Mysidium (Mysidium) integrum W.M. Tattersall, 1951

Wittmann, Karl J. & Wirtz, Peter, 2019, Revision of the amphiamerican genus Mysidium Dana, 1852 (Crustacea: Mysida: Mysidae), with descriptions of two new species and the establishment of two new subgenera, European Journal of Taxonomy 495, pp. 1-48 : 9-11

Mysidium (Mysidium) integrum W.M. Tattersall, 1951

Fig. 2

Mysidium integrum W.M. Tattersall, 1951: 223 –226, fig. 96.

Mysidium integrum – Banner 1954: 447. — Brattegard 1969: 82; 1970: 128; 1973: 50; 1974 a: 69; 1974b: 112, table 1; 1975: 112. — Mauchline 1980: 338 (in list). — Băcescu & Ortiz 1984: 22 (in key). — Modlin 1984: 282; 1987: 115. — Price et al. 1986: table 1; 2002: 46. — Harrison & Bowman 1987: 678 (in comparison). — Zoppi de Roa et al. 1989: 31. — Escobar Briones & Soto 1991: table 1. — Schlacher et al. 1992: table 1. — Ariani et al. 1993: table 1. — Wittmann et al. 1993: fig. 3H. — Price & Heard 2004: 155; 2009: 938 (in list). — Sorbe et al. 2007: table I. — Wittmann et al. 2014: fig. 54.27E. — Ortiz et al. 2017 a: 113; 2017 b: 72. — Ortiz & Lalana 2018: 81.

non Mysidium integrum — Zoppi de Roa et al. 1989: fig. 3.

Type material

Not examined.

Other material examined

CURAÇAO • 18 ♀♀ ad. bl 4.9–6.3 mm, 27 ♂♂ ad. 4.1–5.5 mm, 15 subad.; # C 6; NHMW 26481 • 6 subad. bl 2.8–4.1 mm; # C 7; MINGA MYS 437 • 51 ♀♀ ad. bl 3.8–5.9 mm, 32 ♂♂ ad. bl 4.0– 5.1 mm, 5 subad.; # C 9; MINGA MYS 437 • 88 ♀♀ ad. bl 3.8–5.9 mm, 25 ♂♂ ad. bl 3.2–5.2 mm, 20 subad.; # C 10; ZMH K- 55261 .

SE-BRAZIL • 6 ♀♀ ad. bl 4.8–6.0 mm, 33 ♂♂ ad. bl 4.3–6.1 mm, 6 subad.; # F 13; ZMH K- 55265 .

Type locality

Tropical NW-Atlantic, Cruz Bay, St. John, Virgin Islands ( W.M. Tattersall 1951). Coordinates estimated by present authors as 18.3322° N, 64.7967° W.

Revised definition

All features diagnosed above for genus and subgenus Mysidium Dana, 1852 . Cornea globose in lateral view; calotte-shaped in dorsal view, with diameter 1.6–2.4 times as long as terminal segment of antennular trunk. Eyestalks smooth. Rostrum broadly triangular, apically bluntly pointed to well rounded, not extending beyond basis of eyestalks. Antero-lateral edges of carapace rounded. Only males with anterior margin of antennular trunk dorsally with rounded, shield-like, mediodistal extension ( Fig. 2A–B ); longitudinal series of 4–6 setae all over this extension plus a short proximal stretch. The largest seta 0.3–0.5 times extension length. Appendix masculina bilobate, all along inner margins fringed by large setae; its length 1.1–2.5 times terminal segment of antennular trunk. Length of antennal scale 4–5 times maximum width; scale reaching well beyond antennular trunk. Median segment of mandibular palp with setae on both margins. Weak, about evenly rounded hump on outer face of distal segment of the maxillula. Carpopropodus of first to eighth thoracic endopods with 2, 2, 3, 3, 3, 3–2, 3–2, and 2–3 segments, respectively. Basal segment occupies half total length of carpopropodus of endopod 3. Pleopod 1 representing a stout, bilobate plate in both sexes. Sympod of male pleopod 4 with endite reduced to weak medial hump or missing. Basal segment of exopod measures 49–63% total length. Endopod reduced to setose lobe with 11–24% sympod length; apically with 1–2 setae and more proximally additional 4–6 barbed setae, total of 5–7 setae. Endopod of uropods 0.7 times as long as exopod. Telson spatulate, caudally gradually narrowing; length 1.5–1.8 times maximum width near basis; latero-terminal corners rounded; terminal margin traverse to convex. Proximal 52–62% of lateral margins smooth, distal portion of each margin with dense, continuous series of 13–25 acute spines. This series extending up to the latero-terminal corner. Terminal margin lined by 12–20 densely set, acute ( Fig. 2G ) or blunt ( Fig. 2H ) laminae. These laminae more slender compared to the neighboring lateroterminal spines.

Descriptive notes

Adult females of present material with 3.8–6.3 mm (n = 163) body length, males 3.2–6.1 mm (n = 117). Antennular trunk extends 9–57% its length beyond (artificially aligned) eyes ( Fig. 2A ). Antennal scale 1.3–1.5 times as long as trunk. Sympod of antenna produced into spiniform extension on outer distal corner. Thoracic endopod 8 (when stretched) reaching backwards at most to middle of pleonite 4 and forwards to mandibles; its carpopropodus 69–84% as long as merus or 38–53% times telson length. Pleonites 1–5 are 0.6–0.8, 0.6–0.7, 0.6–0.7, 0.5–0.6 or 0.6–0.7 times as long as pleonite 6, respectively. Sizes increase from pleopods 1 to 4, while pleopod 5 ranges between 1 and 2 in both sexes; amplitude of this variation much stronger in males than females. Pleopod 1 ( Fig. 2D ) stouter compared to the remaining pleopods. Pleopods 2–5 of females and 2, 5 of males are essentially rod-like. Pleopods 1–3 with a ventro-laterally directed fan of plumose setae in both sexes. Setae forming the fan of pleopod 1 are larger compared to those of pleopods 2–5 in females and 2, 3, 5 in males. Male pleopod 4 ( Fig. 2F ) reaching at most to basal third of telson, its subapical seta up to basal third of uropodal exopod. Sympod with field of scales on its medial hump, or in analogous position upon missing hump. Endopod with its larger apical seta 1.8–3.1 times endopod length. Scutellum paracaudale triangular with acute apex; upper margin convex to concave, lower margin straight to slightly convex or S-shaped. Uropodal endopod 1.1–1.2 times, exopod 1.6–1.8 times as long as pleonite 6. Exopod extends 0.2–0.4 times its length beyond endopod, or 0.6–0.7 times beyond telson; endopod 0.5–0.6 times its length beyond telson. Telson ( Fig. 2G–H ) length 0.4–0.5 times uropodal exopod, 0.5–0.7 times endopod or 0.7–0.8 times pleonite 6. Statoliths composed of fluorite. Structure of foregut and nauplioid larvae essentially as in M. triangulare sp. nov. ( Fig. 8A–F, M–N ).

Distribution and habitat

Reported from euhaline coastal waters of Bermuda, Bahamas, Caribbean and Gulf of Mexico ( Brattegard 1970, 1973; Ortiz et al. 2017 b). The present record from the Brazilian coast off Cabo Frio represents a strong extension of the known distribution to the south, yielding a total range from 32° N to 23° S along the coasts of the West Atlantic. According to Zoppi de Roa & Alonso (1997) these mysids form swarms close to the bottom of diverse coral reef and mangrove habitats, also found among spines of the sea urchin Diadema antillarum . The present data from Curaçao and SE-Brazil were recorded during the daytime at a depth of 0–35 m, on swarms mostly hovering around, between or above rock and coral blocks, also from the entrance area of a cave. Most surprising was sample C9 ( Table 1) from the water edge where the mysids showed a striking green body color upon swarming above algae at a depth of only 5 cm.

Figures

Fig. 2. Mysidium integrum W.M. Tattersall, 1951, from Curaçao (A–G) and off Cabo Frio in Brazil (H), non-types. A. ♂, 5.1 mm body length. B. ♂, 5.3 mm. C–G. ♂, 4.6 mm. H. ♂, 6.8 mm. A. Cephalic region; left antennula and setae of antennal scale omitted. B. Mediodistal extension of right antennular trunk, dorsal view. C. Third thoracic endopod, caudal view. D–E. Pleopods 1 and 3, rostral view. F. Pleopod 4, caudal view. G–H. Telson variants. Sample affiliation: Curaçao #C3 (A, C–G), #C9 (B); Brazil #F13 (H)

Fig. 8. Mysidium triangulare Wittmann sp. nov., from Curaçao, paratypes. A–F. ♀, 5.9 mm body length. G, J. ♀, 5.1 mm. H, K–L. ♂, 5.5 mm. A. Foregut; dorsal wall omitted. B–F. Details of panel (A) showing modified spines. G. Basal half of thoracopod 7 with right oostegite, lateral view. H, J. Variants of scutellum paracaudale, lateral view. K. Uropods, ventral view; setae omitted. L. Telson. M. Nauplioid larva at substage N2, lateral view. N. Detail showing tip of abdomen in another nauplioid specimen.