Flexor incus, Conway, Kevin W., Stewart, Andrew L. & Summers, Adam P., 2018

Conway, Kevin W., Stewart, Andrew L. & Summers, Adam P., 2018, A new genus and species of clingfish from the Rangitahua Kermadec Islands of New Zealand (Teleostei, Gobiesocidae), ZooKeys 786, pp. 75-104 : 75

Flexor incus sp. n. Figs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

Aspasmogaster sp.: Stewart 2015: 1539, 1544; Trnski et al. 2015: 473, 476, Table 1.

Holotype.

NMNZ P.060717, 20.8 mm SL; New Zealand, Kermadec Islands, Raoul Island, Fishing Rock Landing (29°15'03.0"S, 177°54'12.0"W), 0-1 meters depth, 18 May 2011, M. Francis.

Paratypes.

All Kermadec Islands. AIM MA655142, 1 (C&S), 20.0 mm SL; Raoul Island, North Meyer Islet, northwest side of island (29°14'40.4"S, 177°52'41.3"W), 0-1.3 meters depth, 13 May 2011. - AIM MA655401, 2, 18.0-24.0 mm SL; Raoul Island, Fishing Rock Landing (29°15'02.7"S, 177°54'11.7"W), 0-1 meters depth, 18 May 2011. - AIM MA655316, 1 (CT scan; https://doi.org/10.17602/M2/M56344), 23.0 mm SL; AMS I.45807-001, 1, 19.7 mm SL; NMNZ P.049965, 1, 24.3 mm SL; NMNZ P.049966, 1, 27.2 mm SL; Raoul Island, Herald Islets, west side of North Chanter Island (29°15'06.0"S, 177°51'21.0"W), 1-12 meters depth, 16 May 2011, A. Ballance. - AMS I.45823-010, 1, 19.1 mm SL; same as holotype. - NMNZ P.017760, 1, 14.0 mm SL; Raoul Island, rockpool on Fishing Rock Landing (29°15'S, 177°54'W) 17 Aug 1985. - NMNZ P.041114, 1, 22.4 mm SL; Raoul Island, Meyer Islet (29°14'48.0"S, 177°52'51.0"W), 0-1.5 meters depth, 7 November 2004. - NMNZ P.024500, 1, not measured; Fishing Rock, Raoul Island (29°10'S, 177°54'W), November 1980 - NMNZ P.025315, 1, 19.4 mm SL; Raoul Island (29°14'55.0"S, 177°58'22.6"W), 1975. - NMNZ P.028570, 1, 27.2 mm SL; Raoul Island, Meyer Islet, Boat Harbour (29°14'54.0"S, 177°52'12.0"W), 0-3 meters depth, 03 June 1992. - NMNZ P.029570, 1, 27.1 mm SL; Meyer Islet, Boat Harbour (29°14'54.0"S, 177°52'12.0"W), 03 June 1992. - NMNZ P.050069, 1, 21.1 mm SL; Raoul Island, Fishing Rock Landing (29°15'04.6"S, 177°54'12.9"W), 1 meter depth, 14 September 2011. - NMNZ P.057561, 1, 16.9 mm SL; Raoul Island (29°14'55.2"S, 177°58'22.8"W), 1975.

Diagnosis.

See generic diagnosis.

Description.

General body shape as in Figures 1, 2. Morphometric characters listed in Table 1. Head relatively small (less than one third of body length), slightly dorso-ventrally compressed. Body moderately elongate, circular in cross-section anteriorly, becoming increasingly laterally compressed posteriorly. Widest point of body immediately behind head; as wide as widest point of head. Body width tapering gradually posteriorly. Body depth relatively uniform anterior to dorsal and anal fins; shallowest along caudal peduncle. Eye large, positioned on dorsolateral surface of head; orbit barely visible in ventral view. Centre of eye closer to tip of snout than to posterior margin of operculum. Snout of moderate length, broad, anterior margin rounded (Figs 1-3). Anterior nostril a small tubular opening (Figure 3). Posterior nostril surrounded by a low, fleshy rim; situated along anterodorsal margin of orbit (Figure 3). Gill membranes free from isthmus.

Mouth terminal, small; posterior tip of upper jaw reaching imaginary vertical line through anterior nostril when mouth closed. Upper and lower lip narrow; upper lip uniform in thickness along length of jaw; lower lip thicker along lateral margins of lower jaw, narrower at jaw symphysis (Figure 3). Upper jaw slightly wider and longer than lower jaw, creating a narrow gap between teeth of upper and lower jaws when jaws closed (Figure 5). Premaxilla with a single row of teeth, comprising 2-3 peg-like, conical teeth anteriorly at and adjacent to symphysis, and 10-12 strongly laterally compressed incisiviform teeth, each with a single strongly recurved cusp, along outer margin of bone (Figure 7 A–C). Dentary with a single row of 14-16 small, conical teeth with sharply pointed and slightly recurved tip (Figure 7D). Pharyngeal jaws comprising patch of 4-6 small conical teeth with slightly recurved tips on pharyngobranchial toothplate 3 and row of 3-5 small conical teeth with slightly recurved tips along ceratobranchial 5 (Figure 8D). 5-6 small triangular gill rakers located along anterior and posterior edge of ceratobranchials 2-3 and anterior edge of ceratobranchial 4; one or two tiny gill rakers located along anterior edge of ceratobranchial 1 (Figure 8D). Paired rows of gill filaments (holobranch) on gill arches I-III (three gill filaments of Briggs 1955). Basihyal an elongate rod, widest posteriorly at point of articulation with dorsal hypohyals; anterior edge tipped with cartilage (Figure 8C). Six brachiostegal rays (Figure 8A); anteriormost ray separate from hyoid bar; second ray articulating medially with hyoid bar along anterior ceratohyal; posterior rays articulating with hyoid bar laterally, including two along posteriormost part of anterior ceratohyal, one straddling junction between anterior and posterior ceratohyals, and posteriormost along anteriormost part of posterior ceratohyal (Figure 8B). Anteriormost branchiostegal ray shorter than posterior rays. Three posteriormost branchiostegal rays similar in width and length, approximately twice as long and thick as anteriormost ray. Intervening rays intermediate in width and length (Figure 8B).

Cephalic lateral-line system with 2 pores in nasal canal; 2 pores in postorbital canal; 2 pores in lachrymal canal; 3 pores in preopercular canal (Figure 3). Mandibular canal absent. Canal pores minute; typically flush with surface of skin and difficult to locate. Supraorbital canals (including nasal canal plus anteriormost region of postorbital canal of Shiogaki and Dotsu 1983) connected across midline via epiphyseal commissure (Figure 6A). Superficial neuromasts on surface of head not arranged in obvious rows (Figure 3); each surrounded by a shallow groove.

Dorsal-fin rays 9 or 10. Anal-fin rays 8 or 9 (first in serial or supernumerary association with anteriormost proximal-middle radial). Principal caudal-fin rays 5+5, dorsal procurrent rays 6 or 7, ventral procurrent rays 6. Pectoral-fin rays 24 or 25; uppermost ray a tiny splint-like element comprised of a single hemitrichium. Pelvic-fin rays I, 4. All fins rays, excluding anteriormost 4-5 procurrent caudal-fin rays, unbranched and segmented; anteriormost 4-5 procurrent caudal-fin rays unsegmented, azygous elements. Caudal fin marginally truncate, tips of principal caudal-fin rays extended beyond fin margin. Caudal-fin skeleton comprised of upper and lower hypural plates; epural triangular, with broad cartilaginous dorsal margin; parhypural absent, parahypural cartilage roughly triangular (Figure 10). Neural and hemal spine of PU2 bifurcated in single CT scanned specimen (Figure 4); singular in C&S specimen (Figure 10). Dorsal-fin origin situated slightly anterior to imaginary vertical line through anal-fin origin (Figs 1, 4). First dorsal-fin pterygiophore inserted between neural spines of vertebrae 17/18. First anal-fin pterygiophore inserted between hemal spines of vertebrae 18/19 or 19/20. Total number of vertebrae 33, consisting of 13 or 14 abdominal vertebrae and 19 or 20 caudal vertebrae (Figure 4). Ribs 12, associated with vertebrae 3-14. Epicentrals 20, associated with vertebrae 2-21.

Adhesive disc small (18-26% of SL), double (Figure 9A); anterior margin weakly crenulated medially, becoming smooth at point corresponding to location of expanded tip of spinous ray; posterior margin bordered by a broad, thin and weakly crenulated skin flap. Skin of posterior flap delicate, easily damaged; supported internally by fimbrae of ventral postcleithrum. Disc region A with 3-4 transverse rows of papillae. Disc region B with 4-5 transverse rows of papillae. Disc region C with 2-3 rows of papillae. Papillae of disc region A decreasing in diameter gradually towards outer margin of disc. Papillae of disc region B and C decreasing in diameter towards outer margin of inner disc. Decrease in size of papillae of disc region C abrupt, with papillae of inner row 2-3 times larger than papillae of outer rows. Dorsal postcleithrum a well ossified shield-shaped bone with ~25 long, poorly ossified and distally bifurcated fimbrae (Figure 9B). Ventral postcleithrum well ossified, irregular in shape; approximately equal in size to dorsal postcleithrum (Figure 9B). ~20 long, poorly ossified and distally bifurcated fimbrae restricted to posterolateral margin of ventral postcleithrum; point of fimbrae bifurcation located distally on medial fimbrae, shifting gradually to a more proximal location on lateral fimbrae. A strong articulation between anteromedial edge of ventral postcleithrum and posterior tip of basipterygium (Figs 5B, 9B). Skin associated with last pelvic-fin ray attaching to base of pectoral fin opposite 5 th– 6th lowermost pectoral-fin rays. Skin over base of ventral pectoral-fin rays smooth. Pectoral radials with well-developed bony struts along ventral (pectoral radial 1), dorsal (pectoral radial 4), or both ventral and dorsal margins (pectoral radials 2 and 3) that interdigitate with struts borne on element(s) directly above and/or below (Figure 9D, E).

Colouration. In alcohol, head and body background colour typically uniformly pale cream to yellow (Figure 3). Holotype (Figure 1) has retained pinkish purple colour of live individuals and is an exception. Fins hyaline.

In life (Figure 2), body uniformly pinkish purple to grey, with diffuse, pale markings ranging from bars to irregular blotches. Head pinkish purple to grey, with diffuse, pale areas around nostrils and tip of snout. Iris red. Fins transparent.

Distribution and habitat. Known to date only from intertidal and subtidal waters of the Kermadec Islands (Figure 11), including Raoul Island (type locality) and L’Esperance Rock. The majority of available specimens were collected from rock pools and from shallower subtidal areas (down to 9 meters) over rock and coral rubble substrates using ichthyocides ( Stewart 2015). However, a single specimen of the new species has been observed (and photographed) at 28 meters in depth (Figure 2).

Etymology. Incus is the Latin word for anvil, in reference to the anvil-like outline of Raoul Island, the largest island in the Kermadec archipelago and type locality of the new species. A noun in apposition.

Gut content. Hard and irregular shaped items ranging in size from 50-300 μm are scattered throughout the stomach of the CT scanned individual (Figure 12A). Smaller elements have smooth surfaces and could not be identified. Several of the larger elements appear to exhibit a porous (potentially stereomic) surface and are tentatively identified as echinoderm remains. Hard elements inside the stomach of the single C&S individual survived the clearing and staining process and could be dissected and photographed (Figure 12B, C). These elements are tentatively identified as either stereomic ossicles from the terminal disc of an echinoid (Figure 12B) or ossicles from the body of a holothuroid (Figure 12C) suggesting that the new species consumes echinoderms or parts of echinoderms.