Deltamysis holmquistae Bowman & Orsi, 1992

Scripter, Matthew J., Price, W. Wayne & Heard, Richard W., 2020, Redescription of Deltamysis holmquistae Bowman & Orsi, 1992 (Crustacea Mysida: Mysidae), a mysid species new to the Atlantic Ocean with observations on the taxonomic status of Kochimysis Panampunnayil & Biju, 2007, Zootaxa 4729 (4), pp. 501-518 : 504-513

Deltamysis holmquistae Bowman & Orsi, 1992

( Figs. 2 , 3 , 4 , & 5)

Synonymy: Deltamysis holmquistae Bowman & Orsi, 1992: 734 , figs. 2–4.— Cohen & Carlton 1995: 81.— Modlin & Orsi 1997: 439.— 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, pl. 2.— Modlin 2007: 492 (key), fig. 221C.— Panampunnayil & Biju 2007: 1962.— Carlton 2009: 35 (table 2.4C).— Ruiz et al. 2011:231, (Appendix 1). Winder & Jassby 2011: 684, (table 3).— Brown et al. 2016: 11 (Table 2).— Hiebert & Rasmusson 2016a: 541.— Hiebert & Rasmusson 2016b: 548.— Price 2016: 706 (key), pls.16.191.02E, 16.191.03J.— Mees & Meland 2012 (in list).

Deltamysis sp. A. [? holmquistae ] Ranasinghe et al. 2005: 681 (tables 1, 4).

Kochimysis pillaii Panampunnayil & Biju, 2007: 1957 , figs. 2–5.— Biju & Panampunnayil 2010: 50, table 1.— Manojkumar & Pavithran 2016: 42.— Mees & Meland 2012 (in list).

Material examined

Type material. Paratypes: All samples from Sacramento–San Joaquin Estuary, collected between Brown’s Island and Jersey Island; bottom to surface tows using a 505 µm plankton net; USNM 251609 , 1 adult male ( Length [ L] 4.5 mm), 4 non-ovigerous females (L 3.6, 3.8, 4.2 mm, 1 damaged), exact location and date unknown, J. J. Orsi coll.; USNM 251618 , 2 adult males (L 3.8 mm, 1 damaged), 2 ovigerous females (damaged), 5 non-ovigerous females (L 3.5, 3.7 mm, 3 damaged), Sta. 56, north of Brown’s Island , date unknown, J. J. Orsi coll.; USNM 251619 , 1 adult male (L 3.2 mm), 1 ovigerous female (damaged), 2 non-ovigerous females (L 3.2, 1 damaged), 1 female (head only), exact location unknown, 29 May 1990, J. J. Orsi coll.

Northwest Atlantic material. Jacksonville, Florida: 11 males (L 2.6–2.9 mm), 14 ovigerous females (L 2.8– 3.2 mm), 15 non-ovigerous females (L 1.9–2.9 mm), 7 juveniles (L 1.4–2.0 mm), 14–15 Oct 2014, temperature 26.6–26.9 °C, salinity 7.1–11.0 PSU, dissolved oxygen 6.0– 6.7 mg /L; 2 ovigerous females (L 2.9, 3.0 mm), 1 non-ovigerous female (L 2.3 mm), 2 damaged, 14–16 Jan 2015, temperature 13.7–14.5 °C, salinity 20.9–22.2 PSU, dissolved oxygen 7.8–8.0 mg/L; 3 males (L 2.1–2.7 mm), 15 July 2015, temperature 29.1 °C, salinity 29.7 PSU, dissolved oxygen 5.4 mg /L; 1 male (L 2.6 mm), 1 non-ovigerous female (L 2.3 mm), 15 Oct 2015, temperature 25.8 °C, salinity 5.6 PSU, dissolved oxygen 6.2 mg /L; 2 males (L 2.2 mm, 1 damaged), 2 ovigerous females (L 3.5 mm, 1 damaged), 1 non-ovigerous female (L 2.1), 12 July 2016, temperature 32.3 °C, salinity 24.3 PSU, dissolved oxygen 5.5 mg /L. Port St. John, Florida: 1 non-ovigerous female (L 3.2 mm), 21 Mar 2018, temperature 21.4 °C, salinity 26.2 PSU, dissolved oxygen 7.8 mg /L; 1 male (L 2.2 mm), 1 ovigerous female (L 2.8 mm), 1 non-ovigerous female (L 2.5 mm), 4 Apr 2018, temperature 25.7 °C, salinity 26.4 PSU, dissolved oxygen 6.4 mg /L; 1 male (L 1.9 mm), 4 June 2018, temperature 29.6 °C, salinity 23.2 PSU, dissolved oxygen 5.1 mg /L. Fort Lauderdale, Florida: 1 non-ovigerous female (L 2.6 mm), 23 Nov. 2015, temperature 26.5 °C, salinity 2.8 PSU, dissolved oxygen 5.3 mg /L; 1 ovigerous female (L 3.4 mm), 2 non-ovigerous females (L 2.1, 2.6 mm), 29 Mar 2016, temperature 26.9 °C, salinity 1.0 PSU, dissolved oxygen 4.9 mg /L; 2 males (L 2.5, 2.6 mm), 2 non-ovigerous females (L 2.5, 3.3 mm), 7 Apr 2017, temperature 31.2 °C, salinity 0.5 PSU, dissolved oxygen 4.5 mg /L. Freeport, Texas: Water quality data not available, 2 males (L 2.1mm, 1 damaged), 21 Oct 2016; 1 non-ovigerous female (L 3.0 mm), 13 July 2017; 1 non-ovigerous female (L 3.2 mm), 20 Nov 2017.

Redescription: General body form: ( Fig. 2A ) moderately slender; length of adult males 2.6–4.5 mm; adult females 2.8–3.8 mm. Note: In the redescription and associated comments, the citations for Bowman & Orsi (1992) and Panampunnayil & Biju (2007) are abbreviated as B & O and P & B, respectively.

Carapace: Anterior margin produced into a short, rounded rostrum; posterodorsal margin emarginated, exposing thoracic somite 8, and at times 7 ( Fig. 2A ) (see B & O, Figs. 2A, B; P & B , Figs. 2A, B ).

Comment: P & B described the posterodorsal margin of the carapace as “leaving last three thoracic somites dorsally exposed.” Somite 6 was never exposed in the material that we examined. Based on the authors’ experience and personal observations, this difference may have been due to the process of preservation, osmotic postmortem swelling, or some other artifact in the process of specimen collection.

Antennular peduncle: Generally as described and illustrated by B & O ( Fig. 2D, E ) and P & B ( Figs. 2 A–E).

Comment: There was, however, a difference in the interpretation by B & O of the presence of a “male lobe.” They described article 3 of the male as having a tuft of setae on the distoventral surface, but lacking a lobe. The material that we examined, including the paratypes of D. holmquistae , agreed with that of P & B ( Fig. 2C, D ) in having a reduced, rounded, sometimes indistinct, setiferous lobe on the ventral surface.

Antenna: Both sexes with scale having length 2.5–3.6 times greatest width, apex with transverse suture (faint at times) separating short distal article, 0.10–0.14 times scale length; antennal peduncle subequal to slightly longer than scale, article 2 0.75–1.20 times length of article 3.

Comment: P & B reported the antennal scale with no distal suture, the antennal peduncle much longer than the antennal scale, and articles 2 and 3 of the peduncle as being subequal (P & B, Figs. 2F, G ). In contrast, we, as well as, B & O ( Fig. 2G ), found distal sutures on all specimens examined, and noted greater variation in the latter two characteristics than reported by P & B (see Table 1 ).

Eye: ( Fig. 2A ) as described and illustrated by B & O ( Fig. 2A ) and P &B ( Figs. 2A, B ).

Comment: We found little variation in the corneal eyestalk width to eyestalk width ratio (0.70–0.96), which is only a marginally wider range than values reported previously.

Mandible: Left mandible ( Fig. 2B , Fig. 5B, D , & F): incisor and lacinia mobilis with 3–4 teeth; spine row with 8–9 serrated spines; well-developed molar process. Right mandible ( Fig. 2B , Fig. 5A, C , & E): incisor with 4 teeth; lacinia mobilis somewhat rectangular with a series of 7–8 tubercles on the long sides and a pair of acute teeth at either end; spine row with 3 large and 8–9 smaller, more slender serrated spines; well-developed molar process. Mandibular palp ( Fig. 4F & G ): 3-articulated; article 1 small, article 2 expanded medially, length 2.1–2.9 times greatest width, about twice as long as article 3, with 3 simple setae on medial margin, 1 short proximolateral simple seta and 1 long simple seta on distolateral margin, 3 setae on distal margin; article 3 with 1 long, strong pennate seta at apex and a series of shorter pennate setae along distomedial margin.

Comment: B & O reported the absence of a lacinia mobilis on the right mandible. For the paratype and northwest Atlantic material, we found this structure on both mandibles as did P & B ( Fig. 3B ). More variation was recorded in the spination of the spine row of our material (right, 11–12 spines: left, 8–9 spines) as compared to either B & O (8, 8) or P & B (3, 4). The length: width ratio of article 2 of the mandibular palp of our material showed more variation than the single illustration of P & B (2.1–2.9 vs. 2.4, Fig. 3A ); however, these ratios were much less than the ratio (3.4) illustrated by B & O ( Fig. 2 H ) that depicted a rather narrow article 2. In addition, the setal (or setation) variation of article 2 of our material was greater than that found in either original description.

Labrum: As described and illustrated by P & B ( Fig. 3C ); middle half of bilobed posterior margin with cluster of short fine setae on one side of emargination and short coarse setae on the other.

Maxillule: Outer lobe apex with 9–10 stout spiniform setae and three subterminal simple (smooth) setae; inner lobe with 3 long plumose setae and 7–9 simple setae (B & O, Fig. 2J; P & B , Fig. 3D ).

Maxilla ( Fig. 2C , 4A ): Sympod and sympodal endites as described and illustrated by B & O ( Fig. 3A ) and P & B ( Fig. 3E ); endopod 2-articulated, proximal article 0.44–0.75 times as long as oval distal article; exopod with 2–5 setae on apex and outer margin, extending beyond proximal margin of article 1 of endopod (P & B, Fig. 3E ).

Comments: The endopod and exopod of the paratype and western Atlantic material exhibited more variation than the descriptions and illustrations of P & B or B & O, but more closely resembled the former. The ratio of endopod lengths of article 1: article 2 was 0.44–0.75 for all material except for those of B & O (<0.25). B & O also reported the exopod not reaching the proximal margin of article 1 of the endopod, whereas it exceeded the margin for all other material. The authors may have misinterpreted the placement of the proximal margin of article 1, thus accounting for these differences.

Thoracic endopods: Endopods generally increasing in length posteriorly, with 6 th the longest.

Thoracic endopod 1 ( Fig. 4B ): As described and illustrated by B & O ( Fig. 3B ) and P & B ( Fig. 3F ).

Thoracic endopod 2 ( Figs. 2D, E , 4C, D , & E): Ischium 0.5–0.6 times length of merus, medial margin with 1 plumose seta; merus 0.7–0.8 times length of carpus, median margin with 3–6 simple or sparsely plumose setae. Carpus subequal in length to combined lengths of propodus and dactylus, medial margin with 2 simple setae; male having 4 papillations along lateral margin; female lacking papillations on lateral margin. Propodus with 4–7 simple setae and serrate setae furnished with bilateral series of spine-like setules along distomedial margin; females with 3 simple setae and no papillations on lateral margin; males with 3 simple seta and 2 papillations along lateral margin; dactylus with 13–16 bilaterally serrate and simple setae on distal and distomedial margin, claw absent.

Comments: The paratypes of D. holmquistae and the western Atlantic material examined most closely resembled the Indian material ( Figs. 3G, H ). Males in all three collections have papillations (“notches” of P & B) on the carpus and propodus; all females examined lack these papillate structures. B & O did not describe or illustrate thoracic endopod 2 of males. Either they did not examine the second thoracic endopods of the males in detail or failed to note the exclusive occurrence of these structures in only males.

Thoracic endopod 3 ( Fig. 2F ): ischium about 2 times length of preischium, medial margin with 4–6 simple setae, lateral margin with 1 simple seta; merus slightly longer than ischium and subequal to 3-articulated carpopropodus, distomedial margin with 2 simple setae, lateral margin with 1 simple seta on proximal half and two simple setae near distolateral margin; carpopropodus proximal article 1.4–1.5 times length of articles 2 and 3, respectively, medial margin with one bilaterally serrate seta and one simple setae at midpoint and another bilaterally serrate seta and two simple setae on distomedial corner, three simple setae on lateral margin; distomedial margin of article 2 with two bilaterally serrate setae and two simple setae (one not shown on Fig. 2F ), distolateral margin with one short and one long simple seta; distal margin of article 3 surrounded by simple setae and one spiniform seta with a unilateral row of thin setules proximally; dactylus with 2 simple setae on apex.

Comments: The illustration of P & B ( Fig. 4A ) differs from the paratype and western Atlantic material in the arrangement of the serrated setae on articles 1 and 2 of the carpopropodus, the lack of a serrated seta on article 3, and the setation (plumose vs. simple) of the medial margin of the ischium.

Thoracic endopod 4 ( Fig. 2G ): Ischium about 3 times length of preischium, medial margin with 2–5 simple setae, lateral margin with 1 simple seta; merus 0.9–1.2 times as long as ischium and subequal to 3-articulated carpopropodus, distomedial and distolateral margins with 1 simple seta each, distal margin with 2 simple setae; carpopropodus proximal article 1.8–2.2 times length of articles 2 and 3, respectively, medial and lateral margins with simple setae only; distomedial margin of article 2 with two bilaterally serrate setae and 1–2 simple setae, distolateral margin with one simple seta; distal margin of article 3 surrounded by simple setae and two spiniform setae with unilateral rows of setules proximally; dactylus with 2 simple setae on apex.

Comment: The serrate setae on the carpopropodus occurred on all material that we examined, but were not described or illustrated by B & O or P & B.

Thoracic endopods 5–6 ( Figs. 3A, B ): Ischium 1.0–1.3 times length of merus, distomedial margin with 1 simple seta, lateral margin with 1 simple seta on distal half; merus 1.1–1.3 times length of carpopropodus, medial margin with 6–8 simple setae along border, distolateral margin with 1 simple seta; carpopropodus 4-articulated, articles 2–4 subequal, each 0.4–0.6 times as long as proximal article, distomedial margin of each article with 2–5 simple setae; dactylus surrounded by simple setae, armed with moderately robust claw (see P & B, Fig. 4C ).

* Information from illustrations only; W** width; L*** length

Thoracic endopods 7–8 ( Fig. 3C ): Ischium 1.4–1.6 times length of merus, distomedial margin with 1 simple seta, lateral margin with 1 simple seta on distal half; merus 1.1–1.2 times length of carpopropodus, medial margin with 6–8 simple setae along border, distolateral margin with 1 simple seta; carpopropodus 4-articulated, endopod 7, articles 2 and 3 subequal, articles 1 and 4 subequal, 2 and 3 each 0.6–0.7 times as long as 1 or 4; endopod 8, articles 2–4 subequal, each 0.5–0.7 times as long as proximal article; dactylus surrounded by simple setae, armed with moderately robust claw (see B & O, Fig.3E; P & B , Fig. 4D ).

Thoracic exopods ( Fig. 2D ): Flagella of exopod 1 with 8 articles, flagella of exopods 2–8 with 9 articles.

Marsupium : Females with pairs of fully developed oöstegites on bases of the medial margins of thoracopods 7 and 8, respectively, pair of small, linguiform oöstegites on thoracopod 6; all oöstegites with sparse plumose setae on ventral and anterior borders.

Penes: Cylindrical, moderate size, stiff with smooth cuticle; 4.4–7.0 times longer than greatest width; extending forward to bases of thoracopods 4–5.

Comment: The length: width ratio of the penis for our material was greater and more variable (5.5–7.0) than reported by B & O (~5.0; Fig. 3F ) or illustrated by P & B (4.4; Fig. 4D ). In addition, the penes extended anteriorly to thoracopod 4–5 for our specimens, but only slightly anterior to thoracopod 8 for B & O’s material.

Pleopods: As described and illustrated by B & O ( Fig. 4 ) and P & B ( Fig. 5 A–E).

Uropods: As described and illustrated by B & O ( Fig. 2C ) and P & B ( Fig. 5F, G ).

Telson ( Fig. 3 D–F): Entire; length 0.95–1.20 times length of abdominal somite 6; 1.0–1.3 times as long as maximum (basal) width; lateral and apical margins armed along posterior 0.25–0.37 length with 12–17 spiniform setae; posterior end truncate or broadly rounded with two pairs of apical setae, inner short setae (2, rarely 3) 0.25–0.40 length of adjacent longer setae, which are 0.2–0.4 times telson length; longer apical setae 0.9–1.7 times lengths of adjacent two pairs of subapical setae which are usually followed by 3–4 pairs of lateral setae that decrease in length anteriorly (see B & O, Fig. 2C; P & B , Fig. 5 F, H, I ).

Comment: P & B state that differences exist between D. holmquistae and K. pillaii in reference to the ratios of short and long apical setal lengths of the telson. An examination of the two original descriptions (text and illustrations), D. holmquistae paratypes, and northwest Atlantic material shows greater variation of this character than reported previously and considerable overlap among the four sources ( Table 1 ).

Concluding Remarks:

To briefly reiterate, Panampunnayil & Biju (2007) state that although Kochimysis and Deltamysis are closely related, the former genus could be distinguished from the latter by a number of characters involving the morphology of the eyes, antennule, antenna, mandibles, maxilla, thoracic endopod 2, and telson. Our research of the paratypes of Deltamysis , northwest Atlantic material, and the two original descriptions revealed that many of these “differences” were due to errors or omissions made in the original descriptions. An examination of other characters (e.g., eyes, antenna, telson, etc.) showed greater variation than previously reported and overlap among the specimen sources (see Redescription and Table 2). The result of the taxonomic data presented above, lead us to emending the diagnosis of Deltamysis , the redescription of D. holmquistae , and to the conclusion that it is a senior synonym of Kochimysis pillai .

Figures

FIGURE 2. Deltamysis holmquistae female, 3.5 mm (A, E, G); female, damaged (B & C), male, 2.9mm (D, F); Jacksonville, Florida. A. Dorsal view. B. Mandibles, gnathobasic processes, posterior (caudal) view. C. Maxilla, coxal endite omitted. D. Thoracopod 2, male with enlargement of papillation. E. Thoracic endopod 2, distal end, female. F. Thoracic endopod 3 with enlargement of distal end. G. Thoracic endopod 4. Scale: A, 0.5 mm; B, 0.15; C-G, 0.1.

FIGURE 3. Deltamysis holmquistae male, B & D (2.9 mm); Jacksonville, Florida, females, A & E (3.0 mm), C (2.3 mm); Jacksonville, Florida; F (3.2 mm); Port St. John, Florida. A. Thoracic endopod 5. B. Thoracic endopod 6. C. Thoracic endopod 7. Telsons, posterior ends D–F. Scale: A–F, 0.1 mm.

FIGURE 4. Photomicrographs of Deltamysis holmquistae appendages. Length of scale bar is given in parentheses for each photo. A) Maxilla (0.05 mm); B) thoracic endopod 1 (0.05); C, D, & E) male thoracic endopod 2 (0.05, 0.01, & 0.02); F & G) mandibular palps (0.05 & 0.03). Abbreviations: car, carpus; dac, dactylus; endi, endite; endo, endopod; exo, exopod; mer, merus; pro, propodus; dam, damaged seta; art, article.

FIGURE 5. Photomicrographs of Deltamysis holmquistae appendages. Length of scale bar is given in parentheses for each photo. A) right mandible (0.07 mm); B) left mandible (0.05); C) right mandible (0.05); D) left mandible (0.04); E) right mandible (0.05); and F) left mandible (0.05). Abbreviations: in, incisor; lm, lacinia mobilis; mo, molar; spr, spine row.

Tables

TABLE 1. Comparison of diagnostic morphological characters of mature Deltamysis holmquistae.

Characters	D. holmquistae Bowman & Orsi, 1992	K. pillaii Panampunnayil & Biju, 2007	D. holmquistae paratypes; present study	D. holmquistae , NW Atlantic; present study
Anterior margin of	Short, rounded	Broadly triangular	Short, rounded	Short, rounded
carapace
Cornea W/eyestalk W**	0.9*; Fig. 2 A	0.75–0.88*; Fig. 2 A, B	0.84–0.96	0.7–0.9
A 1 setiferous male lobe	Lobe not developed	Small setose lobe developed	Most males with small setose lobe developed	Most males with small setose lobe developed
A 2 scale distal	Suture present	Suture absent	Suture present	Suture present
suture
A 2 scale: L***/W	~3.0	3.2*–3.5; Fig. 2 F, G	2.5–3.6	2.5–3.6
A 2 peduncle L: A 2 scale L	~ 1.10* Fig. 2 G	1.18–1.24 Figs.2 F, G	1.10–1.25	1.17–1.44
A 2 peduncle: ar- ticle 2 L/article 3 L	~0.75–0.78*; Fig. 2 G	0.96–1.02; Figs, 2 F, G	0.80–1.01	0.8–1.2
Mandibular palp,	3.4*; Fig. 2 H	2.4*; Fig. 3A	2.10–2.75	2.1–2.9
article 2: L/W
Lacinia mobilis	Right: absent Left: present	Right: present Left: present	Right: present Left: present	Right: present Left: present
Mandible spine row: no. spines	Right: 8 spines Left: 8 spines	Right: 3 spines Left: 4 spines	Right: 11–12 spines Left: 8–9 spines	Right: 11–12 spines Left: 8–9 spines
Mx 2 endopod:	<0.25	0.9*; Fig. 3E	0.44–0.75	0.5–0.7
article 1 L/ article
2 L
Male thoracic endo- pod 2 with papilla-	No mention of papillations	Papillations on carpus and propodus	Papillations on carpus and propodus	Papillations on carpus and propodus
tions
Thoracic endopod 3 serrated setation	No mention of setation on carpopropodus	Carpopropodus with 4 serrated setae on articles 1 and 2; Fig. 4 A*	Carpopropodus with 5 serrated setae on articles 1–3	Carpopropodus with 5 serrated setae on articles 1–3
Thoracic endopod 4 serrated setation	No mention of setation	No mention of setation	Carpopropodus with 4 serrated setae on articles 2 and 3	Carpopropodus with 4 serrated setae on articles 2 and 3
Carapace: postero- dorsal margin	Thoracic somite 8 exposed	Thoracic somites 6–8 exposed	Thoracic somite 8 exposed; somite 7 may be partially exposed	Thoracic somite 8 exposed; somite 7 may be partially exposed
Penis L/W	~5.0	~4.4*; Fig.4D	5.5–7.0	5.8–6.5
Anterior reach of penis	“Slightly beyond basis of pereopod 7” (thoracopod 8); Fig. 3 F	No mention	To base of thoracic leg 5	To base of thoracic legs 4–5
Telson:
Abdominal somite 6 L/telson L	No mention	Telson “longer than last abdominal segment”	0.95–1.10	1.0–1.2
L/W	1.2	~1.1*; Fig. 5 H	1.1–.3	1.1–1.3

....Continued next page