Erdmannichthys alorensis (Allen & Erdmann, 2012) Conway & Fujiwara & Motomura & Summers, 2021

Conway, Kevin W., Fujiwara, Kyoji, Motomura, Hiroyuki & Summers, Adam P., 2021, Erdmannichthys, a new genus of Gobiesocidae (Teleostei: Gobiesociformes), and notes on the rare clingfish E. alorensis (Allen & Erdmann, 2012), new combination, Raffles Bulletin of Zoology 69, pp. 428-437 : 431-436

Notes on Erdmannichthys alorensis , new combination.

Allen & Erdmann (2012) described Erdmannichthys alorensis based on a single individual ( MZB 20588, holotype, 8.2 mm SL) collected in 2011 from a submerged reef on the western side of Alor Island (Nusa Tenggara Province) ( Fig. 1 ). The small size of this specimen presented challenges to the examination of its features, including the configuration of the gill membranes, which are free from the isthmus ( Figs. 4 , 5A ) but were interpreted as fused to the isthmus by

Allen & Erdmann (2012). This misinterpretation of a single character lead Allen & Erdmann (2012) to assign their new species to the subfamily Aspasminae (sensu Briggs, 1955, in which the gill membranes are fused to the isthmus) instead of the Diplocrepinae (sensu Briggs, 1955, in which the gill membranes are free), and ultimately generic assignment to Aspasmichthys . The sole specimen of E. alorensis available to Allen & Erdmann (2012) also precluded the description of internal characters, including features of the skeleton.

In 2016, five additional specimens of E. alorensis were photographed by M. V. Erdmann off the eastern coast of Padar Island (also Nusa Tenggara Province). The resulting series of underwater photographs ( Fig. 3 ) reveals additional features of the live colour pattern of E. alorensis not reported in the original description, including the presence of a black marking on the posterior part of the dorsal fin in one of the individuals photographed ( Fig. 3C ), and the presence of dark brown melanocytes on the lower abdomen of another ( Fig. 3F ; potentially WAM P.34629-005). Dark brown melanocytes are also visible over the surface of the head, around the anus, and the surface of the adhesive disc in a 9.1 mm SL specimen (WAM P.34629-005; Figs. 4 , 5 ) and are also visible on the surface of the adhesive disc in the 8.2 mm SL holotype ( Allen & Erdmann, 2012: 1163; fig. 5). Dark brown melanocytes are common in larval and juvenile stages of gobiesocids (reviewed by Allen, 1984) but are typically absent from adult stages. The largest specimen of E. alorensis recorded to date is only 13.3 mm SL (WAM P.34629-001). If melanocytes are lost ontogenetically in E. alorensis , as they appear to be in other gobiesocids, the presence of melanocytes in the aforementioned specimens may suggest that these individuals are juveniles, and perhaps only recently settled on the reef prior to collection. An alternative explanation could be that E. alorensis is a small-bodied species (i.e., miniature sensu Weitzman & Vari, 1988) and the presence of melanocytes could represent a paedomorphic character. Examination of additional specimens will be needed to confirm both size at maturity and maximum size of E. alorensis .

Two of the five specimens photographed by M. V. Erdmann ( Fig. 3 ) were collected and we have had the opportunity to examine and also CT scan one of these (WAM P.34629- 005, 9.1 mm SL; Fig. 4 ). From the rendering of the CT scan ( Figs. 6 , 7 ) we are able to report the following osteological information: Dorsal-fin rays 7. Anal-fin rays 7. Total caudal-fin rays 20 (17 reported by Allen & Erdmann, 2012), including 5+5 principal rays, 5 dorsal procurrent rays, and 5 ventral procurrent rays (anteriormost procurrent rays are poorly ossified and difficult to observe in the scan rendering presented in Fig. 7D ). Pectoral-fin rays 24 (21 reported by Allen & Erdmann, 2012). Branchiostegal rays 6. Total number of vertebrae 32, comprising 15 abdominal and 17 caudal. Ribs 12, associated with vertebrae 3–14. Epicentrals 14, associated with vertebrae 2–15. The anteriormost epicentral (epicentral 2) is a thin rod ( Fig. 6 ).

A single row of teeth is present along the outer margin of the premaxilla, comprising ca. 4 slightly recurved conical teeth anteriorly at and adjacent to symphysis, and ca. 12 strongly laterally compressed incisiviform teeth, each with strongly recurved cusp. Several replacement incisiviform teeth are also visible lateral to the functional teeth on the outer margin of the premaxilla ( Fig. 6C, D ). A single row of ca. 9 small conical teeth, each with slightly recurved tip, is present along the dorsal ridge of the dentary on each side of the lower jaw. A small oval opening is present between the premaxillae, formed by a semicircular indentation along the medial edge of each premaxilla ( Fig. 6A ). Ceratobranchials 1–4 are represented by poorly ossified rods of bone. Ceratobranchial 5 is approximately half the length of ceratobanchial 4. Other elements of the gill arch skeleton could not be observed in the available scan.

The cephalic lateral-line system comprises the following: supraorbital canal on nasal (pores NC1, NC2) and frontal bone; infraorbital canal on lachrymal (LC1, 2); otic canal on sphenotic (PO1 at junction of frontal and sphenotic) and pterotic (PO2); and preopercular canal on preopercle (PR1, PR3). The second pore of the preopercular canal (PR2) present in most gobiesocids (e.g., see Shiogaki & Dotsu, 1983) is absent in E. alorensis . The subopercle of E. alorensis is poorly ossified and difficult to detect in the rendering of the CT scan ( Fig. 6B, C ). The same is likely the case for the mesethmoid and the central part of the frontal, neither of which are visible in the optimal rendering of the scan.

The dorsal postcleithrum of the left side is a shield-shaped bone ( Fig. 6 ). The dorsal postcleithrum of the right side is severed into two pieces in the individual scanned ( Fig. 6 ). The ventral postcleithrum exhibits a facet on the anteromedial edge which accommodates the posterior tip of the basipterygium. The lateral margin of the ventral postcleithrum is weakly serrated, as is common in other diademichthyine taxa (e.g., see Hayashi et al., 1986: fig. 21). No poorly ossified fimbrae could be observed along the posterior edge of either the dorsal or ventral postcleithra in the renderings of the CT scan.

The new information presented herein on Erdmannichthys alorensis , though scant, complements that available from the original description provided by Allen & Erdmann (2012). Importantly, we have also been able to confirm that E. alorensis exhibits all three of the morphological characters proposed as putative synapomorphies for a monophyletic group of diademichthyine clingfishes (viz. Aspasmichthys , Diademichthys , Flexor, Flabellicauda , “ Lepadichthys ”, Lepadicyathus , Pherallodichthys and Pherallodus ) by Conway et al. (2018, 2020) and Fujiwara et al. (2021b), including: (1) a unique type of laterally compressed incisiviform tooth with a hooked tip; (2) an oval opening (variable in size) visible in dorsal view at the tip of the premaxillae, formed by a semicircular indentation along the medial edge of each premaxilla; and (3) a complex articulation between the posterior tip of the basipterygium and the anteromedial edge of the ventral postcleithrum. Based on the aforementioned characters, and the results of Conway et al. (2020) ( Fig. 2 ), we are confident that Erdmannichthys also is a member of this putative monophyletic group. The results of Conway et al. (2020) suggest that within this larger group, Erdmannichthys is a close relative of Pherallodichthys ( Fig. 2 ). We are not currently aware of any morphological characters that could potentially represent synapomorphies in support of a clade including Erdmannichthys and Pherallodichthys and the comparative work to identify such characters, and refine relationships among the diademichthyine clingfishes, is ongoing.

Comparative material examined

Aspasma ubauo: KAUM –I. 128774, holotype, 32.6 mm SL; NSMT-P 114699 , 1 , 29.9 mm SL; Japan, Honshu .

Aspasmichthys ciconiae: CAS-SU 7136, syntype, 49.9 mm SL; USNM 50760 , syntype, 56.0 mm SL; Japan, Honshu. — KAUM –I. 147708, 1, 26.7 mm SL; KAUM –I. 147568, 1, 43.1 mm SL; Japan , Kyushu. — TCWC 16461.02 , 1 , 26.0 mm SL (CT; https://doi.org/10.17602/M2/M30821); Japan, Kochi .

Aspasmodes briggsi: ANSP 150414, 1, 17.1 mm SL; ANSP 150415, 5 (1C&S), 7.9–15.1 mm SL; Seychelles. — ROM 55927, 1, 6.6 mm SL; Chagos Archipelago.

Briggsia hastingsi: Information on this species obtained from Craig & Randall (2009).

Flabellicauda: See material listed in Fujiwara et al. (2021b). Flexor incus: AIM MA 655142, 1 (C&S), 20.0 mm SL; AIM MA655401, 2 , 18.0–24.0 mm SL; AIM MA655316, 1 , 23.0 mm SL (CT; https://doi.org/10.17602/M2/ M56344 ); AMS I.45807-001, 1, 19.7 mm SL; AMS I.45823-010, 1, 19.1 mm SL; NMNZ P.060717, 1, holotype, 20.8 mm SL; NMNZ P.049965, 1, 24.3 mm SL; NMNZ P.049966, 1, 27.2 mm SL; NMNZ P.017760, 1, 14.0 mm SL; NMNZ P.041114, 1, 22.4 mm SL; NMNZ P.024500, 1, not measured; NMNZ P.025315, 1, 19.4 mm SL; NMNZ P.028570, 1, 27.2 mm SL; NMNZ P.029570, 1, 27.1 mm SL; NMNZ P.050069, 1, 21.1 mm; New Zealand , Kermadec Islands . — AMS I.17424-003, 1, 20.8 mm SL; Australia , Lord Howe Island . — USNM 322448 , 1 , 29.1 mm SL; New Caledonia .

Liobranchia stria: USNM 113992, 1, 15.3 mm SL; Marshall Islands.

Lissonanchus lusheri: SAIAB 342, holotype, 19.1 mm SL; Mozambique.

Pherallodichthys meshimaensis: KAUM –I. 131060, 25.7 mm SL; Japan, Yaku-shima island . — NSMT-P 46752 , holotype, 17.6 mm SL; NSMT-P 46753 , paratype (C&S), 19.2 mm SL; Japan , Kyushu. — NSMT-P 72561 , 1 , 13.0 mm SL; Indonesia, Ambon . — ROM 74264, 1 , 12.5 mm SL; Vietnam . — ROM 55170, 1 , 18.6 mm SL; Philippines . Pherallodus indicus : NSMT-P 114703 , 1 , 25.0 mm SL (CT; https://doi.org/10.17602/M2/ M56337 ); Japan , Honshu. — TCWC 16462.01 , 2 , 16.5–18.1 mm SL; Japan, Kochi .

Propherallodus briggsi : NSMT-P 46749 , holotype, 20.8 mm SL; Japan, Kyusyu .

Propherallodus longipterus: ANSP 193493, 1, 22.3 mm SL; India, Kerala — KUAM –I. 114615, paratype, 17.8 mm; Philippines .

Propherallodus smithi: CAS 131349, holotype, 18.5 mm SL; South Africa, Durban.

Figures

Fig. 1. Map showing locations (red circles) from which specimens of Erdmannichthys alorensis have been collected.

Fig. 4. Erdmannichthys alorensis, WAM P.34629-005, 9.1 mm SL; Indonesia, Nusa Tenggara Province. Dashed white circles highlight location of cephalic lateral line canal pores. Abbreviations: LC1, 2, lachrymal pore 1, 2; NC1, 2, nasal pore 1, 2; PO1, 2, postorbital pore 1, 2; PR1, 3, preopercular pore 1, 3.

Fig. 5. A. Photograph of adhesive disc of Erdmannichthys alorensis, WAM P.34629-005, 9.1 mm SL; anterior margin of disc inserted under gill membrane; dashed grey line highlights posterior margin of gill membrane. B. Schematic line drawing of adhesive disc in A. C. Photograph of adhesive disc of Aspasmichthys ciconiae, KAUM–I. 147568, 43.1 mm SL; disc treated with Cyanine blue (following Saruwatari et al., 1997). D. Schematic line drawing of disc in C. Abbreviations: A–C, adhesive disc regions A–C; GM, gill membrane; LM, larval melanocyte.

Fig. 3. Five individuals of Erdmannichthys alorensis photographed by M.V. Erdmann at a submerged reef (10 metres depth) off south east coast of Padar island, Nusa Tenggara Province, Indonesia. A–C. Not collected, not measured. D. Potentially WAM P.34629-001, 13.3 mm SL; E–F. Potentially WAM P.34629-005, 9.1 mm SL.

Fig. 6. CT scanned anterior skeleton, including cranium, paired-fin girdles and abdominal region of vertebral column, of Erdmannichthys alorensis WAM P.34629-005, 9.1 mm SL. A. Dorsal view. B. Lateral view of right side (image mirrored). C. Ventral view. Right side of specimen damaged. Cephalic lateral line canals highlighted in green. Pores of cephalic lateral line system orange. Anteriormost epicentral (epicentral 2) highlighted in aqua blue. Dorsal postcleithra highlighted in pink. Ventral postcleithra highlighted in yellow. Outline of subopercle highlighted with thin white line in B, C. Abbreviations: ACh, anterior ceratohyal; Ana, angulo-articular; Apa, autopalatine; Boc, basioccipital; Bp, basipterygium; Br, branchiostegal rays; Cb, ceratobranchials; Cl, cleithrum; Cor, coracoid; DHh, dorsal hypohyal; DPcl, dorsal postcleithrum; Ec2, 6, epicentral 2, 6; Ect, ectopterygoid; EPC, epiphyseal commissure; Epoc, epiotic; Exoc, exoccipital; Fr, frontal; Hy, hyomandibular; I, pelvic-fin spine; Iop, interopercle; LC, lachrymal canal; LC1, 2, lachrymal pore 1, 2; LE, lateral ethmoid; Na, nasal; NC1, 2, nasal pore 1, 2; NS1, 5, neural spine of vertebral centrum 1, 5; Op, opercle; Pa, parietal; PecR, pectoral radial; PecFR, pectoral-fin ray; PelFR1–4, pelvic-fin ray 1–4; PO1, 2, postorbital pore 1, 2; Pop, preopercle; PRC, preopercular canal; PR1, 3, preopercular canal pore 1, 3; Pro, prootic; Psph, parasphenoid; Pt, posttemporal; Pte, pterotic; Q, quadrate; Ra, retroarticular; Ri, ribs; Sc, scapula; Scl, supracleithrum; Soc, supraoccipital; Sop, subopercle; SPC, supraorbital canal; Sph, sphenotic; STC, stomach content; Ur, urohyal; V1, vertebral centrum 1; Vo, vomer; VPcl, ventral postcleithrum.

Fig. 7. CT scanned skeleton of Erdmannichthys alorensis WAM P.34629-005, 9.1 mm SL. A. Dorsal view. B. Lateral view. C. Ventral view. D. Caudal-fin skeleton, lateral view. Right side of specimen damaged. Abbreviations: AFR, anal-fin rays; DFR, dorsal-fin rays; DPCR, dorsal procurrent rays; HS1, hemal spine 1; NS1, 10, neural spine 1, 10; PCR, principal caudal-fin rays; PU2, preural centrum 2; VPCR, ventral procurrent rays.

Fig. 2. Phylogenetic relationships of Gobiesocidae modified from Conway et al. (2020; fig. 3) showing placement of Aspasmichthys ciconiae (red) and Erdmannichthys alorensis (blue). Numbers above branches represent bootstrap support values (values below 65 not shown).