On the Mysid Crustacean Genus Deltamysis (Mysidae: Heteromysinae), with a New Species and a New Record from Australia Author Daneliya, Mikhail E. text Records of the Australian Museum 2023 Rec. Aust. Mus. 2023-12-06 75 4 413 430 http://dx.doi.org/10.3853/j.2201-4349.75.2023.1881 journal article 10.3853/j.2201-4349.75.2023.1881 2201-4349 10413846 65F4EF7E-9AD1-4867-AAA5-956B29A17042 Deltamysis holmquistae Bowman & Orsi, 1992 Figs 2–5 Deltamysis holmquistae Bowman & Orsi, 1992: 734–741 , figs 2–4.— Müller, 1993: 218 .— Cohen & Carlton, 1995: 81 , 146, appendix 4-2.— Modlin & Orsi, 1997: 439 , 445.—Smith, 2001: 547.—Bollens et al ., 2002: 91, table 2.— Price, 2004: 68 .— Dean et al ., 2005: 5 , table 1.— Petryashev, 2005: 14 , table 1.— Mecum, 2006: 1 , 4, plate 2.— Panampunnayil & Biju, 2007: 1962 , 1963.— Modlin, 2007: 492 , plate 221C–E.— Carlton, 2009: 35 , table 2.4C.— Ruiz et al ., 2011: 231 , 235, 241, appendix 1.—Simberloff & Rejmanek, 2011: 47.—Winder & Jassby, 2011: 684, table 3.— Brown et al ., 2016: 11 , table 2.— Hiebert & Rasmusson, 2016a: 541 ; 2016b: 548 .— Price, 2016: 706 , plates 16.191.02E, 03J.—Scripter et al ., 2020: 501–515, figs 2–5. Deltamysis sp.A .?— Ranasinghe et al ., 2005: 681 , tables 1, 4. Kochimysis pillaii Panampunnayil & Biju, 2007: 1957–1963 , figs 2–5, [synonymized by Scripter et al ., 2020].—Biju & Panampunnayil, 2010: 50, table 1.— Manojkumar & Pavithran, 2016: 42 . Holotype : Male, USA, California , Sacramento—San Joaquin Estuary, between Brown’s Island and Jersey Island , collection dates unknown, coll. J. J. Orsi (Smithsonian Institution, Washington, D.C. [ USNM ] 251607) . Allotype : Female, collected together with holotype ( USNM 251608 ) . Paratypes : 1 male , 4 females , same as previous ( USNM 251609 ) ; 7 specimens , same as previous ( USNM 251610 ) ; 2 males , 7 females , Sta. 56, north of Brown’s Island , date unknown, coll. J. J. Orsi coll. ( USNM 251618 ) ; 1 male , 4 females , exact location unknown, 29 May 1990 , coll. J. J. Orsi ( USNM 251619 ) . Data on the paratype material from Scripter et al . (2020) . Type locality . USA , California , Sacramento—San Joaquin Estuary, between Brown’s Island and Jersey Island (Bowman & Orsi, 1992) Australian material . Female (+slide), 4 mm , New South Wales , Yamba , northern end of Pippi Beach , 29 ° 26.8'S 153 ° 22.1'E , clean sand, 8 m , st. NSW 326, baited trap , set 16:00, retrieved 08:00, coll. J. K. Lowry , S. J. Keable, 07–08 Jun 1988 , AM P.98703; female, 4.5 mm , New South Wales , Twofold Bay , off entrance to Curalo Lagoon , 37°03.2'S 149°55.4'E , sand bottom, 8 m , baited trap , set 15:00–16:30, retrieved 09:00–12:00, coll. J. K. Lowry & S. J. Keable , 26–27 Nov 1988 , AM P.98704. Diagnosis . Anterior margin of carapace angular, apically rounded ( Fig. 2B ). Cornea about as wide as eyestalk or narrower (0.70–0.96 of stalk width). Telson ( Fig. 2C, D ) 1.1–1.3 times as long as wide anteriorly; apically without cleft, bearing two (rarely three) spinules; its lateral margins with five to eight spiniform setae (including terminal, but not apical); subterminal spiniform setae about as long as or longer than preceding lateral; terminal spiniform setae 0.2–0.4 of telson length. Maxilla 2 ( Fig. 3E ), exopod reaching half of endopod segment 1, without lateral setae, and with zero to five apical setae; endopod segment 2 without lateral setae. Maxilliped 2 without lateral processes on carpus and propodus in females ( Fig. 4B ), and armed with triangular, apically pointed processes in males. Pereopod dactylus rather thick, nearly as long as wide ( Figs 4C, D , 5A–E ). Pereopod 3–6 carpopropodus 4-segmented; segment 1 shorter than segments 2–4 combined. Figure 4 . Deltamysis holmquistae Bowman & Orsi, 1992 , female, 4 mm, New South Wales, Yamba, AM P.98703: ( A ) maxilliped 1 endopod, anterior; ( B ) maxilliped 2 endopod, anterior; ( C ) pereopod 1 endopod, anterior; ( D ) pereopod 1 endopod distal part, anterior. Scales (mm): A, B, D = 0.25; C = 1. Figure 5 . Deltamysis holmquistae Bowman & Orsi, 1992 , female, 4 mm, New South Wales, Yamba,AM P.98703: ( A ) pereopod 2 endopod, anterior; ( B ) pereopod 3 endopod, anterior; ( C ) pereopod 4, anterior; ( D ) pereopod 5 endopod, anterior; ( E ) pereopod 6, anterior; (F) pereopod 6 basis distal part, anterior. Scales (mm): A–E = 0.5; F = 0.25. Body length . Males 2.6–4.5 mm , females 2.8–5 mm (Bowman & Orsi, 1992; Scripter et al ., 2020). Comparison . Deltamysis holmquistae is distinguished from other species of the genus by the telson apically without cleft and armed with two (rarely three) short spinules. It is not possible to establish affinities between the species of Deltamysis at the current state of our knowledge. Comparison of the diagnostic morphological characters can be seen in Table 1 . Description of Australian specimens . Telson shorter than last abdominal segment, 1.2 times as long as wide anteriorly. Lateral spiniform setae, subterminal pair about as long as or longer than previous lateral. Terminal spiniform setae 0.21 times as long as telson and 1.1 times as long as longest posterolateral spiniform setae. Telson apical margin truncated, without cleft, bearing two thin and rather long spinules, set apart, 0.33 of lateral terminal spiniform setae. Cornea well-developed, nearly (0.95) as wide as stalk. Antennular peduncle segment 3 with two plumose and two smooth distomedial setae. Antennal scale 2.9 times as long as wide, nearly reaching distal margin of antennular peduncle segment 3, and about as long as antennal peduncle.Antennal peduncle segment 2 slightly longer than segment 3. Labrum apically nearly rounded. Mandibular palp rather wide; segment 2 with two medial setae. Maxilla 2 exopod reaching half of endopod segment 1, without lateral setae and with zero or two apical setae; endopod segment 2 without lateral setae. Maxilliped 1 dactylar claw with subapical wing-like extensions. Maxilliped 2 endopod with smooth carpus and propodus. Pereopod 1 and 2 endopods with ischium and merus nearly on one line, with slight bending capability in relation to each other; carpopropodus 3-segmented, with rather strong, posteriorly serrated setae. Pereopod 1 endopod, ischium 4.7 times as long as wide, with one lateral and one distomedial seta; merus 4.4 times as long as wide and 0.8 times as long as ischium, with two lateral and one distomedial bunches of setae; carpopropodus 3-segmented, segment 1 is 1.1 times as long as segments 2 and 3 combined, with two distomedial bunches of one thin seta and one strong posteriorly serrated seta; segment 3 with two paradactylary setae, posteriorly finely serrated; dactylus rather strong, nearly as long as wide, 0.4 of carpopropodus segment 3 length. Pereopod 2 exopod 9-segmented. Endopod ischium 6 times as long as wide and about as long as merus, with three medial setae; merus 6 times as long as wide, with distolateral and distomedial bunches only; carpopropodus 3-segmented, segment 1 as long as segments 2 and 3 combined. Table 1 . Comparison of the diagnostic morphological characters between the species of the genus Deltamysis (unique character states indicated in bold).

characters	species (in alphabetic order)
D. holmquistae	D. lowryi sp. nov.	D. nana	D. songkhlaensis
Anterior margin of carapace Apically rounded		Apically rounded	Apically rounded	Apically pointed or blunt
Eye cornea width / stalk width	0. 7–0.96	0.7–0.95	0.8	0.57–0.63
Telson length / width cleft presence cleft / telson length apical spinules number apical spinules length / lateral	1.1–1.3 Absent — 2 or 3 0.23–0.58	1.1–1.4 Present 0.05 7 0.09–0.25	1.5–1.6 Present 0.02 2 0.43	1.1–1.2 Absent — 2 1.0–1.1
terminal spiniform setae length
lateral terminal / subterminal	0.51–1.5	3.1–3.4	0.94	0.95–1.1
spiniform setae length subterminal / previous postero-	1.1–2.4	0.48	1.6	0.95–1.1
lateral spiniform setae length lateral terminal spiniform setae length/ telson length	0.20–0.42	0.22–0.23	0.12	0.27–0.32
Maxilla 2 exopod and endopod lateral setae Absent exopod length Barely reaching half of endopod segment 1		Absent Reaching endopod segment 2	Present Reaching half of endopod segment 1	Present Reaching endopod segment 2
Maxilliped 2 endopod carpus and propodus Present in males lateral processes		Present in males	Absent in females,? in males	Absent
Pereopod dactylus	Thick	Thin	Thin	Thick
Pereopod 3–6 carpopropodus segment number 4 segment 1 / segments 2–4 (5) Shorter combined length		4 or 5 Shorter	4 or 5 Shorter	4 Longer, as long as or only slightly shorter

Pereopod 3–6 basis with distomedial tubercle, endopod long and thin, preischium and ischium without setae; ischium and merus bending in relation to each other; dactylus rather thick. Pereopod 3 ischium 9 times as long as wide; merus 11 times as long as wide and 0.9 of ischium length, with five medial bunches of one or two short setae; carpopropodus 4-segmented, segment 1 is 1.3 times as long as segments 2 and 3 combined. Pereopod 4 endopod long and thin, preischium and ischium without setae; ischium 11 times as long as wide; merus 11 times as long as wide and 0.8 of ischium length, with four medial bunches of one or two short setae; carpopropodus 4-segmented, segment 1 as long as segments 2 and 3 combined. Pereopod 5 endopod long and thin, preischium and ischium without setae; ischium 13 times as long as wide; merus 9 times as long as wide and 0.7 of ischium length, with four medial bunches of one or two short setae; carpopropodus 4-segmented, segment 1 is 1.1 times as long as segments 2 and 3 combined. Pereopod 6 exopod 9-segmented, endopod long and thin, preischium without setae; ischium 11 times as long as wide; merus 8 times as long as wide and 0.6 of ischium length, with four medial bunches of one or two short setae; carpopropodus 4-segmented, segment 1 is 0.9 times as long as segments 2 and 3 combined. Pleopod 2 longest apical seta 0.9 of ramus length. Pleopod 3 longest apical seta 0.8 of ramus length. Pleopod 5 longest apical seta 0.4 of ramus length. Variation . Scripter et al . (2020) provided rather detailed information on the variation in D. holmquistae . I will only mention here the most diagnostically important features. The species has considerable variability in cornea size, from being clearly narrower than the eyestalk (0.7 times as wide as the eye stalk) to nearly as wide (0.96). The antennal scale is 2.5–3.6 times as long as wide and shorter, about as long as or even slightly longer than the antennal peduncle. The telson can be shorter or longer than the last abdominal segment. One of the illustrated males from Florida (Scripter et al ., 2020, fig. 3D) had the terminal lateral spiniform setae less than half as long as the subterminal. The telson apex can be rather smoothly rounded, with apical spinules set close together, like in the specimens from India (cf. Panampunnayil & Biju, 2007 ), or truncated with the spinules set apart, like in the types , illustrated by Bowman & Orsi (1992) and the Australian specimens. Distribution . USA , California : San Joaquin Estuary, Sacramento (Bowman & Orsi, 1992; Dean et al ., 2005 ); Florida : Port of Jacksonville, the lower St. Johns River and surrounding St. Johns estuarine system, the Indian River lagoon, and Fort Lauderdale brackish water canals; Texas : Gulf of Mexico near Freeport (Scripter et al ., 2020). India , Kerala : Arabian Sea inlets near Kochi ( Panampunnayil & Biju, 2007 ). Australia , New South Wales : Coral Sea near Yamba; Tasman Sea, Twofold Bay. Habitat . Estuarine-marine species, found in salinities from 0 to 32‰. The Australian specimens were trapped at open sea sandy beaches, at depth of 8 m . Remarks . Deltamysis holmquistae was originally described by Bowman & Orsi (1992) in detail, but with the sexual dimorphism and other considerable variation unreported. The authors also illustrated maxilla 2 endopod as 3-segmented, while it is always 2-segmented in Mysida . Revising the paratypes together with additional new material, Scripter et al . (2020) revealed discrepancies in the original description and redescribed D. holmquistae . They also synonymized K. pillaii based on the redescription and comparison with the K. pillaii description. The pereopod 1 and 2 carpopropodus segment 1 was originally illustrated as longer than the segments 2 and 3 combined (Bowman & Orsi, 1992, fig. 3D). Later, in Panampunnayil & Biju (2007 , fig. 4A, B) from the Indian coast, and in Scripter et al . (2020, fig. 2F, G) from the US coast the segment 1 was shown to be shorter than the segments 2 and 3 combined. Previous authors did not give detailed illustrations of maxilliped 1 dactylar claw, which may possess the apical wing-like extensions, described above. These could be additional diagnostic features, but further study is necessary to confirm. After the transfer of more species into the genus Deltamysis , it became necessary to provide a diagnosis for D. holmquistae , which was previously analogous to the generic diagnosis. Considering the detailed study of Scripter et al . (2020) and comparing the species with the other three members, I attempted above to compose a new diagnosis.