Malthopsis arrietty, Ho, 2020

Ho, Hsuan-Ching, 2020, Two new deep-water batfish of the genus Malthopsis from the Pacific Ocean (Lophiiformes: Ogcocephalidae), Raffles Bulletin of Zoology 68, pp. 859-869 : 861-865

publication ID	https://doi.org/ 10.26107/RBZ-2020-0094
publication LSID	lsid:zoobank.org:pub:F3C7F60D-7E4A-45AF-B432-715A2D2A1FE8
persistent identifier	https://treatment.plazi.org/id/3122A92C-FF87-FFBC-FE91-46D1FD1CD298
treatment provided by	Diego
scientific name	Malthopsis arrietty
status	sp. nov.

Treatment

Malthopsis arrietty , new species Short-horn triangular batfish

( Figs. 1‒3 View Fig View Fig View Fig ; Table 1)

Holotype. USNM 169204 View Materials (45.4 mm SL), ALBATROSS Philippines Expedition, 1907‒1910, ALBATROSS sta. D 5113, 13°51′29.9″N, 120°50′31.2″E, Balayan Bay, off Batangas, southern Luzon , Philippines, 12-foot Tanner beam trawl and mud bag, 291 m, 17 January 1908. GoogleMaps

Paratypes. Eighty-six specimens, 25.9‒48.5 mm SL, all collected from the Philippines . CAS 34261 (1, 41.0), 13°39′04.3″N, 122°47′57.8″E, Bantuin Point, Ragay Gulf, southern Luzon , 534‒543.2 m, 12 November 1966, coll. J.E. Norton. GoogleMaps CAS 227265 View Materials (1, 44.2), 13°22′54.8″N, 121°49′31.4″E, Tayabas Bay, Marinduque Island , 234‒256 m, 2 October 1966, coll. JE Norton. GoogleMaps MNHN 2005-0666 View Materials (10, 31.6‒48.5 mm SL), 11°57′07.2″N, 121°28′04.8″E, Sibuyan Sea, among Semirara Island, Caluya Island and Sibay Island , 388‒404 m, 4 June 1985 GoogleMaps . NSMT-P96969 (2, 44.7‒45.8) , R / V HAKUHO- MARU, 10°36′32.4″N, 121°31′37.2″E ‒ 10°35′42.0″N, 121°31′12.0″E, off Panay Island, Sulu Sea , 362‒372 m, 8 December 2002 GoogleMaps . USNM 122371 View Materials (15, 34.4‒45.1), ALBATROSS, sta. D 5505, 8°37′14.9″N, 24°36′00.0″E, Macajalar Bay, Bohol Sea, northern Mindanao , 12-foot Tanner beam trawl, 402 m, 5 August 1909 GoogleMaps . USNM 122372 View Materials (12, 25.9‒44.6), ALBATROSS, sta. D 5501, 8°37′36.8″N 124°34′48.0″E, Macajalar Bay, Bohol Sea, northern Mindanao , 12-foot Tanner beam trawl, 391 m, 4 August 1909 GoogleMaps . USNM 150855 View Materials (10, 27.3‒38.3), ALBATROSS, sta. D 5506, 8°40′12.0″N, 124°31′44.4″E, Macajalar Bay, Bohol Sea, northern Mindanao , 12-foot Tanner beam trawl, 479 m, 5 August 1909 GoogleMaps . USNM 168864 View Materials (17, 26.1‒44.9) and NMMB-P34201 (4, 34.1‒43.0), ALBATROSS, sta. D 5502, 8°37′36.8″N, 124°34′48.0″E, Macajalar Bay, Bohol Sea, northern Mindanao , 12-foot Tanner beam trawl, 391 m, 4 August 1909 GoogleMaps . USNM 169203 View Materials (1, 46.2), ALBATROSS, sta. D 5112, 13°48′22.0″N, 120°47′24.0″E, Balayan Bay, southern Luzon, 12-foot Tanner beam trawl and mud bag, 324‒326 m, 17 January 1908 GoogleMaps . USNM 169207 View Materials (1, 39.3), ALBATROSS, sta. D 5371, 13°49′40.1″N, 121°40′15.6″E, Tayabas Bay, southern Luzon, 12-foot Agassiz beam trawl and mud bag, 152 m, 24 February 1909 GoogleMaps . USNM 169209 View Materials (1, 41.8), ALBATROSS, sta. D 5402, 11°11′44.9″N, 124°15′46.8″E, Camotes Sea, between Leyte and Cebu, 12-foot Agassiz beam trawl and mud bag, 0‒344 m, 16 March 1909 GoogleMaps . USNM 169210 View Materials (8, 29.1‒43.5), ALBATROSS, sta. D 5409, 10°37′48.0″N, 124°13′08.4″E, Camotes Sea, between Cebu and Leyte, 12-foot Agassiz beam trawl and mud bag, 0‒346 m, 18 March 1909 GoogleMaps . USNM 169212 View Materials (1, 30.5), ALBATROSS, sta. D 5507, 8°21′11.9″N, 124°12′07.2″E, Iligan Bay, Bohol Sea, northern Mindanao , 12-foot Tanner beam trawl, 777 m, 5 August 1909 GoogleMaps . USNM 169213 View Materials (1, 54.0), ALBATROSS, sta. D 5518, 8°48′00.0″N, 123°31′12.0″E, Bohol Sea, northern Mindanao, 12-foot Tanner beam trawl, 366 m, 9 August 1909 GoogleMaps . USNM 169214 View Materials (1, 48.2), ALBATROSS, sta. D 5542, 8°48′29.9″N, 123°35′31.2″E, Bohol Sea, northern Mindanao, 12-foot Tanner beam trawl, 366 m, 20 August 1909 GoogleMaps . USNM 169215 View Materials (2, 39.8‒44.2), ALBATROSS, sta. D 5503, 8°36′25.9″N, 124°36′07.2″E, Makajalar Bay, Bohol Sea, northern Mindanao , 12-foot Tanner Beam Trawl , 413 m, 4 August 1909 GoogleMaps .

Non-type. USNM 150999 View Materials (1, 15.0), ALBATROSS, sta. D 5503, 8°36′25.9″N 124°36′07.2″E, Makajalar Bay, Bohol Sea, northern Mindanao , 12-foot Tanner Beam Trawl , 413 m, 4 August 1909 GoogleMaps .

Diagnosis. A species of Malthopsis belonging to the species group lacking prickles on interspaces of bucklers and distinguished from all other congeners by having an extremely short rostrum (x =4.1% SL) directed upward rather than forward; a large eye (x = 15.4% SL); a narrow interorbital space (x = 5.5% SL); OD/RL = 2.4‒5.3 and OD/IO = 2.4‒3.2; few scattered bucklers on body with interspaces largely naked on dorsal surface; and ventral surface with few flat bucklers, mostly restricted to around pelvic-fin base, almost naked elsewhere.

Description. Dorsal-fin rays five (mainly five, some with four or six); pectoral-fin rays 12 (mainly 12, rarely 11 or 13); anal-fin rays four (mainly four, rarely three). Body depressed, markedly triangular in dorsal view, posterior portion of skull well elevated above rest of disk; tail base narrow; caudal peduncle slender, semi-cylindrical, flattened ventrally and tapering posteriorly; rostrum very small and short, pointed (some with blunt or strongly reduced rostral spine), with small base, directed upward rather than forward ( Figs. 1B View Fig , 3B View Fig ), barely overhanging illicial cavity and mouth; rostral length 5.7% SL (2.0‒5.7, x = 4.1), much less than half of orbital diameter; OD/RL 2.4 (2.4‒5.3, x = 3.8); orbit larger than most congeners, its width 13.9% SL (13.7‒17.4, x = 15.4), directed dorsolaterally; no pupillary operculum; interorbital space narrow, 5.5% SL (4.7‒6.3, x = 5.5); OD/ IO 2.5 (2.4‒3.2, x = 2.8).

Illicial cavity small, oval, as high as wide; esca a single bulb, bearing one small cirrus (mostly two cirri in paratypes) on dorsal margin; mouth small, terminal; small villiform teeth on jaws forming narrow bands, those on fifth ceratobranchial forming two large, elongated, adjacent patches; teeth on vomer and palatines in quadrangular patch.

Squamation on dorsal surface consisting mainly of pointed, conical, variable-sized bucklers, few in number and scattered in arrangement ( Figs. 1A View Fig , 2A View Fig , 3B View Fig ), interspaces between bucklers largely naked; bucklers on frontal ridge small and pointed, two enlarged preorbital bucklers which overlap anterior border of orbit, upper buckler larger and fused to the base of rostrum, with rostral spine in form of trident ( Fig. 3A View Fig ); usually three (three or four) smaller, subequal- sized bucklers on frontal ridge ( Fig. 3B View Fig ); interorbital space naked; membranes above eyes completely naked ( Fig. 3A, B View Fig ).

Posterior portion of dorsal surface of skull covered by six large bucklers, one laterally on each side, four arranged in two rows medially, naked elsewhere ( Fig. 3A View Fig ) (smaller bucklers in some types); shoulder with large naked areas, extending to gill openings and base of pectoral elbows; a median row of large bucklers predorsally, ending before dorsal-fin origin as a triangular cluster of three large bucklers ( Figs. 1A View Fig , 2A View Fig ). Disk margin with a cluster of suborbital bucklers anteriorly, forming three well-defined rows posteriorly; uppermost row of bucklers elevated, slightly pointed, broad based; middle and lower rows of bucklers depressed and associated with lateral line, apices elevated; those in median row directed laterally, those in lower row directed ventrally; neuromasts well defined along lateral-line channel between median and lower rows of bucklers.

Subopercular buckler moderate in size, extending well beyond disk margin laterally; terminating on uppermost and middle rows of disk-margin bucklers; small spines on buckler tip, one directed forward and one directed backward, two smaller spines directed outward (some extra spines present in some smaller specimens); two post-subopercular bucklers, outer buckler large and bifurcate, inner small and indistinct, mostly covered by skin ( Figs. 1 View Fig , 2 View Fig , 3C, D View Fig ).

Pectoral-fin base on rear part of disk, covered dorsally with few well-developed conical bucklers, four (three to five) fine bucklers over anterior fin ray, naked elsewhere ( Fig. 3C, D View Fig ). Dorsal surface of tail strongly armoured, entirely covered with large, elevated, apically pointed bucklers; a row of four (four or five) large dorsolateral bucklers extending from last pair of predorsal bucklers below dorsal fin; a longer, highly irregular, semi-oblique row of slightly smaller bucklers along lateral margin of tail to caudal-fin base; an irregular row of flattened bucklers on dorsal midline before caudal fin; dorsal tail rows uniting to form a single, slightly elevated buckler at its base. Lateral margin of tail with two rows of small, low bucklers associated with lateral-line channel, similar to those on disk margin.

Ventral surface of disk covered with low bucklers, short apical spines on each buckler; belly nearly naked (one small buckler on belly of holotype, few in some paratypes but most paratypes totally naked); thoracic region with four bucklers (mostly naked in paratypes), few small bucklers on interspaces of pelvic-fin base ( Figs. 1B View Fig , 2B View Fig , 3E View Fig ); posterior portion of anus surrounded by six (four to six) flat bucklers; ventral surface of tail with a regular row of five conical bucklers on each side before anal-fin base; three (two or three) flat bucklers behind anal fin.

Fins generally naked, without bucklers; interradials of pectoral fins thin, transparent; dermal cirri short, thin, flaplike, present on disk margin and lateral sides of tail associated with lateral-line neuromasts.

Colouration. Fresh colour unknown but likely uniformly yellow or perhaps with yellow marks as in many congeners. Preserved specimens uniformly pale brown to brown, paler on ventral surface and fins. Peritoneum pale with scattered black pepper dots.

Distribution. Known from the type series and non-type specimens collected in the Philippines and likely endemic to the region. Bathymetric range 234‒543.2 m, except for one specimen (USNM 169212) collected in 777 m.

Size. A small-sized species, the largest adult measuring 54.0 mm SL, just a few millimetres larger than that of Malthopsis parva (51.1 mm SL), one of the smallest known species of the genus.

Etymology. The specific name, arrietty , used as noun in apposition, is after the miniature character of the Japanese animated fantasy film “Arrietty the Borrower” ( Japan) or “The Secret World of Arrietty” (North America), in reference to the miniature size of the species.

Comparisons. Malthopsis arrietty is most similar to M. parva from New Zealand and Australia in having a small adult size (54.0 mm SL, cf. 51.1 mm SL in M. parva ) and only a few bucklers on the ventral surface with the belly almost completely naked. Malthopsis arrietty differs from M. parva in having all bucklers on the body relatively tall and pointed (vs. low and blunt, or moderately tall with a blunt tip in M. parva ); large naked areas on dorsal surface of body (vs. mostly covered by various-sized small bucklers); two pairs of principal bucklers on posterior portion but naked elsewhere on skull (vs. densely covered by small bucklers on those areas); tip of subopercular buckler with well-developed spinules directed forward, laterally and posteriorly (vs. margin blunt with indistinct spinules); head relatively wide, 22.6‒26.3% SL, x = 24.6% SL (vs. 18.1‒23.9, x = 21.9% SL); usually 12 pectoral-fin rays (vs. usually 13).

Malthopsis arrietty is also similar to Malthopsis annulifera Tanaka, 1908 , from the northwestern Pacific; both species co-occur in the Philippines. Malthopsis arrietty differs from M. annulifera in lacking colour marks on the dorsal surface (vs. four to 12 ocelli on dorsal surface in M. annulifera ) and in having all bucklers on the body relatively tall and pointed (vs. all low and blunt or flat), a larger eye with OD 13.7‒17.4% SL (vs. 10.1‒13.2% SL), a narrower interorbital space of 4.7‒6.3% SL (vs. 6.6‒9.2% SL). Moreover, M. arrietty has a much smaller maximum body size, reaching only 54.0 mm SL, whereas M. annulifera reaches 96.2 mm SL (data of M. annulifera from Ho & Shao, 2010a).