Hippocampus severnsi, Lourie & Kuiter, 2008

Lourie, Sara A. & Kuiter, Rudie H., 2008, Three new pygmy seahorse species from Indonesia (Teleostei: Syngnathidae: Hippocampus), Zootaxa 1963 (1), pp. 54-68 : 61-64

Hippocampus severnsi sp. nov.

Type material. Holotype: MZB 13594 (16.6 mm, male), between Alung Banua and Cela Point, Bunaken, North Sulawesi, Indonesia (1 o 37’07” to 1 o 36’47” N 124 o 45’30” to 124 o 46.03” E, 50 ft (15.2 m) depth, June 2002, M. Severns & H. Pontoh. Figures 2B and 3B .

Paratypes: MZB 13595 (16.5 mm, female), collection details as for holotype; NMV A24980-001 (12.4 mm, female), Milne Bay, Papua New Guinea (10 o 20'S 150 o 25'E), 12 m depth, black coral, November 2002, L. Maleta .

Diagnosis. Extremely small size (height 13 mm, standard length 15 mm); 12 trunk rings; 27 tail rings; reduced ossification of inferior and ventral trunk ridges; 14 dorsal fin rays; 10 pectoral fin rays; small or absent anal fin; medium length snout which lacks a bulbous tip; raised, angular coronet; single gill opening on midline directly behind coronet supported by raised cleithral bone; scattered tubercles on trunk and tail; predominant colour dark brown (sometimes slightly marbled) with large, bright red patch covering dorso-lateral surfaces of TrR 1–4; tiny white dots scattered all over; pale posterior section of tail with dark transverse bands.

Comparison. Hippocampus severnsi shares most meristic characters with H. pontohi . They differ primarily in live colour and pattern.

H. severnsi can be separated from H. colemani in the same way as H. pontohi , with an additional difference being body colour (brown vs white). Tail ring counts are 27 in H. severnsi vs 28–30 in H. colemani . Other differences include H. severnsi’s raised angular coronet and the following proportions: OD:HL (24.1–26.1% vs 18.6–18.9%), TD9:SL (11.9–15.1% vs 18.9–19.5%), DL:SL (8.4–11.3% vs 6.0–6.7%) and overall size (SL 12.4–16.6 mm vs 26.5–27.3 mm).

H. severnsi is much less robust overall than H. bargibanti and lacks H. bargibanti’s very large tubercles, and bulbous snout tip. It can be further distinguished from H. bargibanti by its body colour (brown vs purple with red tubercles or grey with yellow/orange tubercles), fewer tail rings (27 vs 31–33), proportionally larger, but less deep head (HL:SL 20.9–22.4% in H. severnsi vs 14.8–19.5% in H. bargibanti ; HD:HL 51.7–62.5% vs 60.8–70.3%), less pronounced coronet ( CH:HL 44.7–49.9% vs 46.1–64.1%), larger orbit (OD:HL 24.1–26.1% vs 14.2–24.0%), smaller post-orbital (PO:HL 47.4–51.0% vs 51.6–63.3%), longer trunk (TrL:SL 29.9–33.1% vs 25.7–29.5%) and shorter tail (TaL:SL 45.9–48.3% vs 53.3–57.1%).

It can be distinguished from H. denise by its body colour (brown vs orange), deeper head (HD:HL 51.7–62.5% in H. severnsi vs 41.1–55.7% in H. denise ), shorter and deeper snout (SnL:HL 24.2–27.8% vs 27.1–38.7%; SnD:SnL 83.9–97.4% vs 62.7–81.2%), larger orbit (OD:HL 24.1–26.1% vs 18.8–23.5%), larger post-orbital (PO:HL 47.4–51.0% vs 39.1–45.2%), deeper trunk (TD9:SL 11.9–15.1% vs 4.1–15.1%), longer trunk (TrL:SL 29.9–33.1% vs 23.1–31.7%) and shorter tail (TaL:SL 45.9–48.3% vs 47.4–57.2%). Both sexes of H. severnsi have rounded trunk profiles in comparison to female H. denise’s narrow trunk. Furthermore, it has a much more pronounced coronet and fewer tail rings (27 vs 27–30).

Hippocampus severnsi can be differentiated from H. minotaur most clearly on the basis of meristic values: TrR 12 vs 8–9, TaR 27 vs 41, PF 10 vs 11 and DF 14 vs 7–9. It also has a significantly shallower head (HD:HL 51.7–62.5 vs 75.1–80.2%), longer trunk (TrL:SL 29.9–33.1 vs 18.4–24.7%), shorter tail (TaL:SL 45.9–48.3 vs 56.0–66.6%) and longer dorsal fin base (DL:SL 8.4–11.3 vs 1.5–2.4%).

Description. In addition to the characters given in the diagnosis: head length 20.9% (21.6–22.4%) in SL, and depth 60.8% (51.7–62.5%) in HL; snout length 24.2% (25.8–27.8%) in HL without bulbous tip, and depth 83.9% (88.0–97.4%) in SnL; orbital diameter 24.1% (25.2–26.0%) in HL; postorbital length 48.1% (47.4–51.0%) in HL; frontal bone strongly raised posteriorly to form a sharply angled coronet ( Figure 2B ); pectoral fin–base raised; pectoral fin rays 10.

Trunk rings (TrR) 12, the dorsal surface of TrR1 greatly expanded laterally (and TrR2 to a lesser extent) without spines; trunk length 33.1% (29.9–30.0%) in SL; trunk depth just anterior to dorsal fin base 15.1% (11.9–13.6%) in SL; dorsal fin base strongly raised and angled with respect to the trunk (highest posteriorly); dorsal fin base starting immediately posterior to the 9 th trunk ring and ending immediately posterior to the 12 th trunk ring (covering 3+0 rings); dorsal fin rays 14; no external pouch visible in males, developing young housed entirely within trunk region; anal fin not visible in the holotype but present (with 4 fin rays) in paratypes; first tail ring quadrangular; tail rings 27; tail length 45.9% (47.7–48.3%) in SL.

Sexual dimorphism appears to be limited to differences in the genital region: males with vertical pouch slit, females with slightly raised, circular genital opening.

Body ornamentation: prominent rounded spine above each eye, on midline of snout between eyes, and on either side of the head below the coronet; shoulder spine at base of pectoral fin; cheek spine; black orbital ring with 12 small spines; thick branched or unbranched filament attached to anterior part of coronet; small rounded spine on the superior ridge of the 1 st trunk ring; greatly enlarged rounded spines on the superior ridge of the 5 th trunk ring with distinctive branched red filaments attached; greatly enlarged rounded spine also on superior ridge of the 12 th trunk ring and smaller, but still prominent, spines on lateral and inferior ridges of the 8 th and inferior ridge of 11 th trunk ring. In NMV A24980–001 lateral TrR5 and inferior TrR5–10 spines also developed. Enlarged rounded spines on superior ridge of the tail correspond to bands of colour across 5 th, 9 th, and 12 th (or 4 th, 8 th, 11 th, 14 th in NMV A24980–001) rings.

Colour in life: brown (solid, or slightly marbled) with large red patch covering dorsal and lateral surfaces of TrR1–4; posterior part of tail pale, with transverse brown bands at TaR5, 9 and 12 (or 4, 8, 11, 14); scattered white dots on head, trunk and tail ( Figure 4B ). Colour in alcohol: brown with pale posterior part of tail; transverse brown bands visible on tail ( Figure 3B ).

Etymology. Hippocampus severnsi is named in honour of Mike Severns who, with Hence Pontoh, collected the first specimens.

Distribution and ecology. Hippocampus severnsi is known from Indonesia (Bunaken, Wakatobi, Raja Ampat Islands, Kawe Island), Japan (Ryukyu Islands), Papua New Guinea (Milne Bay, Madang), Solomon Islands (Mborokua) and Fiji at depths of 8– 20 m. See figure 5B for map. It has been observed both during the day and the night but is apparently more active in the morning and late afternoon when it is not in direct sunlight (Müller, pers. comm.). In Indonesia it has been recorded in association with a yellow coloured bryozoan, Catenicella sp. , on different kinds of hydrozoans including Lytocarpus phoenicea , Antennellopsis integerrima and Halicordyle disticha (Müller, pers. comm.) as well as in sheltered spots on a reef wall in association with Halimeda (Brett, pers. comm.). It is also recorded from fissures on current–swept walls where it will tend to occur on the side of the fissure that faces away from the current, but in all cases where there is some upward current (Müller, pers. comm.) and has been seen swimming over a fungiid coral (Hardt, pers. comm.). In Papua New Guinea it has been observed in a healthy reef passage with a regular current of up to two knots on a gorgonian of the genus Muricella at 12 m depth (Halstead, pers. comm.) and in Fiji it was found on gorgonian species, possibly Menella sp. ? (Tackett, pers. comm.)

The holotype of H. severnsi , collected in June, had approximately 11 embryos within its pouch.

Figures

FIGURE 2. Radiographs of holotype specimens: A) Hippocampus pontohi (MZB 13593, 16.9 mm), B) Hippocampus severnsi (MZB 13594, 16.6 mm), and C) Hippocampus satomiae (NMV A25420–001, 13.8 mm). Scale bar = 2 mm in each case.

FIGURE 3. Preserved holotype specimens of A) Hippocampus pontohi (MZB 13593, 16.9 mm), B) Hippocampus severnsi (MZB 13594, 16.6 mm), and C) Hippocampus satomiae (NMV A25420–001, 13.8 mm). Scale bar in mm.

FIGURE 4. Live specimens of new species of pygmy seahorses from Indonesia. A) Hippocampus pontohi: Bunaken, Sulawesi, M. Boyer; Bunaken, Sulawesi, M. Aw; Raja Ampat, West Papua, L. Tackett. B) Hippocampus severnsi: Bunaken, Sulawesi, S. Wong & T. Uno; Bunaken, Sulawesi, M. Severns (type specimens); Raja Ampat, West Papua, L. Tackett. C) Hippocampus satomiae: Derawan Kalimantan, S. Wong & T. Uno; Derawan, Kalimantan, J–S. Chen; Derawan, Indonesia, S. Onishi (type specimen).