Hippocampus pontohi Lourie & Kuiter, 2008

Short, Graham, Smith, Richard, Motomura, Hiroyuki, Harasti, David & Hamilton, Healy, 2018, Hippocampusjapapigu, a new species of pygmy seahorse from Japan, with a redescription of H. pontohi (Teleostei, Syngnathidae), ZooKeys 779, pp. 27-49 : 27

Hippocampus pontohi Lourie & Kuiter, 2008 Figures 6, 7, 8, 10, Table 1, 2 Pontoh’s Pygmy Seahorse

Hippocampus severnsi Lourie & Kuiter, 2008: figs. 2B-4B (Bunaken, North Sulawesi, Indonesia); Reijnan et al. 2011: fig. 2B (Siladen I, SE Siladen).

Material.

AMS I.47833-001. 13.9 mm SL, GenBank accession number KY066111, Cape Kri, Raja Ampat, Indonesia. 0°33 ’23.5” S 130°41 ’25.0” E, depth 6 m, collected by Otto Awom, Gerry Allen, and Mark Erdmann using hand net in small clump of algae and hydroids on vertical surface, 1 January 2007. Mitochondrial COI sequence data and corresponding Genbank accession numbers for additional vouchered specimens of H. pontohi (Table 2).

Diagnosis.

Hippocampus pontohi differs from its congeners by the following combination of characters: subdorsal rings 4; two pairs of bilaterally wing-like protrusions formed by a pair of large truncate spines projecting laterad on both first and second superior trunk ridges; laterodorsal surface flat on the third and fourth trunk rings; tail rings 28; dorsal fin rays 12; pectoral fin rays ten.

Description.

General body shape as in Figure 6. Morphometric characters listed in Table 1. Head length 21.6% in SL, head depth 64.4% in HL; snout length 24.1% in HL, bulbous tip absent, snout depth 89.0% in SnL; post-orbital 50.9% in HL; distinct, angular coronet, coronet height 46.2% in HL, unbranched dermal appendage attached to anterior part of coronet; single gill-opening on midline behind coronet supported by elevated cleithral ring; dorsal fin 14 rays; pectoral-fin rays nine; anal fin rays four; trunk rings 12, trunk length 33.0% in SL, trunk depth just anterior to dorsal fin base 14.4% in SL; dorsal fin base strongly raised posterodorsad; subdorsal rings four, dorsal fin base starting immediately posterior to ninth trunk ring and ending immediately posterior to first tail ring; no external pouch visible; tail rings 28, tail length 45.3% in SL. Body ornamentation: prominent spine dorsal of eye, small spine ventroposterior to eye; lateral head spine ventral of coronet; two moderately large spines on cleithral ring, upper spine at level of last pectoral fin ray, lower spine at ventral extent of ring; snout spine on midline between eyes; nape spine absent; subdorsal spines four, superior trunk ridge ending with three rounded spines protruding laterad, the posterior spine greatly enlarged on 12th trunk ring; superior trunk ridge with large bilaterally paired truncate spines projecting laterad on first and second trunk rings, laterodorsal surface flat on second, third, and fourth trunk rings, large bilaterally paired spines on fifth trunk ring, and small pair of spines dorsally on sixth trunk ridge; lateral trunk ridge with small spine on fifth trunk ring and large spine on eighth trunk ring; inferior trunk ridge with spines of moderate size beginning on fifth trunk ring and and ending on 11th trunk ring; superior tail ridge spines well developed anteriorly, becoming smaller posteriorly, with enlarged spines on fifth and ninth tail rings; inferior tail ridge spines absent; caudal fin absent.

Remarks.

Although Hippocampus pontohi was distinguished from H. severnsi primarily by features of coloration ( Lourie and Kuiter 2008), meristic, morphometric, and diagnostic morphological characters in the original description did not support the separation of these seahorses into two species. The invalidity of H. severnsi was subsequently recognised due to the unreliability of employing coloration as a useful diagnostic character in order to distinguish between species of seahorses ( Lourie et al. 2016). Here we further support the synonymization of H. severnsi under H. pontohi based on partial mitochondrial COI genetic data collected from additional 21 vouchered specimens of H. pontohi and those referred to as H. severnsi (Table 2). Genetic distance analysis (uncorrected p distances) failed to discriminate H. severnsi from H. pontohi (Suppl. material 1), which revealed an average intraspecific divergence of 0.2%. A neighbour joining tree of the COI sequence data, including COI data from H. bargibanti , H. denise , and H. japapigu , is supplied here as Suppl. material 2.

Comparative remarks.

The combination of characters provided in the diagnosis that distinguishes H. japapigu from all congeners are presented in Table 3 and summarized below. The new species is unique in Hippocampus in possessing a distinct elevated dorsal ridge internally formed by triangular bony mounds in the anterodorsal area of the trunk directly posterior to the head, which we propose as an apomorphy for this species. All currently recognized seahorse species, including the pygmy seahorse congeners, differ in the absence of triangular bony mounds and the presence of typical flat surfaces dorsally on the second to fourth superior trunk rings. Hippocampus japapigu is most similar to H. pontohi (Fig. 8, Table 3) in meristics, overall body ornamentation, and the presence of a distinct coronet. They differ primarily on the basis of bilaterally paired wing-like protrusions directly posterior to the head, which are internally formed by a single connected pair of large, truncate spines projecting dorsolaterad on the first superior trunk ridge in H. japapigu , as opposed to a double pair of large truncate spines projecting strongly laterad on both the first and second superior trunk ridges in H. pontohi . Additional distinctions include patterns of the anterodorsal trunk rings (elevated dorsal ridge formed by triangular bony mounds dorsad on the second to fourth trunk rings in H. japapigu , laterodorsal surface flat on the third and fourth trunk rings in H. pontohi ); eighth lateral trunk ridge spine (very large and prominent spine projecting laterad in H. japapigu , small in H. pontohi ); color pattern (brown with white reticulation, thin red line tracing the superior trunk ridge anterior to dorsal fin base in H. japapigu , white, brown, or black color with elliptical markings, each outlined with thin red lines, tracing the entire superior trunk ridge and extending ventrally around the fifth superior and eighth lateral trunk ridge spines in H. pontohi ). Hippocampus japapigu and H. pontohi can be further be distinguished by the number of tail rings (28 vs. 28-30), dorsal fin rays (14 vs. 12), and pectoral fin rays (9 vs. 10).

Several other pygmy seahorse species are morphologically similar to Hippocampus japapigu , including H. colemani , H. satomiae , and H. waleananus . The following characters support the distinctions among these species: number of tail rings (28 in H. japapigu vs. 26 in H. colemani , 27-28 in H. satomiae , 32 in H. waleananus ); dorsal fin rays (14 in H. japapigu vs. 13 in H. satomiae , 12 in H. waleananus ); coronet (distinct in H. japapigu vs. low and rounded in H. colemani , low double mound in H. waleananus ); cleithral ring spines (at pectoral fin base and ventral of head in H. japapigu vs. pectoral fin base in H. waleananus ); eye spine dorsally (double spine in H. satomiae ), eye spine ventrally (absent in H. satomiae ); superior tail ridge spines (fifth, ninth, 12th vs. absent in H. colemani , fourth, eighth, 12th in H. waleananus ); inferior tail ridge spines (absent vs. present on last 28 tail rings in H. waleananus ).

Hippocampus japapigu shares with H. pontohi , H. colemani , H. satomiae , and H. waleananus 12 trunk rings, strongly raised continuous cleithral ring, and presence of diagnostic body ornamentation (snout spine, eye spines, two cliethral spines, lateral head spine, large spine on fifth superior trunk ridge, large spine on eighth lateral trunk ridge, small spine on fifth lateral trunk ridge, Table 2), including wing-like-protrusions immediately posterior to the head. Based on careful visual examinations of in situ underwater photographs, x-rays, and type material ( Kuiter 2003; Lourie and Kuiter 2008; Gomon and Kuiter 2009; Smith 2017), it appears H. japapigu shares with H. waleananus a single pair of bilaterally paired wing-like protrusions (vs. double pair in H. colemani and H. satomiae ). In the original description of H. colemani (Kuiter, 2003), the number of trunk rings was diagnosed as 11, however in our comparative analysis of trunk ring counts, we detected the presence of 12 trunk rings in the x-ray of the holotype of H. colemani (Gomon & Kuiter, 2009, AMS I.41181-001, fig. 3B). Furthermore, we noted 4 subdorsal rings (three trunk and one tail rings) via μCT in H. japapigu and the non-type H. pontohi , and similarly four subdorsal rings in our examination of the radiographs of H. colemani , H. pontohi , and H. satomiae ( Kuiter 2003, fig. 3B; Lourie and Kuiter 2008, figs 2A,C; Gomon and Kuiter 2009, fig. 3B). In contrast, three subdorsal trunk rings were noted in the original diagnoses of these pygmy seahorses. Hippocampus japapigu and H. pontohi retain the ring and ridge structure of larger seahorses, and with μCT scans, we can detect well-developed ossification of the skeleton, including the strong ossification of the inferior and ventral trunk area (Figs 8-10). Similarly, Gomon & Kuiter (2009, fig. 3B) detected a well-formed skeleton in H. colemani via x-ray. In contrast, H. bargibanti and H. denise reveal incomplete ossification of the inferior and ventral trunk ridges anteriorly, the ridges reduced to star-shaped dermal ossifications ( Gomon 1997; Lourie and Randall 2003; Gomon and Kuiter 2009).

Genetic comparisons.

Suppl. material 1 shows genetic distance analysis at the COI gene (uncorrected p distances) between H. japapigu and previously sequenced non-type specimens of the pygmy seahorses H. pontohi , H. bargibanti , and H. denise ( Hamilton et al. 2017), and additional vouchered specimens of H. pontohi . Hippocampus japapigu differs from H. pontohi by 10.1%, from H. bargibanti by 13.0%, and H. denise by 10.1%. Reported mtDNA clock rates of approximately 1.2% per million years in marine teleosts ( Reece et al. 2010) indicate divergence between H. japapigu and H. pontohi approximately 8.4 million years ago.

Distribution and habitat.

Hippocampus japapigu sp. n. is only known to occur in Japan, from scattered localities including Kashiwa-jima Island, Sukumo Bay; Kushimoto, Kii Peninsula; Osezaki, Izu Peninsula; the Izu Islands of Miyake and Hachijo; Sagami Bay; and Chichi-jima, Ogasawara Islands. The specimens described herein were found off the northwest coast of Hachijo-jima Island at a depth of 10-13 m, and have been anecdotally reported elsewhere at 5-22 m by local divers. Owing to its diminutive size and extraordinary crypsis, this species may have a wider distribution within Japan. The new taxon is not associated with a particular host, and has been observed in association with mixed soft coral, the coralline algae Halimeda sp., and hydroids on rocky reef walls and large boulders in both exposed and semi-sheltered locations. During 15 dives initially spent searching ad hoc for this species by the second author in July 2013, 13 individuals were observed in an approximately 100 m stretch of rocky reef. These ranged in depth from 10 to 20 m and water temperature fluctuated between 19-24°C over 6 days. When one individual was discovered, another was often found in close proximity and appeared to represent male-female pairs. Returning in June 2015 with a larger group of experienced dive guides, with 10 dives searching for the species, only a single individual was found, possibly suggesting fluctuations in the abundance of the species. Several pregnant males were observed in July 2013, but it is unknown whether reproduction occurs seasonally or year-round.

Etymology.

The specific epithet is from the colloquial Japanese name of the new species, Japan Pig, Japapigu, or 日本のピグミ ータツノオトシゴ.

Common name.

New common English and Japanese names, Japanese Pygmy Seahorse and Hachijo-tatsu, respectively, are proposed here for Hippocampus japapigu .