Mysidium (Mysidium) rubroculatum Băcescu & Ortiz, 1984

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 : 14-16

Mysidium (Mysidium) rubroculatum Băcescu & Ortiz, 1984

Fig. 4

Mysidium rubroculatum Băcescu & Ortiz, 1984: 20 –21, fig. 1F–P.

Mysidium rubroculatum – Harrison & Bowman 1987: 674 (in comparison). — Ortiz & Lalana 1988: 14 (in list); 2018: 73. — Escobar-Briones & Soto 1991: table 1. — Ortiz 2001: 100 (in list). — Petrescu & Wittmann 2009: 64. — Price & Heard 2009: 939 (in list). — Ortiz et al. 2017a: 113; 2017b: 79–81.

Type material examined

Paratypes CUBA • 10 ♀♀ ad. bl 3.7–4.8 mm, 7 ♂♂ ad. bl 3.5–3.8 mm, 2 ♂♂ subad.; 10 m; Sep. 1983; Manolo Ortiz leg.; Mihai Băcescu det.; MINGA 49342 /600 .

Type locality

Miramar, La Habana, Cuba ( Băcescu & Ortiz 1984), 23.1334° N, 82.3334° 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 1.9–2.9 times as long as terminal segment of antennular trunk. Eyestalks smooth. Rostrum (sub)triangular, with rounded to acute apex, rostrum 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. 4A– B ) bearing a longitudinal series of 4–5 setae. The largest seta 0.1–0.3 times extension length. Appendix masculina bilobate, along inner margins fringed by large setae; its length 1.3–2.0 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. Large, moderately unevenly rounded hump on outer face of distal segment of the maxillula. Carpopropodus with two segments in thoracic endopods 1–2, 8, versus three segments in endopods 3–7. Basal segment occupies half total length of carpopropodus of endopod 3. Pleopod 1 minute, rod-like ( Fig. 4D ) in both sexes, not considering the weak median widening at its vestigial endopodal portion. Sympod of male pleopod 4 with endite reduced to a weak medial hump or missing. Exopod with basal segment occupying 52–63% total length. Endopod reduced to lobe with 13–17% sympod length; apically with a long seta plus a minute seta and more proximally 2–4 additional small barbed setae. Endopod of uropods 0.7–0.8 times as long as exopod. Telson subrectangular, caudally narrowing by 30–54%; length 1.5–1.8 times maximum width near basis; lateral margins slightly concave to almost straight; latero-terminal corners rounded; terminal margin slightly convex to traverse. Proximal 50–60% of lateral margins smooth, distal portion of each margin with dense, continuous series of 8–12 acute spines. This series extending up to the rounded, latero-terminal corner. Terminal margin lined by 11–18 strong, apically blunt laminae; these last stouter compared to the neighboring latero-terminal spines.

Descriptive notes

Antennular trunk extends 0–30% its length beyond (artificially aligned) eyes ( Fig. 4A ). First to third segments occupy 40–43%, 16–20% or 39–44% total length, respectively. Appendix masculina 0.5–0.7 times total trunk length. Antennal scale 1.2–1.4 times antennular trunk, its terminal segment occupying 12–19% total length and bearing five plumose setae. Sympod of antenna produced into spiniform extension on outer distal corner. Thoracic endopod 8 (when stretched) reaching backwards at most to the middle of pleonite 4 and forwards to maxillula; its carpopropodus 62–69% as long as merus or 0.3–0.5 times telson length. Pleonites 1–5 are 0.7–0.8, 0.6–0.8, 0.6–0.8, 0.5–0.6 or 0.5–0.6 times the length of pleonite 6, respectively. Both sexes with pleopods 1–3 bearing a ventro-laterally directed fan of plumose setae. Setae of pleopod 1 ( Fig. 4D ) on average longer than those of pleopods 2, 3, 5 ( Fig. 4E ). Male pleopod 4 ( Fig. 4F ) reaching at most to middle of telson; its subapical seta up to ¾ as long as endopod of uropod. Endopod of male pleopod 4 with its apical seta 2.1–3.6 times endopod length. Sympod with field of scales on its medial hump, or in analogous position upon missing hump. Scutellum paracaudale triangular with acute apex; upper and lower margins weakly convex to concave. Uropodal endopod 1.0–1.5 times, exopod 1.3–1.8 times as long as pleonite 6. Exopod extends 0.2–0.3 times its length beyond endopod, or 0.5–0.7 times beyond telson; endopod 0.4–0.7 times its length beyond telson. Telson ( Fig. 4G ) 0.4–0.5 times as long as exopod of uropods, 0.4–0.6 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

Marine coastal waters of the Gulf of Mexico, Cuba ( Ortiz et al. 2017b), 22–23° N.

Figures

Fig. 4. Mysidium rubroculatum Băcescu & Ortiz, 1984, from Cuba, paratypes. A. ♂, 3.6 mm body length. B–G. ♂, 3.8 mm. A. Cephalic region, left antennula and setae of antennal scale omitted. B. Mediodistal extension of left antennular trunk, dorsal view. C. Third thoracic endopod, rostral view. D–E. Pleopods 1 and 3, rostral view. F. Pleopod 4, caudal view. G. Telson.

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.