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Description of a new snake eel (Pisces: Ophichthidae: Myrichthys) from the Philippines.

INTRODUCTION

The snake eels of the cosmopolitan genus Myrichthys were revised by McCosker & Rosenblatt (1993). They recognized nine valid species and 28 synonyms. We are unaware of subsequent publications that have either described additional species or changed the taxonomy of the taxa treated therein. We herein describe a tenth species from the Verde Passage, southern Luzon Island, Philippines. Two specimens of this vividly patterned snake eel were collected by Peri Paleracio, an avid naturalist, diver, and fish collector, and we are pleased to name it in his honor.

MATERIALS AND METHODS

Measurements are straight-line, made either with a 300 mm ruler with 0.5 mm gradations (for total length, trunk length, and tail length) and recorded to the nearest 0.5 mm, or with dial calipers (all other measurements) and recorded to the nearest 0.1 mm. Body length comprises head and trunk lengths. Head length is measured from the snout tip to the posterodorsal margin of the gill opening; trunk length is taken from the end of the head to mid-anus; and maximum body depth does not include the median fins. Head-pore terminology follows that of McCosker et al. (1989: 257), such that the supraorbital pores are expressed as the ethmoidal pore + pores in supraorbital canal, i.e., 1 + 3, and the infraorbital pores are expressed as pores along the upper jaw + those in vertical part of canal behind eye (the "postorbital pores"), i.e., 4 + 2, in that frequently the last pore included along the upper jaw is part of the postorbital series. Vertebral counts (which include the hypural) were taken from radiographs. The mean vertebral formula (MVF) is expressed as the average of predorsal, preanal, and total vertebrae (Bohlke 1982). Institutional abbreviations follow the Standard Symbolic Codes for Institutional Research Collections in Herpetology and Ichthyology (Leviton et al. 1985).

Myrichthys paleracio, n. sp.

Peri's snake eel (Figs 1-3)

Holotype: CAS 233313, 311 mm, an immature male, Layag Layag, 13.688[degrees] N 120.841[degrees] E, Luzon Island, Batangas Province, Philippines, hand net, P. Paleracio, 15 May 2011.

Paratype: WAM 33154.001, 315+ mm (tail bro-ken and healed), ripe female, Caban Island, 13[degrees]41.376' N 120[degrees]50.374' E), Verde Passage, Batangas Province, Philippines, mixed sand, rubble and coral, 33m, hand net, P. Paleracio, 12 June 2009.

Diagnosis: An elongate species of Myrichthys with depth 43 times and tail 1.8 in TL; pectoral fin minute, its length about twice in eye; numerous large brown spots on head and body; and total vertebrae 183, mean vertebral formula 3/77.5/183.

Counts and measurements (in mm) of the holo-type (followed by those of the paratype in paren-theses): Total length 311 (315+, damaged tail); head 23.7 (35.3); trunk 120.3 (186.7); tail 167 (?); predorsal distance 13.6 (23.6); pectoral fin length 1.2 (2.1); pectoral fin base 2.2 (4.4); body depth at gill openings ~7.2 (~16); body width at gill openings ~5.5 (~10.5); snout 4.2 (6.9); tip of snout to rictus of jaw 6.6 (10.5); tip of chin to rictus of jaw 5.0 (7.9); eye diameter 2.2 (3.9); interorbital distance 3.6 (6.6); gill opening height 2.1 (4.0); isthmus width ~3.8 (~7.0). Predorsal vertebrae 2 (4), preanal vertebrae 79 (76); total vertebrae 183. Ten lateral line pores in left branchial region; remainder small and difficult to discern.

Description: Body elongate, its depth at gill openings 43 in TL; head and trunk 2.16 and head 13.1 in TL; snout rounded, conical when viewed from above; lower jaw included, snout tip reaching base of anterior nostrils; eye large, 2.7-3.0 in upper jaw, its center well behind midpoint of upper jaw; anterior nostrils tubular, elongate, about twice in eye, with small lappet extending from each side; posterior nostrils in upper lip, not visible externally, beginning before eye and ending beneath middle of pupil; upper lip papillate, particularly between anterior and posterior nostrils; broad fleshy chevron dividing snout between anterior nostrils; dorsal fin origin on head, well in advance of gill opening, 1.5-1.7 in HL; pectoral fin minute, much shorter than its base, nearly twice in eye diameter.

Head pores minute, but typical of Myrichthys (McCosker 1977); five mandibular, two preopercular, single ethmoidal + 3 supraorbital, 4 + 2 infraorbital, three temporal and single interorbital and supratemporal pores; preopercular, temporal, suborbital, postorbital and other series present; single median interorbital and temporal pores; two preopercular pores; four mandibular pores; lateral line pores present, 10 before the gill openings, remainder too difficult to ascertain.

Teeth granular, small and fixed, irregularly biserial in jaws and on vomer; small intermaxillary chevron anteriorly, followed by gap.

Colour in life (Figs 1-3) and in preservation: white to pale, overlain on head, trunk and tail with about 50 or more brown saddles, extending from base of dorsal fin to ventral edge of flank (many saddles incomplete, some irregular, and all wider than pale interspaces, meeting along ventral surface posterior to anus); snout, chin, and anterior nostrils markedly white; eye within brown mask, followed by two diagonal bands and several eye-sized brown spots; throat and anteroventral trunk region overlain with several eye-sized brown spots; pectoral fins pale; median fin margins pale, brown body saddles extending onto base of dorsal fins; tail tip pale.

Remarks: The new species differs from its congeners on the basis of its coloration, reduced pectoral fin and vertebral number. It is most closely related to the dark-spotted and banded Indo-Pacific species Myrichthys maculosus (Fig. 3) and M. colubrinus and differs from them in the distribution, number and size of its spots and in its vertebral number. Myrichthys maculosus (Fig. 3) and M. colubrinus also occur in shallow water within the Philippines Archipelago, however none were observed at the locations where M. paleracio was captured. Other individuals were seen but not collected from Layag Layag.

The paratype, although a larger specimen than the holotype, has had much of its tail bitten off and regrown (we calculate that it may have been approximately 480mm in length). We have therefore selected the smaller but complete specimen to be the holotype.

Key: to the species of Myrichthys (modified from McCosker and
Rosenblatt 1993)

la.  Body coloration pale, overlain with 25-55       2
     black or brown rings or saddles, separated by
     white or pale interspaces, encircling or
     partially encircling the body; body very
     elongate, its depth 43-70 times in total
     length

lb.  Body coloration pale or dark, overlain with     3
     round spots which are either dark, pale, or
     dark diffuse spots with bright centers; anal
     and dorsal fin end about equally relative to
     tail tip; body moderately elongate, its depth
     25-45 times in total length

2a.  Anal fin ends about 2 head lengths before tail  M. colubrinus
     tip, well in advance of end of dorsal fin;      (Boddaert)
     body overlain with 25-35 black or brown rings   (Indo-Pacific)
     or saddles, separated by white or pale
     interspaces which are equal to or wider than
     the darker rings; body extremely elongate, its
     depth 50- 70 times in total length

2b.  Anal fin ends less than a head length before    M. paleracio n.
     tail tip, at the same level as the end of the   sp.
     dorsal fin; body overlain with 50-55 brown     (Philippines)
     rings and saddles, separated by white
     interspaces which are narrower than the darker
     rings; body depth 43 times in total length

3a.  Body coloration of round pale spots on a dark   M. breviceps
     background of brown or green                    (Richardson)
                                                     (western
                                                     Atlantic)

3b.  Body coloration pale, overlain with dark spots  4
     or diffuse dark spots with bright centers

4a.  Spots on body diffuse with bright centers       5
     (gold in life)

4b.  Spots on body dark and distinct, without pale   6
     or bright centers

5a.  Total vertebrae 151-159                         M. pardalis
                                                     (Valenciennes)
                                                     (eastern
                                                     Atlantic)

5b.  Total vertebrae 164-173                         M. ocellatus
                                                     (Lesueur)
                                                     (western
                                                     Atlantic)

6a.  Pectoral fin reduced, its length less than the  7
     width at its base; dorsal fin origin above
     1st, 2nd or 3rd vertebra, 1.4-2.0 in head
     length; total vertebrae 149-197

6b.  Pectoral fin developed, longer than the width   M. aspetocheiros
     at its base; dorsal fin origin above 6th, 7th   McCosker &
     or 8th vertebra, 1.1-1.4 in head length; total  Rosenblatt
     vertebrae 159-167                               (eastern
                                                     Pacific).


7a.  Total vertebrae 177-197                         8

7b.  Total vertebrae 149-168                         9

8a.  Total vertebrae 177-183; spotting on chin and   M. magnificus
     throat of adults smaller than or equal to eye,  (Abbott)
     spotting on flanks round                        (Hawaii, Leeward
                                                     and Johnston
                                                     islands).

8b.  Total vertebrae 180-197; spotting on chin and   M. maculosus
     throat of adults larger than eye, spotting on   (Cuvier)
     flanks generally ovoid                          (Indo-Pacific)

9a.  Total vertebrae 149-156                         M. tigrinus
                                                     Girard (eastern
                                                     Pacific)

9b.  Total vertebrae 158-168                         M. pantostigmius
                                                     Jordan &
                                                     McGregor
                                                     (Revillagigedo
                                                     and Clipperton
                                                     islands).


Behaviour and ecology: The new species was observed underwater with the use of scuba gear by the second author at Caban Island (capture site of paratype). Three individuals were seen at depths of 25-35 m on a relatively flat, low relief bottom with mixed sand, rubble and small coral formations. The eels were invariably encountered in the open and were swimming slowly, apparently searching the bottom for prey (probably small fishes or crustaceans).

Distribution: Myrichthys paleracio is currently known only from the Verde Channel area of southern Luzon, Batangas Province, Philippines in 25-35 m.

Etymology: We take pleasure in naming this new eel in honor of its collector, Peri Paleracio, to be treated as a noun in apposition.

ACKNOWLEDGEMENTS

We are grateful to the California Academy of Sciences, which sponsored the first author's participation in the 2011 Hearst Expedition to the Philippines. Collection and curatorial assistance for this trip was kindly provided by David Catania (CAS). We also thank Roger Steene of Cairns, Australia, for his companionship and diving assistance during the second author's 2009 trip to the Verde Channel area during which the first specimen was collected. Roger Steene and Robert Myers generously provided underwater photographs.

Received: 13 September 2011 - Accepted 10 October 2011

REFERENCES

BOHLKE, E. B. 1982. Vertebral formulae of type specimens of eels (Pisces: Anguilliformes). Proceedings of the Academy of Natural Sciences of Philadelphia 134: 31-49.

LEVITON, A. E., GIBBS, R. H. JR., HEAL, E. & DAWSON, C. E. 1985. Standards in herpetology and ichthyology: part I. Standard symbolic codes for institutional resources collections in herpetology and ichthyology. Copeia 1985: 802-832.

MCCOSKER, J. E, 1977. The osteology, classification, and relationships of the eel family Ophichthidae. Proceedings of the California Academy of Sciences series 4, 41 (1): 1-123.

MCCOSKER, J. E., BOHLKE, E. B. & BOHLKE, J. E. 1989. Family Ophichthidae. In: Fishes of the Western North Atlantic, Part 9, Volume 1, Bohlke, E. B. (Ed.), pp. 254-412. Memoirs of the Sears Foundation for Marine Research, New Haven.

MCCOSKER, J. E. & ROSENBLATT, R. H. 1993. A revision of the snake eel genus Myrichthys (Anguilliformes: Ophichthidae) with the description of a new eastern Pacific species. Proceedings of the California Academy Sciences 48 (8): 153-169.

John E. McCosker (1) and Gerald R. Allen (2)

(1.) California Academy of Sciences, San Francisco, CA 94118, USA. E-mail: JMcCosker@calacademy.org

(2.) Western Australian Museum, Locked Bag 49, Welshpool DC, Perth, Western Australia 6986.

E-mail: tropical_reef@bigpond.com
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Author:McCosker, John E.; Allen, Gerald R.
Publication:aqua: International Journal of Ichthyology
Date:Jan 15, 2012
Words:1871
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