Scolamblyops muehlenhardtae, 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 : 87-95

Scolamblyops muehlenhardtae sp. nov.

urn:lsid:zoobank.org:act:E52C7FCF-C335-468C-ABF5-D50EF34E8649

Figs 45–49

Diagnosis

Based on adults of both sexes. Covers all features of generic diagnosis. Carapace anteriorly with very short, obtuse-angled rostrum with rounded apex. Freely projecting portion of rostrum up to ⅒ length of terminal segment of antennular trunk. Sub-quadrate eye rudiments with disto-lateral process narrowing to a blunt apex, no ocular papilla. Median segment of antennal peduncle four times as long as basal segment. Terminal lobe of antennal scale short, not or only slightly projecting beyond apical tooth. Scale extending one third its length beyond antennular trunk. Clypeus with long hastate unpaired process projecting anteriorly between antennulae up to basal third of terminal segment of antennular trunk. Labrum with short, tooth-like, rostral projection. Thoracic sternites 2–8 each with one median process in adult male, none in adult female. Marsupium with three pairs of oostegites. Penes short, stout. Female pleopods increasing in length caudally. Endopods of male pleopods 1–5 with 1, 11, 12, 12–13 and 11 segments, exopods with 13, 13, 13, 13 and 12 segments, respectively; no modified setae. Uropods without spine; exopod extending ⅓ its length beyond telson. Distal ⅚ of telson densely furnished with spines along lateral and terminal margins; transversely truncate terminal margin with pair of minute paramedian spines flanked by 5–6 pairs of large spines continuously increasing in length laterally, no setae. Telson with total of 52–74 spines, no laminae, no setae.

Etymology

The species name is a noun in genitive singular with feminine ending, dedicated to Ute Mühlenhardt-Siegel (Hamburg) in recognition of her important contributions to peracarid taxonomy and biogeography.

Material examined

Holotype SOUTHERN OCEAN • 1 ov. ♀ ( BL = 20.1 mm, 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 epinet; ZMH 64686 .

Paratypes SOUTHERN OCEAN • 1 ♂ ad. ( BL = 16.5 mm, on slides); 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; ZMH 64688 • 1 juv. ( BL = 5.3 mm); Drake Passage , NW of Elephant Island, ANDEEP-I station 041-3; 59°22.24ʹ S, 60°04.06ʹ W to 59°22.40ʹ S, 60°03.99ʹ W; depth 2375– 2372 m; 26 Jan. 2002; EBS epinet; ZMH 64687 • 1 juv. (BL = 6.0 mm); Powell Basin , SW continental slope of South Orkney Islands, ANDEEP-III station 150-6; 61°48.70ʹ S, 47°28.04ʹ W to 61°48.57ʹ S, 47°28.19ʹ W; depth 1996– 1993 m; 20 Mar. 2005; EBS epinet; ZMH 64689 .

Type locality and distribution

The type locality is ANDEEP I station 114-4: Drake Passage, N of South Shetland Islands, 61°43.54ʹ S, 60°44.20ʹ W to 61°43.54ʹ S, 60°44.55ʹ W, depth 2914–2920 m. This species is only known from the Drake Passage and Powell Basin, total ranges of 59– 62° S, 47– 61° W, depth 1993–2920 m.

Description

Holotype (♀)

All female features as in specific diagnosis. Female with BL 20.1 mm carrying 16 eggs with diameter 0.73–0.80 mm. Rostrum contributes 1% to BL, thorax 29%, pleon 51%, telson 19% and carapace without rostrum 27%. Carapace with smooth surface ( Fig. 46D ), no pores detected. Eye rudiments without pigment; tooth-like rostral process 7–9% of eye length ( Fig. 46D ). Rostral process of clypeus spit-like in dorsal view (as in Fig. 45D ), while blade-like with distally converging margins in lateral view (as in Fig. 46C ). Blade with only one minute subapical tooth, less than in adult male paratype ( Fig. 46C ).

ANTENNULA ( Fig. 46A ). Trunk not dorsoventrally compressed. Basal segment with disto-lateral, setose lobe extending beyond proximal half of median segment; distinct antennular bursa. Each segment about mid-dorsally near distal margin with setose apophysis (lobe), basal segment with additional, small dorsal apophysis. Segmental border between median and terminal segment slightly oblique in dorsal as well as lateral view. Terminal segment without female lobe; disto-median lobe armed with one comparatively large tooth and four barbed setae. Basal portion of lateral flagellum 1.5–1.7 times as wide as in mesial flagellum.

ANTENNA ( Fig. 46B ). Two-segmented sympod with a strong tooth (dashed line in Fig. 46B ) dorsally above basis of scale, and another less strong tooth (solid line) ventrally shortly behind scale, accompanied by additional tooth near disto-lateral edge of sympod. Peduncle 3-segmented, its basal segment contributes 13%, median segment 52% and terminal segment 36% to total length. Basal segment bare; median segment setose on distal third of mesial margin; terminal segment setose all along mesial margin.

PRIMARY MOUTHPARTS ( Figs 46E–H , 48A ). Labrum and labium as in Figs 46H , 48A . Mandibular palp with basal segment contributing 7%, median segment 60% and terminal segment 33% to total palp length. Palp not hispid, its basal segment without setae. Length of median segment three times maximum width, its mesial margin convex, lateral margin sigmoid, mesial and lateral margins well setose. Terminal segment 4–5 times as long as broad and half as long as median segment. Terminal segment without seta on mesial margin, while comparatively sparsely setose along proximal ⅔ of lateral margin, though with dense series of short microserrated setae on distal third. Pars incisiva of right mandible ( Fig. 46G ) 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 many acute, stiff bristles proximally followed by dense series of eight subequal subtriangular spines, in part smooth, in part bearing a few stiff bristles. Processus molaris with large masticatory plate formed by densely set cuticular lamellae. Left mandible ( Fig. 46F ) normal, pars incisiva and digitus mobilis each with four large, blunt teeth. Pars centralis with six 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. 47 ). Gross structure of foregut normal ( Fig. 47A ). Lateralia with brushes of slender, proximally smooth, apically coronate spines ( Fig. 47B ) of various length, and with slender, apically pronged spines ( Fig. 47C ) densely coated with minute teeth along at least distal ⅔ of shaft. Posterior part of lateralia with dense cluster of four toothed spines of various size ( Fig. 47D ). Dorsolateral infoldings on each side with a pair of large spines, unilaterally strongly serrated along distal ⅔ ( Fig. 47E ). Storage volume full with food material (removed on right in Fig. 47A ) including masticated organic material, crustacean remains, diatoms and mineral particles. Midgut densely filled with finely masticated material. Anal lobe distinct, weakly cuticularized (dashed lines in Fig. 49K ).

MAXILLULA ( Fig. 48B ). Distal segment with 10–11 strong, smooth spines on transverse terminal margin. This segment subterminally with three densely set setae bearing long stiff barbs; no pores close to these setae. Lateral margin of 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 dorsally (on left in Fig. 48B ) with four more slender, shorter setae of that kind decreasing in size proximally. Ventral margin with seven barbed setae also decreasing in size proximally. Distal half of endite in addition with 13 smooth setae.

MAXILLA ( Fig. 48C ). Sympod with three mesial, only distally strongly setose lobes plus a less conspicuous more proximal lobe. The latter with field of acute triangular scales ( Fig. 45E ) on rostral face. Exopod extends shortly beyond basal segment of palp. Exopod with numerous plumose setae all along lateral margin; apical seta longest; no seta on mesial margin except for a medium-sized seta close to disto-mesial edge. Palp with two subequal segments. Basal segment with three barbed, basally thick setae (below drawing plane, visualized by dashed lines in Fig. 48C ). Terminally rounded distal segment 1.7 times as long as maximum width; densely setose on distal 5/9, remaining basal portion bare; no spines.

THORACIC STERNITES ( Fig. 48D ). Sternite 1 with the usual median lobe contributing to caudal closure of mouth field, no additional median processes, no setae. Sternites 2–8 with groups of 2–5 barbed setae on intersegmental joint with each thoracic sympod, no median processes. Within groups, lateral setae mostly shorter though with longer, more densely set cils compared to setae in more mesial position ( Fig. 48F ).

THORACOPODS ( Figs 45A , 48D–E, I–K , 49A–B ). Basal plates of exopods 1 and 8 comparatively slender ( Fig. 48D ); relative width increasing from exopods 1 to 3 and decreasing from 3 to 8. Disto-lateral edge of basal plate in all exopods with tooth-like projection ( Fig. 48D ). Flagellum of exopods 1 and 8 with 12 segments, flagella 2–7 with 13. Basis of endopod 1 with setose endite (below drawing plane, visualized with dashed lines in Fig. 48D ), remaining segments without endite. Endopod 1 strongly setose along mesial margin; disto-lateral edge of basis produced in an acute tooth; lateral margin of basis and ischium without setae; smooth apical nail ( Fig. 48E ) about as long as propodus. Epipod 1 linguiform (somewhat distorted in Fig. 48D ), about as long as combined basis, ischium and merus of endopod 1, no seta. Endopods 1–2 with six segments including basal segment, this last fused with sympod. Endopod 2 with ischium and dactylus strongly setose, remaining segments sparsely setose; dactylus reflexed ( Fig. 48I–J ), nail smooth, comparatively stout ( Fig. 48J ). Endopod 2 without endite. Endopod 3 with eight segments ( Fig. 49A ); its carpopropodus 3-segmented; strongly oblique suture between carpus and 2-segmented propodus; transverse suture between two propodal segments; dactylus slender, hidden in dense brush of setae. Dactyli 1–3 with weakly bent, smooth nail ( Figs 48E, J , 49B ). Endopods 4–8 broken.

MARSUPIUM ( Fig. 48K ). Oostegites 1–3 with smooth surface not considering setae; basally with great numbers of setae microserrated by minute acute bristles; no spiniform setae. Dorsal margin of oostegite 1 with tiny hairs along subbasal to apical portions; corresponding stretch bare along ventral margin. Apical portions of oostegite 1 in addition with a few barbed setae. Dorsal margin of oostegite 2 with tiny hairs along subbasal to subapical portions. Distal third of dorsal margin and distal ¾ of ventral margin with dense series of plumose setae; plumose aspect of setae increasing rostrally. Outer face of oostegite 2 with a few short smooth setae. Oostegite 3 with more such setae loosely 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 45A , 49G–I ). Pleomeres 1–5 each 0.6 times as long as pleomere 6; this value 1.1 for telson. Scutellum paracaudale triangular with acute apex. Pleopods 1–5 short, increasing in length caudally. Each pleopod widening from basis to roughly ⅔ total length; followed by more slender, straight distal portion. Relative width of distal portion decreasing from pleopod 1 to 5. Setation as in Fig. 49G–I .

TAIL FAN ( Fig. 49J–M ). Statoliths composed of fluorite, diameter 0.13–0.16 mm (n = 2). Telson ( Fig. 49K–M ) with total of 74 spines, including 30 spines of various size on each lateral margin, no pores and no scales detected. Each margin with basal 24 lateral spines slightly discontinuously, weakly increasing in size distally, adjoining six lateral spines strongly increasing distally. Transverse terminal margin with pair of minute paramedian spines flanked by six large spines on each side. Most terminal spines smooth, a few rugged due to minute bristles ( Fig. 49M ) along subbasal to submedian portions.

Paratype (♂)

All male features as in specific diagnosis. Body length 16.5 mm. Rostrum contributes 1% to BL, thorax 30%, pleon 53%, telson 16% and carapace without rostrum 28%. Appendix masculina well developed.

THORAX ( Fig. 48G–H ). Each thoracic sternite with one sub-conical to pyriform median process ( Fig. 48G ). Distal ⅗–⅘ of processes with acute triangular scales ( Fig. 48H ) increasing in numbers while decreasing in size towards tip. Average size and structure of scales about same as on sympod of maxilla ( Fig. 45E ). Sternites 2–8 with groups of 2–6 barbed setae ( Fig. 48G ) on intersegmental joint with respective thoracic sympod; structure of setae as in holotype ( Fig. 48F ). Penes ( Fig. 48G ) short, sub-conical, stouter than sternal processes. Penes apically trilobate, with two subapical and six apical, short setae.

PLEON ( Figs 45B , 49C–F ). Pleomeres 1–5 are 0.5, 0.4, 0.4, 0.4 and 0.5 times as long as pleomere 6, respectively; this value 1.0 for telson. Exopod of pleopods 1–5 and endopods 2–5 subequal ( Fig. 49C–D, F ), endopod 1 ( Fig. 49C ) much shorter, unsegmented. All sympods sub-quadrate, without setae. Sympod 2 larger than remaining sympods. All pseudobranchial lobes, entire endopod 1, basal ¼ of endopods 2–5 and all exopods with barbed setae. Distal ¾ of endopods 2–5 and all exopods with on average shorter, smooth setae. These setae slightly modified (thicker) on distal six segments of endopod 4, two setae of that type per segment ( Fig. 49E ). Compared with modified setae on endopod 4 of Amphiakrops brandtae gen. et sp. nov. ( Fig. 61D ), corresponding setae of S. muehlenhardtae sp. nov. ( Fig. 49E ) thinner and not overlapping like roofing tiles.

TAIL FAN ( Figs 45B , 49N ). Telson with total of 52 spines, including 19–21 spines of various sizes on lateral margins, no pores detected. Each lateral margin with 18–20 spines somewhat discontinuously increasing in size distally. Transverse terminal margin with pair of minute paramedian spines flanked by five pairs of larger spines continuously increasing in size laterally. Terminal spines rugged due to minute bristles ( Fig. 49N ) along subbasal to subapical portions; clearly with more and larger bristles compared with those of female holotype ( Fig. 49M ).

Figures

Fig. 45. Scolamblyops muehlenhardtae sp. nov., holotype, adult female with BL of 20.1 mm (A, E: ZMH 64686) and paratype, adult male 16.5 mm (B–D: ZMH 64688). A. Female holotype in toto, lateral view (carapace accidentally lifted). B. Male paratype in toto, lateral view (thoracopods 2–8 broken). C–D. Cephalon of male, dorsal (C) and ventral (D) views. E. Scales on rostral face of basal lobe of sympod of maxilla. Abbreviations: as = antennal sympod; cp = clypeus with rostral process; la = labrum; le = left eye. A–B. Objects artificially separated from background.

Fig. 46. Scolamblyops muehlenhardtae sp. nov., holotype, adult female with BL of 20.1 mm (A–B, E–G: ZMH 64686) and paratype, adult male 16.5 mm (C–D, H: ZMH 64688). A. Antennula, dorsal view. B. Antenna, dorsal view; setae omitted from antennal scale. C. Rostral process of clypeus, lateral view. D. Carapace with eyes expanded on slide, dorsal view. E. Mandible with left palpus, rostral view. F–G. Masticatory part of left (F) and right (G) mandibles, rostral view. H. Labium.

Fig. 47. Foregut in Scolamblyops muehlenhardtae sp. nov., holotype, adult female with BL of 20.1 mm (ZMH 64686). A. Foregut expanded on slide, dorsal view. B–E. Details of A, arrows point to modified spines of foregut. Abbreviations: di = dorsolateral infolding; la = lateralia; mg = midgut; sp = storage space. A. Object artificially separated from background.

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.

Fig. 49. Scolamblyops muehlenhardtae sp. nov., holotype, adult female with BL of 20.1 mm (A–B, G–M: ZMH 64686) and paratype, adult male 16.5 mm (C–F, N: ZMH 64688). A. Thoracic endopod 3 with part of sympod, caudal view. B. Detail of A, showing dactylus with nail, setae omitted. C. Male pleopod 1, caudal view.D. Male pleopod 2, rostral view. E. Distal fourth of endopod of male pleopod 4, rostral view. F. Male pleopod 5, rostral view. G. Female pleopod 1, rostral view. H. Female pleopod 2, caudal view. I. Female pleopod 5, rostral view. J. Uropods, ventral, setae omitted. K. Telson, dorsal view. L. Detail of K, showing terminus of telson. M–N. Terminal spines of telson in female (M) and male (N).

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.