Heteromysis (Olivemysis) smithsoniana, Wittmann & Abed-Navandi, 2021

Wittmann, Karl J. & Abed-Navandi, Daniel, 2021, Four new species of Heteromysis (Crustacea: Mysida) from public aquaria in Hawaii, Florida, and Western to Central Europe, European Journal of Taxonomy 735, pp. 133-175 : 144-150

Heteromysis (Olivemysis) smithsoniana sp. nov.

urn:lsid:zoobank.org:act:4B3ABD3F-EF26-4C69-B951-C81B6FE5DCFE

Figs 1–3

Diagnosis

Rostrum ( Figs 1C , 2F ) forms a triangular plate between the eyes, rostrum 58–83% length of terminal segment of antennular trunk; apex acute to narrowly rounded. Disto-mesial edge of eyestalks with welldeveloped tooth ( Fig. 1C ). Cornea occupies distal 25–30% of eye surface. Antennular trunk ( Fig. 2 A–C) with strong, subapically flagellate spines in addition to setae, namely one spine on dorsal apophysis of basal segment and a somewhat larger one on disto-mesial edge of terminal segment. Antennal scale ( Fig. 2E ) with small apical segment; antennal scale reaches 0–20% of its length beyond antennal peduncle. Scale length is 3.0–3.3 times maximum width. Male thoracic sternites 1–8 ( Fig. 1D ) each with mid-ventral process. Female sternites without processes. Both sexes with flagellum of thoracic exopods 1–8 showing 8, 9, 9, 9, 9, 9, 9–10, and 9–8 segments, respectively ( Fig. 3F ). Carpopropodus of thoracic endopods 1–8 with 2, 2, 2, 4–3, 7, 7, 7, and 7 segments, respectively ( Figs 2L, O , 3C, F ). No visible difference between left and right thoracic endopods 3. Shape of carpopropodus 3 sexually dimorphic ( Figs 2L vs 2O), length 2.1–2.7 times maximum width in males vs 2.9–3.4 in females. Disto-mesial edge of merus 3 without tooth-like extension. Carpus and propodus separated by a distinct suture. Carpus with six flagellate spines ( Fig. 2M, P ) on distal 45–55% of inner margin in both sexes. Propodus without paradactylary setae and without spines. Ischium of endopod 5 without excavation. Penes 58–67% length of ischium of endopod 8; proximal ⅔ tube-like, distal ¼ narrowing ( Fig. 3F ). Pleopods rudimentary, unsegmented, with residual differentiation of endopod (pseudobranchial lobe). All female pleopods and male pleopod 5 without spines. Pleopods 1–4 dimorphic ( Fig. 3 H–L vs 3O): male pleopods 1–2 end with a long smooth spine (stylet); distal half of pleopods 3–4 knife-shaped, with broadly rounded terminal margin; pleopod 3 with 25–30 small, flagellate spines, densely set along ‘blade’; pleopod 4 with 28–33 spines of same structure and size; flagella same-sized or longer than spines. Exopod of uropods 1.1–1.4 times length of endopod ( Fig. 1E ); endopod with 3 (rarely 2) spines on inner margin near statocyst; distal spine-free portion 55–62% length of endopod. Proximal 21–33% of lateral margins of telson without spines, distal portion with 7–11 spines. Telson ( Fig. 3R ) with U- to V-shaped apical cleft penetrating 29–36% telson length; cleft with 22–30 laminae along basal 75–86% of its margins. Apical lobes of telson each with two spines; latero-apical spines are 14–18% telson length; medio-apical spines are 0.5–0.6 times length of latero-apical spines.

Etymology

The species name is a Latinized adjective with female ending, referring to the Smithsonian Marine Ecosystems Aquarium (Fort Pierce, Florida).

Type material

Holotype FLORIDA • ♂ ad., BL 3.6 mm (in vial); Fort Pierce , Smithsonian Marine Ecosystems Aquarium; Dec. 2019; Bill Hoffman leg.; NHMW 26968 .

Paratypes FLORIDA • 3 ♀♀ ad., BL 3.3–4.0 mm, 2 ♂♂ ad., BL 3.6–3.8 mm (in vial); same collection data as for holotype; USNM 1622569 • 2 ♀♀ ad., BL 3.9–4.0 mm, 3 ♂♂ ad., BL 3.4–3.6 mm (in vial); same collection data as for holotype; NHMW 26969 • 1 ♀ ad., BL 4.2 mm (on slides); same collection data as for holotype; NHMW 26970 • 1 ♂ ad., BL 4.8 mm (on slides); same collection data as for holotype; NHMW 26971 • 1 ♂ ad., BL 4.2 mm (on slides); same collection data as for holotype; NHMW 26972 .

Description

All features of the Diagnosis. Size of adult females 3.3–4.2 mm, males 3.4–4.8 mm. Cephalothorax comprises 22–33% body length, pleon (without telson) 50–65%, carapace (without rostrum) 20–25%, and rostrum 4–5%. Abdominal somites 1–5 measure 0.6–0.8, 0.6–0.9, 0.6–0.8, 0.5–0.9, and 0.6–0.9 times the length of somite 6, respectively.

CARAPACE ( Fig. 2 F–H). Carapace covers 65–87% of cephalothorax dorsally. Rostrum reaches at most to distal ⅔ of artificially straight forward-oriented eyestalks (without cornea). Cervical and cardial sulcus short but distinct. Posterior margin leaving 0.8–1.5 posterior thoracic somites mid-dorsally exposed. Cervical pore group formed by 8–11 pores each with about 1 µm diameter arranged in a wide arc ( Fig. 2G ). The posterior group of pores ( Fig. 2H ) closely behind cardial sulcus; it consists of 10–12 such pores, each with about 1.2 µm diameter surrounding a larger but indistinct, rounded structure.

EYES ( Fig. 1 A–C). Eyestalks and cornea dorsoventrally strongly compressed. Eyestalks without scales. In dorsal view the cornea appears calotte-shaped, measuring 0.6–0.9 times the length of eyestalk (cornea not included). In lateral view ( Fig. 1B ) the cornea appears kidney-shaped, length 1.6 times maximum width.

ANTENNULAE ( Fig. 2 A–D). Trunk extends 46–61% its length beyond eyes, 15–33% beyond antennal scale. Measured along dorsal midline, the basal segment is 32–47% trunk length, median segment 12– 18%, and terminal segment 38–49%. Basal segment on basal half of its outer face with two small, stout, barbed setae ( Fig. 2D ). Its dorsal apophysis with 3–2 barbed setae, one flagelliform seta, and one flagellate spine ( Fig. 2C ). Lateral apophysis with one plumose and one shorter barbed seta, and one flagelliform seta. Median segment dorsally with large apophysis with 3–4 barbed plus one flagelliform seta. Terminal segment 1.4–1.5 times as long as wide. Its mid-dorsal apophysis with 4–2 barbed setae. Disto-mesial edge of terminal segment with flagellate spine ( Fig. 2B ) resembling certain flagellate spines ( Fig. 2P ) of gnathopods. In both sexes the outer antennular flagellum is thicker than the inner one by a factor of 1.5–2.3 when measured near basis of flagella. Male lobe well setose, inserts ventrally close to terminal margin of antennular trunk, almost spherical, length is 20–24% width of terminal segment of trunk, its width 19–26%.

ANTENNAE ( Fig. 2E ). Three-segmented antennal peduncle: basal segment is 18–23% peduncle length, second segment 43–49%, and third segment 29–32%. Sympod with tongue-like process on ventral face.

MOUTHPARTS ( Fig. 2 I–K). Labrum not produced into a spiniform process; caudally with small, stiff bristles, fields of setae on caudal and ventral faces. Mandibular palp ( Fig. 2I ) three-segmented. Its proximal segment without setae, 10–15% length of palp. Length of median segment 2.1–2.3 times its maximum width and 65–72% palp length. Inner margin of median segment with two smooth setae in subapical and subbasal position, respectively, and with 6–7 modified setae along proximal half in both sexes. These setae increasing in length distally; their basal half thickened, bearing unilateral series of stiff barbs; distal half with smooth flagellum ( Fig. 2K ). Mid-caudal face with 0–1 weakly barbed seta, outer margin with smooth setae all along. Rostral face only in males with longitudinal series of scales near inner margin from subbasal to subterminal portions; scales triangular, facing distally, arranged in groups formed by mostly 7–9 peripheral scales around a central scale ( Fig. 2J ). Terminal segment strongly setose, 17–21% palp length. Pars molaris with well-developed grinding surface in both mandibles. Pars incisiva with 4–5 teeth, digitus mobilis with 3–4 teeth, and pars centralis with 3–4 spiny teeth. Labium normal, comprising two hairy lobes with dense set of stiff bristles on distal half of inner face. Maxillula as normal in this genus; distal segment terminally with 11–12 mostly smooth, in part weakly serrated spines; subterminally with three setae barbed on their distal half; transverse series of three pores closely adjoining the outer (= most ventral) seta. Endite of maxillula terminally with three strong, distally spiny setae accompanied by 3–4 proximally thick, barbed setae; inner and outer margins with numerous less thick setae. Maxilla as normal in this genus; terminal segment of endopod with maximum width 53– 66% length. Outer margin of exopod all along with 16–19 mostly plumose setae, the two apical setae larger than the remaining ones.

MALE THORACIC STERNITES ( Fig. 1D ). Median processes of sternites 2–8 emerge from socket-like elevations. Some intermediate sternites with additional, small submedian processes not fused together with median processes. Size increases from processes 1 to 6, is smaller in process 7, and then increases again to 8. Processes 1–3 terminally rounded, processes 4–7 acute-angled with acute tip.

THORACOPODS (general; Figs 2 L–S, 3C–G). Length of flagella as well as of basal plates increases from exopod 1 to 6, and decreases from exopod 6 to 8. Basal plates ( Fig. 3F ) expanded, 1.7–2.3 times as long as wide in both sexes. Outer margin of the plates ends in a well-rounded edge. First thoracopods with large, leaf-like, smooth epipod. As in many species of this genus, a plumose seta plus a shorter barbed seta present at the intersegmental joint connecting sympod of thoracopod 2 with corresponding thoracic sternite; no such setae in remaining thoracopods. Length of ischium and total length of endopod increase in series of thoracopods 1, 2, 4, 3, 5–8. Basis of endopods 4–8 ( Fig. 3F ) with a small, lappet-like apophysis on rostral face below endopod. Ischium becomes more slender from endopods 1 to 5, and its shape remains subequal among endopods 5–8. Ischium shorter than merus in endopods 1–4 ( Fig. 2L, O ), but longer than merus in endopods 5–8 ( Fig. 3F ). Thoracic endopods with claw 3 longest; claws 1, 4–8 ( Figs 2R , 3 D–E, G) about half as long as claw 3; claw 2 not detected (presence not excluded). Claws 1, 5–8 subapically unilaterally serrated ( Figs 2R , 3E, G ), claws 3–4 smooth ( Figs 2S , 3D ). Claw 4 straight ( Fig. 3D ), claws 1, 3 weakly bent ( Fig. 2 R–S), claws 5–8 strongly bent ( Fig. 3E, G ). When stretched anteriorly, endopod 8 reaches to maxillula, when stretched posteriorly to end of pleonite 5. Penes with small subapical excavation, tip trilobate; no setae ( Fig. 3F ).

MAXILLIPEDS. Coxa of first maxilliped with small endite bearing one barbed seta at tip. Basis with large, prominent endite that is densely setose on inner margin. Ischium and merus each with one smaller but distinct, medially setose endite. Basis of second maxilliped with large, distinctly medially projecting endite. In both sexes, combined praeischium plus ischium are 0.7–0.9 times length of merus, carpopropodus plus dactylus 1.0–1.2 times merus. Dactylus very large, with dense brush formed by large numbers of normal setae and 10–12 modified setae, the latter apically bent, bearing two symmetrical series of denticles (stiff barbs) on either side in subbasal to median portions.

GNATHOPODS (thoracic endopods 3; Fig. 2 L–Q, S). Ischium 1.5‾2.0 as long as wide; merus 2.3‾3.8 as long as wide and 1.5‾1.7 length of ischium. Carpus 0.6–0.8 times length of merus, 1.1–1.3 times ischium. Claw 2.4–4.0 times length of dactylus and 41–43% of carpopropodus. Distal third of ischium with 3–7 short whip setae on mesial margin, each whip seta on tip of short tooth-like projection ( Fig. 2L ) in males, the latter projection shorter in females ( Fig. 2O ). Series of 2–5 unilaterally barbed setae in males ( Fig. 2N ), 6–9 in females ( Fig. 2Q ), on basal 50–60% of outer face of merus, plus single seta in subterminal position. These setae with series of normal barbs (cilia) along median to subapical portions, basal portions thickened. Subterminal seta without, remaining setae at end of thickened portion with 1–2 modified, spine-like barbs; mainly two such ‘spines’ in males ( Fig. 2N ), only one in females ( Fig. 2Q ). Proximal 60–80% of merus with 3–7 short whip setae on mesial margin, whip setae alternating with longer smooth setae; no tooth-like projections. Carpus with flagellate spines ( Fig. 2M, P ) arranged as two single spines and more distally two pairs of spines; all these spines with subapical flagellum positioned on smooth posterior (proximal) face; four distal spines rugged to various degrees on anterior face.

MARSUPIUM. Oostegites 1–2 (derivates of thoracopods 7–8) without setae on upper (dorsal) margins. Lower margins from subbasal region up to the rounded tip bearing series of setae, most of which are barbed by fine cilia along subbasal to median portions. Oostegite 1 near basis with 7–10 setae, oostegite 2 with 2–4 setae which are microserrated along distal half. Ventral and rostral portions of outer face of only second oostegite with total of 7–11 slender whip setae, but shorter than barbed setae. Thoracopod 6 with rudimentary oostegite represented by small, rounded lobe terminally with two setae which are microserrated on distal half.

PLEOPODS ( Fig. 3 H–O). Female pleopods increase in length caudally. Length of male pleopods increases in series of pleopods 1, 2 = 5, 3, 4. For presence and numbers of spines on male pleopods 1–4, see ‘Diagnosis’ above. Stylet of pleopod 1 shorter than that of pleopod 2. Single smooth seta at outer terminal edge of male pleopods 3–4; all other setae of pleopods 1–5 are plumose or barbed in both sexes (not counting flagellate spines).

TAIL FAN ( Figs 1 E–F, 3P–R). Scutellum paracaudale triangular, tip acute or narrowly ( Fig. 3P ) to broadly ( Fig. 3Q ) rounded. Exopod of uropods extends by 12–23% its length beyond endopod, or 26–48% beyond telson; endopod 11–30% its length beyond telson. Diameter of fluorite statoliths is 44–59 µm (n=9 statoliths from six specimens). Statoliths discoidal with shallow fundus and distinct tegmen. Statolith formula not available in this material. Telson length 1.2–1.3 times its maximum width or 1.0– 1.3 times length of sixth pleonite. For further details of telson, see ‘Diagnosis’ above.

FOREGUT ( Fig. 3 A–B). Gross structure as described by Wittmann & Abed-Navandi (2019) for H. domusmaris . Lateralia anteriorly with apically coronate spines with smooth shaft and long spines armed with loose series of small denticles along shaft. Lateralia more caudally with separate group of 4–6 centrally, unilaterally serrated spines ( Fig. 3B ). Dorsolateral infoldings with two longer, apically pronged spines furnished with series of acute teeth ( Fig. 3A ) along subbasal to subapical portions. Gut contents of three examined H. smithsoniana sp. nov. were mostly unidentifiable material, minor amounts of crustacean remains and even fewer mineral particles.

Distribution

The species is so far known only from tanks in the ‘Smithsonian Marine Ecosystems Aquarium’, Fort Pierce, Florida. Origin most likely in coastal marine waters of the subtropical NW-Atlantic ( Table 1 ).

Larvae

In the ethanol-fixed material, three out of six adult females examined had 1–2 nauplioid larvae in the brood pouch; three lacked a brood. A female with 4.2 mm body length carried two nauplioid larvae at substage N1 with 0.66–0.69 mm, a female of 3.9 mm had one N3 with 0.78 mm, and a female of 3.6 mm had one N4 with 0.84 mm. Larvae at substages N3 and N4 with smooth cuticle all around. The two N 1 larvae ( Fig. 3S ) also with smooth cuticle except for minute down-like structures ( Fig. 3T ) at tip of abdomen. Remaining features in Fig. 3S are typical of the state of development.

Figures

Fig. 1. Heteromysis smithsoniana sp. nov. A–C. Holotype, ♂ with body length 3.6 mm (NHMW 26968). D–F. Paratype, ♂ 4.8 mm (NHMW 26971). A. Cephalothorax, dorsal.B. Cephalothorax, lateral.C. Head region, obliquely dorsal; dashed line illustrates anterior contour of carapace. D. Thoracic sternites expanded on slide, ventral. E. Uropods, dorsal. F. Detail of uropods (E) showing spines of endopod. A–F. Ethanol–fixed materials on petri dishes (A–C) and slides (D–F).

Fig. 2. Heteromysis smithsoniana sp. nov., paratypes, ♂♂ with body length 4.8 mm (A–D, I–K, R–S: NHMW 26971), 4.2 mm (E–H, L–N: NHMW 26972), and ♀ 4.2 mm (O–Q: NHMW 26970). A. Male antennula, dorsal. B–D. Details of antennula (A) showing modified spines (B–C) and setae (D). E. Antenna with antennal gland, dorsal. F. Carapace expanded on slide. G–H. Details of carapace (F) showing pore groups in front of cervical sulcus (G) and behind cardial sulcus (H). I. Palp of left mandible, rostral. J–K. Details of mandibular palp (I) showing three scale groups (J) and one modified seta (K) from inner margin of median segment; most setae of terminal segment are below drawing plane. L. Right male thoracic sympod and endopod 3, rostral. M–N. Details of male endopod 3 (L) showing modified spine (M) of carpus and modified seta (N) of merus. O. Left female thoracic endopod 3, rostral. P–Q. Details of female endopod 3 (O) showing modified spine (P) of carpus and modified seta (Q) of merus. R–S. Dactyli 1 and 3, with claw, setae omitted.

Fig. 3. Heteromysis smithsoniana sp. nov., holotype, ♂ with body length 3.6 mm (P: NHMW 26968) and paratypes, ♀ 4.2 mm (A, B, O, Q: NHMW 26970) and ♂♂ 4.8 mm (C–G, I–N: NHMW 26971), 4.2 mm (H, R: NHMW 26972). A–B. Modified spines from dorsolateral infoldings (A) and lateralia (B) of foregut. C. Tarsus of thoracic endopod 4, caudal. D. Detail of tarsus 4 (C) showing dactylus with nail. E. Dactylus 5 with nail. F. Thoracopod 8 with penis, rostral. G. Detail of endopod 8 (F) showing dactylus with nail. H–L. Series of male pleopods 1–5, rostral. M–N. Details of male pleopods 3 (J) and 4 (K) showing flagellate spines. O. Female pleopod 4, rostral. P–Q. Variants of scutellum paracaudale, lateral. R. Telson. S. Nauplioid larva at substage N1, ventral. T. Detail of nauplioid larva (S) showing tip of abdomen.