Microstoma australis, Gon, Ofer & Stewart, Andrew L., 2014

Gon, Ofer & Stewart, Andrew L., 2014, Description of a new species of Microstoma (Pisces, Microstomatidae) from the southwestern Pacific Ocean, Zootaxa 3884 (1), pp. 55-64 : 56-63

Microstoma australis , new species

( Figures 1 a–c; Table 1 )

Holotype. AMS I.27328-002, 140.5 mm, Australia, New South Wales, off Cape Hawke (32°19’S, 152°59’E), midwater trawl, 0–366 m, FRV Kapala , 13 August 1985.

Paratypes. AMS I.21749-001, 50.2 mm, Australia, New South Wales, east of Jarvis Bay (35°02’S, 152°48’E), midwater trawl, 0–210 m, CSIRO RV Sprightly, 26 October 1979. AMS I.21770-001, 35.0 mm, Australia, New South Wales, east of Tuross Heads (36°04'S, 152°45'E), midwater trawl, 0–152 m, CSIRO RV Courageous, 3 December 1978. NMNZ P.11011, 69.15 mm, New Zealand, Chatham Rise, off Cape Palliser, southern Hikurangi Trench (41° 55.100'S, 175° 44.925'E), midwater trawl, 0–210 m, RV James Cook, 27 June 1975. NMNZ P. 39873, 221.7 mm, New Zealand, Campbell Plateau, NE off Campbell Island (52°6.750'S, 171°0.250'E), midwater trawl, 0–493 m, FV Alexander Buryachenko, 13 September 2003. NMNZ P. 46668, 266.2 mm, New Zealand, Snares Islands, Pukaki Rise (49°08.47'S, 172°36.72'E), bottom trawl, 0–483 m, RV Tangaroa , November 2009. SAIAB 194659 (previously AMS I.16494-042), 54.9 mm, Australia, New South Wales, 50 miles off Sydney Heads (34°08’S, 152°13’E), midwater trawl, 0–600 m, FRV Kapala , 25 March 1971.

Comparative material. Microstoma microstoma , Mediterranean: Sicily, Strait of Messina, AMS B. 6798, 160 mm; AMS B.6799, 155.0 mm; AMS B.6800, 80 mm; AMS B.6801, 69.8 mm; MCZ 40833, 2: 178.0– 179.2 mm. Eastern Atlantic: off Azores, MCZ 66009, 75.1 mm; MCZ 66043, 35.25 mm. Off Mauritania, MCZ 66004, 2: 41.0–47.0 mm; MCZ 66037, 32.4 mm. Senegal, CAS 234808, 80 mm (x-ray image). Off Guinea, N of Equator, MCZ 66000, 35.9 mm; MCZ 66003, 26.5 mm; MCZ 66008, 53.6 mm; MCZ 66010, 92.9 mm; MCZ 96852, 38.6 mm. Western Atlantic: Middle N Atlantic, MCZ 66040, 22.75 mm. NE of Bermuda, MCZ 101633, 80.25 mm; S of Florida, MCZ 66039, 24.2 mm; Caribbean Sea, MCZ 159281, 76.0 mm. N of Equator, MCZ 61960, 2: 83.3–103.7 mm and 1 cleared & stained (head and body separated). Microstoma sp., NE Pacific Ocean: California, CAS 38796, 43 mm; CAS 98481, 104 mm; CAS (SU) 49797, 36 mm (all x-ray images).

Diagnosis. A species of Microstoma with 25–29 gill rakers, 52–54 vertebrae, slender body (depth at pectoralfin base 6.6–8.3), dorsal and pelvic fins set far back on body (predorsal length 69.0–74.5 and prepelvic length 67.8–71.4) and short space between pelvic and anal fins (distance from pelvic-fin insertion to anal-fin origin 12.5–14.5).

Description. Morphometric data for selected type specimens are shown in Table 1 . In the description below data in parentheses refer to the paratypes. Dorsal-fin rays 12 (11), anal-fin rays 7 (7–8), pectoral-fin rays 7 (7–8) and pelvic-fin rays 9 (8–9). Lateral-line scales (52–53, two paratypes), gill rakers 7+18 (8–9 + 17–20), branchiostegal rays 3 in all, pyloric caeca (5–8, two paratypes) and vertebrae 52 (52–54). Body slender, of similar depth from head to dorsal-fin origin; body depth at preopercle edge 7.4 (7.2–9.0), at pectoral-fin base 7.6 (6.6–8.3) and at pelvic-fin insertion 8.2 (5.8–9.3); behind dorsal fin body becomes even more slender, reaching depth of 6.2 (4.5–7.5) at anal-fin origin and 3.7 (3.2–5.4) on caudal peduncle. Body almost cylindrical anteriorly, body width 7.8 (6.6–7.6), gradually becoming more laterally compressed behind anal-fin origin. Head small, its length 20.85 (19.5–20.75). Snout short, 5.1 (3.9–5.7); eye very large, slightly oval, bulging into dorsal profile of head ( Fig. 1 a), its horizontal diameter 7.0 (6.6–7.0) and interorbital width (3.9–5.6); supraorbital length (5.05–5.1), overlapping postorbital more or less over middle of eye. Mouth small, jaws not reaching vertical at front edge of eye; upper jaw length 3.1 (3.0–3.55) and lower jaw length 4.0 (3.6–4.6). Dorsal, anal and pelvic fins on posterior third of body; predorsal distance 70.0 (69.0–74.5); pelvic-fin length (7.3–9.2, two largest paratypes), fin inserted slightly in front of dorsal-fin origin, prepelvic distance 67.9 (68.2–71.4); preanal distance 80.7 (82.6–85.3). Pectoral-fin length 11.4 (10.2–12.95); pectoral fin placed on lower third of body, distance from its upper base to dorsal midline of body 5.7 (4.3–5.6). Distance from upper pectoral-fin base to pelvic fin insertion 48.0 (46.5–51.7) and distance from pelvicfin insertion to anal-fin origin 13.2 (12.55–14.5). Caudal peduncle slender and fairly short, its depth 3.7 (3.2–5.4) and its length 15.6 (11.2–16.1).

Colour when fresh, silvery grey, gradually changing to dark brown with purplish tinge from about pelvic-fin insertion posteriorly ( Fig. 1 ). Jaws black, iris silvery. Fins pale, except for black, square to semi-circular spot on proximal part of middle caudal-fin rays.

Colour in alcohol, body brown on anterior half to two thirds, gradually becoming darker posteriorly to dark brown on caudal peduncle. Tip of snout and jaws dark brown and opercle with some dark pigment. Fins pale, except semi-circular dark brown spot proximally on middle caudal-fin rays. Mouth cavity, gill chamber and peritoneum dark brown in specimens larger than 100 mm SL.

Distribution. This species is currently known only from the type specimens, four of which were collected east of New South Wales, Australia, and the remaining three in the EEZ of New Zealand ( Fig. 2 ).

Etymology. This species is named australis, Latin for southern, reflecting its distribution.

Remarks. Cohen (1964) examined morphometric characters of 11 juvenile and adult specimens (20–161 mm) of Microstoma from the Mediterranean, the Gulf of Mexico and the NE Pacific Ocean, and found “considerable allometric growth”. This seems to also be the case in M. australis , but it needs to be confirmed with a larger sample. Specimens smaller than 100 mm have a relatively deeper body ( Fig. 3 a, Table 2 ), and the caudal peduncle seems to become longer and more slender as the fish grow ( Fig. 3 b). Allometric growth also occurs in the length of the dorsal fin of both species, showing an inverse relationship to the fish length ( Fig. 4 a). This may also occur in the anal and pelvic fins lengths. The 28.3 mm juvenile illustrated by Moser and Butler (1996) has high dorsal and anal fins that seem to reach as far back as caudal-fin base, and a pelvic fin reaching beyond anal-fin origin. The long dorsal and pelvic fins are also evident (the anal fin is shorter or damaged) in the radiograph of a 43 mm fish from California ( Fig. 1 e). In a 33.6 mm specimen of M. microstoma (MCZ 66041) the anal fin reached the caudalfin base and the pelvic fin reached the anus. In a 50.2 mm specimen of M. australis (AMS I.21749-001) the dorsal fin reached beyond the middle of the caudal peduncle, though the tips of the longest rays were damaged.

As in other microstomatids, the branchiostegal rays of Microstoma are very thin, transparent and pliable, and difficult to distinguish from skin, especially when the ventral part of the head is damaged. Cohen (1964) was uncertain about his count of two branchiostegal rays in M. microstoma ; Moser and Butler (1996) found four rays in juveniles of Microstoma sp. from the NE Pacific; and we observed three rays in all our specimens where they could be confidently counted, including those of Altantic and Mediterranean M. microstoma . Interspecific variation in the number of branchiostegal rays was observed in species of the microstomatid genus Nansenia ( Kawaguchi & Butler 1984) and in species of the bathylagid genus Bathylagichthys ( Kobyliansky 1990) . While such variation could be present in Microstoma , this character needs re-examination when material in better condition becomes available for study.

Cohen (1964) identified all his specimens as M. microstoma . He did not find differences between specimens from the Mediterranean-Atlantic and NE Pacific regions probably because he overlooked the importance of the vertebral count, and because he counted gill rakers in only one specimen.

Comparisons. The number of gill rakers ( Table 3) and the number of vertebrae ( Table 4, Figs. 1 c, d) clearly distinguish between the two Microstoma species as both counts are lower in M. microstoma . In comparing morphological characters ( Fig. 4 ) comparisons were done according to size groups because of the allometric growth patterns observed in both species (see Remarks above). Non-overlapping characters in both size-groups are potentially useful for species discrimination ( Table 2 ), but this requires confirmation from a larger sample size. For example, the predorsal distance ( Fig. 4 b) of M. australis is longer than that of M. microstoma in the smaller sizegroup (72.3–74.5% versus 66.7–69.4% of SL, respectively) as well as in the larger size-group (69.0–70.2% versus 63.8–68.4% of SL, respectively). Similarly, the distance between pelvic-fin insertion and anal-fin origin ( Fig. 4 c) is shorter in M. australis in both size-groups (12.5–13.9% versus 15.3–17.05% of SL and 13.2–14.5% versus 16.4–17.9% of SL, respectively). The dorsal fin of M. australis is higher ( Fig. 4 a).

Number of gill rakers

19 20 21 22 23 24 25 26 27 28 29 Microstoma australis (NewZealand & Australia) 1 3 1 1 Microstoma sp. (NE Pacific)* 1* M. microstoma (Mediterranen) 3

M. microstoma (E Atlantic) 1 1 1 2 2

M. microstoma (W Atlantic) 1 1 1 1

*Data source: Moser & Butler (1996); number of specimens counted unknown

Number of vertebrae

43 44 45 46 47 48 49 50 51 52 53 54 Microstoma australis (NewZealand & Australia) 5 1 1 Microstoma sp. (NE Pacific)* 2+1* 1+1* M. microstoma (Mediterranen) 3 3

M. microstoma (E Atlantic) 1 6 1 3

M. microstoma (W Atlantic) 1 3 2

*Data source: Moser & Butler (1996); number of specimens counted unknown The new species is markedly larger, at 266.2 mm SL (280 mm SL freshly thawed), than has been recorded for Microstoma microstoma (210 mm TL: Cohen 1986).

The illustration of a 28.3 mm juvenile from the NE Pacific in Moser and Butler (1996) shows the melanophores on the side of the body arranged along the myomere septa, and melanophores present on the middle section of dorsal-, anal- and pelvic-fin rays. The same pattern of melanophores is also visible along the side of the body of the smaller specimens of M. australis and is still visible in a 54.9 mm paratype (SAIAB 194659); a similar pattern was described by Cohen (1964) in Microstoma microstoma . We observed dark pigment near the edge of the dorsal and anal fins, but not on the pelvic fin in a 33.6 mm specimen of M. microstoma (MCZ 66041) that had relatively undamaged fins. None of the specimens of M. australis had pigment on these three fins.

Microstoma sp. of the NE Pacific ( Moser & Butler 1996) differs from M. australis in having fewer vertebrae and gill rakers. In addition, Moser and Butler (1996) counted 11 pectoral-fin rays in their specimens, a significantly higher count compared to the 7–8 rays found in M. australis and M. microstoma ( Table 5, Cohen 1986, McEachran & Fechhelm 1998). This count (if correct), together with the aforementioned two characters, suggest that the NE Pacific fish represent another undescribed species.

Pectoral-fin rays

7 8 9 10 11

Microstoma australis ( New Zealand & Australia) 2 4

Microstoma sp. (NE Pacific)* 1* M. microstoma (Mediterr.) 3

M. microstoma (E Atlantic) 4

M. microstoma (W Atlantic) 2 1

*Data source: Moser & Butler (1996); number of specimens counted unknown

Figures

FIGURE 1. Images of Microstoma australis AMS I. 27328 - 002, holotype, 140.5 mm, off Cape Hawke, NSW: (a) fresh specimen (K. Graham, NSW Fisheries), (b) preserved specimen (O. Gon), and (c) radiograph (S. Reader, AMS); and positive radiographs of (d) Microstoma microstoma MCZ 61960, 103.7 mm, Western Atlantic (A. Williston, MCZ), and (e) Microstoma sp. CAS 38796, 43 mm, California (J. Fong, CAS).

FIGURE 2. Map of the southwestern Pacific Ocean with collection sites of Microstoma australis. The circle with the cross represents the holotype.

FIGURE 3. Examples of allometric growth in morphometric characters of Microstoma australis. (a) body depth at pectoral-fin base. (b) caudal peduncle depth and length.

FIGURE 4. Comparison of selected morphometric characters in Microstoma australis and M. microstoma. (a) dorsal fin length. (b) predorsal distance. (c) distance between pelvic-fin insertion and anal-fin origin.

Tables

TABLE 1. Proportional measurements (expressed as percentage of the standard length) of selected type specimens of Microstoma australis.

	Holotype	Paratype	Paratype	Paratype	Paratype	Paratype
Standard length (mm)	AMS I.27328-002 140.5	AMS I.21749-001 50.2	SAIAB 194659 54.9	NMNZ P.11011 69.15	NMNZ P.39873 221.7	NMNZ P.46668 266.2
Head length (mm)	29.3	10.3	10.85	14.35	43.2	51.9
Body depth @ preopercle	7.4	9.0	8.5	8.5	7.2	7.4
Body depth @ Pectoral-fin base	7.6	8.3	8.2	7.9	6.6	6.8
Body depth @ pelvic-fin insertion	8.2	9.3	7.0	8.4	5.8	7.3
Body depth @ anal-fin origin	6.2	7.5	6.8	6.5	4.5	5.75
Lengthofhead	20.85	20.5	19.8	20.75	19.5	19.5
Lengthofsnout	5.1	3.9	5.2	4.05	5.4	5.7
Eyediameter	7.0	7.0	6.6	6.7	6.6	6.6
Interorbitalwidth	Damaged	5.6	Damaged	5.2	4.5	3.9
Length of upper jaw	3.1	Damaged	3.55	3.3	3.1	3.0
Length of lower jaw	4.0	4.6	4.4	4.1	3.9	3.6
Dorsal-fin length	19.0	20.5	Damaged	Damaged	Damaged	Damaged
Anal-fin length	Damaged	Damaged	Damaged	Damaged	Damaged	Damaged
Pectoral-fin length	11.4	12.95	Damaged	Damaged	12.1	10.2
Pelvic-fin length	Damaged	Damaged	Damaged	Damaged	9.2	7.3
Depth of caudal peduncle	3.7	5.1	5.4	4.6	3.2	3.4
Length of caudal peduncle	15.6	11.2	11.5	12.5	16.1	15.4
Snout to dorsal-fin origin	70.0	72.3	74.5	73.5	69.0	70.2
Snout to anal-fin origin	73.6	83.6	85.3	85.3	Damaged	82.6
Snout to pelvic-fin insertion	67.9	70.6	71.4	71.4	68.2	67.7
Upper pectoral-fin base to pelvic-fin insertion	48.0	50.8	51.7	50.6	48.35	46.5
Pelvic-fin insertion to anal-fin origin	13.2	12.55	13.6	13.9	13.9	14.5
Greatestbodywidth	7.8	7.6	6.6	7.2	6.6	7.5
Upper pectoral-fin base to dorsal midline of body	5.7	5.6	5.4	5.6	4.3	5.4
Length of supraorbital bone	Damaged	Damaged	Damaged	Damaged	5.1	5.1

TABLE 2. Comparison of proportional measurements (expressed as percentage of the standard length) of Microstoma australis and M. microstoma in two size classes.

	Microstoma australis	Microstoma microstoma	Microstoma australis	Microstoma microstoma
	(<100 mm SL)		(>100 mm SL)
Standard length (mm)	50.2–69.15 (n=3)	32.4–92.9 (n=7)	140.5–266.2 (n=3)	103.7–178 (n=3)
Body depth @ preopercle	8.5–9.0	8.7–9.3	7.2–7.4	8.5–8.9
Body depth @ Pectoral-fin base	7.9–8.3	8.4–9.1	6.6–7.6	8.05–8.8
Body depth @ pelvic-fin insertion	7.0–9.3	8.1–9.2	5.8–8.2	8.05–8.8
Body depth @ anal-fin origin	6.5–7.5	6.7–7.3	4.5–6.2	6.0–7.2
Length of head	19.8–20.75	20.1–21.1	19.5–20.85	19.1–19.8
Length of snout	3.9–5.2	3.6–4.6	5.1–5.7	4.2–4.7
Eye diameter	6.6–7.0	7.3–8.3	6.6–7.0	6.6–7.6
Interorbital width	5.2–5.8	4.7–5.4	3.9–4.5	4.9–5.1
Length of upper jaw	3.3–3.5	3.3–3.6	3.0–3.1	2.9–3.2
Length of lower jaw	4.1–4.6	4.1–4.5	3.6–4.0	3.6–3.9
Dorsal-fin length	20.5 (1 fish)	16.7–17.6	19.0 (1 fish)	11.2–13.55
Pectoral-fin length	12.95 (1 fish)	11.9–13.9 (2 fish)	10.2–12.1	10.5–12.8
Pelvic-fin length	Damaged	9.6–11.9 (2 fish)	7.3–9.2	7.7–8.1
Depth of caudal peduncle	4.6–5.4	4.5–4.7	3.2–3.7	4.1–4.3
Length of caudal peduncle	11.2–12.5	13.85–15.6	15.4–16.1	15.0–17.5
Snout to dorsal-fin origin	72.3–74.5	66.7–69.4	69.0–70.2	63.8–68.4
Snout to anal-fin origin	83.6–85.3	78.5–84.4	73.6–82.6	78.8–81.9
Snout to pelvic-fin insertion	70.6–71.4	57.6–66.85	67.7–68.2	60.0–64.6
Upper pectoral-fin base to pelvic-fin insertion	50.6–51.7	41.7–45.9	46.5–48.3	41.2–44.8
Pelvic-fin insertion to anal-fin origin	12.5–13.9	15.3–17.05	13.2–14.5	16.4–17.9
Greatest body width	6.6–7.6	7.8–8.7	6.6–7.8	7.6–8.6
Upper pectoral-fin base to dorsal midline of body	5.4–5.6	5.1–5.6	4.3–5.7	4.8–5.8
Length of supraorbital bone	5.1 (1 fish)	5.0–5.4	5.1 (2 fish)	4.65–5.0