Hebefustis clareolithis, Kaiser, Stefanie, 2008

Kaiser, Stefanie, 2008, First record and new species of the genus Hebefustis Siebenaller & Hessler, 1977 (Isopoda: Asellota: Nannoniscidae) from the deep Weddell Sea Basin *, Zootaxa 1866, pp. 467-481 : 470-479

publication ID	https://doi.org/ 10.5281/zenodo.183769
DOI	https://doi.org/10.5281/zenodo.5670990
persistent identifier	https://treatment.plazi.org/id/530887A4-E066-FFD3-9DEA-5F78FA5AFBC7
treatment provided by	Plazi
scientific name	Hebefustis clareolithis
status	sp. nov.

Treatment

Hebefustis clareolithis View in CoL sp. nov.

( Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Material examined

Holotype: female, (preparatory, 1.9 mm), eastern Weddell Sea, 70°31.08'S – 70°32.23'S, 14°34.82'W – 14°34.90'W, PS ANT XXII/3, Station 81–8, 4382 m, 24.02.2005, ZMH K–41261.

Paratypes: 9 females (7 preparatory, 1 juvenile, 1 damaged), 1 male (juvenile), same station as holotype, ZMH K–41262; 1 male (adult, 1.4 mm), same station as holotype, ZMH K–41263.

Diagnosis. Pereonite 2 with a robust spine on anterolateral margins. Pereonites 6 and 7 with acute, distally directed posterolateral margins. Second article of antennula with 4 broom setae distally. Antenna with 12 flagellar articles. Posterolateral spines well developed and acute, halfway along margin. Pleopod 1 widest distally.

Description. Habitus of female holotype ( Figs 1 View FIGURE 1 A–C): Body dorsoventrally slightly flattened and broadened, 3.7 times longer than wide. Surface of dorsal cuticle with numerous setules ( Fig. 2 View FIGURE 2 H). Ventral surface alveolarly structured ( Fig.1 View FIGURE 1 B). Coxae not visible in dorsal view. Pereonites 1–3 with frontally directed laterofrontal margins. Pereonite 1 and 2 nearly of same length and width, p ereonite 2 widest, 4 times longer than wide, with a robust spine anterolaterally. Pereonite 4 longest, nearly twice as wide as long. Pereonites 1–4 decreasing, pereonites 5–7 increasing in width distally. Body gradually flattening from pereonites 1–4 and slightly increasing in height from pereonites 5–7. Pereonites 6 and 7 medially fused, with acute, distally directed posterolateral margins and 2 ventral depressions. Pleotelson 0.23 times body length, as long as wide, width 0.9 times pereonite 2 width, with well-developed posterolateral spines, halfway along margin. Posterior margin strongly convex, anterior dorsal margin straight. Anus ( Fig. 1 View FIGURE 1 B) covered by anus valves laterally. Uropods inserting closely to the anus valves, short in relation to pleotelson, hardly projecting above posterior margin. Operculum about 0.6 times pleotelson length (ventrally measured).

Cephalothorax ( Fig. 1 View FIGURE 1 A, B) as wide as long, rostral crest slightly developed, anterior margin of head strongly, posterior margin slightly rounded, lateral margins straight. Antennae inserting frontolaterally in a deep fold.

Antennula ( Fig. 2 View FIGURE 2 B) of female paratype 0.16 times body length, with 5 articles. Basal article short, nearly as long as wide, with 2 broom setae of varying size and 2 slender seta distally. Article 2 slender, 2.1 times longer than wide, with 2 long and 2 shorter broom setae distally, with 1 simple seta distally. Articles 3 and 4 short, almost of same length and width, each about 0.3 times article 2 length. Article 4 with 2 simple setae distally (1 broken off). Article 5 long and slender, nearly 3 times longer than article 4, 3.9 times longer than wide, with 2 long, slender setae and 1 aesthetasc terminally.

Antenna ( Fig. 2 View FIGURE 2 A) length 0.6 times body length, with 6 peduncular and 12 flagellar articles. Peduncular articles 1–4 short; article 3 with 1 robust spine tipped with a small seta distally, with 2 slender setae of same size and 1 small spine distally and a fringe of short setules laterally. Article 4 with a single small seta distally.

Article 5 nearly as long as articles 1–4 combined, about 3.4 times longer than wide, with 4 simple setae laterally, with 1 small broom seta and 4 simple setae distally. Article 6 length 1.3 times article 5 length, about 4.6 times longer than wide; with 5 short simple setae laterally, with 4 broom setae and 5 slender setae distally. Flagellar article 1 longest, about 0.5 times peduncular article 6 length, 3.6 times longer than wide, with 3 simple setae laterally and 3 simple setae distally. Flagellar articles 2–10 of similar length; width decreasing distally, each article with 1–4 short simple setae distally. Articles 11–12 somewhat shorter; article 11 with 3 simple setae distally, article 12 with 6 long slender setae terminally.

Mandibular palp of left and right mandible ( Fig. 2 View FIGURE 2 C, D) well developed, consisting of 3 articles and almost reaching incisor. Palpal article 1 of right mandible 1.6 times longer than article 2. Terminal article tapering distally, with a fringe of small setules ventrally and 2 robust setae terminally. Article 1 and 2 of left mandible of similar length, article 2 with fringe of fine setules and 2 simple setae distally; article 3 tapering in width distally, with a fringe of fine setules and 2 longer simple setae ventrally. Incisor of right mandible with 3 teeth, of left mandible with 6 teeth. Lacinia mobilis of left mandible with 4 teeth ( Fig. 2 View FIGURE 2 D). Setal row of right mandible with 9 robust setae and several slender setae in between; distal robust setae dentate, dentation decreasing proximally. Setal row of left mandible with 8 setae; distal setae 1–3 most robust, proximal setae more slender. Molar of right and left mandible triangular, on right mandible with 15 long, slender setae distally, on left mandible with 11 long, slender serrate setae distally.

Outer endite of maxillula ( Fig. 2 View FIGURE 2 F) with 11 robust spine-like setae distally. Outer margin with 7 slender setae, inner margin with several (=15) slender setae. Inner endite 0.6 times outer endite length, with numerous (=20) fine setae distally.

Maxilla ( Fig. 2 View FIGURE 2 G) outer margins of lateral and inner endites with several setae. 3 strong setae on lateral and medial endites. Distal margin of inner endite with numerous long setae of varying size. Surface of inner endite with several short setules.

Left and right maxilliped ( Fig. 2 View FIGURE 2 E) connected by 3 retinacula. Epipodite smooth, triangular, slender, 3.5 times longer than wide, reaching to mid of palpal article 3. Palpal article 1 short, about 2.5 times wider than long. Article 2 longest, 3 times longer than article 1, almost quadrangular. Palpal article 3 length 2.3 times article 1 length, 1.4 times wider than long, with 3 robust sensory setae and 2 more slender setae distally. Article 4 about 1.4 times article 1 length, 1.6 times longer than wide, with a projection reaching to mid of article 5, with 3 slender setae distally. Article 5 about 0.7 times article 4 length, twice as long as wide, with 3 long, slen- der setae terminally. Endite distal margin with some robust, dentate setae and several fine setae laterally. Protopod nearly triangular, about 3 times wider than long.

Pereopod 1 ( Fig. 3 View FIGURE 3 D) more robust than pereopods 2–7. Basis 3.6 times longer than wide, with 5 short simple setae dorsally and 4 simple setae ventrally. Ischium length 0.7 times basis length, 2.3 times longer than wide; with 2 simple setae dorsally (one broken off) and 2 simple setae ventrally. Merus length 0.6 times ischium length, 1.3 times longer than wide; with 2 long robust setae distally and a smaller seta on a small projection distodorsally, with 4 setae ventrally. Carpus length 1.5 times merus length, 2.4 times longer than wide; with 2 slender setae dorsally, ventral margin slightly concave, with numerous small setae, membranously embedded, and 3 robust unequally bifid setae in between ventrally and 1 very long simple seta distally. Propodus length 0.9 times carpus length, 3 times longer than wide; with 3 slender simple setae dorsally, with numerous small setae, membranously embedded, 1 robust unequally bifid seta in between ventrally and 2 more slender setae distally. Dactylus nearly half of propodus length, 2.8 times longer than wide; with 3 slender setae medially and with 1 spine-like appendix ventrally. Unguis with 1 robust cuspidate seta dorsally and with 2 slender, longer setae ventrally.

Basis of pereopod 2 ( Fig. 3 View FIGURE 3 A) proximally damaged during dissection, about 4.1 times longer than wide; with 3 simple setae (one broken off) dorsally, with 4 long setae ventrally and 2 setae distally. Ischium about half of basis length, 2.5 times longer than wide; with 1 simple seta distodorsally and 3 simple setae ventrally. Merus length 0.6 times ischium length, 1.7 times longer than wide, with 2 robust simple setae distodorsally and with 3 more slender setae ventrally. Carpus length 2.6 times merus length, 4.6 times longer than wide; with 1 slender seta dorsally and 2 simple setae distally, with numerous small setae, membranously embedded, and with 4 stout unequally bifid setae in between ventrally. Propodus length 0.8 times carpus length, 6.6 times longer than wide, with 4 simple setae and 1 small broom seta dorsally, with numerous small setae, membranously embedded, and with 3 stout unequally bifid setae and 1 slender seta ventrally. Dactylus length nearly half of propodus length, 4.3 times longer than wide; with 3 thin, simple setae medially, with numerous small setae, membranously embedded, and 1 spine-like appendix ventrally. Unguis with 1 robust cuspidate seta dorsally and 2 slender setae ventrally.

Basis of pereopod 3 ( Fig. 3 View FIGURE 3 B) 4.3 times longer than wide; with 1 broom seta and 4 long slender setae dorsally, with 4 long simple setae (2 broken off) setae ventrally, with 2 long, slender setae distally. Ischium length about half of basis length, 2.3 times longer than wide; with 3 simple setae dorsally, and 3 simple setae ventrally. Merus length 0.6 times ischium length, 1.4 times longer than wide; with 2 long setae distodorsally and 2 simple setae of varying size ventrally. Carpus length 2.6 times merus length, 4.6 times longer than wide; with 4 slender setae dorsally, with numerous small setae, membranously embedded, and 4 stout unequally bifid setae in between ventrally, with a small, stout setae distally. Propodus length 0.9 times carpus length, 6.5 times longer than wide, with 3 simple setae dorsally, with numerous small setae, membranously embedded, and 3 stout unequally bifid setae ventrally, with 1 slender longer seta distally. Dactylus length half of propodus length, 4.5 times longer than wide; with 1 spine-like appendix ventrally. Unguis with 1 robust cuspidate seta dorsally and 2 slender setae ventrally.

Basis of pereopod 4 ( Fig. 3 View FIGURE 3 C) 4.1 times longer than wide; with 2 long broom setae and 3 smaller simple setae dorsally, with 4 simple setae ventrally and 2 robust setae distally. Ischium length 0.6 times basis length, 2.5 times longer than wide; with 3 simple setae and 1 more robust seta dorsally, with 4 simple setae ventrally. Merus length 0.6 times ischium length, 1.6 times longer than wide; with 2 long setae distodorsally and 2 long setae ventrally. Carpus length 2.6 times merus length, 5.9 times longer than wide, with 2 long simple setae dorsally, 1 simple seta medially and 1 broom seta and 1 small simple seta distally, with numerous small setae, membranously embedded, and 4 stout unequally bifid setae ventrally. Propodus length about carpus length, 7.5 times longer than wide; with 2 long simple setae and 1 broom seta dorsally, with numerous small setae, membranously embedded, and 3 stout unequally bifid setae and 1 slender, simple seta in between ventrally, with 1 long simple seta distally. Dactylus length 0.4 times propodus length, 3.4 times longer than wide; with 3 thin, simple setae medially and 1 spine-like appendix ventrally. Unguis with 1 robust cuspidate seta dorsally and 2 slender setae ventrally.

Pereopods 5–7 more slender and longer than pereopods 1–4, due to comparably increased length of basis, carpus and propodus. Basis of pereopod 5 ( Fig. 4 View FIGURE 4 A) 4.6 times longer than wide; with 2 long broom setae and 5 simple setae dorsally and with 4 long simple setae ventrally. Ischium length 0.7 times basis length, 3.6 times longer than wide; with 3 simple setae (1 broken off) dorsally and with 2 simple setae ventrally. Merus length 0.4 times ischium length, 1.6 times longer than wide; with 2 long robust setae distodorsally and with 3 slender setae of different size ventrally. Carpus length 2.3 times merus length, 5 times longer than wide; with 4 simple setae (3 broken off) dorsally and with 5 robust setae ventrally. Propodus length 1.1 times carpus length, 7.7 times longer than wide; with 1 small simple seta dorsally, with 2 long and 1 small simple setae and 1 long broom seta distally, with numerous small setae, membranously embedded, and 3 stout unequally bifid setae in between ventrally and 1 longer simple seta distally. Dactylus length half of propodus length, 6.1 times longer than wide; with 3 slender setae medially and with 1 spine-like appendix ventrally. Unguis with 1 robust cuspidate seta dorsally and 2 slender setae ventrally.

Basis of pereopod 6 ( Fig. 4 View FIGURE 4 B) 4.7 times longer than wide; with 5 slender, simple setae and 1 long broom seta dorsally, with 5 long, slender setae ventrally. Ischium length 0.7 times basis length, 3.7 times longer than wide; with 2 slender simple setae dorsally and 2 ventrally. Merus length 0.5 times ischium length, 1.8 times longer than wide; with 1 robust long setae distodorsally and 2 slender setae ventrally. Carpus length 2.5 times merus length, 7.6 times longer than wide; with 3 simple setae dorsally, and 5 simple setae ventrally. Propodus length about carpus length, 8.7 times longer than wide; with 2 long simple setae and 1 broom seta distodorsally, with numerous small setae, membranously embedded, 2 robust unequally bifid setae and 1 slender simple seta ventrally. Dactylus length half of propodus length, 5.4 times longer than wide; with 3 slender setae medially and with numerous small setae, membranously embedded, and 1 spine-like appendix ventrally. Unguis with 1 robust cuspidate seta dorsally and 2 slender setae of similar size ventrally.

Basis of pereopod 7 ( Fig. 4 View FIGURE 4 C) 5 times longer than wide; with 3 simple setae dorsally and 5 simple setae (1 broken off) ventrally. Ischium length 0.7 times basis length, 3.7 times longer than wide; with 2 slender simple setae dorsally and 2 ventrally. Merus length about half of ischium length, 1.8 times longer than wide; with 1 robust long and 1 smaller, slender seta distodorsally and with 2 slender simple setae ventrally. Carpus length 2.4 times merus length, 4.7 times longer than wide; with 4 simple setae dorsally, and 4 more robust simple setae ventrally. Propodus length 1.1 times carpus length, 7.3 times longer than wide; with 2 long slender setae and 1 broom seta distodorsally, with 2 robust unequally bifid setae and 2 simple setae ventrally. Dactylus length half of propodus length, 5.7 times longer than wide; with 4 slender setae medially and with numerous small setae, membranously embedded, and 1 spine-like appendix ventrally. Unguis with 1 robust cuspidate seta dorsally and 2 slender setae (1 broken off) ventrally.

Pleopod 2 (operculum, Fig. 4 View FIGURE 4 D) almost as long as wide; ventral surface smooth. Lateral and posterior margins with several (>20) medium-sized slender setae.

Protopodite of pleopod 3 ( Fig. 4 View FIGURE 4 E) almost as long as wide, length 0.6 times endopodite length. Exopodite about half of endopodite length, 1.3 times longer than wide, tapering in width distally; with numerous simple setae laterally and 1 very long, robust seta distally. Endopodite 1.5 times longer than wide, with 3 long plumose setae distally.

Protopodite of pleopod 4 ( Fig. 4 View FIGURE 4 F) rectangular, 1.5 times wider than long. Exopodite slender, about as long as endopodite, 6 times longer than wide; with several thin setules laterally and 1 long robust plumose seta distally. Endopodite ovoid-shaped, 1.7 times longer than wide.

Pleopod 5 ( Fig. 4 View FIGURE 4 G) small oval lobe, without setation. 1.9 times longer than wide.

Uropods ( Fig. 4 View FIGURE 4 H) biramous. Protopodite trapezoid, about as long as wide, as long as endopodite; with 2 robust setae (broken off). Exopodite 0.8 times endopodite length. 2.9 times longer than wide, with 2 setae (broken off) terminally. Endopodite twice as long as wide; with 1 robust simple seta laterally, with 4 broom setae (1 broken off) and 2 simple setae (1 broken off) terminally.

Differences in paratype male ( Fig. 5 View FIGURE 5 ). Habitus ( Fig. 5 View FIGURE 5 A) very similar to holotype, dorsal cuticle also with numerous setules, but lateral margins of pereonites 1–3 more frontally directed, anterolateral spines on pereonite 2 more robust and pereonite 4 shorter than in female.

Rostral crests well developed compared to female.

Antenna ( Fig. 5 View FIGURE 5 E) with 6 peduncular and 9 flagellar articles. Articles 5–7 stouter than in female. Article 5 about 2.7 times longer than wide, with 4 simple setae and two broom setae laterally, with 1 broom seta and 1 simple seta medially. Article 6 length 1.2 times article 5 length, about 3.2 times longer than wide, with 4 simple setae laterally, with 2 broom setae and 2 small simple setae distally. Flagellar article 1 longest, length 1.1 times peduncular article 6 length, 3.2 times longer than wide, with 4 simple setae laterally and 4 long simple setae (1 broken off) distally. Flagellar articles 2–7 of similar length, width decreasing distally, each article with 1–2 short simple setae distally. Articles 8 and 9 somewhat shorter, article 8 with 2 short simple setae distally, article 9 with 6 long, slender setae terminally.

Pleopod 1 ( Fig. 5 View FIGURE 5 B, C) 1.7 times longer than distal width; tips slightly rounded in ventral view, with a few simple setae.

Sympod of pleopod 2 ( Fig. 5 View FIGURE 5 D) 2.4 times longer than wide; outer margin rounded; with 5 slender simple setae laterally, inner margin slightly concave. Endopod inserting 0.6 from distal tip of sympod; stylet about half of sympod length, slightly curved, distal end reaching tip of sympod. Exopod short and rounded.

Type locality. Eastern Weddell Sea basin.

Distribution. The species is only known from the eastern Weddell Sea basin.

Etymology. Clareolithis (masculine) is dedicated to an invaluable friend.

Remarks. Hebefustis clareolithis sp. nov. belongs to a cluster of species in the genus Hebefustis possessing acute, distally directed posterolateral margins of the sixth and seventh pereonite (see Siebenaller & Hessler 1977:30). This cluster comprises, besides the new species, Hebefustis cornutus Siebenaller & Hessler, 1977 , H. dispar Siebenaller & Hessler, 1977 , H. hexadentium Siebenaller & Hessler, 1977 , H. hirsutus ( Menzies, 1962) , and H. vitjazi Mezhov, 1986 .

H. clareolithis differs from all other species of this cluster by the following characters: robust spine on the anterolateral margins of pereonite 2 in male and female; female antenna bearing 12 flagellar articles; second article of antennula with 4 broom setae; pleopod 1 widest distally.

H. clareolithis View in CoL is most similar to Hebefustis cornutus Siebenaller & Hessler, 1977 View in CoL ; the latter can be distinguished from the new species by the following characters: female antenna with 9 flagellar articles; second article of antennula with just 2 broom setae distally; male antenna more robust: peduncular article 5 about 1.6 times longer than wide, article 6 about 2.3 times longer than wide, first flagellar article 1.8 times longer than wide; posterior margin of male pleotelson with double angles.

The new species also resembles H. hexadentium Siebenaller & Hessler, 1977 View in CoL which can be distinguished from H. clareolithis View in CoL as follows: second article of antennula with 2 broom setae distally; female antenna with 7 flagellar articles, first flagellar article relatively short, about 0.25 times peduncular article 6 length; pereonites 2 and 3 long compared to pereonite 1; male posterior margin of pleotelson softly curved.

Siebenaller & Hessler (1977) pointed out remarkable similarities between H. hexadentium and H. hirsutus ( Menzies, 1962) , which were both first recorded from the South Atlantic ( Table 1 View TABLE 1 ). The male holotype and only specimen of H. hirsutus is no longer extant ( Siebenaller & Hessler 1977), and the drawings by Menzies (1962) are rudimentary, i.e. appendices were just partly drawn. Therefore, the comparison of this species to both H. clareolithis and H. hexadentium remains difficult (cf. Key). However, H. hirsutus can be distinguished from H. clareolithis by the following characters: pereonite 2 with a robust seta on anterolateral margins; maxilliped with 2 coupling hooks, incisor of right mandible with 4 teeth, posterior margin of pleotelson softly curved.

H. dispar can be distinguished from H. clareolithis as follows: anterolateral margins of pereonites 6 and 7 more rounded; pleotelson 1.2 times wider than long, posterior margin softly curved, posterolateral spines 0.7 from anterior margin, spines less produced.

H. vitjazi differs from the new species by the following characters: operculum relatively long, length 0.9 times pleotelson length (measured in ventral view), posterolateral spines about 0.8 from anterior margin; sympod of pleopod 1 with numerous setae (>15), endopodal stylet overlapping distal end of sympod about a third.