Urstylis zapiola, Riehl & Wilson & Malyutina, 2014

Riehl, Torben, Wilson, George D. F. & Malyutina, Marina V., 2014, Urstylidae - a new family of abyssal isopods (Crustacea: Asellota) and its phylogenetic implications, Zoological Journal of the Linnean Society 170 (2), pp. 245-296 : 256-267

URSTYLIS ZAPIOLA GEN. ET SP. NOV.

FIGURES 1–9

Zoobank registration urn:lsid:zoobank.org:act:3948B113-52B4-4CF5-93B7-710C67C9EA25

Etymology

This name refers to the type locality on the Zapiola Drift, a topographical feature in the Argentine Basin underlying a deep-sea current strongly influencing the deep Argentine Basin sediments ( Flood, Shor & Manley, 1993) called the Zapiola Anticyclone ( de Miranda, Barnier & Dewar, 1999). It is a feminine noun in apposition.

Type fixation

Adult male holotype USNM 1208013 , designated here .

Type material examined

USNM 1208013 : adult male holotype, 1.9 mm. USNM 1208014 : adult female paratype, 1.8 mm. AM P.90631: adult male paratype [dissected, parts on two slides (AM P.90631.001)]. USNM 1208015 : adult male, 1.9 mm, head damaged, uropod ∼ 0.8 mm; adult male 1.9 mm. AM P.67340: four brooding females, 1.7 mm; two brooding females, 1.6 and 1.8 mm; four females, 1.6, 1.8, 1.9 mm (twice); three adult males, 1.5 mm (twice), 1.7 mm; three individuals fragmented, two females, male. George D. F. Wilson ( GDFW) collection: male paratype (sectioned on four slides), 1.6 mm .

Type locality

Argentine Basin , 43°33.0′S, 48°58.1′W, 5208–5223 m, Woods Hole Oceanographic Institution Research Vessel ( R / V) Atlantis II cruise 60, benthic station 247A, 17.iii.1971, epibenthic sled. Urstylis zapiola was collected in a particularly large epibenthic sample. The isopod composition of this sample is provided in Supporting Information Appendix S 2 .

Further records

Known only from the type locality.

Type material – remarks

Only two specimens, both male, retained uropods and so the least damaged specimen was used for the holotype. Of the brooding females, two had embryos in the brood pouch, only three each. The males were typically heavily calcified whereas the females were not.

Diagnosis

Body subcylindrical; pleotelson length/width ratio 1.5, waist well pronounced, paired dorsal sensory organ located in tergal cuticular tubercles; pereonites 4 and 5 subequal; pereonite 6 slightly longer than pereonite 5; pereonite 7 posterolateral margins not projecting posteriorly; pereopod I ischium dorsal lobe with one seta. Pereopods V–VII ischium and carpus without strong seta mid-dorsally.

Description of female

Body ( Fig. 2C ) length 1.8 mm, 4.0 width. Ventral spines on pereonites 1–7 absent. Cephalothorax– pleotelson with imbricate ornamentation covering all tergites, sternites, and opercular pleopods.

Cephalothorax ( Figs 2C , 6C ) length 0.80 width, 0.18 body length; frons in dorsal view convex, smooth, frontal furrow present, convex anterior margin adjacent to clypeus, not projecting; antennal articulations anteriorly. Posterolateral margins angular, blunt (angle> 90°). Posterolateral setae on cephalothorax and pereonites 1–7 asensillate, simple. Pereonites 1–3 with row of setae on anterior tergite margin. Pereonite 1 length 0.2 width, 0.05 body length, anterior margin concave. Pereonite 2 length 0.36 width, 0.09 body length. Pereonite 3 length 0.35 width, 0.09 body length. Pereonite 4 width 1.2, pereonite 5 width, length 0.42 width, 0.10 body length; lateral margins anteriorly and posteriorly convex with medial concavity. Posterolateral margins rounded.

Pereonites 5–7 length subequal, each 0.08–0.09 body length, narrowing from 5 to 7. Posterior margins setose; setae asensillate, simple, flexibly articulating, short. Posterolateral margins produced posteriorly, rounded. Pereonite 5 length 0.42 width, 0.85 pereonite 4 length. Posterior margin with four setae. Pereonite 6 length 0.49 width, 1.1 pereonite 5 length. Posterior margin with six setae. Pereonite 7 length 0.51 width. Posterior margin with six setae.

Pleonite 1 length 0.25 pereonite 7 length, width 0.52 pereonite 7 width. Pleotelson length 0.22 body length, 1.5 width, width 0.95 pereonite 7 width; paired dorsal organ on the tergal surface in cuticular tubercles; apex length 0.13 pleotelson length, laterally with four simple setae. Pleopodal cavity width 0.79 pleotelson width.

Antennula ( Fig. 3F ) relative length ratios of articles 1.0, 0.70, 0.33, 0.33, 0.33, 0.33, L/W ratios of articles 1.5, 2.0, 1.0, 1.0, 2.0, 2.0. Article 1 with one simple seta. Article 2 with one simple seta. Article 4 with two simple setae. Article 6 with two aesthetascs, aesthetascs simple, tubular. Antenna ( Fig. 3F ) length 0.18 body length. Ischium angular with medial projection, about as long as coxa. Merus about as long as coxa, basis, and ischium together, articulating distolaterally on ischium, antennal proximodistal axis with distinctly sharp bend. Carpus longer than merus, articulating distolaterally on merus, antennal proximodistal axis with distinctly sharp bend between merus and carpus. Flagellum with eight articles and two to six short setae distally on each article.

Pereopod I ( Fig. 4 ) length 0.26 body length; article L/W ratios 3.3, 1.3, 0.67, 1.2, 1.5, 1.0; relative article length ratios 1.0, 0.40, 0.20, 0.35, 0.30, 0.10. Ischium longer than wide, dorsal margin with two setae: one long, simple on dorsal lobe apex and one short, simple proximally. Merus dorsal margin with two long, simple setae, ventral margin with two setae: one simple, one robust, bifid. Carpus distodorsally with two long, simple setae, ventrally with three setae: one short, robust, bifid, one long, slender, one monoserrate, robust, bifid. Propodus dorsally with two simple setae: one long distally and one small, more proximally; ventrally with two setae: one simple, slender, one bifid, robust; with row of setules proximally to bifid seta. Dactylus distally with three sensillae, dorsal claw length 1.0 dactylus length, robust.

Pereopod II slightly longer than pereopod I. Ischium dorsally with one simple seta on dorsal lobe apex. Merus dorsally with two simple setae distally on apex, ventrally with one simple seta distally. Carpus with one distodorsal and two ventral simple setae.

Pereopod III ( Fig. 4F ) length 0.34 body length; article L/W ratios 3.6, 2.2, 1.0, 3.0, 3.3, 2.5; relative article length ratios 1.0, 0.61, 0.28, 0.67, 0.56, 0.28. Ischium dorsal lobe flat and rounded; proximally and on apex without seta; distally with one simple seta. Merus dorsally on apex with one simple seta, ventrally with two simple setae. Carpus dorsally with four setae: one simple medially, one broom seta and two simple distally, ventrally with three simple setae. Dactylus distally with two sensillae.

Operculum ( Fig. 5C ) length 1.5 width, 0.82 pleotelson dorsal length. Apical width 0.82 operculum maximal width. Lateral fringe of setae absent. With 14 pappose setae on apex, completely covering anal opening. Uropod broken in female.

Female genital system: Female copulatory duct (cuticular organ) ( Fig. 1 ). The opening for the spermathecal duct is located ventrally adjacent to the articular membrane at the anterior corner of pereonite 5. The spermathecal duct extends medially toward the posterior margin of the ovary and then has a sharp turn posteriorly. Rather than intersecting the oviduct midway, the duct ends in an indistinctly demarcated region just inside the oopore; the position of this structure is consistent with it being the spermatheca, although no sperm were observed in that region. The duct was highly reflective in the preparatory female specimen studied (USNM 1208014), so it may have contained sperm from a prior mating encounter as insemination in janiroideans occurs well before the parturial moult ( Veuille, 1980; Wilson, 1987b, 1991). The oopore was medial and anterior to the coxa of pereopod V, and the oviduct continued in a dorsomedial direction to the ovary, which terminated just beyond the anterior margin of pereonite 5. The ovae were indistinct and did not fill the lumen of the ovary, indicating that the female was not fully in reproductive condition. The female was at least in preparatory condition because developing oostegites were observed on pereonites 1–4 beneath the cuticle adjacent to the coxae ( Fig. 1 ).

Description of adult male

Body ( Figs 2 , 6 ) length 2.0 mm, 4.5 width. Cephalothorax ( Fig. 6 ) frontal ridge absent; length/width ratio subequal to female, length 0.83 width, 0.16 body length; without setae dorsally, posterolateral corners rounded, posterolateral setae present. Pereonite 1 length 0.31 width, 0.06 body length. Pereonite 2 length 0.37 width, 0.07 body length. Pereonite 3 length 0.41 width, 0.08 body length. Pereonite 4 width 1.1 pereonite 5 width, length 0.56 width.

Pereonites 5–7 similar in shape, size and setation, subequal in length to pereonite 4. Length 0.6 width. Pleonite 1 length 0.23 pereonite 7 length, with two simple setae. Pleotelson in dorsal view similar to female. Length 1.4 width, 0.22 body length, width 0.95 pereonite 7 width. Posterior apex length 0.13 pleotelson length, pleopodal cavity width 0.81 pleotelson width.

Antennula ( Figs 2D , 6C ) length 0.48 head width, 0.50 antenna length, width 1.0 antenna width; article L/W ratios 1.8, 1.3, 0.5, 1.0, 0.5, 3.0; relative article length ratios 1.0, 0.57, 0.14, 0.29, 0.14, 0.43; of six articles; terminal and penultimate articles with two tubular aesthetascs, respectively.

Antenna ( Fig. 2D ) length 0.18 body length, basal articles slightly more stout than in female, flagellum of nine articles, precoxa–ischium squat, globular, coxa–ischium longer than precoxa; ischium distally with one simple seta. Merus longer than ischium, distally with one simple seta. Carpus slightly stouter than in female, with two subdistal setae.

Mandibles ( Fig. 3 ) molar with two spines and two to three setulate spines; left mandible incisor process with five cusps, lacinia mobilis with four denticles; right mandible incisor process with four cusps, lacinia mobilis spine-like, with eight denticles.

Maxillula ( Fig. 7B, C ) lateral lobe terminally with 11 robust and three slender setae. Maxilla ( Fig. 7D ) lateral lobe length subsimilar to middle lobe length, with six setae terminally, four long, two shorter distomedially; middle lobe with five setae terminally, four long, one short distomedially; medial lobe terminally with seven setae, medially with a setal row.

Maxilliped ( Figs 6C , 7E, F ) basis length 3.9 width, with two coupling hooks; endite distally truncate, with three fan setae, eight slender setae, and one spine-like seta distomedially, lateral margin with row of setae; epipod length 2.8 width, 0.81 basis length. Palp article 1 shorter than article 3, distomedially with one seta, distolateral extension short, length 0.21 article 1 length, rounded; article 2 wider than articles 1 and 3, with two distomedial setae; article 3 with five medial setae; article 4 distomedial extension minute, with four setae; article 5 terminally with four setae.

Pereopods’ I–VII ( Figs 4 , 5 ) dactylus dorsal claw subequal to dactylus in length with one sensilla inserting terminally.

Pereopod I ( Fig. 4A ) length 0.22 body length; article L/W ratios 3.0, 1.8, 0.80, 1.4, 1.7, 2.0; relative article length ratios 1.0, 0.5, 0.22, 0.39, 0.28, 0.11. Ischium dorsally with one simple seta. Merus setation as in female, dorsally with two long, bifid setae, ventrally with three setae: one thin, one robust, bifid distally and one small more laterally at mero-carpal articulation. Carpus with two distodorsal long setulate, bifid setae, ventrally with three setae: one thin, two robust, bifid. Propodus with one long distodorsal seta and two short, ventral setae.

Pereopod II ( Fig. 4B ) length 0.27 body length; article L/W ratios 3.4, 2.0, 1.0, 2.8, 4.0, 4.0; relative article length ratios 1.0, 0.59, 0.29, 0.65, 0.47, 0.24. Ischium dorsally with one simple seta on apex. Merus dorsally with two simple setae on apex, ventrodistally with one simple seta. Carpus dorsodistally with one small, simple seta, ventrally with two setae.

Pereopod III ( Fig. 4D ) length 0.30 body length; article L/W ratios 3.6, 2.5, 0.80, 3.0, 3.3, 2.5; relative article length ratios 1.0, 0.56, 0.22, 0.67, 0.56, 0.28. Setation as in female.

Pereopod IV ( Fig. 4E ) length 0.3 body length; article L/W ratios 3.4, 2.8, 1.0, 3.3, 3.3, 2.5; relative article length ratios 1.0, 0.65, 0.29, 0.76, 0.59, 0.29.

Pereopods V–VII ( Fig. 8 ) similar to pereopods II–IV in size, carpi and propodi slightly more elongate; setation similar: ischium dorsally without seta; midventrally with two simple setae. Merus distodorsally with two setae: one minute, one long, prominent; midventrally and distoventrally with one simple seta; distodorsally with one bifid seta; midventrally with two robust, bifid setae; distoventrally with one robust, bifid seta.

Pereopod V ( Fig. 8A ) 0.31 body length; article L/W ratios 3.0, 2.75, 1.25, 3.25, 6.5, 2.5; relative article length ratios 1.0, 0.73, 0.33, 0.87, 0.87, 0.33.

Pereopod VI ( Fig. 8B ) length 0.34 body length; article L/W ratios 3.4, 3.0, 1.5, 3.5, 4.3, 2.0; relative article length ratios 1.0, 0.71, 0.35, 0.82, 0.76, 0.24.

Pereopod VII ( Fig. 8C ) length 0.31 body length, slightly smaller pereopod VI length; article L/W ratios 3.5, 2.5, 2.0, 4.7, 6.5, 2.0 relative article length ratios 1.0, 0.71, 0.43, 1.0, 0.93, 0.29.

Pleopod I ( Figs 5B , 9A, B ) length 0.73 pleotelson length, 2.5 width, distal width 1.3 proximal width. Distomedial lobes with ten long, simple setae altogether; distoventrally with minute, simple setae present, in semicircular arrangement on both sides.

Pleopod II ( Fig. 9C ) protopod apex tapering, with rounded tip, distolateral margin with ten thin setae. Endopod distance of insertion from protopod distal margin 0.36 protopod length. Stylet sinuous, narrowing distally to sperm-duct opening, extending beyond distal margin of protopod, length 0.95 protopod length; sperm-duct opening located 0.17 stylet length from stylet proximal margin. Exopod length 0.32 protopod length, with rows of fine and minute setae laterodistally.

Pleopod III ( Fig. 9D ) length 2.1 width, protopod length 1.7 width, 0.53 pleopod III length; endopod plumose terminal setae longer than endopod, medial seta longest, 0.80 pleopod III length. Exopod length 0.84 pleopod III length, proximal article broadened distally, width 0.85 endopod width; distal article length 0.30 proximal article length, width 0.30 proximal article width, subterminally with one seta; lateral fine setae about as long as exopod width.

Pleopod IV ( Fig. 9E ) length 1.9 width, endopod length 1.8 width, about twice as long as protopod. Exopod length 3.3 width, 1.1 endopod length; terminal plumose seta length 0.88 exopod length. Pleopod V ( Fig. 9F ) length 2.4 width.

Uropod ( Fig. 2A, B ) length 2.4 pleotelson length; protopod length 17.6 width; with numerous scattered simple setae. Endopod inserting terminally, length 0.28 protopod length, 8.6 width, width narrower than protopod. Exopod minute, length about 0.05 endopod length, globular, with two setae.

Remarks

Urstylis zapiola was collected in a particularly large epibenthic sample (WHOI 247) from the abyssal plain of the Argentine Basin: 1316 individuals and 72 species of isopods. This locality is below 5200 m, showing that isopod species richness can be high, even at the greatest abyssal depths, contra the source-sink theory of Rex et al. (2005) that abyssal diversity should be a subset of and therefore smaller than bathyal diversity. For a detailed taxa list see also Supporting Information Appendix S2.

Figures

Figure 1. Urstylis zapiola gen. et sp. nov., adult female paratype USNM 1208014, ventral view of pereonites (Per) 4, 5, showing arrangement of reproductive organs, internal oostegite and gut; legs omitted for clarity. Scale bar = 0.1 mm.

Figure 2. Urstylis zapiola gen. et sp. nov. A, B, adult male holotype USNM 1208013. C, adult female paratype USNM 1208014. D, adult male paratype, AM P. 90631. A, dorsal habitus with enlargement of uropodal exopod. B, lateral habitus. C, dorsal habitus with enlargement of structure on pleotelson. D, antennula and antenna, in situ, lateral view. Scale bars = 0.5 mm, (A–C); 0.1 mm (D); 0.05 mm (C enlargement).

Figure 3. Urstylis zapiola gen. et sp. nov., mandibles. A–E, adult male paratype AM P. 90631, F, adult female paratype USNM 120801. A, left mandible, dorsal view. B, right mandible, dorsal view. C, right incisor process. D, E, left mandible, medial view and lateral view, respectively. F, head, left lateral view, showing position of mandible (darkened). Scale bars = 0.1 mm (A–C); 0.1 mm (D, E); 0.2 mm (F).

Figure 4. Urstylis zapiola gen. et sp. nov., anterior pereopods. A, B, D, E, adult male paratype AM P. 90631. C, F, adult female paratype USNM 120801. A, C, pereopod I. B, D, E, pereopods II–IV; E, pereopod IV with enlargement of dactylus and claws (arrow). F, pereopod III. Scale bar = 0.1 mm.

Figure 5. Urstylis zapiola gen. et sp. nov., pleotelson. A, B, adult male paratype AM P. 90631, dorsal and ventral views, respectively. C, adult female paratype USNM 120801, ventral view. D, section through transversal plane of the pleotelson at the location of the paired dorsal cuticular tubercles (arrow). Scale bar = 0.2 mm.

Figure 6. Urstylis zapiola gen. et sp. nov., views of head. A–C, adult male paratype, AM P. 90631. A, dorsal view, dotted structures showing internal attachment of mandibular muscles. B, C, ventral view, without and with maxilliped, respectively. Scale bar = 0.2 mm.

Figure 7. Urstylis zapiola gen. et sp. nov., mouthparts in ventral view. A–F, adult male paratype AM P. 90631. A, paragnaths. B, maxillula. C, maxillula lateral lobe, medial view. D, maxilla. E, maxilliped. F, maxilliped endite, distal margin, enlargement of E. Scale bars = 0.1 mm (A–D); 0.1 mm (E).

Figure 8. Urstylis zapiola gen. et sp. nov., posterior pereopods. A–C, adult male paratype AM P. 90631, pereopods V–VII. Scale bar = 0.1 mm.

Figure 9. Urstylis zapiola gen. et sp. nov., pleopods, adult male paratype AM P. 90631. A, B, pleopod I, ventral and dorsal view, respectively. C–E, pleopods II–V, ventral view. Scale bar = 0.1 mm (A, C–F).