Heteromysis (Olivemysis) waikikensis, 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 : 159-165

Heteromysis (Olivemysis) waikikensis sp. nov.

urn:lsid:zoobank.org:act:C1DBD087-302A-47F9-BD48-7924DB1BBFBE

Figs 9–11

Diagnosis

Rostrum ( Fig. 9A ) forms a triangle with an acute or narrowly rounded tip, 50–65% length of terminal segment of antennular trunk. Cornea ( Fig. 9 A–C) occupies distal 30–40% eye surface. Eyestalks with smooth surface except for a prominent tooth on disto-mesial edge. Antennular trunk ( Fig. 10 A–D) with two large, subapically flagellate spines in addition to normal setae, namely one spine on disto-mesial edge of median segment, and a broader one on disto-mesial edge of terminal segment. Distal 8–12% of the latter spine rugged on its obliquely truncate margin. Dorsal apophysis of basal segment with one strong, apically rugged, non-flagellate spine. Antennal scale ( Fig. 10E ) and antennal peduncle ending at about same height; scale length is 2.9–3.3 times maximum width; scale with small apical segment separated by a transverse suture. Male thoracic sternites 1–8 each with one median, ventral process ( Fig. 9D ). Females with smooth thoracic sternites. Both sexes with flagellum of thoracic exopod 1 showing eight segments, exopods 2–8 with nine segments ( Fig. 11A ). Carpopropodus of thoracic endopods 1–8 with 2, 2, 2, 4, 7, 7, 7, and 7 segments, respectively ( Figs 10I, L ; 11A ). Thoracic endopod 3 ( Fig. 10I, L ) without tooth-like extension on disto-mesial edge of merus; carpopropodus length 2.2–2.7 times maximum width in both sexes. Distal 37–50% of carpus 3 with total of 6–9 flagellate spines along inner margin; propodus without paradactylary setae or spines. Thoracopods 7–8 with large oostegites, thoracopod 6 with rudimentary oostegite. Penes ( Fig. 11A ) cylindrical, 80–89% length of ischium 8. Penes with setae on basal half; penes apically blunt, ending in four lobes. Pleopods ( Fig. 11 C–L) rudimentary, unsegmented, with residual differentiation of endopod (pseudobranchial lobe). Female pleopods 1, 3–5 and male pleopods 1, 5 with normal setae only, no spines. Pleopod 2 of both sexes with smooth spine (stylet) on apex and 5–6 minute flagellate spines in series along outer (= lateral) margin of elongate distal portion. Pleopods 3–4 dimorphic. Male pleopod 3 with 2–7 large flagellate spines (numbers include bilateral variability), densely set along obliquely truncate, terminal margin; male pleopod 4 with dense series of 11–12 (intermediate in size between the spines of pleopods 2 and 3) flagellate spines in analogous position. Exopod of uropods ( Fig. 9E ) 1.2–1.4 times length of endopod. Endopod with only one small spine near statocyst; distal spine-free portion is 67–82% length of endopod. Each lateral margin of telson ( Fig. 9F ) with 8–10 spines along distal 48–52%, proximal portion smooth. U-shaped apical cleft penetrates 25–30% length of telson; proximal 87–90% of cleft with 25–32 laminae. Disto-lateral lobes each with two spines on narrowly truncate apex. The outer apical spines are 15–17% length of telson; inner apical spines are 0.3–0.5 times length of outer ones.

Etymology

The species name is a feminine adjective formed by the addition of location suffix, related to the ‘Waikiki Aquarium’ (Honolulu, Hawaii) where the new species was detected.

Material examined

Holotype HAWAII • ♂ ad., BL 3.9 mm (in vial); Honolulu, Waikiki Beach , Waikiki Aquarium ; Jan. 2020; Gwen Lentes leg.; NHMW 26965 .

Paratypes HAWAII • 1 ♀ ad., BL 4.2 mm (on slides); same collection data as for holotype; NHMW 26966 • 1 ♂ ad., BL 4.2 mm (on slides); same collection data as for holotype; NHMW 26967 .

Description

All features of diagnosis. General appearance small, robust ( Fig. 9A ). For body size see above ‘Material examined’. Cephalothorax comprises 28–34% of body length, pleon (without telson) 54–67%, and carapace (without rostrum) 20–31%. Abdominal somites 1–5 measure 0.7–1.0, 0.6–1.0, 0.7–0.9, 0.7– 0.9, and 0.6–1.0 times the length of somite 6, respectively.

CARAPACE ( Fig. 9B ). Carapace covers 70–81% of cephalothorax dorsally. Rostrum reaches at most to distal ⅔ of artificially straight forward-oriented eyestalks (without cornea). Cervical sulcus short but strong. Cervical pore group consists of 11–15 pores with about 1 µm diameter in a roughly U-shaped arrangement. Posterior margin leaving 1–2 posterior thoracic somites mid-dorsally exposed.

EYES ( Fig. 9 A–C). Eyestalks and cornea dorsoventrally compressed ( Fig. 9A ). Eyestalks without scales. In dorsal view ( Fig. 9 B–C) the cornea appears calotte-shaped, measuring 0.8–1.0 times length of eyestalk (cornea not included). In lateral view ( Fig. 9A ) the cornea appears ovoid with flattened ventral margin, length 1.5 times maximum width.

ANTENNULAE ( Fig. 10 A–D). Trunk extends 40–58% its length beyond eyes, 19–40% beyond antennal scale. Measured without apophysis along dorsal midline, basal segment is 32–47% trunk length, median

segment 13–16%, and terminal segment 48–54%. Basal segment on basal half of outer face with two small, stout, barbed setae as in Fig. 2D . Its dorsal apophysis with 4–5 barbed setae, one flagelliform seta and one strong, apically rugged, non-flagellate spine ( Fig. 10B ). Lateral apophysis with 4–5 barbed plus one smooth seta. Median segment dorsally with large apophysis bearing three barbed plus one flagelliform seta. Terminal segment 1.2–1.5 times as long as wide. Mid-dorsal apophysis with 4–5 barbed setae. Outer antennular flagellum thicker than inner one by a factor of 1.3–1.5 when measured near basis of flagella. Male lobe setose, inserts ventrally close to terminal margin of antennular trunk, length is 18–26% width of terminal segment of trunk, its width 15–28%.

ANTENNAE ( Fig. 10E ). Three-segmented antennal peduncle with basal segment 16–22% peduncle length, second 44–49%, and third 33–36%. Sympod with tongue-like, terminally broad process on ventral face.

MOUTHPARTS ( Fig. 10 F–H). Labrum as given above for H. smithsoniana sp. nov. Mandibular palp ( Fig. 10 F–H) three-segmented. Its proximal segment without setae, 11–15% length of palp. Length of median segment 2.3–2.6 times its maximum width and 60–67% palp length. Inner margin of median segment with 4–2 smooth and sparsely barbed setae in subapical to subbasal position, and with 6–8 short setae along proximal half in both sexes. These setae increasing in length distally; their basal half thickened; only in males with unilateral series of stiff barbs; distal half smooth ( Figs 10G vs 10H). Outer margin of median segment all along with basally barbed setae. Only males with small field of scales near inner basal edge on rostral face; size and shape of scales as in H. smithsoniana sp. nov. ( Fig. 2J ). Terminal segment densely setose, 18–27% palp length. Pars molaris with well-developed grinding surface in both mandibles. Pars incisiva with four teeth, digitus mobilis with three teeth, and pars centralis with 2–3 spiny teeth. Labium as described above for H. smithsoniana sp. nov. Maxillula as normal in this genus; distal segment terminally with 12–14 smooth, in part weakly serrated spines; subterminally with three setae barbed on distal half; two pores closely adjoining outer (= most ventral) seta. Endite of maxillula terminally with three strong, distally spiny setae accompanied by four 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 54–64% length. Outer margin of exopod all along with 15–17 mostly plumose setae, two apical setae larger than remaining ones.

MALE THORACIC STERNITES. Size increases from sternal processes 1–3, remains subequal from 3 to 6, and decreases from 6 to 8 ( Fig. 9D ).

THORACOPODS (general; Figs 10 I–M, 11A–B). 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. 11A ) expanded, length 1.6–2.1 times width in both sexes. Outer edge of plates angular, tip pointed or narrowly rounded. First thoracopods with large, leaf-like, smooth epipod. Basis of endopods 4–8 with small, lappet-like apophysis on rostral face below endopod (below drawing plane, therefore visualized by dashed lines in Fig. 11A ). Total length of endopods increases in series of thoracopods 1, 2, 4, 3, 5–8. Ischium becomes longer and more slender from endopods 1–6, while both features remain subequal among endopods 6–8. Ischium shorter than merus in endopods 1–4 ( Fig. 10I, L ), but longer than merus in endopods 5–8 ( Fig. 11A ). Thoracic endopods with claw 3 longest, claw 1 about half length of claw 3, claws 4–8 measure ¼ to ½ of claw 3; claw 2, if any, not detected. Claws 3–4 smooth ( Fig. 10I, L ), claws 5–8 subapically unilaterally serrated ( Fig. 11B ), claw 1 uni- or bilaterally serrated (as in Fig. 5 O–P). Claw 4 straight, claws 1, 3 weakly bent ( Fig. 10I, L ), claws 5–8 strongly bent ( Fig. 11B ). When stretched anteriorly, endopod 8 reaches to labrum, when stretched posteriorly to end of pleonite 5. Penes with 2–3 barbed plus one smooth seta on proximal half ( Fig. 11A ).

MAXILLIPEDS. First maxilliped as described above for H. smithsoniana sp. nov. Basis of second maxilliped with large, distinctly medially projecting endite. In both sexes, combined praeischium plus ischium are 0.8–0.9 times length of merus, carpopropodus plus dactylus 0.9–1.1 times merus. Dactylus very large, with dense brush formed by large numbers of normal setae and 11–13 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. 10 I–M). Ischium 1.2‾2.2 times as long as wide; merus 2.0‾3.6 as long as wide and 1.5‾2.2 length of ischium. Carpus 0.5–0.8 times length of merus, 0.9–1.1 times ischium. Claw 2.6–3.9 times dactylus length, and 45–50% carpopropodus. Both sexes with series of basally thickened, unilaterally barbed setae ( Fig. 10M ) on distal 71–80% of outer face of merus. These setae with series of normal barbs (cilia) along median to subapical portions, basal portions thickened. Distal half of ischium with 4–5 short whip setae on mesial margin, each whip seta on tip of a short rounded projection in males, no such projections in the only female available in the present material. Proximal ⅔ of merus with 3–6 short whip setae on mesial margin, the whip setae alternating with longer smooth setae; these setae not implanted on projections. Carpus 3 with proximal 1–2 flagellate spines ( Fig. 10K ), in case of two spines one behind the other; distal spines arranged in 2–4 pairs (one pair after the other); spines of only the most distal 2–3 pairs with rugged anterior margins ( Fig. 10J ).

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 barbed by fine cilia along subbasal to median portions. Oostegite 1 near basis with 6–9 setae, oostegite 2 with 5–7 setae which are sparsely microserrated along distal half. Ventral and rostral portions of outer face of only second oostegite with total of 9–11 whip setae, but shorter than barbed setae. Thoracopod 6 with rudimentary oostegite represented by small, rounded lobe terminally with four setae which are microserrated on their distal half.

PLEOPODS ( Fig. 11 C–M). Length increases in series of pleopods 1, 3 = 4, 5, 2 in females, and 1, 5, 3 = 4, 2 in males. For presence and numbers of spines on pleopods 2–4, see ‘Diagnosis’ above. In Fig. 11D , the flagellate spines are perspectively shortened by slightly oblique orientation of pleopod. All setae of pleopods 1–5 plumose or barbed in both sexes.

TAIL FAN ( Figs 9 E–F, 10N). Scutellum paracaudale triangular, tip acute or narrowly rounded ( Fig. 10N ). Exopod of uropods extends by 14–21% its length beyond endopod, or 40–49% beyond telson. Endopod reaches with 24–29% its length beyond telson. Statoliths mineralised with fluorite, diameter 70–110 µm, thickness 40–45 µm (n = 4). Statoliths discoidal with shallow fundus and distinct tegmen. Statolith formula 2 + (2–3) + (1–2) + (5–9) + (4–5) = 15–20. Telson length 1.3–1.4 times its maximum width or 0.9–1.0 times length of endopod of uropod, 0.8–0.9 times exopod of uropod, and 1.1–1.4 times last abdominal somite, respectively. For further details of telson, see ‘Diagnosis’ above.

FOREGUT ( Fig. 10 O–P) essentially as described above for H. smithsoniana sp. nov. ( Fig. 3 A–B). However, certain modified spines more similar to those ( Fig. 6 A–B) of H. hornimani sp. nov., namely 1–2 large, apically pronged, serrated spines ( Fig. 10O ) on dorsolateral infoldings, and group of 4–5 smaller, centrally serrated spines ( Fig. 10P ) on posterior part of lateralia. Gut contents of two dissected specimens were mostly unidentifiable material, few mineral particles and crustacean fragments.

Distribution

The species is so far known only from an aquarium tank of the ‘Waikiki Aquarium’, Honolulu, Hawaii. Origin most likely in coastal marine waters of the Central Pacific ( Table 1 ).

Figures

Fig. 9. Heteromysis waikikensis sp. nov., holotype, ♂ with body length 3.9 mm (A–B: NHMW 26965), paratypes, ♀ 4.2 mm (C: NHMW 26966) and ♂ 4.2 mm (D–F: NHMW 26967). A. ♂ in toto, lateral view; figure artificially separated from background. B. Cephalothorax, dorsal view; dashed line illustrates the anterior contour of carapace. C. Right eye, dorsal view; object somewhat compressed by cover glass pressure. D. Thoracic sternites 1–8 expanded on slide, ventral. E. Uropods, ventral. F. Telson. A–F. Ethanol-fixed materials on petri dishes (A–B) and slides (C–F).

Fig. 10. Heteromysis waikikensis sp. nov., holotype, ♂ with body length 3.9 mm (N: NHMW 26965), paratypes, ♂ 4.2 mm (A–E, L–M, O–P: NHMW 26967) and ♀ 4.2 mm (F–K: NHMW 26966). A. Male antennula, dorsal.B–D. Details of male antennula (A) showing modified spines. E.Antenna with antennal gland, dorsal. F. Palp of left mandible, caudal. G–H. Setae from outer margin of median segment of mandibular palp in ♀ (G) versus ♂ (H). I. Left female thoracic endopod 3, rostral. J–K. Details of female endopod (I) 3 showing modified spines of carpus. L. Left male thoracic sympod and endopod 3, rostral. M. Detail of male endopod 3 (L) showing modified seta of merus. N. Scutellum paracaudale, lateral. O–P. Modified spines from dorsolateral infoldings (O) and lateralia (P) of foregut.

Fig. 11. Heteromysis waikikensis sp. nov., paratypes, ♂ 4.2 mm (A–J: NHMW 26967) and ♀ 4.2 mm (K–M: NHMW 26966). A. Thoracopod 8 with penis, rostral view. B. Detail of thoracic endopod 8 (A) showing dactylus with nail. C–G. Male pleopods 1–5, represented by left (C, F–G) and right (D–E) ones; caudal. H–J. Flagellate spines of male pleopods 2–4 (D–F). K. Right female pleopod 2, rostral. L. Detail of female pleopod 2 (K) showing flagellate spine. M. Left female pleopod 4, caudal.

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. 5. Heteromysis hornimani sp. nov., paratypes from London, ♀ with body length 5.2 mm (A, H–K, P: NHMW 26975), ♂ 4.7 mm (B–E, G, L–O: NHMW 26976), and non-type from Wroclaw, ♀ 6.5 mm (F: NHMW 26982). A. Palp of left mandible, caudal; most setae of terminal segment are below drawing plane. B. Male antennula, dorsal. C–E. Details of male antennula (B) showing modified seta (C) and spines (D, E). F. Non-type variant of flagellate spine of terminal segment of antennula. G. Antenna with antennal gland, ventral. H. Right female thoracic sympod and endopod 3, rostral. I–K. Details of female endopod 3 (H) showing modified spines (I–J) of carpus and modified seta (K) of merus. L. Left male thoracic sympod and endopod 3, caudal. M. Detail showing modified seta of merus of male endopod 3 (L). N. Dactylus 1, setae omitted. O–P. Claw variants of dactylus 1 (N).

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.

Fig. 6. Heteromysis hornimani sp. nov., paratypes, ♀ with body length 5.2 mm (A–C, H–I: NHMW 26975) and ♂ 4.7 mm (D–G: NHMW 26976). A–B. Modified spines from dorsolateral infoldings (A) and lateralia (B) of foregut. C–E. Series of dactylus 3–5, with claws, setae omitted. F. Thoracopod 8 with penis, rostral. G. Detail of endopod 8 (F) showing dactylus with nail. H. Scutellum paracaudale, lateral. I. Telson.