Dellichthys trnskii, Conway, Kevin W., Stewart, Andrew L. & Summers, Adam P., 2018

Conway, Kevin W., Stewart, Andrew L. & Summers, Adam P., 2018, A new species of sea urchin associating clingfish of the genus Dellichthys from New Zealand (Teleostei, Gobiesocidae), ZooKeys 740, pp. 77-95 : 79-89

Dellichthys trnskii sp. n. Figs 1, 2A, 3, 4A, 5A, 6, 7 A–B, 8 A–C

Holotype.

AIM MA73570, 22.8 mm SL, New Zealand, Northland, Tutukaka, Pacific Bay, 35°37'07.2"S, 174°32'03.8"E, 0-2 meters depth, 8 March 2016, T. Trnski, I. Middleton, K.W. Conway, S. Hannam, & G. Short.

Paratypes.

All New Zealand. Auckland: NMNZ P.028060, 4 (1 CT [https://doi.org/10.17602/M2/M40584]), 20.1-29.7 mm SL; NMNZ P.060626, 2 (C&S), 21.0-25.0; Hauraki Gulf, Matatuahu Point, Tawharanui Peninsula, 0-5 meters depth (36°23'00.0"S, 174°49'00.0"E), 8 April 1992. Bay of Plenty: NMNZ P.035572, 1, 46.0 mm SL; Rurima Islets, 7-10 meters depth (37°49'47.0"S, 176°52'38.0"E), 02 June 1998. Marlborough: NMNZ P.025671, 2, 42.0-45.6 mm SL; NMNZ P.060627, 1 (C&S), 41.8 mm SL; Gorse Bay, Port Underwood (41°18'27.1"S, 174°09'39.7"E), 25 September 1989. Hawke’s Bay: NMNZ P.057592, 1, 32.7 mm SL; Bare Island (39°49'54.0"S, 177°01'30.0"E), 09 December 1991. - NMNZ P.057600, 1, 43.3 mm SL; south of Aramoana, 0-3 meters depth (40°09'42.0"S, 176°50'18.0"E), 19 January 1991. Northland: AIM MA4341, 1, 45.8 mm SL, Poraenui Point, Bay of Islands (35°11'34"S, 174°4'8"E), 15 December 1983. - AIM MA6395, 1, 11.9 mm SL, Kerikeri Inlet, Bay of Islands, 7 meters depth (35°12'0.0"S, 174°02'43.0"E), 28 Jan 1972. - AIM MA7070, 1, 33.0 mm SL, Te Puna off Mataka, Bay of Islands (35°09'0.0"S, 174°06'12.0"E), 20 March 1988. - AIM MA73571, 2 (ethanol preserved DNA vouchers), 17.0-20.0 mm SL; TCWC 17264.03, 1 (C&S), 18.0 mm SL, same as holotype. - AIM MA75372, 1, 18.8 mm SL, Rawhiti, Taupiri Bay (35°16'58.4"S, 174°17'38.0"E), 10 March 2016. - AIM MA73573, 1, 21.3 mm SL, Bland Bay, 0-3 meters depth (35°20'47.8"S, 174°21'57.6"E), 11 March 2016. - NMNZ P.057601, 1, 31.3 mm SL; north side of the Matapouri Peninsula, 0-8 meters depth (35°33'15.0"S, 174°30'00.0"E), 09 April 1992. - TCWC 17171.04, 1 (ethanol preserved DNA voucher), 25.5 mm SL, Tutukaka, rocky bay between Tutukaka reserve and Kukutauwhao Island (35°36'40.7"S, 174°32'29.8"E), 1 March 2015. Wellington: NMNZ P.048189, 1, 45.0 mm SL; Wellington Port, overseas passenger terminal (41°17'19.6"S, 174°47'09.5"E), 23 November 2001. - NMNZ P.048197, 1, 37.0 mm SL; Wellington Port, Burnham Wharf (41°18'42.0"S 174°48'12.0"E), 20 November 2001.

Other material.

AMS I.34453-005, 1, 20.0 mm SL; New Zealand: locality unknown.

Diagnosis.

Dellichthys trnskii is diagnosed by the following combination of characters: snout broad, short (length less than or equal to interorbital distance); upper and lower jaws equal in length or lower jaw only slight shorter than the upper; upper jaw teeth not visible or only few teeth visible in gap between upper and lower lip at tip of jaws when jaws are closed; patch of teeth on lingual surface of premaxilla roughly rectangular, with ~50 small conical teeth; skin fold on surface of snout directly posterior to fold of upper lip; postorbital lateral line canal pore 2 located directly above preopercular lateral line canal pore 3; tip of snout and lower jaw pale pink in life; dorsal and lateral surface of head light yellow to green in life; body pale orange to yellow in life; and median fins transparent and without faint brown reticulate markings in life.

Description.

General body shape as in Figure 1. Morphometric characters listed in Table 1. Head large, slightly dorsoventrally compressed. Body moderately dorsoventrally compressed anteriorly, becoming increasingly laterally compressed posteriorly at region of dorsal and anal fins. Widest point of head wider than widest point of body (immediately behind head). Body width tapering gradually posteriorly. Eye large, positioned on dorsolateral surface of head; orbit visible in ventral view. Centre of eye closer to tip of snout than to posterior margin of operculum. Snout short, broad; anterior margin rounded. Transverse skin groove present across dorsal surface of snout; skin anterior to groove thin and transparent (Fig. 2A). Anterior nostril a small tubular opening, with short, thin blade-like flap extending from posterior margin. Posterior nostril tubular, situated along anterdorsal margin of orbit. Gill membranes united and free from isthmus.

Mouth terminal, small; posterior tip of upper jaw reaching imaginary vertical line through anterior margin of orbit when mouth closed. Upper lip narrow; thickest along lateral margin of upper jaw; thinnest at snout tip. Lower lip thin at jaw symphysis; expanded into fleshy lobes adjacent to symphysis. Premaxilla with outer row of larger conical teeth with strongly recurved tips (Figs 3B, 4A, 5A) and medial, roughly rectangular patch of ~50 smaller conical teeth on lingual surface posterior to outer row of larger teeth (Fig. 5A). Dentary with broad patch of conical teeth with recurved tips anteriorly, tapering to single row of larger conical teeth posteriorly (Fig. 4A). Pharyngeal jaws comprising patch of 16-18 small conical teeth with slightly recurved tips on pharyngobranchial toothplate 3 and two rows of 5-8 small conical teeth with slightly recurved tips along ceratobranchial 5. 10-12 gill rakers located along anterior and posterior edge of ceratobranchials 2-3 and anterior edge of ceratobranchial 4; 7 gill rakers located along anterior edge of ceratobranchial 1. Gill filaments associated with ceratobranchials 1-4 (3.5 gill filaments of Briggs (1955)); ceratobranchial 1-3 each with holobranch; hemibranch only on ceratobranchial 4. Basihyal elongate, widest anteriorly (Fig. 3C); anterior edge tipped with cartilage. Branchiostegal rays 6; two anteriormost rays articulating medially with hyoid bar along anterior ceratohyal; posterior rays articulating with hyoid bar laterally, including 3 along posteriormost part of anterior ceratohyal and 1 straddling junction between anterior and posterior ceratohyals (Fig. 3C). Anteriormost branchiostegal rays shorter than posterior rays; orientated with posterior tips directed towards ventral midline. Two posteriormost branchiostegal rays approximately twice as long as short anterior rays; orientated with posterior tips directed towards posterior. Intervening rays intermediate in length; orientated with posterior tips directed towards posterior.

Cephalic lateral-line system with 2 pores in nasal canal; 2 pores in postorbital canal; 3 pores in lachrymal canal; 3 pores in preopercular canal; 2 pores in mandibular canal (Fig. 2A). Postorbital canal pore 2 located directly above preopercular canal pore 3. Mandibular and preopercular canals continuous; connected via unossified canal; anteriormost pore of preopercular canal (PR1) located at center of unossified canal between anguloarticular and preopercle (Fig. 2A). Superficial neuromasts on head isolated or arranged in rows (Fig. 2A). 4 superficial neuromasts in suborbital row; 2 superficial neuromasts in postorbital row; 2 superficial neuromasts in mandibular row.

Dorsal-fin rays 9. Anal-fin rays 7 (1), 8 (2) or 9 (1). Principal caudal-fin rays 5+5, dorsal procurrent rays 6 (2) or 7 (2), ventral procurrent rays 5 (1), 6 (2) or 7 (1). Pectoral-fin rays 22 (3) or 23 (1). Pelvic-fin rays I,4. All fin rays unbranched and segmented. Caudal fin rounded, tips of principal caudal fin rays extended slightly beyond fin margin. Caudal-fin skeleton comprised of upper and lower hypural plates; epural and parhypural poorly ossified, triangular and similar in size (Fig. 6D). Dorsal-fin origin opposite anal-fin origin. First dorsal-fin pterygiophore inserted between neural spines of vertebrae 15/16. First anal-fin pterygiophore inserted between hemal spines of vertebrae 15/16. Total number of vertebrae 30 (3) or 31 (1), consisting of 13 abdominal and 18 (3) or 19 (1) caudal vertebrae (Fig. 6). Ribs 10, associated with vertebrae 3-12. Epicentrals 17 (3), associated with vertebrae 2-18, or 21, associated with vertebrae 2-22.

Adhesive disc large, double (Fig. 7A); anterior and posterior margin weakly crenulated. Disc region A with 5-6 transverse rows of papillae. Disc region B with 6-7 transverse rows of papillae. Disc region C with 4-5 rows of papillae. Papillae of disc region A decreasing in diameter towards outer margin of disc. Papillae of disc region B and C decreasing in diameter towards outer margin of inner disc. Dorsal postcleithrum a thin irregular shaped bone; larger than ventral postcleithrum (Fig. 7B). Ventral postcleithrum irregular in shape; lateral edge rounded; medial edge roughly triangular, with point directed toward ventral midline (Fig. 7B). Fimbrae along posteroventral margin of dorsal postcleithrum and posterior margin of ventral postcleithrum well-developed. Skin associated with last pelvic-fin ray attaching to base of pectoral fin opposite 5th lowermost pectoral-fin ray. Skin over base of ventral pectoral-fin rays smooth.

Colouration.

In alcohol, body background colour pale yellow. Median fins pale yellow to white along bases, transitioning to hyaline along distal margins. Paired fins hyaline; papillae on adhesive disc translucent white. In formalin and shortly after initial transfer to alcohol (Fig. 1), body background colour pale orange to yellow with darker orange markings along dorsal midline and ventral midline posterior to adhesive disc. Snout and lips orange. Orange to light brown stripe on lateral side of head posterior to orbit. Dorsal and anal fins orange along base, transitioning to white along distal margins. Base and center of caudal fin pale orange, transitioning to white along distal margins. Pectoral fin hyaline. Distal margin of pelvic fin whitish; papillae on adhesive disc light orange.

In life, background colour translucent orange to pale yellow (Fig. 8 A–C). Lateral body surface with faint to distinct irregular white to pale blue lines that may or may not connect with counterparts along dorsal midline. In some individuals (potentially female), irregular lines replaced by irregular rows of small white to pale blue spots (Fig. 8C). Light brown pigment surrounding nerve cord and darker content in stomach visible through body. Dorsal surface of head translucent light yellow to pale green with three or four white to pale blue lines that become more obvious anteriorly. Lateral surface of head posterior to orbit with two white to pale blue lines flanking a central light brown to pale green region (equivalent to orange to light brown stripe on lateral side of head posterior to orbit described above for specimens in formalin). In some individuals (potentially female), white to pale blue lines on dorsal and lateral surfaces of head are replaced by rows of small white to pale blue spots. Tip of snout and adjacent portions of lips pink. Iris orange. Fins clear to translucent orange/yellow.

Distribution.

Dellichthys trnskii is endemic to New Zealand coastal waters, currently known only from shallow (0-7 meters in depth) waters along the northeastern coast of both the North Island (Auckland, Bay of Plenty, Hawke’s Bay, Northland, and Wellington) and South Island (Marlborough Sounds) (Fig. 9). Its occurrence further south may be confirmed by further sampling and by a better understanding of the differences between the two species.

Notes on biology

. At the type locality, D. trnskii was found primarily under rocks or boulders covered with filamentous algae or low macroalgae often in close proximity to the sea urchin Evechinus chloroticus . Small dense objects, possibly sand grains, are visible in the pharyngeal cavity and gut of the CT scanned paratype (NMNZ P.028060, 25.0 mm SL; Figs 3, 6). A single ctenoid scale also is lodged in the opercular opening of this individual (Fig. 3). Whether this scale was ingested or entered the opercular opening subsequent to capture is difficult to confirm. The specimen was collected with a large number of associated sub-tidal species including triplefins, some of which could have shed scales in the bag.

Sexual dimorphism.

No obvious sexual dimorphism is present in the available material. Potential sexual dichromatism is described above in the section on colouration.

Etymology.

Named for Tom Trnski, who played a key role in the discovery of the new species by collecting in depths beyond the reach of the first author. A noun in the genitive.

Genetic Distances.

The sequences of COI (684bp) obtained from two specimens of D. trnskii (Genbank numbers [GB#] MF621939-40) were identical and differed from sequences obtained from six specimens of D. morelandi (GB# MF621941-44, MF318544-45) by 11.7 % (uncorrected p-distance). Similarly, the sequences of 12S (365bp) obtained from three specimens of D. trnskii (GB# MF621933-35) were identical and differed from sequences obtained from five specimens of D. morelandi (GB# MF318559-60, MF621936-38) by 3.4% (uncorrected p-distance).

Comparisons.

Dellichthys trnskii is most easily distinguished from D. morelandi by features of the colour pattern in life (Fig. 8), including a pale orange to yellow background colour on the body (vs. light brown to dark orange, red or purplish), areas between white to pale blue markings (most commonly stripes) on dorsal and lateral surface of head light yellow to green (vs. brown to dark orange or red), tip of snout and lower jaw pale pink (vs. brown to dark orange or red), and the absence (vs. presence) of faint brown reticulate markings on the median fins.

Dellichthys trnskii is further distinguished from D. morelandi by features of the oral jaws, including having the upper and lower jaws equal in length or the lower jaw only slight shorter than the upper, with few upper jaw teeth visible in the gap between the upper and lower lip when the jaws are closed (vs. upper jaw notably longer than lower jaw, with many upper jaw teeth visible in the gap between the upper and lower lip when the jaws are closed) (Fig. 4), a small, roughly rectangular patch of ~50 small conical teeth on the lingual surface of the premaxilla that flanks the posterior margin to the larger conical teeth along the outer margin of the bone (vs. large, roughly triangular patch of ~90 small conical teeth that extends over much of the anterolingual surface of the premaxilla) (Fig. 5). Dellichthys trnskii also can be distinguished from D. morelandi by its slightly shorter snout (snout length 24-29 % HL vs. 26-34 % HL in D. morelandi ), the length of which is equal to or less than the interorbital distance (vs. snout length greater than interorbital distance), and by having the transverse skin fold on the surface of snout located directly posterior to the fold of the upper lip (vs. transverse skin fold on the surface of the snout separated from the fold of the upper lip by a broad band of thin, transparent skin). Finally, D. trnskii is distinguished from D. morelandi by the location of postorbital lateral line canal pore 2, which is located directly above preopercular lateral line canal pore 3 (vs. postorbital lateral line canal pore 2 anterior to preopercular lateral line canal pore 3) (Fig. 2).

Remarks.

Briggs (1955) erected Dellichthys for the sole inclusion of D. morelandi , which he considered to be an "interesting species with no known close relatives" ( Briggs 1955: 15). We assign the new species to Dellichthys because it exhibits all of the diagnostic characters listed by Briggs (1955:14), including: a narrow upper lip, separated by a broad frenum at tip of snout; small, sharp, conical teeth arranged in a deep patch on both the upper and lower jaw, tapering to a single row of larger, strongly recurved, “canine-like” teeth posteriorly; a relatively high number of narrow pointed gill-rakers on the second gill arch (10-12 in D. trnskii ; 14 listed by Briggs for D. morelandi , 1955); a poorly developed fleshy pad at lowest part of pectoral-fin base; and ventral postcleithrum with a “characteristic” shape in ventral view (i.e., lateral margin rounded and medial margin roughly triangular; Briggs 1955: fig. 44).

Briggs (1955: 14) also listed the absence of the subopercle as diagnostic for Dellichthys and considered the opercle to form the terminal element of the operculum in D. morelandi . Our investigation of the osteology of Dellichthys morelandi and D. trnskii has revealed the subopercle to be present (Figs 3A,B, 4). In both cases, the subopercle is comprised of a small, heavily ossified anterior part at the point of articulation with the opercle and preopercle, and a very poorly ossified posterior portion, represented by a thin, yet extensive, lamina of dermal bone that does not take up alizarin red S when cleared and double stained (Fig. 4) nor render well in reconstructions of the CT scan data (e.g., Fig. 3). The poorly ossified posterior margin to the subopercle in D. morelandi and D. trnskii differs markedly from the heavily ossified and often spine-like posterior margin to the subopercle present in other gobiesocids (e.g., see fig. 12 in Conway et al. (2017c)) and we consider this unique condition (not absence) of the subopercle to be diagnostic for Dellichthys .

Though Briggs (1955) provided a detailed diagnosis for Dellichthys , derived from multiple external and internal morphological features, the diagnosis provided for D. morelandi (also on pg. 14) is relatively short and lists characters that apply to both D. morelandi and D. trnskii . A rediagnosis for D. morelandi is provided below.

Dellichthys trnskii is sympatric with D. morelandi , at least along the coast of Northland, and specimens of the two species were commonly collected from within close proximity, in some cases from under the same rock. Paulin and Roberts (1992: 52) described the head and body colour of D. morelandi as "purple or cream with blue spots and a band of pale colour across the nape". Stewart (2015: 1545) used the same description for juveniles of D. morelandi but described adults as "more olive grey-brown, sometimes flushed with red to orange around ventral part of head." Given that D. morelandi and D. trnskii occur together and are similar in appearance, we suspect that these previous published descriptions of live colouration in D. morelandi are based on observations of both species, with purple specimens representing D. morelandi (e.g., see Francis 2012: 54) and cream specimens representing D. trnskii (e.g., see Fig. 8C). We note here that the cream coloured specimen figured in the account for D. morelandi in Stewart (2015: 1545, fig. 218.2) is instead a small specimen of Trachelochismus melobesia .