Mysidopsis intii Holmquist 1957
Creators: name: Price, W. Wayne
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Mysida
Mysidae
Mysidopsis
Mysidopsis intii

description: Mysidopsis intii Holmquist, 1957
(Figs. 6–9)
Mysidopsis intii Holmquist, 1957: 23, fig. 6; O. Tattersall, 1969: 66, 68 (key); Băcescu & Gleye1979: 131; Gleye 1982: 320; Price et al., 1994: 684 (table); Langdon et al. 1996: 1815, figs. 1–3; Brandt et al. 1998: 6 (table); Price 2004: 62; Verslycke et al. 2007: 207, 208 (table); Hernández-Payán & Hendrickx 2020: 53 (table); Mees & Meland, 2023 (list).
Remarks. Holmquist’s description of Mysidopsis intii is based on only two 5.0 mm males collected from Canal Chacao, Ancud, Chile over sand at a depth of 6 m with a plankton net that “touched the bottom and contained benthic as well as planktonic species”. The type material consisting of one intact male (Type-3933) and one dissected male (Type-9794) on a slide is housed in the Swedish Museum of Natural History (NRM). The next records of this species are from Southern California in which Băcescu & Gleye (1979) and Gleye (1982) briefly mention its occurrence. In 1996 (Langdon et al. 1996) reported the laboratory culture of M. intii collected from the outer harbor of Los Angeles, California for its potential use in toxicity testing of pollutants from Pacific coastal waters. Although this publication includes illustrations of males and females (lateral, anterior and posterior dorsal views), no morphological information is given in the text. Results for toxicity tests for marine pollutants using M. intii are provided by Langdon et al. (1996) and Harmon & Langdon (1996); Verslycke et al. (2007) includes information on this species in their review of mysids as models for testing endocrine-disrupting chemicals.
Because little morphological information has accrued since the original description of the two males of M. intii, a supplementary description of the male and a description of the previously unknown female are presented. These new descriptions are based on a collection made at a beach just south of Coquimbo, Chile, approximately 1300 km north of the type locality.
Material examined. 1 mature male [BL 4.8 mm (partially dissected)], USNM 1606868; 19 ovigerous females (BL 4.5–5.4 mm), 6 non-ovigerous females (BL 4.1– 4.5 mm), 3 mature males (BL 4.7 –5.0 mm) USNM 1606869; 3 ovigerous females (BL 4.7–5.3 mm), 2 adult males (4.6, 5.6 mm), SCBUCN 5596; Chile, Coquimbo, Elqui, 30°04’26.9’’S, 71°22’30.8’’W,low energy sand beach, kicknet, intertidal zone, depth 0.5–1.0 m, R. Heard coll., 5 Oct 2002.
Diagnosis. Carapace with anterior margin produced into a short, bluntly rounded, subtriangular rostrum, barely extending to proximal part of article 1 of antennular peduncle; moderate cervical sulcus. Antennal scale lanceolate, extending well beyond antennal peduncle, apex rounded with moderately distinct suture; 3.7–3.9 times as long as maximum width. Thoracic endopods 3–8 with carpopropodus 2-articulated, first article 1.2–1.4 times length of second. Male pleopod 1 with uniarticulated endopod, 0.1–0.2 length of 7-articulated exopod. Male pleopod 4 exopod with terminal article having one large apical spiniform biserrate seta and one shorter, more slender, simple seta on disto-lateral margin. Telson entire, linguiform, 1.5–1.7 times as long as wide at base. Lateral margins with 44–57 spiniform setae; 6–9 short, moderately spaced setae along anterior 0.4–0.5 of each margin; posterior 0.5–0.6 of telson densely armed with 15–30 larger setae increasing in length posteriorly on each margin. Apex rounded, with three pairs of setae subequal in length, about 0.08 times length of telson. Uropodal endopod with 30-43 short spines in 8–10 groups of 2–7 spines each extending along straight or slightly undulating ventro-medial margin from region of statocyst to apex.
Description of adult female: General body form (Fig. 6A): moderately robust. Body length to 5.4 mm. Carapace with anterior margin produced into a short, bluntly rounded, subtriangular rostrum, barely extending to proximal part of article 1 of antennular peduncle; carapace with moderate cervical sulcus; postero-dorsal margin broadly emarginate, leaving last thoracic somite exposed.
Eyes (Fig. 6A): Cornea large, calotte-shaped in dorsal view, 1.1–1.2 times as wide as eyestalk, occupying distal 0.4–0.5 of eye, extending to proximal half of article 3 of antennular peduncle. Eyestalk anterior and posterior margins with minute setae basally.
Antennulae (Fig. 6B): Peduncle less robust in females than males; extending 0.7–0.8 times length of antennal scale, 3-articulated. Article 1 subrectangular, 1.6–1.7 times as long as wide, 1.1–1.2 times length of article 3 (measured at dorsal midline), disto-lateral epiprocess with 5-6 plumose setae, lobe near disto-medial margin with 6–7 simple (smooth) and plumose setae. Article 2 short, subtriangular, lobe near disto-medial margin with group of 4–5 simple and plumose setae; 1 long simple seta on disto-medial margin. Article 3 subquadrangular with 1 long plumose seta midway along medial margin of females only; 1 long simple seta and 1 short plumose seta in disto-lateral to mid-lateral region; group of 4–5 simple setae on disto-medial corner; distal border with dorso-medial lobe bearing two large and 1–2 small tooth-like processes and 4 plumose setae. Ventrally, terminal article with flabellum formed by 5 long plumose setae. Outer antennular flagellum slightly thicker than inner.
Antennae (Fig. 6C): Scale lanceolate, extending well beyond antennular peduncle; 3.7–3.9 times as long as maximum width; outer margin straight; inner margin moderately convex; apex with suture, tip about 0.10 times scale length; all margins covered with plumose setae. Peduncle 3-articulated, extending 0.6–0.7 scale length. Article 1 slightly shorter than article 3 and about 0.6 times as long as article 2. Article 2 with 2 plumose setae and 1 simple seta on disto-medial margin and 1 plumose seta on distolateral margin. Article 3 with 6–7 simple and plumose setae on disto-medial margin and 2-3 plumose setae along lateral margin. Sympod with spiniform process on disto-lateral corner.
Labrum (Fig. 6D): Well rounded, slightly asymmetrical, wider than long; anterior margin rounded on ventral surface; middle 0.6–0.7 of bilobed posterior margin with clusters of short fine setae.
Labium (not figured): Paragnaths roughly symmetrical, basis and inner face of each lobe densely setose with mostly fine setae, with spine-like bristles anteriorly.
Mandibles (Fig. 6F–H): Palp 3-articulated; article 1 small with no setae; article 2 with simple setae on most of outer and inner margins. Article 3 0.4–0.5 times as long as article 2, mostly with simple setae, apex with one long moderately curved spiniform seta; distal part of outer margin with 4–5 shorter spiniform setae bilaterally serrated along distal 0.8–0.9 of shaft. Gnathobasic surfaces of both mandibles without molar process. Left mandible, incisor process with series of 9–10 acute or rounded teeth; lacinia mobilis with series of 5–6 subequal teeth; spine row with bristles and 2–4 subequal acute teeth. Right mandible, incisor process with series of one large acute tooth and 5–6 smaller acute or rounded teeth; lacinia mobilis with series of 4–5 acute teeth; spine row with fine bristles and 2–3 large subequal spiniform teeth.
Maxillulae (Fig. 6E): Outer lobe, truncate apex with 9 strong spiniform setae, 7 with bilateral microserrations (middle third or distal half of shaft) and 2 simple setae; inner lobe with two apical setae, one sparsely plumose, the other with microserrations; one smaller microserrated seta about halfway along outer margin.
Maxillae (Fig. 6I): Exopod narrow, reaching about 0.1 length of terminal article of endopod; with 8–10 plumose setae along most of outer margin and apex. Endopod 2-articulated, articulation between endopod and basis inconspicuous, but proximal article appears to be about 0.5 length of distal article; distal article oval-shaped, narrowing distally, 1.9–2.2 times as long as greatest width; apex and inner margin with series of mostly long setae, some simple, some plumose on basal halves and others with microserrations on distal halves. Sympod with three endites; distal two endites with series of simple setae and a few setae bearing microserrations on distal halves; apex of most proximal endite with 4 setae, two with microserrations on distal halves and two plumose.
Thoracic endopods (Figs. 7A–G, 8A): Endopod lengths increase from endopods 1 to 3, decrease from 3 to 8. Distinct dactylus with curved terminal spiniform seta (claw) on all endopods, claws 1 and 2 strongest; claw lengths increase from endopods 1 to 2, decrease from 2 to 3, 3–8 subequal.
Thoracic endopod 1 (Fig. 7A): Short and robust, typical of genus. Epipod leaf-like without setae. Inconspicuous articulation between coxa and basis. Coxa with 1 plumose seta on lateral margin near insertion of exopod, 2 plumose setae on medial margin near insertion of epipod. Basis with 2 short plumose setae on proximo-medial margin, 2–3 microserrated setae on disto-medial border. Merischium (ischium and merus fused) and propodus subequal in length, each about 2 times carpus length, simple and microserrated setae along most of medial margin of merischium. Carpus with 3 microserrated setae (mid-part) on medial margin, 1 large spiniform seta on disto-lateral margin. Propodus bent inward, a few simple and microserrated setae on distal half, mostly on disto-medial and disto-lateral borders, with one stout spiniform seta just medial to disto-lateral margin on anterior face. Dactylus densely setose with row of microserrated setae along medial margin and series of distally hooked spiniform setae on apex and lateral margin.
Thoracic endopod 2 (Fig. 7B): Ischium about 0.5–0.8 length of merus, short and longer simple setae along medial margin, three plumose setae along lateral margin. Merus 0.9–1.3 times longer than carpopropodus, with 2–3 simple setae along mid-third of medial margin and 2 simple setae disto-laterally. Carpopropodus with 1 short and 2 longer simple setae on disto-medial corner; series of several simple, sparsely setose and microserrate setae on distal 0.6 of lateral margin and near lateral margin on anterior face; grouping of 5–6 simple setae on mid-distal border of anterior face. Dactylus width and length subequal, row of simple setae along medial margin and apex; row of biserrate setae on lateral margin, apex and anterior face.
Thoracic endopods 3–8 (Figs. 7C–G, 8A): Basis with soft lobe-like process near disto-lateral margin on anterior face. Ischium length as compared to merus length decreases steadily from 0.8–0.9 (endopods 3, 4) to 0.4–0.6 (endopods 7, 8); distal 0.5–0.7 of medial margin of ischium of endopods 3–5 with series of 8 or more simple setae; endopods 6–8 with 2–6 simple setae along distal 0.4 or less of medial margin. Merus, endopods 3 and 4 1.6–1.8 times length of carpopropodus, endopods 5–8 1.3–1.6 times length of carpopropodus; distal 0.8–0.9 of medial margin armed with simple setae; 4–7 simple setae along distal 0.5–0.7 of lateral margins and distolateral corner. Carpopropodus 2-articulated. First article 1.2–1.4 times length of second. Two unilaterally serrated setae (proximal-mid-part) on disto-lateral half of first article of endopods 3–7. Article 2 apex of endopods 3–8 with 3–4 large simple (paradactylary) setae. Dactylus with simple setae, medial margin with small papilla-like evagination.
Thoracic exopods (Fig. 7A, G): Basal plates rectangular with rounded outer distal corners. Basal plates 1.5–1.8 times as long as greatest width for all exopods. 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 3 (3–7 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 0.8–1.0, 0.6–0.8, 0.6–0.9, 0.6–0.8, and 0.5–0.6 times length of somite 6, respectively.
Pleopods (Fig. 8B–D): Uniarticulate, reduced setose plates. Pleopod lengths (excluding terminal setae)increasing from 1 to 3, 3 and 4 subequal, increasing to 5; pleopod 5, reaching 0.6–0.7 length of abdominal somite 6.
Telson (Fig.8E): Entire, linguiform, 1.1–1.2 times length of last abdominal somite, 1.5–1.7 times as long as wide at base. Lateral margins with 44–57 spiniform setae on posterior 0.8 of telson; 6–9 short, moderately spaced setae along anterior 0.4–0.5 of each margin; posterior 0.5–0.6 of telson densely armed with 15–30 larger setae increasing in length posteriorly on each margin. Apex rounded, with three pairs of setae subequal in length, about 0.08 times length of telson.
Uropods (Fig. 8F): Exopod leaflike, outer margin straight, inner margin moderately convex, setose all around; 1.2–1.3 times as long as endopod, 1.3–1.5 times as long as telson, extending 0.3–0.4 times its length beyond telson. Endopod, outer margin straight or slightly concave, inner margin straight or slightly undulating, setose all around; 1.2–1.3 times as long as telson, extending 0.2–0.3 times its length beyond telson. Ventro-medial margin with 38-43 short spines in 8–10 groups of 2–7 spines each extending from the region of the statocyst to the apex with a plumose seta inserted between each grouping of short spines.
Description of adult male. Morphological features of the male essentially agree with the description of the adult female and Holmquist’s (1957) original description. The following description of the male refers to differences related to size, individual variation and secondary sexual characteristics.
General body form: moderately robust. Body length to 5.6 mm.
Antennulae (Fig. 9A): Article 1 subrectangular, 1.1–1.2 times as long as wide, 0.8–1.1 times length of article 3 (measured at dorsal midline). Article 3 subquadrangular with no long plumose seta near disto-medial margin. Ventrally, terminal article with male lobe (appendix masculina) more than two times longer than wide and densely setose, subequal to combined length of distal 2 articles of peduncle.
Penes (Fig. 9B): Length about 0.7 length of exopodal basal plate of thoracopod 8; well developed, cylindrical. Each penis with two apical lobes with smooth terminal margins.Apex of anterior lobe with 1 long, smooth posteriorly bent seta. Outer face with series of 10 plumose setae.
Thoracic exopods: Lengths (basal plate plus flagellum) increasing from exopods 1 to 3 (3–6 subequal), then decreasing from 6 to 8.
Pleopods (Fig. 9C–E): Pleopod well developed. Lengths (excluding terminal setae) decreasing from 1 to 3, 3 to 5 subequal; pleopods 4 and 5 (excluding terminal setae) reaching 0.5–0.6 length of abdominal somite 6 and end of somite 6, respectively. Basal articles of endopods of all pleopods with rectangular pseudobranchial lobe (exite) bearing 5 plumose setae on outer borders. Pleopod 1, uniarticulated endopod; posterior face with 3 distal simple setae and 1 plumose seta on mid-medial margin; anterior face with group of 5 plumose setae. Exopod 7-articulated, 7–8 times length of endopod. Pleopods 2-5 biramous; endopods and exopods 7-articulated. Endopods slightly shorter than exopods; endopod articles each with 2 plumose setae on distal margins; basal articles with 2–3 plumose setae on medial margin. Basal article of pleopod 5 with large simple seta on lateral 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 and one shorter, more slender, simple seta on disto-lateral margin. Spiniform seta biserrated along distal 0.4–0.5 of its length.
Uropods: Endopod, ventro-medial margin slightly undulating with 30-39 short spines in 8–10 groups of 2–6 spines each extending from the region of the statocyst to the apex with a plumose seta inserted between each grouping of short spines.
Colour. Most ethanol-preserved specimens exhibited moderately heavy black/brown pigmentation on corneas, near postero-ventral margins of abdominal somites 1–5 and dorsally at the base of the telson. Although a few specimens were devoid of pigmentation, diffuse patterns of brown often persisted on the following areas: antennular peduncles, antennal scales, eyestalks, distal articles of thoracic endopods, basal plates of thoracic exopods, posterior-most pair of oostegites, lateral areas of abdominal somites 1–5 and uropods.
Larvae. One female (BL 5.4 mm) carried a full marsupium of 11 postnauplioid larvae, substage P3 (0.93–1.12 mm) (n=5). All other ovigerous females had disturbed marsupia, some with partial broods: one female (BL 4.7 mm with two embryonic larvae, substage E5 (0.31, 0.33 mm); two females (BL 4.60, 4.74 mm) with four or five nauplioid larvae each, substage N3 (0.61–0.78) (n=9).
Habitat. Collected in coastal waters over sand in depths of 0.5–6.0 m by plankton net, epibenthic sled and kicknet.
Type locality. Canal Chacao, Ancud, Chile, 41° 52’ 06’’ N, 73° 50’ 58’’ W, sand, depth 6 m.
Distribution. Chile (Holmquist 1957; present study); Southern California, USA (Băcescu & Gleye 1979; Gleye 1982; Langdon et al. 1996).
description: Published as part of 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), pp. 397-417 in Zootaxa 5399 (4) on pages 406-413, DOI: 10.11646/zootaxa.5399.4.6, http://zenodo.org/record/10513808