Mysidopsis jenseni, Price, 2024

Price, W. Wayne, 2024, Mysidopsis jenseni n. sp. from the Pacific coast of Washington, with first description of female M. intii Holmquist, 1957 (Crustacea: Mysida: Mysidae), Zootaxa 5399 (4), pp. 397-417 : 399-406

Mysidopsis jenseni n. sp.

( Figs 1–5 )

Type material. Holotype: adult female (Body length [BL] 10.9 mm), Sekiu , Strait of Juan de Fuca, Washington, USA, 48° 16’ 2.40’’ N, 124° 17’ 51.18’’ W, sand, manual collection using SCUBA with re-sealable zipper storage bags, depth 8.0 m, G. Jensen coll., 2 Mar 2003, USNM 1606864 ; Paratypes: 2 adult males [BL 8.7, 8.1 mm (partially dissected)], USNM 1606865 ; 1 ovigerous female [BL 8.5 mm (dissected)], USNM 1606866 ; 2 ovigerous females ( BL 9.6 , 9.2 mm) , 1 subadult female ( BL 6.4 mm) USNM 1606867 ; Alki Point , Puget Sound, Seattle, Washington, USA, 47° 34’ 44.82’’ N, 122° 34’ 54.06’’ W, sand/algae/eelgrass, manual collection using SCUBA with re-sealable zipper storage bags, depth 8–15 m, G. Jensen , R. Green coll., 3 Feb 2020 .

Diagnosis. Carapace with anterior margin produced into a subtriangular rostrum with a rounded tip extending mid-length to distal end of article 1 of the antennular peduncle; distinct cervical sulcus. Females with ovoid to trilobed lappet attached near midline of postero-dorsal margin of carapace. Antennal scale lanceolate, apex rounded with indistinct suture, 3.4–3.9 times as long as maximum width. Thoracic endopods 3–8 with carpopropodus 3- articulated, middle article 0.3–0.5 length of other two articles. Male pleopod 1 with uniarticulated endopod, about 0.2 length of 10-articulated exopod. Male pleopod 4 exopod with terminal article having one large apical spiniform seta, biserrate along distal 0.4–0.5 of its length. Telson entire, linguiform, 1.4–1.5 times as long as wide at base; lateral margins with 21–25 short spiniform setae along each entire margin; apex rounded, with two pairs of fairly stout spiniform setae, inner pair longer, about 0.08 times length of telson, outer pair shorter, 0.65-0.75 times length of inner setae; spacing between the inner pair of setae at base equal to basal width of either seta; spacing between the inner and outer setae at base less than basal width of either seta. Uropodal endopod with 8–9 spiniform setae along ventro-medial margin extending distally from region of statocyst.

Description. General body form ( Figs. 1A–F , 2A, B ): robust, adult males to 8.7 mm and females to 10.9 mm in length. Carapace with anterior margin produced into a subtriangular rostrum; carapace with distinct cervical sulcus; postero-dorsal margin broadly emarginate, leaving last 1 or 2 thoracic somites exposed. Females with ovoid to trilobed lappet attached close to midline of margin; antero-lateral and postero-lateral margins rounded.

Eyes ( Fig. 2A ): Cornea large, globular, slightly broader than eyestalk, occupying distal 0.5–0.6 of eye, extending to distal half of article 3 of antennular peduncle.

Antennulae ( Fig. 2C, D ): Peduncle more robust in males than females, extending 0.5– 0.75 times length of antennal scale; 3-articulated. Article 1 subrectangular, 1.0–1.5 times length of article 3, disto-lateral epiprocess with 4-6 plumose setae, lobe near disto-medial margin with 3–5 simple (smooth) and 2–4 plumose setae. Article 2 short, lobe near disto-medial margin with 5–7 simple setae and plumose setae in both sexes; 1 long plumose seta on disto-medial margin, reaching distal end of article 3 in females only. Article 3 subquadrangular with 1 long plumose seta near disto-medial margin of females only; in both sexes, 1 long simple seta and 1 short plumose seta in disto-lateral to mid-lateral region; group of 2–3 simple setae on disto-medial margin; distal border with dorso-medial lobe bearing two large tooth-like processes and 3–5 plumose setae. Ventrally, females with flabellum formed by several long plumose setae; males with male lobe (appendix masculina) large and densely setose, longer than combined distal 2 articles of peduncle. Outer antennular flagellum slightly thicker than inner.

Antennae ( Fig. 2F ): Scale lanceolate, extending well beyond peduncle; 3.4–3.9 times as long as maximum width; outer margin slightly concave to straight; inner margin moderately convex; apex with indistinct suture, tip about 0.06 times scale length; all margins covered with plumose setae. Peduncle 3-articulated. Article 1 slightly shorter than article 3 and about half as long as article 2. Article 2 with 2 plumose setae and 1–2 simple setae on inner disto-medial margin and 1 simple seta on outer distal margin. Article 3 with 4 simple setae and 2 plumose setae on inner disto-medial margin and 3 plumose setae along outer distal margin. Sympod with rounded process on distolateral corner.

Labrum ( Fig. 2G ): Well rounded, wider than long, middle 3/4 of bilobed posterior margin with cluster of short fine setae on one side of emargination and short coarse setae on the other.

Labium ( Fig. 2E ): Paragnaths roughly symmetrical, basis and inner face densely setose, with spine-like bristles anteriorly.

Mandibles ( Fig. 2H–J ): Palp 3-articulated. Article 1 small with no setae. Article 2 with simple setae on outer, inner, and distal margins.Article 3 0.4–0.5 times as long as article 2, mostly with simple setae, but disto-lateral margin with 6–7 short spiniform setae bilaterally serrate along distal 0.7 of length. Gnathobasic surfaces of both mandibles without molar process. Left mandible, incisor process with 2 large teeth and series of 6–7 smaller rounded or blunt teeth; lacinia mobilis with series of 5–6 strong subequal teeth; spine row with bristles and 4 subequal spiniform teeth. Right mandible, incisor process with 5–6 teeth; lacinia mobilis spherical process with cluster of 6–7 tuberculate teeth; spine row with bristles and series of 4–5 fairly equally spaced spiniform teeth decreasing in size distally.

Maxillulae ( Fig. 3C ): Outer lobe with 9 strong setae on transversely truncate apex; inner lobe with three apical setae and one smaller seta along outer margin. All setae appear microserrated along a part of their distal halves.

Maxillae ( Fig. 3D ): Exopod relatively narrow, reaching 0.3–0.4 length of terminal article of endopod; with 11–12 plumose setae along most of outer margin, apex and distal 0.10–0.15 of inner margin. Endopod 2-articulated, distal article oval-shaped, narrowing distally, 2.0–2.1 times as long as greatest width; apex and inner margin with series of mostly large basally plumose setae; basal article 0.3-0.4 times length of distal article. Three endites of sympod with mostly simple robust setae; only most distal and most proximal endites with two plumose setae each.

Thoracic endopods ( Figs. 3A, B, E, F ; 4A–D ): Lengths increase from 1 to 4, then decrease from 5 to 8. Distinct dactylus with strong, curved terminal spiniform seta (claw) on all endopods; claw length increasing from endopods 1–4, decreasing discontinuously from 5–8.

Thoracic endopod 1 ( Fig. 3B ): Short and robust, typical of genus. Epipod leaf-like with large simple seta proximally. Coxa with endite on disto-medial margin terminating in 1 long plumose seta. Basis with group of 4–5 simple setae on disto-medial border. Ischium and merus fused (merischium), about 1.5 times carpus length, slightly shorter than combined propodus and dactylus lengths; simple setae along medial margin. Carpus with 2 simple setae on medial margin, 1 seta on disto-lateral margin. Propodus bent inward, several simple setae on distal half, mostly on disto-lateral and disto-medial borders. Dactylus densely setose with series of distally hooked and distally attenuated, curved simple setae.

Thoracic endopod 2 ( Fig. 3A ): Ischium about 0.8–0.9 length of merus, mostly long simple setae along medial margin, single long plumose seta disto-laterally. Merus 1.1–1.2 times longer than carpopropodus, with 3 simple setae on distal half of medial margin and 2–3 simple setae and 1 long plumose seta disto-laterally. Carpopropodus with 1 long and 2–3 shorter simple setae on disto-medial corner; dense grouping of simple and biserrate setae (basal part) on distal 0.4 of lateral margin. Dactylus width slightly greater than length, row of simple setae along inner margin and apex, row of biserrate setae on outer margin and apex.

Thoracic endopods 3–8 ( Figs. 3E, F , 4A–D ): Basis with soft lobe-like process near disto-lateral margin on anterior face. Ischium length as compared to merus length decreases steadily from 1.4 (endopod 3) to 0.8–0.9 (endopods 7, 8); distal 0.6–0.9 of medial margin of ischium of endopods 3–6 with series of simple setae; endopods 7 and 8 with simple setae along distal 0.4 or less of medial margin. Merus 1.1–1.4 times as long as carpopropodus, distal 0.75 of medial margin densely setose with simple setae; endopods 3–5 with 2–5 unilaterally serrate setae (proximal-mid-part) and 1–5 spiniform setae along distal 0.6 of lateral margins. Carpopropodus 3-articulated; middle article 0.3–0.5 length of other two articles. Two unilaterally serrate setae (proximal-mid-part) on disto-lateral corner of first article of endopods 3–5. One unilaterally serrate seta (proximal-mid-part) on disto-lateral corner of second article of endopods 3 and 4. Article 3 apex of endopods 3–8 with 3–4 large simple (paradactylary) setae. Dactylus with simple setae, medial margin with small papilla-like evagination.

Penes ( Fig. 5A ): Length subequal to length of basis of thoracopod 8; well developed, cylindrical. Each penis with two apical lobes, anterior lobe widest distally with 1 apical and 1 subapical smooth posteriorly bent seta, posterior lobe without setae. Distal half of outer face with series of 4–5 plumose setae.

Thoracic exopods ( Figs. 3B , 4C ): Basal plates rectangular with rounded outer distal corners. Basal plates 1.5– 1.8 times as long as wide for exopods 1–6, 2.2–2.6 times for exopods 7 and 8. Flagella of exopods 1 and 8 each with 8 articles, flagella of exopods 2–7 each with 9 articles. Lengths (basal plate plus flagellum) increasing from exopods 1 to 4 (4–7 subequal) then decreasing from 7 to 8.

Marsupium: Female thoracopods 6–8 with pairs of developed oostegites; first pair smaller than posterior ones.

Abdomen: Abdominal somites 1–5 are 0.9–1.0, 0.6–0.7, 0.6–0.7, 0.6–0.7, and 0.6–0.7 times length of somite 6, respectively.

Pleopods: Female ( Fig. 4E– G ), uniarticulate, reduced setose plates Pleopod lengths (excluding terminal setae) increasing from 1 to 3, 3 and 4 subequal, increasing to 5; pleopod 5, reaching about 0.5–0.7 length of abdominal somite 6. Male pleopods ( Fig. 5B–D ) well developed. Lengths (excluding terminal setae) increasing from 1 to 2, 2 to 4 subequal, decreasing to 5; pleopods 4 and 5 reaching 0.1–0.4 length of telson. Basal articles of endopods of all pleopods with rectangular pseudobranchial lobe (exite) bearing 4–5 plumose setae on outer borders. Pleopod 1, uniarticulated endopod with 1 distal simple seta and 1 plumose seta on mid-medial margin; anterior face with group of 5–6 plumose setae; exopod 10-articulated, about 5 times length of endopod. Pleopods 2-5 biramous, endopods and exopods 9–10-articulated. Endopods slightly shorter than exopods; endopod articles each with 2 plumose setae on distal margins; basal articles with 1–2 plumose setae on medial margin and anterior face, respectively; basal article of pleopod 5 with large plumose seta on distolateral margin. Exopods 1–5, articles each with 2 plumose setae on distal margins, except for terminal article of exopod 4. Exopod 4 with terminal article having one large apical spiniform seta, biserrated along distal 0.4–0.5 of its length; seta as long as the 4–5 distal articles of exopod combined.

Telson ( Fig. 5F ): Entire, linguiform, 1.1–1.3 times length of last abdominal somite, 1.4–1.5 times as long as wide at base. Lateral margins moderately concave with 21–25 short spiniform setae along each entire margin, anterior half of margins with 6–7 slightly longer moderately spaced setae, posterior half with shorter more closely spaced setae. Apex rounded, with two pairs of fairly stout spiniform setae, inner pair longer, about 0.08 times length of telson, outer pair shorter, 0.65-0.75 times length of inner setae; spacing between the inner pair of setae at base equal to basal width of either seta; spacing between the inner and outer setae at base less than basal width of either seta. Most posterior pair of lateral setae about 0.6 times length of outer apical setae.

Uropods ( Fig. 5E ): exopod oblong, outer margin straight to slightly convex, inner margin moderately convex, setose all around; 1.4–1.5 times as long as endopod, 1.2–1.3 times as long as telson, extending about 0.3 times its length beyond telson. Endopod, outer margin concave, inner margin straight, setose all around; 0.8–0.9 times as long as telson, extending about 0.1 times its length beyond telson. Proximal 0.6–0.7 of ventro-medial margin with a series of 8–9 mostly subequal spiniform setae extending distally from region of statocyst, proximal spines more crowded than distal ones.

Colour. ( Fig. 1 ) The general appearance of live specimens observed in situ and the laboratory occurred in four color morphs: brown (raw umber/burnt sienna), yellowish orange, red and pale/translucent. Consistent features for all morphs included the transparency of the posterior portion of the telson and distal portions of the uropods.Also, the antennular and antennal flagellae and scales appeared to be mostly transparent. The most often encountered morph was brown and exhibited a raw umber to burnt sienna cephalothorax, carapace and thoracic legs with numerous torquoise-blue chromatophore spots and patches. Females exhibited raw umber oostegites and brown to raw umber lapettes often with beige distal portions or borders. Live specimens of both sexes had burnt sienna eyes, antennular and antennal peduncles with few turquoise spots. Each abdominal somite showed uniformly raw umber to burnt sienna pigmentation or had lighter pigmentation anteriorly and darker posteriorly. Specimens preserved in ethanol retained some diffuse brown pigmentation on most of the body without torquoise-blue chromatophore spots and patches. Heavier pigmentation persisted at times near postero-ventral margins of abdominal somites 1–5, posterior portion of somite 6, dorsal base of telson, and posterior-most pair of oostegites.

Eggs. An 8.5 mm female carried a full marsupium containing 17 eggs (diameter 0.42–0.48 mm) (n=7).

Etymology. The species name is dedicated to Gregory C. Jensen, who photographed, collected and made observations on behavior and coloration of the new species over a period of two decades. The dedication is also made in recognition of his contributions to the study of the marine invertebrate fauna of the west coast of North America.

Habitat/Behavior. Solitary individuals cruised slowly or hovered just above open sand bottoms or among rocks occasionally landing on scraps of algae or eelgrass, Zostera marina in depths of 8 to 15 m. The dorsal lappet of females was kept upright unless folded down when subjected to strong currents or surges.

Type locality. Sekiu , Strait of Juan de Fuca, Washington, USA, 48° 16’ 2.40’’ N, 124° 17’ 51.18’’ W, sand, depth 8 m.

Distribution. At present, confirmed specimens are known only from the Puget Sound area along the coast of Washington, USA. A possible occurrence of the new species was recorded in a photograph from Catalina Island, California (https://www.diverkevin.com/NorthAmerica/Invertebrates-Eastern-Pacific/Crustaceans-Eat/i-sd44CrC/ A), but confirmation awaits the availability of specimens from this area for morphological study.

Figures

FIGURE 1. Mysidopsis jenseni n. sp.: in situ images of ovigerous females (A–D) and laboratory images of adult males (E–F) photographed or collected from sand or hard substrates in subtidal habitats of the Puget Sound area, Washington, USA. Photographs by Billy Ball (C)), Gregory Jensen (A, D–F) and Sara Thiebaud (B).

FIGURE 2. Mysidopsis jenseni n. sp. adult female BL 8.5 mm (A–C, E–J), adult female BL 10.9 mm (B), subadult female BL 6.4 mm (B). adult male BL 8.1 mm (D). A. Dorsal view. B. Lappets, lateral, variation in morphology. C. Left antennula, female, dorsal. D. Right antennula, male, dorsal. E. Labium with part of sternum, posterior. F. Right antenna, dorsal. G. Labrum, posterior. H, I. Gnathobasic parts of right (H) and left (I) mandibles, posterior. J. Left mandibular palp, posterior. Scale: A, 1.0 mm; F, 0.25 mm; B, D, 0.20 mm; C, J, 0.15 mm; E, G–I, 0.10 mm.

FIGURE 3. Mysidopsis jenseni n. sp. adult female, BL 8.5 mm (A–F). A. Thoracic endopod 2, posterior with enlargement of modified seta from dactylus. B. Thoracopod 1, anterior with enlargement of distal end (posterior). C. Maxillule. D. Maxilla. E. Right thoracic endopod 3, anterior. F. Right thoracic endopod 4, anterior with enlargement of modified setae from merus and carpopropodus. Scale: A, E, F, 0.2 mm; B, 0.25 mm; C, D, 0.1 mm.

FIGURE 4. Mysidopsis jenseni n. sp. adult female, BL 8.5 mm (A–G). A. Right thoracic endopod 5, anterior. B. Right thoracic endopod 6 with enlargement of dactylus, anterior. C. Right thoracopod 7, anterior. D. Right thoracic endopod 8, anterior. E. Right pleopod 1, anterior. F, G. Left pleopods 4, 5, anterior. Scale: A–D, 0.2 mm; E–G, 0.1 mm.

FIGURE 5. Mysidopsis jenseni n. sp. adult female, BL 8.5 mm (E–F), adult male, 8.1 mm (A–D). A. Penis. B. Right pleopod 1, posterior with enlargement of endopod. C, D. Right pleopods 4, 5, posterior. E. Right uropod, ventral. F. Telson, dorsal. Scale: A, 0.1 mm; B–F, 0.2 mm.