Schizurakrops meesi Wittmann, 2024, gen. et sp. nov.

Schizurakrops meesi gen. et sp. nov.

urn:lsid:zoobank.org:act: A99E05AD-A910-483E-B6EE-B03FB5C839DE

Figs 54–57

Diagnosis

Based on adult female only. All features as in generic diagnosis. Rostrum reaching beyond antennal scale. Eye rudiments with strong tooth-like anterior projection extending beyond basal segment of antennular trunk; this segment without ventral carina. Antennal sympod with three teeth near disto-lateral edge; median segment of peduncle five times as long as basal segment; scale length four times as long as maximum width. Blade-like extension of clypeus proceeds anteriorly between antennae up to end of second segment of antennular trunk. Uropods without spine. Telson trapezoid not considering terminal incision. Terminal incision ⅐ of telson length, lined all along with densely-set, slender laminae. Lateral margins distally converging; basal 3/10 bare except for small stand-alone spine at ⅕ of telson length from basis; distal 7/10 with discontinuous series of large spines with 1–2 small spines in between; large spines increasing in length distally. Each disto-lateral lobe with two spines, outer spine ⅔ length of incision, inner spine ⅓. Telson with total of ≈ 34 spines and ≈ 35 laminae, no setae.

Etymology

The species name is a noun with Latinized masculine ending in genitive singular, dedicated to Jan Mees in recognition of his important contributions to the taxonomy and ecology of mysids.

Material examined

Holotype SOUTHERN OCEAN • 1 ov. ♀ ad. (BL = 13.8 mm, on slides); 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 64685.

Type locality

The type locality is ANDEEP III station 150-6: Powell Basin, SW continental slope of South Orkney Islands, 61°48.70ʹ S, 47°28.04ʹ W to 61°48.57ʹ S, 47°28.19ʹ W, depth 1996– 1993 m.

Description

Holotype (♀)

All features as in specific diagnosis. Female with BL 13.8 mm carried eleven eggs with a diameter 0.64–0.67 mm. Rostrum contributing 11% to BL, carapace 26% (without rostrum), thorax 29%, pleon 44% and telson 16%. Carapace with smooth surface, disto-lateral edges well rounded (Fig. 55D), no pores. Eye rudiments (Fig. 55A) dorsoventrally compressed by a factor of 4.7, without pigment, no pores, no organ of Bellonci.

ANTENNULA (Figs 54A, 55A). Basal segment of trunk with disto-lateral, setose lobe extending beyond proximal half of median segment. Basal and median segments each with dorsal apophysis bearing a few setae on tip. Terminal segment about as long as combined median and basal segments (not counting apophyses). Terminal segment with disto-median lobe armed with three barbed setae and with three teeth, teeth increasing in length laterally (as in Fig. 33C). Basal portion of mesial flagellum 0.8 times as wide as base of lateral flagellum.

ANTENNA (Fig. 55B). Sympod 2-segmented, caudally in addition with large end sac of antennal gland. Sympod with two strong teeth, one above and one below basis of antennal scale, a third strong tooth on disto-lateral edge; distally rounded, linguiform lobe mesially positioned near peduncle. Peduncle 3-segmented, its basal segment contributing 11%, median segment 60% and terminal segment 30% to total length. Basal segment bare, median segment with a few barbed setae near distal margin, terminal segment with a few setae on distal, mesial and lateral margins.

PRIMARY MOUTHPARTS (Fig. 55E–I). Labrum and labium normal (Fig. 55E, I). Mandibular palp (Fig. 55F) with basal segment contributing 9%, median segment 59% and terminal segment 32% to total palp length. Palp not hispid, its basal segment without setae, median segment setose along both margins. Length of median segment 2.6 maximum width, its mesial margin convex, lateral margin sigmoid. Terminal segment 3.7 times as long as broad and 0.6 times as long as median segment. Terminal segment well setose, with dense series of short microserrated setae on distal ⅖ of lateral margin. Right mandible (Fig. 55H) with three large teeth on pars incisiva and with only two smooth blunt teeth on small digitus mobilis. Pars centralis modified, with continuous series of 13 smooth, subtriangular, tooth-like spines, proximally (with respect to mouth field) decreasing in basal width rather than length. Processus molaris with most masticatory lamellae bearing small teeth. Left mandible (Fig. 55G) essentially as in most Mysidae, pars incisiva with three large teeth, digitus mobilis with one large plus five small, blunt, distal processes. Pars centralis with six slender spines bearing stiff bristles. Processus molaris with strong grinding lamellae, and with minute teeth on and close to proximal edge. Processus molaris of both mandibles with bundle of stiff bristles on ventro-lateral edge (distally with respect to mouth field).

GUT (Fig. 56). Foregut with normal gross structure. Spines similar to those of Stellamblyops doryphorus sp. nov. (Fig. 52). Lateralia of Schizurakrops meesi gen. et sp. nov. with dense series of slender, apically pronged spines (Fig. 56B 1 –B 2) coated with tiny teeth along most of shaft. Lateralia also with slender, seta-like spines (Fig. 56C) coated with micro-teeth most densely along distal half. Posterior part of lateralia with complex of about ten serrated (toothed) spines of various sizes (Fig. 56D). Dorsolateral infoldings on each side with three larger spines, unilaterally serrated on ⅕ to ⅔ of length from basis (Fig. 56E). Three large toothed spines (Fig. 56F) at half foregut length to the right appear not fixed to foregut and show no counterparts to the left; their affiliation with S. meesi appears unclear (extraneous origin not excluded). Foregut with almost full storage volume containing great numbers of crustacean remains, also sponge spicules, foraminiferans, masticated organic material and mineral particles. Midgut less densely filled with finely masticated material. Anal lobe distinct, weakly cuticularized (dashed line in Fig. 57J).

MAXILLULA (Fig. 55J–K). Distal segment with 11–12 strong spines on transverse terminal margin; the most distal spine smooth, remaining spines mostly unilaterally, also bilaterally serrated, armed with acute to blunt micro-teeth (examples in Fig. 55K). This segment subterminally with three setae bearing long, stiff barbs. Lateral margin of basal segment furnished with longitudinal, comparatively long series of densely set, long hairs. Endite terminally with three large, distally spiny (by stiff bristles) setae flanked by several less strong, shorter setae.

MAXILLA. Most similar to that of Stellamblyops doryphorus sp. nov. (Fig. 51H). Sympod with three mesial, only distally strongly setose lobes. Additional mesial protrusion short, not clearly classified as lobe. Exopod extends shortly beyond basal segment of palp. Exopod with numerous plumose setae all along lateral margin; tip with 2–3 large plumose setae almost twice as long as largest lateral setae, mesial margin bare. Palp with two segments subequal in length. Apical segment 1.6 times as long as maximum width. Basal segment less wide, its mesial margin with two barbed, basally thick setae in subbasal position, and with a smaller barbed seta in subterminal position. Distal ⅗ of apical segment with well setose margins, proximal ⅖ bare, no spines.

THORACOPODS (Fig. 57A–D). Intersegmental joints between sternites and sympods 2 and 5–7 with basally thick, all along barbed seta (Fig. 57C); on sympod 6 accompanied by one smaller seta of that type. Such setae not seen, possibly broken on sympods 3–4 and 8, though expected in analogy to D. benthophilus sp. nov. (Fig. 7H). Basal plates of exopods 2 and 5–6 slender, disto-lateral edge with tooth-like projection (Fig. 57C); flagellum of these exopods with ten segments; remaining exopods broken. Basis of endopod 1 with setose endite (below drawing plane, visualized as dashed line in Fig. 57A), remaining segments without endite. Endopod 1 strongly setose along mesial margin, much less along lateral margin; its smooth apical nail (Fig. 57B) slightly longer than propodus. Epipod 1 (Fig. 57A) linguiform, about as long as combined ischium, merus, and carpus of endopod 1; tip with five minute bristles. Endopod 2 (Fig. 57C) with six segments including basal segment, the latter fused with sympod; ischium and dactylus strongly setose, remaining segments less setose; no endites; dactylus not reflexed, claw (Fig. 57D) smooth, slender, about as long as dactylus. Endopods 3–8 broken.

MARSUPIUM (Fig. 57E). Oostegites with smooth cuticle on outer and inner faces, not counting setae. Proximal portion of oostegites 1–3 on inner face with 5–8, 8–10 and 10–13 long setae, respectively; setae microserrated by series of stiff, acute bristles along distal half. Oostegite 1 with only two additional, plumose setae near terminus. In contrast, oostegites 2–3 with ventral and anterior margins plus part of posterior margin bearing dense series of setae contributing to ventral and caudal, ventilation-pervious closure of marsupium. Proximal setae smooth but numbers of barbs per seta increase distally, yet not attaining configuration of typical plumose seta. Basal portions of dorsal margin without setae in oostegites 2–3. Only oostegite 3 with numerous slender whip setae loosely scattered over its outer face.

PLEON AND TAIL FAN (Figs 54A, 57F–K). Pleomeres 1–5 are 0.6, 0.5, 0.6, 0.4 and 0.5 times as long as pleomere 6, respectively (Fig. 54A); this value 1.2–1.3 for exopod of uropods, 1.2 for endopod and 1.4 for telson (telson inserts more rostrally than rami of uropods). Pleopods 1–5 representing distally widening plates bearing narrow digitus on top; setation as in Fig. 57F–H. Pleopod length increasing caudally. Scutellum paracaudale triangular. Statoliths composed of fluorite, diameter only 0.08–0.10 mm (n = 2). Lateral margins of telson (Fig. 57J–K) (almost) straight, no pores or scales detected.