Amblyopsoides fenestragothica, 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 : 60-69

Amblyopsoides fenestragothica sp. nov.

urn:lsid:zoobank.org:act:D3EB1FB5-FE5F-4F7A-A756-492E2B9D7BE7

Figs 31–36

Diagnosis

Based on immature specimens of both sexes. All features within limits of generic diagnosis. Rostrum wide-angled, broadly rounded, short, dorsally covering short subrostral lobe and less than half rostral extension of eyes. Eye rudiments separate, dorsoventrally compressed, reduced to roughly trapeziform pads without visual elements. Rudiments mid-rostrally with ocular papilla as long as ⅐ of antero-posterior extension of eye. Antennal scale extends half its length beyond antennular trunk. Scale with minute apical segment separated by a transverse suture. Lateral margin of scale bare up to a tooth at ⅓–½ of length from basis, remaining distal portion densely setose. Mouthparts normal, labrum rostrally rounded. Thoracic exopods 3–8 with 10-segmented flagellum. Endopods 4, 6 and 8 with unsegmented carpus separated from 2-segmented propodus by an oblique articulation (endopods 3, 5 and 7 broken). Immature male pleopods 1–5 biramous, well setose, no spines. Uropods setose all around, no spine. Telson roughly trapeziform, length twice maximum width and 6/5 times length of ultimate pleomere; terminal margin with ogival disto-median indentation with depth ⅘ of indentation width and 1/20 of telson length. Each lateral margin of the indentation with one seta (only setal bases preserved in Fig. 36F ) near tip and a small lamina near basis. Indentation flanked by 3–4 pairs of large spines on terminal margin of telson. Telson with distal ⅗ of each lateral margin armed with series of 21–26 spines, distally somewhat discontinuously increasing in size; proximal ⅖ bare; telson with total of 48–59 spines, two laminae and two setae.

Etymology

The species name is an adjective with feminine ending, formed by linking the Classic Latin noun ‘ fenestra ’ (‘window’) with the late Latin adjective ‘ gothica ’ (‘gothic’), related to the most significant and practical feature of determination at species level, namely the mid-terminal indentation of the telson resembling a gothic window ( Fig. 36F ).

Material examined

Holotype SOUTHERN OCEAN • 1 ♂ imm. ( BL = 16.2 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 64660 .

Paratype SOUTHERN OCEAN • 1 ♀ imm. ( BL = 14.1 mm); 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; ZMH 64661 .

Type locality and distribution

The type locality is ANDEEP I station 046-7: Drake Passage, South Shetland area, NE of Elephant Island, 60°38.35ʹ S, 53°57.36ʹ W to 60°38.12ʹ S, 53°57.49ʹ W, depth 2893.6– 2893.2 m. A second record was made in the NW Weddell Sea at ANDEEP II station 132-2. The resulting total range is 61– 65° S, 53– 54° W, 2086–2894 m.

Description

Holotype (♂)

All features within ranges of specific diagnosis. Immature male with BL 16.2 mm. Rostrum measures 1% of BL, carapace without rostrum 35%, cephalothorax 41%, pleon without telson 43% and telson 15%. Clypeus with short, acute, mid-rostral process (visible only in ventral view: Fig. 31C ) about half as long as basal segment of antennal peduncle.

CARAPACE ( Figs 31D , 33A ). Normal, disto-lateral edges broadly rounded, cervical sulcus strong, no cardial sulcus visible; posterior margin concave, terminal indentation broadly rounded. Median pore group located 5% of carapace length in front of posterior margin of carapace (position indicated by arrows in Fig. 33A ). This group constituted by eight pores flanking a larger pore-like structure on top of a small bulge ( Fig. 31D ). Carapace leaves 1½ thoracomeres mid-dorsally exposed.

EYES ( Figs 32C–F , 33A ). Eye rudiments large, their antero-posterior extension 0.8 times maximum width and 1.5 times length of terminal segment of antennular trunk. Large portions of dorsal face covered by tiny ‘hairs’ ( Fig. 32F ) which become stiff and spiniform near and on transverse terminal margin. Eye papilla ends in a toroid with central pore ( Fig. 32E ). Organ of Bellonci near ocular papilla.

ANTENNULA ( Fig. 33B–C ). Trunk measures 11% of BL, extending half its length beyond eyes. Transverse articulations between three trunk segments. Measured along dorsal midline, basal segment 0.4 of trunk length, median 0.2 and terminal 0.4. Length of basal segment 0.6 times width. Basal segment produced into a short lobe at disto-lateral edge, lobe distally with 4–5 setae; antennular bursa well developed. Terminal segment 1.2–1.3 times as long as wide, no callynophore. Disto-median lobe armed with four minute teeth increasing in size laterally, lobe disto-laterally with three barbed setae ( Fig. 33C ). Appendix masculina inserts ventrally near terminal margin of antennular trunk; appendix conical, apically rounded. Flagella large, width of outer flagellum measured near basis 1.1–1.2 times as wide as that of inner flagellum.

ANTENNA ( Figs 31C , 33D ). Sympod 2-segmented, caudally in addition with large end sac of antennal gland. Sympod angular on slightly produced disto-lateral edge, not forming a tooth-like projection. Antennal scale measures 0.2 BL, 1.6–1.7 times as long as antennular trunk and 1.7–1.8 times as long as antennal peduncle. Scale length 3.5–3.6 times maximum width. Scale well setose along mesial margin and on distal lobe. Peduncle 3-segmented, its basal segment contributes 23%, median segment 43% and terminal segment 34% to total length.

PRIMARY MOUTHPARTS ( Fig. 33E–G ). Labrum and labium normal. Mandibular palp as long as antennal scale. Basal segment contributes 10%, median segment 59% and apical segment 32% to total palp length. Length of median segment 3.1 times maximum width; its mesial margin convex, lateral margin slightly sigmoid. Length of apical segment 4.2 times maximum width. Palp not hispid, its basal segment without setae, median segment densely setose along lateral and mesial margins, apical segment densely setose along lateral margin and less densely along mesial margin. Right mandible ( Fig. 33F ): pars incisiva with three large and three small teeth; digitus mobilis with two large and several small teeth; pars centralis with series of nine tooth-like spines increasing in size distally, only five proximal spines (below drawing plane in Fig. 33F ) armed with stiff bristles on basal half. Left mandible ( Fig. 33G ): pars incisiva with five large and several small teeth; digitus mobilis with four large teeth; pars centralis with seven slender spines distally increasing in size, all along armed with stiff bristles. Processus molaris of left ( Fig. 33G vs 21D) and right ( Fig. 33F vs 21E) mandibles as in Amblyops bipapillatus sp. nov.

GUT ( Fig. 34 ). Similar to that of Amblyops bipapillatus sp. nov. ( Fig. 22 ). As minor differences, apically coronate spines ( Fig. 34B ) and apically pronged spines ( Fig. 34C ) of lateralia in Amblyopsoides fenestragothica sp. nov. coated with minute teeth along at least distal ⅔ of shaft. Posterior part of lateralia with dense cluster of eleven spines of various size, most unilaterally serrated ( Fig. 34D ). Dorsolateral infoldings with cluster of five large spines, most unilaterally serrated along distal ⅔ ( Fig. 34E ). Storage volume filled to about ⅔ with mainly masticated, unidentifiable organic materials (detritus), mineral particles, a few sponge spicules and crustacean remains. Midgut full with organic material and a few mineral particles. Anal lobe caudally strongly cuticularized (lobe located ventrally, nonetheless visible in dorsal view through artificially bleached telson in Fig. 36A, E ).

MAXILLULA ( Fig. 33H ). Distal segment with 12–13 strong spines on transverse terminal margin, unilaterally serrated along median portions, seven dorsal (= oral) spines serrated along aboral margin, 5–6 ventral (= aboral) spines along oral margin. This segment subterminally with three setae bearing long stiff barbs; no nearby pores detected. Endite of maxillula terminally with four large, distally spiny setae, on both sides accompanied by numerous, less strong setae. As a striking feature, two most proximal setae closely set and backward curved.

MAXILLA ( Fig. 33I ). Basal segment of sympod laterally with field of triangular scales similar to that ( Fig. 36B ) of telson but more variable in length and not organized in clusters. Distal segment of sympod with three mesial lobes, densely setose along disto-mesial margins. Convex mesial portion of sympod bearing a large, dense fan of setae. One large seta extends shortly beyond fan; on caudal face, at margin near distally neighboring lobe; with a unilateral dense series of stiff barbs along distal half. Exopod of maxilla extends shortly beyond terminal margin of basal palp segment. Exopod with dense series of plumose setae all along lateral margin. Tip of exopod with two large setae (dashed lines in Fig. 33I ), mesial margin bare. Maxillary palp with distal segment contributing 57% of palp length. This segment 1.8 times as long as maximum width; segment densely setose all along distal ¾, no spines. Mesial margin of proximal segment with three basally thick barbed setae (visualized as dashed lines in Fig. 33I ).

THORAX ( Fig. 35A–I ). Sternite 1 with distally rounded median lobe distally bearing slender triangular scales as in process from sternite 2 ( Fig. 35C ). A median lobe on sternite 1 is normal in Mysidae . Five basally thick, barbed setae on intersegmental joint between sternite 2 and sympod 2 ( Fig. 35D ). Sternites 2–4 with short, rounded median processes decreasing in size caudally ( Fig. 35A ); only process 2 covered with scales ( Fig. 35C ). Basal plates of thoracic exopods 3–8 with smooth cuticle, length twice maximum width ( Fig. 35I ), plates with minute tooth-like projection on disto-lateral edge (exopods 1–2 broken). Epipod 1 leaf-like, about as long as combined ischium and merus of endopod 1, no seta ( Fig. 35A ). Endopods with smooth cuticle, not considering setae and pores. Coxa of endopod 1 ( Fig. 35A ) with small mesial lobe apically bearing one small barbed seta; basis with large, setose endite, remaining segments without clear endite. About nine pores with diameter <3 µm on caudal face of dactylus and about 15 pores on propodus (only six pores on distal part of propodus visualized in Fig. 35B ). Endopods 1–2 with six segments ( Fig. 35A, D ), endopods 4, 6 and 8 with eight segments counting from basis to dactylus ( Fig. 35I ; endopods 3, 5 and 7 broken). Dactylus of endopod 2 not reflexed. Dactyli 4, 6 and 8 ( Fig. 35H ) only slightly more slender than dactyli 1–2 ( Fig. 35B, E ). All available dactyli with weakly curved claws; claws 1, 4, 6 and 8 smooth ( Fig. 35B, H ), claw 2 subapically microserrated on inner margin ( Fig. 35F ). Endopod 8 extends to mandibles when stretched anteriorly, and to basal third of telson when stretched posteriorly. Penes ( Fig. 35I ) of immature male mid-laterally with longitudinal series of 7–8 barbed setae and basally with dense coat of small, fine ‘hairs’. No spermatozoa detected.

PLEON ( Figs 31A , 35J–K ). Length of pleomeres 1–5 is 0.4, 0.5, 0.5, 0.5 and 0.6 times length of pleomere 6, respectively ( Fig. 31A ). Pleomere 6 shorter than combined length of pleomeres 4–5. Pleopods 1–5 of immature male without setae on sympod ( Fig. 35J–K ). Endopod and exopod still unsegmented at this stage of maturity, endopod with large pseudobranchial lobe. Endopod well setose, exopod with only few setae on and near apex. Scutellum paracaudale triangular with narrowly blunt apex.

TAIL FAN ( Figs 31A , 35L , 36 ). Endopod and exopod of uropods 1.5 and 2.0 times as long as sixth pleomere, respectively. Exopod 5/3 times telson length; endopod 6/5 times telson length and 0.7 times exopod length ( Fig. 35L ). Exopod extends 0.3 times its length beyond endopod and 0.6 times beyond telson; endopod 0.4 times its length beyond telson. Exopod with slightly concave, almost straight lateral margin and with convex mesial margin; its terminus broadly rounded, convex. Margins of endopod converge in narrow V-shaped manner up to blunt apex. Uropods with smooth cuticle, not considering setae. Statoliths composed of fluorite, diameter 0.31–0.32 mm. Telson subbasally with pair of pore fields flanking midline ( Fig. 36C–D ); fields with 24 and 27 pores, respectively, with diameter <3 µm. Telson with 2–6 µm long and 0.6–1.0 µm wide triangular scales organized in clusters of about 10–20 scales ( Fig. 36B ). Clusters together form narrow longitudinal ribbon (as in Fig. 19D but shorter), proceeding close to each lateral margin between ⅕ and ½ of telson length from basis. Lateral margins ( Fig. 36A ) armed with 25–26 spines; telson with total of 59 spines.

Paratype (♀)

Terminal segment of antennular trunk without female lobe. Position of tooth at outer margin of antennal scale at one-third of scale length in immature female with BL 14.1 mm (vs at half scale length in holotype with BL 16.2 mm). Terminal margin of telson with three pairs of large spines flanking mid-terminal indentation (vs four pairs in holotype). Each lateral margin of telson armed with 21 spines; telson with total of 50 spines.

Figures

Fig. 31. Amblyopsoides fenestragothica sp. nov., holotype, immature male with BL of 16.2 mm (ZMH 64660). A. Holotype in toto, lateral view. B. Cephalon, dorsal view. C. Cephalon, ventral view, dashed line indicates clypeus (right half covered by left mandibular palp). D. Pore group close to posterior margin of carapace. A. Object artificially separated from background.

Fig. 32. Amblyopsoides fenestragothica sp. nov., holotype, immature male with BL of 16.2 mm (D–F: ZMH 64660) and paratype, immature female 14.1 mm (A–C: ZMH 64661). A. Anterior half of cephalothorax, left eye removed, lateral view. B. Detail of A, showing rostral and subrostral processes. C. Right eye, antennula and antennal scale, dorsal view. D. Eye rudiments expanded on slide, dorsal view. E. Detail of D, showing tip of ocular papilla with toroidal bulge. F. Detail of D, showing coverage with thin, mostly hair-like scales. Abbreviations: ca = carapace; er = eye rudiment; op = ocular papilla; ro = rostrum;sr = subrostral process;tb = toroidal bulge. D. Object artificially separated from background.

Fig. 33. Amblyopsoides fenestragothica sp. nov., holotype, immature male with BL of 16.2 mm (ZMH 64660). A. Carapace with eyes expanded on slide, dorsal view, arrows point to minute pore group (detail in Fig. 31D). B. Antennula, dorsal view. C. Detail of B, showing disto-median lobe of antennular trunk. D. Antenna with antennal gland, ventral view, setae omitted from antennal scale. E. Mandible with right palpus, caudal view. F. Masticatory part of right mandible, caudal view. G. Masticatory part of left mandible, rostral view. H. Maxillula, caudal view. I. Maxilla, caudal view.

Fig. 34. Foregut in Amblyopsoides fenestragothica sp. nov., holotype, immature male with BL of 16.2 mm (ZMH 64660). 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. 35. Amblyopsoides fenestragothica sp. nov., holotype, immature male with BL of 16.2 mm (ZMH 64660). A. Thoracic endopod 1 with epipod and sternites 1–5 (exopod broken). B. Detail of A, showing dactylus with nail, pore diameters not to scale, setae omitted. C. Detail of A, showing median process of sternite 2. D. Thoracic endopod 2, caudal view. E. Detail of D, showing dactylus with nail, setae omitted. F. Detail of E, showing distal part of nail. G. Tarsus of thoracic endopod 4. H. Detail of G, showing dactylus with nail, setae omitted. I. Thoracopod 8 with penis, caudal view. J. Pleopod 1, mesial = caudal view. K. Pleopod 3, lateral = rostral view. L. Uropods, dorsal view, setae omitted.

Fig. 36. Telson in Amblyopsoides fenestragothica sp. nov., holotype, immature male with BL of 16.2 mm (ZMH 64660). A. Telson expanded on slide, dorsal view. B. Detail of A, showing scale fields close to lateral margin of telson. C. Detail of A, showing basal portion of telson with two pore fields. D. Detail of C, showing part of left pore field (some pores not in focus). E. Detail of A, showing ventral anal lobe, focused through the artificially transparent tissue, dorsal view. F. Detail of A, showing distal portion of telson. Abbreviations: al = anal lobe; an = anus; lf = mid-longitudinal fold; pf = pore fields. A. Object artificially separated from background.

Fig. 22. Foregut in Amblyops bipapillatus sp. nov., holotype, adult female with BL of 16.7 mm (ZMH 64659). 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; pf = primary cardiac filter; sm = superomedianum; sp = storage space. A. Object artificially separated from background.

Fig. 19. Pleopods and tail fan in Amblyops arianii sp. nov., holotype, adult female with BL of 25.8 mm (C: ZMH 64653) and paratype, subadult female 24.2 mm (A–B, D–E: ZMH 64655).A. Pleopod 4, mesial (= caudal) view, most setae broken. B. Pleopod 5, lateral (= rostral) view, most setae broken. C. Uropods, dorsal view, setae omitted. D. Telson, dorsal view. E. Detail of D, showing terminus of telson.