Dactylamblyops benthophilus Wittmann, 2024, sp. nov.

Dactylamblyops benthophilus sp. nov.

urn:lsid:zoobank.org:act: 986D4F91-F730-429C-9071-BC6015BE7D26

Figs 3–8

Dactylamblyops sp. A – Wittmann & Chevaldonné 2021: fig. 24c–d.

Diagnosis

Covers adults of both sexes. All features within limits of generic diagnosis. Carapace with triangular, distally broadly rounded rostrum covering only small portion of eyestalks. Eyes shortly set apart, pyriform to sub-conical, dorsoventrally compressed; sub-conical cornea with residual visual elements, cornea not divided by a ledge; ocular papilla near antero-mesial edge, length of papilla ⅒–⅕ cornea diameter, not extending beyond cornea. Antennal peduncle with oblique border between median and terminal segment. Scale with small terminal segment, scale length 4.4–5.5 times maximum width; scale extending 0.3–0.4 of its length beyond antennular trunk; mesial margin setose, bare outer margin ending in a tooth. Setose terminal lobe of scale not projecting beyond disto-lateral tooth. Mouthparts normal, labrum rostrally rounded. Thoracic endopods not subchelate. Females with three pairs of oostegites. Endopods of male pleopods 1–5 with 1, 13–14, 14, 13–14 and 12–13 segments, exopods with 13–14, 14, 14, 14 and 14 segments, respectively. No modified setae on pleopods of both sexes. Endopod of uropods with one minute spine on inner margin below statocyst. Telson elongate triangular with slightly sigmoid, continuously converging lateral margins, length 1.6–1.9 times maximum width near basis; proximal half with bare lateral margins, distal half of each lateral margin with 24–31 densely set spines increasing in length distally; apex with three large spines in continuous series with lateral spines, no small spine and no seta between large apical spines; telson with total of 51–64 spines. Differentiation from similar taxa given in ‘Discussion’.

Etymology

The species name is an adjective with Latinized masculine ending, underlining the more benthophilic habit compared with the sympatric, more pelagic congener D. hodgsoni.

Material examined

Holotype SOUTHERN OCEAN • 1 ♂ ad. (BL = 22.6 mm); South Sandwich Trench, E of Montagu Island, ANDEEP-II station 141-10; 58°25.08ʹ S, 25°00.77ʹ W to 58°24.93ʹ S, 25°00.95ʹ W; depth 2313– 2281 m; 23 Mar. 2002; EBS supranet; ZMH 64669.

Paratypes SOUTHERN OCEAN • 2 ♀♀ ad. (BL = 20.9–25.4 mm), 2 damaged juv.; same collection data as for holotype; ZMH 64672 • 1 ♂ ad. (BL = 19.9 mm); SE Weddell Sea,ANDEEP-III station 074-6; 71°18.35ʹ S, 13°57.71ʹ W to 71°18.28ʹ S, 13°57.31ʹ W; depth 1030–1040 m; 20 Feb. 2005; EBS supranet; ZMH 64673 • 1 ♀ ad. (BL = 23.9 mm), 1 ♀ subad. (in 2 parts, BL = 16.0 mm); eastern Weddell Slope, Kapp Norvegia, ANDEEP-III station 078-10; 71°09.39ʹ S, 13°59.30ʹ W to 71°09.36ʹ S, 13°58.81ʹ W; depth 2156– 2147 m; 21 Feb. 2005; EBS epinet; ZMH 64675 • 1 ♂ ad. (fragment, BL = 17.0 mm, on slides); same collection data as for preceding; ZMH 64674 • 4 ♀♀ ad. (BL = 17.8–24.0 mm), 1 ♂ ad. (BL = 20.0 mm), 2 ♀♀ subad., 3 ♂♂ subad., 1 imm.; same collection data as for preceding except for occurrence in EBS supranet; ZMH 64677 • 1 ♀ ad. (BL = 21.8 mm, on slides); same collection data as for preceding; ZMH 64676 • 1 ♂ ad. (BL = 20.3 mm, on slides); Drake Passage, N of South Shetland Islands, ANDEEP-I station 046-7; 60°38.35ʹ S, 53°57.36ʹ W to 60°38.12ʹ S, 53°57.49ʹ W; depth 2893.6– 2893.2 m; 30 Jan. 2002; EBS supranet; ZMH 64670 • 1 ♂ ad. (BL = 24.4 mm); Drake Passage, N of South Shetland Islands, ANDEEP-I station 114-4; 61°43.54ʹ S, 60°44.20ʹ W to 61°43.54ʹ S, 60°44.55ʹ W; depth 2914–2920 m; 18 Feb. 2002; EBS supranet; ZMH 64671 • 1 ♀ ad. (BL = 19.3 mm), 1 ♂ subad. (damaged, BL ≈ 15 mm); Bellingshausen Sea, NW of Anvers Island, ANDEEP-III station 153-7; 63°19.31ʹ S, 64°36.94ʹ W to 63°19.15ʹ S, 64°37.18ʹ W; depth 2092–2118 m; 29 Mar. 2005; EBS supranet; ZMH 64678.

Other material

SOUTHERN OCEAN • 1 juv. (BL = 6.7 mm); South Sandwich Trench, SE of Montagu Island, ANDEEP-II station 143-1; 58°44.69ʹ S, 25°10.27ʹ W to 58°44.49ʹ S, 25°10.47ʹ W; depth 773.9– 755.6 m; 25 Mar. 2002; EBS epinet • 3 juv. (BL = 4.8–6.9 mm); same collection data as for preceding except for occurrence in supranet • 1 ♂ subad. (BL = 17.3 mm), 1 imm. (BL = 15.4 mm, in 2parts), 1juv.; NW Weddell Sea, ANDEEP-II station 132-2; 65°17.74ʹ S, 53°22.82ʹ W to 65°17.56ʹ S, 53°22.83ʹ W; depth 2086– 2086 m; 6 Mar. 2002; EBS supranet • 1 ♀ subad. (BL = 16.7 mm); NW Weddell Sea, ANDEEP-II station 133-3; 65°20.15ʹ S, 54°14.35ʹ W to 65°20.06ʹ S, 54°14.51ʹ W; depth 1122– 1119 m; 7 Mar. 2002; EBS supranet • 1 ♂ imm. (BL = 12.1 mm); Weddell Abyssal Plain, ANDEEP-III station 102-13; 65°34.32ʹ S, 36°31.32ʹ W to 65°34.40ʹ S, 36°31.07ʹ W; depth 4805– 4803 m; 6 Mar. 2005; recovered from sediment in web mug • 1 ♀ imm. (BL = 7.9 mm); Powell Basin, SW continental slope of South Orkney Islands, ANDEEP-III station 151-7; 61°45.52ʹ S, 47°07.68ʹ W to 61°45.42ʹ S, 47°08.04ʹ W; depth 1182– 1185 m; 21 Mar. 2005; EBS epinet • 10 juv. (BL = 4.8–7.9 mm); same collection data as for preceding except for occurrence in supranet • 1 imm. (damaged, BL = 11.0 mm), 1 imm. (strongly damaged, BL ≈ 15 mm); Drake Passage, N of South Shetland Islands, ANDEEP-I station 046-7; 60°38.35ʹ S, 53°57.36ʹ W to 60°38.12ʹ S, 53°57.49ʹ W; depth 2893.6– 2893.2 m; 30 Jan. 2002; EBS supranet • 1 juv. (BL = 6.7 mm); Drake Passage, N of South Shetland Islands, ANDEEP-I station 105-7; 61°24.16ʹ S, 58°51.55ʹ W to 61°24.26ʹ S, 58°51.83ʹ W; depth 2297.9–2307.5 m; 12 Feb. 2002; EBS supranet.

Type locality and distribution

The type locality is ANDEEP II station 141-10: South Sandwich Trench, E of Montagu Island, 58°25.08ʹ S, 25°00.77ʹ W to 58°24.93ʹ S, 25°00.95ʹ W, depth 2313– 2281 m. The species was recorded in most major parts of the W Antarctic examined, range 58– 71° S, 14– 65° W, depth 756–4805 m. It was captured in the supranet in 11 out of 14 successive mysid samples taken with a self-closing epibenthic sledge, suggesting a suprabenthic mode of life close above the deep-sea floor.

Description

Body length 17.8–25.4 mm (n = 9) in adult females, 17.0– 24.4 mm (n = 6) in adult males. Rostrum measures 2–3% of BL, carapace without rostrum 31–36%, thorax 37–44%, pleon without telson 46– 52% and telson 6–9%.

CARAPACE (Figs 3A, 4D). Normal, antero-lateral edges produced, broadly rounded (Fig. 4D). Cervical sulcus strong, cardial sulcus indistinct, posterior margin concave, terminal indentation broadly rounded. No pores seen (though not excluded). Carapace leaving ½–1½ thoracomeres mid-dorsally exposed.

EYES (Figs 3A, 4D, 5F). Ocular symphysis with unpaired, proximally trapeziform, distally triangular, apically rounded interocular lobe (Fig. 4D), in dorsal view mistakable with an anterior extension of rostrum. Eyestalks smooth all around, 0.7–0.9 times as long as terminal segment of antennular trunk. Cornea obliquely, laterally positioned on eyestalk (Figs 3A, 4D), kidney-shaped in dorsal view, apparent length 0.7–0.8 of total eye length, width 0.3–0.4. Cornea appears whitish in ethanol-preserved material. Its antero-posterior extension 1.0–1.2 times length of terminal segment of antennular trunk. Eye papilla ends in a toroid with pore in center (Fig. 5F). Organ of Bellonci present near ocular papilla.

ANTENNULA (Figs 4A–B, 5A–E). Antennular trunk measures 10–12% of BL. It extends half its length beyond eyes. Measured along dorsal midline, basal segment 0.3–0.4 of trunk length, median segment 0.1–0.2 and terminal segment 0.4–0.6. Length of basal segment 0.7–0.8 of width; mid-dorsally with deep antennular bursa (Figs 4A, 5C–D) leading down to a striated pad at bottom. Basal segment not produced at outer distal edge (Fig. 4A); no mid-ventral carina. Disto-median lobe (Fig. 4B) of terminal segment with three teeth increasing in size laterally, lobe disto-laterally with four barbed setae. Appendix masculina (Figs 4A, 5A) inserts ventrally near terminal margin of antennular trunk; appendix conical, apically rounded, 0.5–0.9 times as long as terminal segment of trunk, strongly setose. Female lobe (Fig. 5B) 0.3 times as long as terminal segment, well-developed, albeit less strongly setose. Wittmann & Chevaldonné (2021: fig. 24c–d) correctly figured this lobe as inserting ventrally but accidentally indicated it in text as inserting dorsally. Flagella large, width of outer flagellum measured near basis 1.3– 1.7 times width of inner flagellum. Basal portion of outer flagellum with ventral callynophore bearing broad row of densely set aesthetascs (Fig. 5E) in both sexes. Callynophore 0.6–0.7 times as long as terminal segment of antennular trunk.

ANTENNA (Fig. 4C). With smooth cuticle all around, not considering setae and disto-lateral tooth of antennal scale. Sympod 2-segmented, with large end sac of antennal gland. Sympod angular on disto-lateral edge, not forming a tooth-like projection. Antennal scale measures 16–20% of BL, 1.4–1.7 times as long as antennular trunk and 2.2–2.4 times as long as antennal peduncle. Scale 4.4–5.5 times as long as wide. Peduncle 3-segmented, its basal segment contributes 41–44% to total length, median segment 28–31% and terminal segment 27–29%.

LABRUM AND LABIUM (Fig. 4E, G). Labrum normal, rostrally forming a broad, rounded bulge; most caudal portions with strong lamellae and cover of scale-like fringes. Paired labia with stiff and normal setae, no spines, no teeth.

MANDIBLES (Fig. 4F). Palp 0.6–0.7 times as long as antennal scale. Palp not hispid, its basal segment without setae, remaining segments densely setose along mesial and lateral margins. Basal segment contributes 10–13%, median segment 49–54% and apical segment 37–40% to total palp length. Length of median segment 2.6–3.2 times maximum width; its mesial margin convex, lateral margin sigmoid. Length of apical segment 3.3–3.9 times maximum width. Masticatory part of mandibles normal, left and right mandibles alike: pars incisiva of both mandibles with 4–5 large teeth, and digitus mobilis with 5–9 teeth. Processus molaris with strong grinding lamellae not ending in teeth and with dense bundle of stiff bristles on proximal edge. Pars centralis of left mandible with series of 10–13 spines becoming more slender and with greater numbers of stiff bristles proximally, distalmost spine stout with few bristles. Pars centralis of right mandible with 6–9 slender, subequal spines bearing numerous stiff bristles.

GUT (Fig. 6). Foregut with lateralia, infoldings and superomedianum of cardiac chamber densely covered by smooth, slender setae and spines. Lateralia anteriorly with dense series of slender, apically coronate, bluntly pronged spines (Fig. 6B) of various length and with slender, mostly blunt spines, in part with minute apical tooth (Fig. 6C). Posterior part of lateralia on each side of foregut with a complex of three unilaterally finely serrated spines arising from a common base (Fig. 6D 2) and a second complex with four medium-sized plus at least three small spines of that kind (Fig. 6D 1). Dorsolateral infoldings on each side with a pair of larger, unilaterally more coarsely serrated, bent spines (Fig. 6E). Content of five foreguts mainly masticated, unidentifiable organic material (detritus), mineral particles, foraminifera and one fragment of a polychaete larva. Telson with ventrally prominent anal lobe (Fig. 6F–G, dashed line in Fig. 8G). Lobe caudally bifid with thick cuticle, superficially resembling glutei separated by an intergluteal furrow (Fig. 6G).

MAXILLULA (Fig. 4H). Distal segment with 10–12 strong spines on transverse terminal margin, several spines subterminally serrated on outer margin. This segment subterminally with 7–10 setae bearing stiff barbs; total of 7–9 pores flanking outer (= most ventral = aboral) seta on both its sides. Endite of maxillula terminally with three large, distally spiny setae, on both sides accompanied by numerous less strong setae. As a striking feature, most proximal seta of endite long, slender and curved backward.

MAXILLA (Fig. 7A). Sympod with four mesial lobes, densely setose along their disto-mesial margins. Large proximal lobe with large, dense fan of simple setae. Only one large seta extends beyond this fan, on caudal face, at margin near distally neighboring lobe; this seta bears a dense unilateral series of stiff barbs along its distal half. It is proximally followed by loose series of 7–13 shorter, thin setae unilaterally microserrated at least on their distal half (these setae covered by fan in Fig. 7A); this series extends over ⅔ of fan length. All four lobes with furry stripes of fine hairs on mesial portions of only caudal face; this is below drawing plane, thus stripes not visualized in Fig. 7A. Exopod of maxilla ends shortly before terminal margin of basal segment of palp. Exopod with total of 24–33 plumose setae all along lateral margin, subapically with only 0–1 seta on mesial margin; tip with 1–2 comparatively large setae; lateral margin with 19–26 intermediate-sized setae, subequal among each other, plus 3–5 large setae in most basal position. Mesial margin bare except, if any, for above-mentioned subapical seta. Maxillary palp with apical segment contributing 55–64% to palp length, no spines. Apical segment 1.6–1.8 times as long as maximum width. Basal segment less wide, subbasally with mesial bulge (endite) bearing 5–7 barbed, basally thick setae. Distal ¾ of apical segment all around with barbed setae except for a bare sector along central third of terminal margin. Mesial third of this segment with furs of tiny hairs on rostral and caudal faces (only rostral fur visualized in Fig. 7A).

THORAX (Figs 3C–D, 7B–K). Intersegmental joints between sternites and sympod 2 with basally thick, all along barbed seta accompanied by five smaller barbed setae (Fig. 7F). Sympods 3–8 with one large seta accompanied by one smaller seta of that type (Fig. 7H). No such setae on sympod 1. Thoracic sternites to various extent covered by fur of minute hairs in both sexes (shaded areas in Fig. 7B). Basal plates of thoracic exopods with smooth cuticle, length twice maximum width (Fig. 7B), plates widening distally up to ⅔ of length, plates with rectangular disto-lateral corner. Epipod 1 leaf-like, about as long as combined ischium, merus and carpus of endopod 1, no seta (Fig. 7B). Endopods with smooth cuticle, not considering setae and pores. Coxa of endopod 1 (Fig. 7B) with small mesial lobe apically bearing one barbed seta; basis with large, setose endite, remaining segments without endite; dactylus with field of about 40–60 pores, diameter <2 µm, on caudal face (Fig. 7C, E). Endopods 1–2 with six segments (Fig. 7B, F), remaining endopods with eight segments counting from basis to dactylus (Fig. 7H). Carpus 3–8 unsegmented; strongly oblique suture between carpus and propodus; less oblique, almost transverse suture between two segments of propodus (Fig. 7H). Dactyli 3–8 more slender than dactyli 1–2. Dactylus 1 with almost straight, subapically slightly serrated nail (Fig. 7C–D); dactylus 2 not reflexed; dactyli 2–8 with short, more slender, slightly bent, smooth nail (Fig. 7G, I). Endopod 3 extends shortly beyond antennular trunk when stretched anteriorly, endopod 8 to mandibles. Endopod 8 extends to pleomere 4 when stretched posteriorly. Penes (Fig. 7K) with subterminal ejaculatory opening, with setose, terminally rounded caudal lobe, and with non-setose, terminally rugose, triangular rostral lobe.

MARSUPIUM (Fig. 7J). Empty in all females of this material. Oostegite length increases by a factor of 2.8 from oostegite 1 to 3. Basal portions of dorsal margin without setae in oostegites 1–2 and from basal to subapical portions in oostegite 3. All oostegites with smooth cuticle, not considering setae. Their ventral and anterior margins plus part of posterior margin with dense series of barbed setae. Posterior parts of oostegites 1–3 on inner face with comparatively long setae microserrated on their distal half. Only oostegites 2–3 with numerous, on average shorter, slender smooth setae on outer face. These setae positioned all along ventral portions in large oostegite 3, and only in median to subapical portions on ventral fifth of oostegite 2.

PLEON (Figs 3C–D, 8A–E). Length of pleomeres 1–5 is 0.5–0.8, 0.6–0.8, 0.5–0.6, 0.4–0.6 and 0.5–0.7 times length of pleomere 6, respectively. Pleomere 6 shorter than combined length of pleomeres 4–5. Male pleopods with longitudinal series of setae on lateral (= rostral) face of sympod 1 (Fig. 8A), no setae on sympods 2–5 (Fig. 8B). Basal segment of endopod in all male pleopods with subrectangular, terminally rounded, setose pseudobranchial lobe; exopods of subequal size. Size of female pleopods increasing caudally. Female pleopod 1 with residual differentiation of pseudobranchial lobe (endopod), in pleopods 2–5 represented only by a short setose bulge. Scutellum paracaudale well rounded, sinusoid.

TAIL FAN (Fig. 8F–I). Telson, endopod and exopod of uropods are 1.0–1.2, 1.2–1.4 and 1.8–2.1 times length of sixth pleomere, respectively. Exopod of uropods (Fig. 8F) straight, 1.8–2.1 times as long as telson, endopod 1.1–1.5 times as long as telson and 0.7 times as long as exopod. Exopod extends 0.3–0.4 times its length beyond endopod and 0.5–0.6 times beyond telson; endopod extends 0.3 times its length beyond telson. Exopod with slightly convex, almost straight lateral margin and with weakly convex mesial margin. Both margins about parallel on proximal half, then converging up to truncate terminus with rounded edges. Margins of endopod converging in a V-shaped manner up to narrowly blunt terminus. Uropods (Fig. 8F) with smooth cuticle, not considering setae and single spine. Statoliths composed of fluorite, form sub-hemispherical with roughly plane fundus, as also found in other Erythropinae by Wittmann et al. (1993). Diameter 0.25–0.35 mm (n = 6), thickness ⅔ of diameter; no tegmen differentiated. Statolith formula 1 + 3 + (5–6) + (10–19) = (20–29) (n = 4). Telson (Fig. 8G, I) with pair of paramedian subbasal fields of 90–125 pores (Fig. 8G–I), pore diameters <3 µm. Telson with 2–7 µm long and 0.5–0.8 µm wide triangular scales (as in Fig. 36B) organized in clusters of about 10–25 scales. Clusters together form a narrow longitudinal ribbon (nearly as in Fig. 19D but shorter and partly broader) proceeding close to each lateral margin along ⅓–⅔ of telson length from basis (shaded areas in Fig. 8G).