Trimma irinae, Winterbottom, 2014

Winterbottom, Richard, 2014, Trimma irinae, (Pisces; Gobioidei) a new species of gobiid fish from Milne Bay Province, Papua New Guinea, Zootaxa 3802 (2), pp. 209-216 : 210-215

Trimma irinae n. sp.

( Figures 1–5 )

Suggested common name: Irina’s pygmy goby

Material Examined. One lot, 3 specimens (14.3–19.7 mm SL, all females) from Milne Bay Province, Papua New Guinea. The description is based primarily on the two formalin-fixed specimens, with some additional information from the tissue specimen ( T 12776, originally preserved in 95% ethanol, genetic analysis pending) .

Holotype. ROM 94505, 19.7 mm SL female, Milne Bay Province, on northern shore of East Cape at Lawadi (10° 15.395’ S, 150° 41.975’E), 65 m, clove oil. 15 July , 2013, M. V. Erdmann.

Paratypes. ROM 94506, 18.6 mm SL female, and ROM T 12776, 14.3 mm SL female, collected with the holotype .

Diagnosis. Trimma irinae has 8–9 scales in the predorsal midline, usually cycloid scales along the upper border of the opercle which may be in up to three horizontal rows, no cheek scales, a very elongate second dorsal spine reaching posteriorly to the end of the second dorsal fin or beyond this (in specimens> 18 mm SL), the middle rays of the pectoral fin branched, a fifth pelvic fin ray which branches once dichotomously and is 52–64% the length of the fourth ray, and the basal membrane connecting the inner margins of the fifth pelvic fins rays is less than 15% the length of the fifth ray.

Description. Dorsal fins VI + I 9, second spine elongated, reaching posteriorly to between the base of ray 3 of second dorsal fin (14.3 mm SL) to beyond the base of the last ray when adpressed, rays all branched except posterior element of last ray, last ray reaching posteriorly 49 –65% of distance from its base to first dorsal procurrent ray; anal fin I 8, all but first and posterior element of posteriormost ray branched; posteriormost ray 50 –54% of distance from its base to first ventral procurrent ray; pectoral fin 17, 3 and 3– 5 unbranched dorsal and ventral rays respectively, middle 9 –11 rays branched, fin reaching posteriorly to a vertical line between urogenital papilla and anal-fin origin; pelvic fin I 5, no frenum, basal membrane reduced and 10 –13% length of fifth ray, first four rays with one sequential branch, fifth ray branched once dichotomously and 52– 55 –64% length of fourth, fourth ray reaching posteriorly to between bases of anal rays 3 –4. Lateral scales 23; anterior transverse scales 9; posterior transverse scales 8; predorsal scales 8 –9; no scales on cheek; opercle apparently with 2– 3 rows of 2– 3 usually cycloid scales (scales mostly missing); pectoral base with 3 vertical rows of scales with 4 cycloid scales in posterior row; 6– 7 cycloid prepelvic scales (in midline anterior to basal membrane); 12 circumpeduncular scales; body scales ctenoid except for cycloid scales on anterior belly midline; and on, beneath and just posterior to pectoral fin base; body scales extend anteriorly to just behind eye. Gill opening extending anteroventrally to a vertical below mid- pupil. Teeth not examined in detail due to the paucity of specimens, but appear to be typical of other Trimma , although apparently less robust. Cephalic sensory papillae ( Figs. 1–3 ) row counts given in Table 1 . Tongue truncate and bilobed, with rounded edges. Gill rakers on first arch 4 + 15 –16 = 19 –20. Anterior nasal opening a short tube extending out over upper lip, posterior nasal opening a pore with a raised rim, both protruding from slightly raised oval sac confined to anterior half of snout. Bony interorbital 38 –42% pupil width, with a broad moderately developed U-shaped interorbital furrow and no postorbital groove. No ridge of tissue (or dermal crest) extending anterior to first dorsal spine. Epaxialis extending anteriorly to above a vertical with posterior margin of pupil. Vertebral transition (as defined by Winterbottom, 2011: 130) not examined, but predicted to be Type B (see Winterbottom, 2003, Fig. 14, inset, and Winterbottom & Zur, 2007, Fig. 3B ).

Colour pattern (live and freshly collected, from a total of four images of at least two specimens, Figs. 4 , 5 A & B ). Background colour of head and anterior half of body pinkish-grey, grading to translucent orange at level of origin of second dorsal fin. Snout and cheek immaculate. Numerous orange to red spots, often with diffuse darker centers and pupil-diameter in width, on top of head, nape, opercular region and anterior half of body. Spots separated by narrow interstices which are frequently invested heavily with iridocytes. Up to three such spots on vertical limb of preopercle, which may coalesce to form an irregularly outlined bar. Below this, a dark red halfpupil diameter sized spot on branchiostegal membrane. Interorbital region crossed by up to three thin transverse white lines. Spots on body decrease somewhat in size posteriorly, and grade into irregular rows of diffuse yellow spots which may be dorso-ventrally elongate behind second dorsal fin. First dorsal fin with two dark, basal markings, an oval-shaped one about eye diameter in width between shafts of the first to fourth spines, and second smaller rounded spot centered on shaft of sixth spine. Both are dark red to black, ocellated with lighter red to orange. A similar, but much smaller rounded spot centered on shaft of fourth spine about two-thirds of the way up shaft, and this may be preceded by a thin, diffuse orange stripe. Membrane of fin a mix of melanophores and iridocytes (and may appear to be white – Fig. 5 B ). Tip of first spine and main shaft of second spine bright white or pale blue. Second dorsal fin with two small basal ocellated spots similar to the one on fourth spine situated between rays 1 and 2, and on shaft of ray 5, and, in middle portion of fin, there may be an irregular series of small yellow spots centered on some of fin rays. Distal part of fin with a flush of yellow, whole membrane with scattered iridocytes. Caudal fin rays mostly reddish-orange with scattered small yellow spots. Anal fin rays pale reddishyellow with some diffuse yellow spots, fin membranes with iridocytes and dark pigment (unclear whether these are melanophores or very dark chromatophores). Pectoral and pelvic fin rays pale pinkish red, membranes hyaline. A specimen photographed just after collection is similar to above, but scattered iridocytes are visible over most of body.

Colour pattern in alcohol: Background colour pale straw-yellow, all traces or red, orange, yellow and pink absent. Centres of head and anterior body spots with numerous dark pigment cells, much fewer at periphery of spots, thin white network separating spots in live fishes now consists of lines of brown chromatophores. Black spots in dorsal fins remain black, dark spot on branchiostegal membrane is also black ( Fig. 3 , red arrow).

Comparisons. Trimma irinae belongs to a group of nine described species which all have a scaled predorsal midline, no cheek scales, a scaled opercle, and at least the middle rays of the pectoral fin branched ( Winterbottom, 2006). Within this group, Trimma caesiura Jordan & Seale, 1906, T. fraena Winterbottom, 1984 , and T. milta Winterbottom, 2002 lack an elongate second spine in the first dorsal fin (vs. present). Of the remaining species, T. mendelssohni ( Goren, 1978) has multiple branches in the fifth pelvic fin ray, and T. nomourai Suzuki & Senou, 2007 has two branches (for a total of four tips) whereas all the others have a single branch point in this ray. Trimma lantana Winterbottom & Villa, 2003 has deep, vertically sided trenches in the interorbital and postorbital regions of the head (vs. moderate trough and none respectively in T. irinae ). Trimma cheni Winterbottom, 2011 , and T. okinawae ( Aoyagi, 1949) have only moderately elongate second dorsal spines that do not extend beyond about the middle of the second dorsal fin when adpressed (vs to last ray or further back). Trimma papayum Winterbottom, 2011 appears closest morphologically to T. irinae in having a poorly developed postorbital trough or none, in possessing a greatly elongate second dorsal spine, and in several details of colour pattern. However, T. papayum has more pectoral fin rays (18–19 vs. 17) and fewer lower gill rakers (13–14 vs. 15–16) than T. irinae , in additional to trenchant differences in live and preserved colouration. These include the presence in T. irinae of a distinctive dark spot on the branchiostegal membrane below the vertical limb of the preopercle (vs. absent - a larger such spot is also evident in T. hayashii Hagiwara & Winterbottom, 2007 , which usually lacks scales in the predorsal midline and on the opercle), and two large black spots basally in the first dorsal fin (vs. one small dark spot).

Distribution. Trimma irinae is currently known only from the type locality in Milne Bay Province, Papua New Guinea at a depth of 65 m.

Etymology. The species is named in honour of my wife, Irina, as a small token of my appreciation and gratitude for her patience and forbearance of what she once referred to as my “magnificent obsession” with coral reef fishes. This species has been informally referred to as Trimma RW sp. 100.

Figures

FIGURE 1. Trimma irinae, 19.7 mm SL holotype, ROM 94505. Left lateral view of head to show cephalic sensory papillae (image reversed). Specimen stained with cyanine blue. Photo: R. Winterbottom.

FIGURE 2. Trimma irinae, 19.7 mm SL holotype, ROM 94505. Dorsal view of head to show cephalic sensory papillae. Specimen stained with cyanine blue. Photo: R. Winterbottom.

FIGURE 3. Trimma irinae, 18.6 mm SL paratype, ROM 94506. Ventral view of head to show cephalic sensory papillae. Specimen not stained. Photo: R. Winterbottom.

FIGURE 4. Trimma irinae, 19.7 mm SL holotype, ROM 94505. Freshly collected, left lateral view. Photo: G. R. Allen.

FIGURE 5. Trimma irinae. A and B: Live specimens. Photos: M. V. Erdmann.