Heteromysis S.I. Smith, 1873

Wittmann, Karl J., Abed-Navandi, Daniel, Dubois, Maude & Chevaldonné, Pierre, 2021, Three new species of Heteromysis (Crustacea: Mysida) from coral reef aquaria in Florida and Central Europe, Zootaxa 4980 (3), pp. 490-520 : 492

Genus Heteromysis S.I. Smith, 1873

Features shared by the three here described Heteromysis species. Carapace normal, without apparent sexual dimorphism ( Fig. 9D ). Rostrum represents a distinct horizontal, triangular plate. Cervical sulcus well developed; no cardial sulcus visible. Posterior margin of carapace evenly rounded, mid-caudally weakly emarginated.

Antenna. Presence of previously not described crescent-shaped shield proximally behind antennal peduncle on ventral face of antennal sympod. Size and shape of crescents may differ between species, e.g. H. korntalensis sp. nov. ( Fig. 6I ) versus H. schoenbrunnensis sp. nov. (dashed line in Fig. 9L ).

Mouthparts and foregut. Labrum ( Fig. 9M ) caudally with small, stiff bristles. Fields of setae on caudal and ventral faces. Labium ( Fig. 9N ) normal, comprising two hairy lobes with short, dense set of stiff bristles on distal half of mesial face. Maxilla ( Fig. 10E ) normal, densely setose, with various types of setae, but no spines or teeth. Its leaf-like exopod not extending beyond basal segment of endopod. This segment plus the sympod, and all three large endites of the sympod, with densely setose distal margins. Mesial margin of sympod with a long seta bearing stiff bristles along its distal third; this seta extending beyond the dense brush of plumose setae. Gross structure of the foregut ( Fig. 13A–E ) as given in the first description of H. abednavandii Wittmann, 2020 .

Thoracic sternites. Sternite 1 anteriorly produced into a large lobe in both sexes ( Fig. 10F versus 10I) contributing to the caudal closure of the mouth field as usual in Mysidae . Pair of barbed setae on intersegmental joint between thoracic sternite 2 and sympod 2. These setae show characteristic differences in size, thickness, and arrangement of barbs among each other ( Fig. 10F ). No such setae on sternites 1, 3–8.

Maxillipeds (thoracic endopods 1, 2). Coxa of maxilliped 1 ( Fig. 10F ) with small endite bearing one barbed seta at its tip. Basis with large, prominent endite that is densely setose on mesial margin. Ischium and merus each with one smaller but distinct, medially setose endite. Basis of maxilliped 2 with large, medially projecting endite ( Fig. 10J ).

Marsupium. Female thoracopods 7, 8 bear large oostegites 1 and 2, respectively. Each oostegite without setae on upper (dorsal) margin. Ventral margin and part of posterior margin, from subbasal region up to rounded tip, with dense series of plumose setae, together with the bilaterally opposite oostegite forming a gate contributing to the ventral and caudal closure of the marsupium. Marsupium inside with comparatively long setae microserrated on their distal half. Outer face of marsupium with short whip setae. Thoracopod 6 with small, terminally rounded, rudimentary oostegite ( Fig. 11F ) not contributing to wall of brood pouch. This rudiment may have some function by reaching into the brood pouch with a few microserrated setae.

Uropods. Exopod stout, its mesial margin more strongly convex than lateral margin ( Fig. 4J ). Mineral composition of statoliths is fluorite as also in 18 other Heteromysis species examined by Wittmann & Ariani (2019).

Figures

FIGURE 4. Heteromysis gulfarii sp. nov. from aquaria in Florida, paratypes, male with body length 3.8 mm (A–D, F–G, J–K: NHMW–27017) and females 3.7 mm (E, H: NHMW–27015), 4.5 mm (I: MNINGA MYS 440); A–C, modified spines of foregut; D, male pleopod 1, caudal; E, female pleopod 2, caudal; F, male pleopod 3, rostral; G, male pleopod 4, rostral; H, female pleopod 5, caudal; I, scutellum paracaudale, lateral; J, uropods, ventral; K, telson; L, nauplioid larva at late substage N3, anteriorly distorted, lateral; M, tip of nauplioid abdomen in another specimen, lateral.

FIGURE 6. Heteromysis korntalensis sp. nov. from aquaria in Korntal (Germany), paratypes male with body length 4.4 mm (A–D, I–O: NHMW–27018) and female 3.5 mm (E–H, P: NHMW–27020); A, right male antennula, dorsal; B–D, details of male antennula (A) showing whip setae of basal (B), median (C) and terminal (D) segments of trunk; E, left female antennula together with associated processes from frons, dorsal; F–H, details of female antennula (E) showing whip setae of basal (F), median (G) and terminal (H) segments of trunk; I, antenna, ventral, arrow points to scale field below drawing plane on dorsal face; J, labrum, ventral; K, right male gnathopod, rostral, details show ridge on disto-mesial edge of merus (L) and (M–N) modified spines of carpus; O, propodus plus dactylus of right male gnathopod, rostral; P, dactylus of right gnathopod in female, caudal.

FIGURE 9. Heteromysis schoenbrunnensis sp. nov. from aquaria in Vienna (Austria), paratypes, male with body length 4.8 mm (A–B, D–F, N: NHMW–27021), and female 4.9 mm (C, G–M: NHMW–27022); A, anterior body region of male, dorsal aspect, left antennula, right antenna and setae of left antenna omitted, detail (B) shows left eye in lateral view; C, left eye of female, dorsal, object somewhat compressed by pressure exerted by cover glass; D, carapace expanded on slide, details (E–F) showing pore groups; G, female antennula together with associated processes from frons, dorsal; H–K, details of female antennula (G) showing modified spines (H, J) and setae (I, K); L, antenna, dorsal; M, labrum, ventral; N, labium, compared with left lobe, the right one appearing more slender due to artificial, vertical inclination.

FIGURE 10. Heteromysis schoenbrunnensis sp. nov. from aquaria in Vienna (Austria), paratypes, male with body length 4.8 mm (A, C–D, F–G, K–L, N–P: NHMW–27021) and female 4.9 mm (B, E, H–J, M: NHMW–27022); A, left mandible, caudal face, arrow points to field of scales visible through the transparent object with focus on rostral face; B, masticatory portion of right mandible in another specimen; C, maxillula, caudal, detail (D) shows pores of distal segment; E, maxilla, rostral; F, male first thoracopod (caudal) with sternites 1–8 (ventral); G–H, variants of claw of first thoracic endopod; I, female thoracic sternites 1–8; J, second thoracic endopod, caudal; K–P, dactylus with claw in thoracic endopods 3–8, setae omitted, note varying scales.

FIGURE 11. Heteromysis schoenbrunnensis sp. nov. from aquaria in Vienna (Austria), paratypes, male with body length 4.8 mm (A–B, E, G: NHMW–27021) and female 4.9 mm (C–D, F: NHMW–27022); A, right male thoracopod 3, rostral aspect, detail (B) shows barbed whip seta of merus; C, ‘tarsus’ and part of merus of left female thoracic endopod 3, rostral, detail (D) shows flagellate spine of carpopropodus; E, thoracic endopod 4, caudal; F, sympod of thoracic endopod 6 with rudimentary oostegite, rostral; G, male thoracic endopod 8 with basal plate of exopod and penis, caudal.

FIGURE 13. Heteromysis schoenbrunnensis sp. nov. from aquaria in Vienna (Austria), paratypes, female with body length 4.9 mm (A–F: NHMW–27022) and male 4.8 mm (G–H: NHMW–27021). A, cardiac portion of foregut, dorsal view, dorsal wall omitted, details (B–E) showing modified spines; F, scutellum paracaudale, lateral; G, uropods, ventral, setae and ventral wall of statocyst omitted; H, telson; I, nauplioid larva at late substage N2, lateral, detail (J) shows tip of abdomen.