna 1 (Fig. 8J) flagellum with 3 articles, article 3 with 1 aestetasc.

Antenna 2 (Fig. 8A) article 5 length 2.35 width, article 6 length 3.85 width. Flagellum with 8 articles.

Pereopod 7 ( Fig. 14 C) developing, shorter than pereopod 6, without unguis and setae; merus and carpus fused; strongly flexed at partly fused basis-merus joint; both pereopods 7 adjoined between merus and dactylus and extending along midline of body to the anterior margin of operculum.

Description of manca II. Size range: Length 1.29–1.75 mm, width 0.37–0.46 mm

Body ( Figs 2 E; 3F; 5G; 6H) rectangular, length 3.6 width. Rostrum length 0.6 head length, distodorsal margin strongly curved. Pereonites 2–6 of subequal width; processes of pereonite 6 extending beyond posterior margin of pereonite 7. Pleotelson length 1.35 width, lateral margins nearly parallel; pleotelson process length 0.2 pleotelson length.

Antenna 1 (Fig. 8K) flagellum with 3 articles, article 3 with 1 aestetasc.

Antenna 2 (Fig. 8B) article 5 length 2.3 width, article 6 length 3.7 width. Flagellum with 8 articles, with up to 6 setae per article

Description of manca I. Size range: Length: 1.22–1.32 mm, width: 0.34–0.41 mm

Body ( Figs 3 E; 5F; 6I) rectangular, length 3.5 width. Rostrum length 0.3 head length, distodorsal margin strongly curved. Pereonites 1 6 of subequal width; processes of pereonite 6 extending beyond posterior margin of pereonite 7. Pleotelson length 1.65 width, very slightly tapering distally; pleotelson process length 0.1 pleotelson length.

Antenna 1 (Fig. 8L) flagellum with 3 articles, article 3 with 1 aestetasc.

Antenna 2 (Fig. 8C) article 5 length 2.0 width, article 6 length 2.9 width. Flagellum with 8 articles, with up to 5 setae per article.

Uropods ( Fig. 6 J) large in relation to pleotelson, length 0.35 pleotelson length, extending beyond pleotelson processes.

Size parameters. Some overlap in size exists between successive stages ( Fig. 16 B), but overall female specimens tend to be larger than males of the same age. The moult from stage V to stage VI females does not lead to a significant increase in length, but specimens become distinctly wider. Among the other stages the length-width ratio remains more or less stable. The relative length of the rostrum differs between males and females, the males having a larger rostrum than the females. This difference becomes more pronounced with increasing age.

Figures

FIGURE 2. Haploniscus rostratus (Menzies, 1962). Habitus dorsal view (A – C) and heads (D – F): A, female VI; B, female V; C, female IV; D, female V, head, dorsal view; E, manca I, head, ventral view; F, male V, head, ventral view. Scale bars 1.0 mm for A – C and E – F, 0.5 mm for D.

FIGURE 3. Haploniscus rostratus (Menzies, 1962). Habitus dorsal view: A, male VI; B, male V; C, male IV; D, male VI, head, dorsal view; E, manca I; F, manca II; G, manca III. Scale bar 1.0 mm.

FIGURE 4. Haploniscus rostratus (Menzies, 1962). Habitus lateral view: A, female VI, lateral view (eggs in marsupium shaded); B, female V, lateral view; C, female IV, lateral view. Scale bars 1.0 mm.

FIGURE 6. Haploniscus rostratus (Menzies, 1962). Posterior body, ventral view (A – I) and uropods (J – L): A, female VI; B, female V; C, female IV; D, male VI; E, male V; F, male IV; G, manca III; H, manca II; I, manca I; J, manca I; K, manca II; L, female VI. Scale bars 1.0 mm for A – I, 0.1 mm for J – L.

FIGURE 7. Haploniscus rostratus (Menzies, 1962). Antenna 2: A, male VI; B, male V; C, male IV; D, female VI; E, female IV; F, female V. Scale bar 0.1 mm.

FIGURE 9. Haploniscus rostratus (Menzies, 1962). Female VI (A, D) and female V (B, C): A, right mandible; B, left mandible; C, right mandible D, left mandible. Scale bar 0.1 mm.

FIGURE 10. Haploniscus rostratus (Menzies, 1962). Female VI: A, maxilla 2; B, maxilla 1; C, maxilliped, with detail of distal margin enlarged, D, hypopharynx. Scale bars 0.1 mm.

FIGURE 11. Haploniscus rostratus (Menzies, 1962). Female V pereopods and pleopods: A, pereopod 1; B, pereopod 2; C, pleopod 3; D, pleopod 4; E, pleopod 5. Scale bars 0.1 mm.

FIGURE 13. Haploniscus rostratus (Menzies, 1962). Female V (A, B, D) and manca III (C): A, pereopod 6; B, pereopod 7; C, pereopod 7; D, operculum (pleopods 2). Scale bars 0.1 mm.

FIGURE 14. Haploniscus rostratus (Menzies, 1962). Female VI pereopods with oostegites: A, pereopod 2; B, pereopod 3, with enlarged detail of closing mechanism; C, pereopod 4. Scale bar 1.0 mm

FIGURE 15. Haploniscus rostratus (Menzies, 1962). Male pleopods 1 (A – C) and 2 (D – F): A, stage IV, dorsal view; B, stage V, dorsal view; C, stage VI, dorsal view; D, stage VI, ventral view; E, stage V, dorsal view; F, stage IV, dorsal view. Scale bar 0.1 mm.

FIGURE 16. Haploniscus rostratus (Menzies, 1962). A, stage VI male, pleopod 2 endopod sperm duct. Layers above and below the basal chamber of the sperm duct (arrow) omitted from Z-stack. Scale bar 0.1 mm. B, body-lengthfrequency histograms for the stages (x-axis: body length in mm, y-axis: number of specimens one unit is equivalent to one specimen).