Amphiakrops brandtae, Wittmann, 2024

Wittmann, Karl J., 2024, The Mysidae (Crustacea, Mysida) of the ANDEEP I-III expeditions to the Antarctic deep sea with the description of twelve new species, establishment of four new genera and with world-wide keys to the species of Erythropinae and Mysidellinae, European Journal of Taxonomy 940, pp. 1-180 : 110-117

Amphiakrops brandtae gen et. sp. nov.

urn:lsid:zoobank.org:act:129A500D-3F04-43AF-A2EB-B78CDC5A6A0B

Figs 58–61

Diagnosis

Based on adults of both sexes.All features as in generic diagnosis. Carapace with broadly rounded anterior and disto-lateral margins; rostrum almost non-existent, forming very narrow transverse prolongation of carapace. Eye rudiments dorsoventrally flattened, without visual elements, set apart, with concave anterior and mesial margins, and with weakly convex lateral margin; both anterior corners produced into tooth-like processes.Antennular trunk without mid-ventral carina. Median segment of antennal peduncle 4–5 times as long as basal segment. Antennal scale not subdivided; length three times maximum width. Terminal lobe of scale clearly projecting beyond tooth on lateral margin. Scale extending ⅓–⅔ of its length beyond antennular trunk. Clypeus with unpaired, short triangular rostral process. Labrum normal, with short, broadly rounded to bluntly triangular rostral projection. Thoracomeres 2–8 with unpaired mid-sternal processes in adult male, none in adult female. Marsupium with three pairs of oostegites. Penes short, stout. Female pleopods increasing in length distally; no modified setae. Male pleopods with large quadrangular sympod; endopods 1–5 with 1, 11, 11, 11 and 9 segments, exopods with 11, 11, 11, 11 and 9 segments, respectively; distal half of endopod 4 with longitudinal series of basally thickened smooth setae. Endopod of uropods with single spine below statocyst. Lateral margins of telson straight, moderately converging, proximally bare; distally with (almost) continuous series of about 13–16 spines increasing in length distally. Terminal margin with pair of long, barbed setae in median position, flanked by pair of minute spines, in turn flanked by 3–4 pairs of large spines subequal among each other. Telson with total of ≈36–40 spines and two setae.

Etymology

The species name is a noun with feminine ending in genitive singular, dedicated to Angelika Brandt in recognition of her role as leading scientist of the ANDEEP expeditions and of her important contributions to peracarid taxonomy and biogeography.

Material examined

Holotype SOUTHERN OCEAN • 1 ♂ ad. ( BL = 17.5 mm, on slides); 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 epinet; ZMH 64667 .

Paratype SOUTHERN OCEAN • 1 ♀ ad. ( BL = 23.8 mm, marsupium empty, on slides); 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 64668 .

Other material

SOUTHERN OCEAN • 1 juv. (only cephalothorax); same collection data as for holotype .

Type locality and distribution

The type locality is ANDEEP II station 132-2: NW Weddell Sea, 65°17.74ʹ S, 53°22.82ʹ W to 65°17.56ʹ S, 53°22.83ʹ W, depth 2086 m. This species has also been recorded in the deep waters of the Drake Passage. Total ranges 62– 65° S, 53– 61° W, depth 2086–2920 m.

Description

Holotype (♂)

All male features as in specific diagnosis. Body length 17.5 mm. Thorax contributes 37% to BL, pleon 50%, telson 14% and carapace 30%. Crescent-shaped subrostral plate (as in Fig. 59C ), 0.1–0.3 times length of terminal segment of antennular trunk. Carapace with smooth surface, anteriorly broadly rounded, no pores detected. Eye rudiments in dorsal view roughly parallelogram-shaped, without pigment; disto-lateral tooth-like process ⅕ of eye length, disto-mesial process ⅒; organ of Bellonci in basal position. Clypeus with short rostral process ( Fig. 58C ). Labrum with bluntly obtuse-angled rostral projection ( Figs 58C , 59D ).

ANTENNULA ( Figs 58C , 59A ). Trunk dorsoventrally weakly flattened by a factor of 1.2. Basal segment contributes 30%, median segment 14% and terminal segment 55% to total length of antennular trunk. Basal segment with antennular bursa and with disto-lateral, setose lobe extending beyond proximal half of median segment. Each segment about mid-dorsally near distal margin with setose apophysis, basal segment with additional, small dorsal apophysis. Segmental border between median and terminal segments slightly oblique in dorsal as well as lateral view. Terminal segment with disto-median lobe bearing four barbed setae, no tooth. Basal portion of lateral flagellum 1.3 times as wide as in mesial flagellum. Appendix masculina large, 0.1 times BL and 1.2 times length of terminal segment of antennular trunk ( Fig. 59A ).

ANTENNA ( Fig. 59B ). Two-segmented sympod (not considering end sac of antennal gland in Fig. 59B ) dorsally with tooth (dashed line in Fig. 59B ) above basis of antennal scale and another stronger tooth (solid line) ventrally shortly behind scale, accompanied by additional small tooth near disto-lateral edge of sympod. Peduncle 3-segmented, its basal segment contributes 15%, median segment 61% and terminal segment 24% to its total length. Basal segment bare; median and terminal segments sparsely setose on mesial and lateral margins.

MANDIBLES ( Fig. 59E–G ). Palp with basal segment contributing 13%, median segment 56% and terminal segment 31% to total palp length. Palp not hispid, its basal segment without setae, median segment densely setose along lateral and mesial margins. Length of median segment twice maximum width, mesial and lateral margins convex. Terminal segment 3–4 times as long as broad and about half as long as median segment. Terminal segment with great numbers of smooth setae, only its distal fifth with dense series of short, microserrated setae. Pars incisiva of right mandible ( Fig. 59F ) with four large teeth, digitus mobilis with only two large teeth, each serrated by small secondary teeth. Pars centralis modified, with strong tooth-like spine bearing several acute, stiff bristles. This spine proximally followed by dense series of nine subequal, about triangular, slender tooth-like spines also bearing stiff bristles. Processus molaris with large masticatory plate formed by densely set cuticular lamellae. Left mandible ( Fig. 59G ) normal, pars incisiva and digitus mobilis each with four large, blunt teeth. Pars centralis with seven slender spines each bearing stiff, acute bristles. Processus molaris with strong but fewer grinding lamellae compared to right mandible. Processus molaris of both mandibles with bundles of long bristles on proximal margin.

GUT ( Fig. 60B–E ). Foregut as in Paramblyops petrescui sp. nov. ( Fig. 43 ) except that cluster on posterior part of lateralia contains fewer (four vs six) all along unilaterally more strongly serrated spines ( Fig. 60D vs Fig. 43D ) and that cluster on dorsolateral infoldings contains fewer (six vs nine), unilaterally more strongly serrated (toothed) spines along distal ⅔ ( Fig. 60E vs Fig. 43E ). Holotype of A. brandtae gen. et sp. nov. with storage volume ¾ filled with unidentifiable masticated organic material and great numbers of mineral particles. Abundant mineral particles also found in midgut. Anal lobe distinct, weakly cuticularized.

MAXILLULA ( Fig. 59I ). Distal segment with 13 strong spines on transverse terminal margin, 10–11 proximal (= oral) spines slightly serrated in median to subapical portions, remaining (distal = aboral) spines smooth. This segment subterminally with three densely set setae bearing long stiff barbs, no pores beneath setae. Basal segment furnished with longitudinal, comparatively long series of densely set long, fine hairs. Endite terminally with three large, distally spiny (by stiff bristles) setae, in between and more orally (to the left in Fig. 59I ) with three more slender, shorter setae of that type decreasing in size proximally. Aboral margin with five barbed setae also decreasing in size proximally. Distal half of endite in addition with five smooth setae.

MAXILLA ( Fig. 60A ). Sympod with four mesial, only distally strongly setose lobes. Longest seta extends beyond dense fan of barbed setae on proximal lobe, this seta (sub)-apically rugged by stiff bristles. Exopod extends shortly beyond basal segment of palp. Exopod with numerous plumose setae all along lateral margin (position of broken setae indicated by dashed lines in Fig. 60A ); two longest setae on apex; no seta on mesial margin except for medium-sized seta at disto-mesial edge. Distal segment of palp terminally rounded, two times as long as maximum width, 1.3 times length of proximal segment. Distal segment densely setose on distal half of mesial margin, remaining portions sparsely setose, no spines. Proximal segment with three barbed setae on rostral face plus 3–4 smaller barbed setae on caudal face (caudal setae visualized by dashed lines in Fig. 60A ).

THORAX ( Fig. 60F–H ). Sternite 1 ( Fig. 60F ) with usual median lobe contributing to caudal closure of mouth field, no additional median processes, no setae. Sternites 2–8 ( Fig. 60F ) each with one triangular, mostly acute median process, surface of process covered by minute, acute triangular scales (as in Fig. 48H ). Only sternite 2 on each side with cluster of 2–6 barbed setae ( Fig. 60H ) on intersegmental joint with sympod 2. Penes ( Fig. 60F ) short, tube-like, distally trilobate with eight setae.

THORACOPODS ( Fig. 60F–H, J–K ). Length of basal plates increases from exopod 2 to exopod 5 and then decreases to exopod 7, plate of exopod 8 as in exopod 7; exopod 1 broken. Ratio of length to maximum width 2.2, 2.1, 1.7, 1.8–1.9, 1.6–1.7, 1.6 and 1.9 in series of plates 2–8. Disto-lateral edge of basal plate in exopods 2–8 with small, tooth-like projection ( Fig. 60J ). Flagellum of exopods 2–8 with 16, 17, 17–18, 18, 18, 17–18 and 18 segments, respectively. Basis of endopod 1 with setose endite (dashed line in Fig. 60F ); no tooth-like process. Endopod 1 strongly setose along mesial margin, much less so along lateral margin; lateral margin of basis and ischium without setae. Weakly curved, smooth apical nail ( Fig. 60G ) longer than dactylus, though shorter than propodus. Epipod 1 linguiform, about as long as combined ischium, merus and carpus of endopod 1, no seta. Endopods 1–2 with six segments including basal segment, the latter fused with sympod. Endopod 2 with carpopropodus and dactylus strongly setose, remaining segments sparsely setose; dactylus not reflexed, nail smooth, comparatively stout ( Fig. 60K ); no endite. Endopods 3–8 broken.

PLEON ( Figs 58A , 61B–E ). Pleomeres 1–5 are 0.4, 0.5, 0.4, 0.4 and 0.6 times as long as pleomere 6, respectively; this value 1.1 for telson. Sympods of pleopods 1–5 sub-quadrate, without setae ( Fig. 61B– C, E ). Sympod 2 wider than remaining sympods. Total length increases by ¼ in series from pleopod 1 ( Fig. 61B ) to pleopod 4; pleopod 5 ( Fig. 61E ) not in series, about as long as pleopod 2 ( Fig. 61C ). Pseudobranchial lobes 1–5 and basal ⅓–½ of endopods 2–5, as well as exopods 2–5, with barbed setae. Distal portions of exopods 1–5 and of endopods 2–5 with on average shorter, smooth setae. Only endopod 4 with modified, basally thickened setae ( Fig. 61D ) on lateral margin of segments 4–10; one such seta per segment, setae of adjoining segments overlapping like roofing tiles. Scutellum paracaudale triangular with acute apex.

TAIL FAN ( Figs 58F , 61I–K ). Exopod of uropods ( Fig. 61I ) extends ¼ of length beyond endopod and half-length beyond telson (in part due to telson inserting more rostrally). Statoliths composed of fluorite, diameter 0.20–0.21 mm (n = 2). Telson length 1.7 times maximum width. Telson with total of 36 spines, including 13–14 spines on each lateral margin ( Fig. 61J ). Transverse terminal margin with two barbed setae ( Fig. 61K ), two minute spines and seven large spines; only large spines ( Fig. 61J ) with furrowed surface ( Fig. 58F ). Telson without pores or scales.

Paratype (♀)

All female features as in specific diagnosis. Body length 23.8 mm. Rostrum contributes 1% to BL, thorax 36%, pleon 49%, telson 14% and carapace without rostrum 33%. Basal segment contributes 32%, median segment 18% and terminal segment 50% to total length of antennular trunk. Terminal segment of antennular trunk without female lobe.

THORAX ( Fig. 58B , 60I ). Sternite 1 with usual median lobe contributing to caudal closure of mouth field, no additional median processes; no setae. Sternites 2–8 ( Fig. 60I ) without median process. Sternite 2 on each side with group of seven barbed setae (structure as in Fig. 60H ) on intersegmental joint with sympod 2. Endopods 3–8 broken.

MARSUPIUM ( Figs 58B , 61A ). Oostegites 1–3 with smooth surface not counting setae (hairs); basally with many setae microserrated by minute acute bristles; no spiniform setae. Dorsal margin of oostegite 1 ( Fig. 61A ) with tiny hairs along subbasal to apical portions; no such hairs along ventral margin. Distal half of ventral margin and (sub)-apical portions of dorsal margin with barbed setae. Dorsal margin of oostegite 2 with tiny hairs along subbasal portions. Distal third of dorsal margin and distal ¾ of ventral margin with dense series of plumose setae. Only oostegite 3 with numerous whip setae, widely scattered over outer face. Dorsal margin mostly bare along subbasal to subapical portions. Posterior and ventral (mesial) margins densely furnished with plumose setae interlocking with setae of opposite oostegite.

PLEON ( Figs 58B , 61F–H ). Pleomeres 1–5 are 0.5, 0.6, 0.6, 0.6 and 0.5 times as long as pleomere 6, respectively; this value 1.1 for telson. Pleopod size increases caudally. Pleopods 1–3 widening from basis to roughly half-length, then converging up to blunt apex ( Fig. 61F–G ); pleopods 4–5 with longer, subrectangular basal portion ( Fig. 61H ). Setation of pleopods as in Fig. 61F, H ; most setae broken in pleopod 3 ( Fig. 61G ).

TAIL FAN. Exopod of uropods extends 44% of its length beyond telson (in part due to telson inserting more rostrally; Fig. 58B ). Endopods with slender spine on mesial margin below statocyst. Statoliths composed of fluorite, diameter 0.16–0.19 mm (n = 2). Telson length 1.8 times maximum width. Each lateral margin with 16 spines. Left half of truncate terminal margin with three large and one minute spine plus one barbed seta, only large spines with furrowed surface; right half of terminus broken. Telson with extrapolated total of 40 spines plus two barbed setae.

Figures

Fig. 58. Amphiakrops brandtae gen. et sp. nov., holotype, adult male with BL of 17.5 mm (A, C–D, F: ZMH 64667) and paratype, adult female 23.8 mm (B, E: ZMH 64668). A. Male holotype in toto, lateral view (thoracic endopods 3–8 broken). B. Female paratype in toto, lateral view (thoracopods 3–8 and part of uropods broken). C–D. Cephalon of male, ventral (C) and dorsal (D) views. E. Rostral margin of female cephalon, lateral view. F. Surface cuticle structures of spine on terminal margin of telson. Abbreviations: as = antennal sympod; cp = clypeus with short rostral process; fg = foregut; la = labrum; le = left eye; lt = left antennular trunk; mp = mandibular palp; rt = right antennular trunk; sr = subrostral lobe. A–E. Objects artificially separated from background.

Fig. 59. Amphiakrops brandtae gen. et sp. nov., holotype, adult male with BL of 17.5 mm (A–B, E–I: ZMH 64667) and paratype, adult female 23.8 mm (C–D: ZMH 64668). A. Male antennula, dorsal view. B. Antenna, dorsal view, setae omitted from antennal scale. C. Carapace with subrostral plate and left eye, expanded on slide, dorsal view.D. Labrum, dorsal = oral view. E. Mandible with left palpus, caudal view. F–G. Masticatory part of right (F) and left (G) mandibles, caudal view. H. Labium. I. Maxillula, caudal view.

Fig. 60. Amphiakrops brandtae gen. et sp. nov., holotype, adult male with BL of 17.5 mm (A–H, J–K: ZMH 64667) and paratype, adult female 23.8 mm (I: ZMH 64668). A. Maxilla, rostral view, thin dashed lines indicate position of broken setae of exopod. B–E. Modified spines of foregut, from anterior (B), median (C) and posterior (D) parts of lateralia and from dorsolateral infolding (E). F. Male thoracic endopod 1 (exopod broken) with epipod 1 (caudal view) and sternites 1–8 with right penis (ventral view). G–H. Details of F, showing dactylus with nail (G, setae omitted) and setae on sternite 2 (H). I. Female sternites 1–8, ventral view. J. Thoracopod 2, rostral view. K. Detail of J, showing dactylus with nail, setae omitted.

Fig. 61. Amphiakrops brandtae gen. et sp. nov., holotype, adult male with BL of 17.5 mm (B–E, I–K: ZMH 64667) and paratype, adult female 23.8 mm (A, F–H: ZMH 64668). A. Oostegite 1, outer face. B. Male pleopod 1, rostral view. C. Male pleopod 2, rostral view. D. Distal half of endopod of male pleopod 4, caudal view. E. Male pleopod 5, caudal view. F. Female pleopod 1, caudal view. G. Female pleopod 3, caudal view, setae bases in series along mesial margin are remnants of broken setae. H. Female pleopod 5, caudal view. I. Uropods, ventral view, setae omitted. J. Telson, dorsal view. K. Detail of J, showing median portion of terminal margin of telson.

Fig. 43. Paramblyops petrescui sp. nov., holotype, adult female with BL of 38.7 mm (ZMH 64684). A. Maxilla, rostral view. B–E. Modified spines of foregut, from anterior (B), median (C) and posterior (D) parts of lateralia and from dorsolateral infolding (E). F. Thoracopod 1 with epipod 1 (caudal view) and sternites 1, 2 (ventral view); setae omitted from right endopod (drawn to the left). G. Detail of F, showing dactylus with nail, setae omitted. H. Thoracopod 2, caudal view. I. Oostegite 1, inner face.

Fig. 48. Scolamblyops muehlenhardtae sp. nov., holotype, adult female with BL of 20.1 mm (B–F, I–K: ZMH 64686) and paratype, adult male 16.5 mm (A, G–H: ZMH 64688). A. Labrum, ventral = aboral view. B. Maxillula, caudal view. C. Maxilla, caudal view. D. Female thoracic sternites 1–8 (ventral) with thoracopod 1 and epipod 1 (caudal). E. Detail of D, showing dactylus with nail, setae omitted. F. Detail of D, showing setal group of sternite 2. G. Male sternites 1–8 with penes, ventral view. H. Detail of G, showing median process from sternite 2. I. Thoracic endopod 2, rostral view. J. Detail of I, showing dactylus with nail, setae omitted. K. Oostegite 1, inner face.