Callogobius aquilus, Li & Chen, 2024

Li, Hsien-En & Chen, I-Shiung, 2024, Descriptions of a new species of Callogobius with a congeneric new record and comments on previous records of the genus from Taiwan, Zootaxa 5550 (1), pp. 159-173 : 160-167

Callogobius aquilus sp. nov.

(AENJȒoeḃm)

( Figs. 1–4 )

Materials Examined

Holotype.— NTOUP-2023-11-007 , male, 1 (24.2 mm SL); about 4 meters, eastern side out of Kihaw Harbour , Chenggong Township, Taitung County, Taiwan; coll. Hsien-En Li & Muhammad Cesar Brilliandi, 7 Nov. 2023.

Paratypes.— NTOUP-2021-08-011 , male, 1 (13.4 mm SL); about 5 meters, northeastern side out of Kihaw Harbour , Chenggong Township, Taitung County, Taiwan; coll. Hsien-En Li et al., 11 Aug. 2021 ; NTOUP-2021-09- 024 , female, 1 (17.4 mm SL); about 4 meters, Xiaogang Harbour , Chenggong Township, Taitung County, Taiwan; coll. Hsien-En Li et al., 24 Sep. 2021 .

Diagnosis

Callogobius aquilus sp. nov. can be well distinguished from its congeners by the following unique combination of characters (counts for holotype marked with an asterisk or shown in brackets): (1) meristic features: D VI-I, 9*; A I, 7*; P 1 16*; P 2 I, 5*; LR 27*–28; TR 9*–10; D-P 5; Pred 11–12*; V 10+16=26*; P-V 3/22110/9*; (2) head lateral-line system: papillae ridge row i in 12 rows of short, transverse flaps; anterior oculoscapular canal with paired pores σ and α, and unpaired pore κ; preopercular canal with paired pores δ and ε; posterior oculoscapular canals absent; and (3) specific coloration pattern: body brownish white with 6 brown cross blotches; dorsal fins goldish brown with dark brown blotches.

Description

Body proportions as shown in Table 1 , counts for holotype marked with asterisk. Body robust, subcylindrical anteriorly and laterally compressed posteriorly. Head depressed, moderately large. Snout short, mouth slightly oblique, with posterior end of gape not reaching anterior edge of orbit. Both anterior and posterior nostril openings protruding in short tubes, anterior tube reaching upper lip when depressed. Eye positioned dorso-laterally. Both cheeks not exceptionally prominent. Postorbital origin over half of head length. Tongue with rounded margin. Vertebrate 10+16=26*, dorsal pterygiophore formula 3/22110/9*.

Fins. First dorsal fin elements VI* (3); second dorsal fin elements I, 9* (3); anal fin elements I, 7* (3); pectoral fin elements 16* (1) or 17 (2); pelvic fin elements I, 5* (3). In larger individuals, both dorsal fins with slight reduced membrane, resulting in slight filamentous fin rays. Posterior edge of second dorsal fin slightly rounded in juveniles ( Fig. 2A ); second dorsal fin base longer than anal fin base. Pectoral fins oval shaped, without free rays, posterior end extending beyond anal fin origin. Pelvic fin spines fused with a very thin frenum, and fifth segmented ray of both pelvic fins also fused with a thin membrane, altogether forming a very weak disk ( Fig. 4 ). Anal fin with latter three segmented rays slightly elongated than others. Caudal fin rounded in juveniles, then gradually becoming ovalshaped in larger individuals.

Squamation. LR 27* (2) or 28 (1); TR 9* (2) or 10* (1); D-P 5*; Pred 11 (1) or 12* (2). Body covered in both cycloid and ctenoid scales, all scales moderately large, inserted loosely and covered with fragile, thin skin. Cycloid scales shaping from oval to circular shaped with an outlined centre; ctenoid scales with one to four ctenii located at posterior edge, number of ctenii increases from anterior most scale to posterior most one. All ctenoid scales without exceptionally elongated ctenii. Ctenoid scales covering body from the vertical position of first dorsal fin base until posterior end of caudal peduncle (both dorsal fin base with a few cycloid scales). Cheek, operculum, and predorsal region weakly embedded with cycloid scales. Coverage of cycloid scales on thorax and abdomen does not reach beyond vertical position of preopercle anteriorly and vertical position of posterior end of first dorsal fin base, respectively. Fleshy pectoral fin base with small cycloid scales. Head naked at snout, interorbital region, lower jaw, and ventral side of head.

Head lateral line system

Canals.—Head lateral line systems including oculoscapular canal openings (sensory pores) and sensory papillae ridge patterns shown in Fig. 3 . All sensory pores with tubular openings. Anterior oculoscapular canals present with paired openings pores σ (located at anterior edge of orbit) and α (located at posterior edge of orbit), and single unpaired pore κ (located at interorbital region). Postorbital part of anterior oculoscapular canal paired pores β and ρ located above preopercle. Preopercular canals with paired pores δ and ε. Posterior oculoscapular canal absent. Anterior oculoscapular canals not continuous with preopercular canals.

Sensory papillae.—Most sensory papillae rows in single rows and located on raised ridges of skin flaps, with some rows in single rows of papillae without ridges. Postorbital row n separated into two sections. Row r separated into two sections, r 1 (located beside nasal region) and r 2 (located at the anterior end of interorbital region), with row r 2 further separated into left and right sections. Cheek with horizontal rows b and d, separating vertical row 4 into 4s (further separated into 4s 1 and 4s 2, located side by side) and 4i; row d and row e not separated into two segments. Rows z and ot joined together, forming a single skin ridge of z+ot. Row i in form of a row of 12 short flaps arranged longitudinally, each flap with 4–5 papillae. Lower jaw with single row f, arranged longitudinally. Vertical rows of papillae located transversely along middle line of body laterally.

Coloration when fresh. Body brownish white with small, delicate dark brown specks scattered, abdomen and thoracic region snowy white. A total of five large, transversely arranged brown blotches located on body: first one located below first dorsal fin, shaping like a triangular patch with a pointy lower end; second one located at origin of second dorsal fin, in form of a small patch not extending downwards beyond horizontal position of upper gill opening; third one located at lower half of body, in form of a short band extending down diagonally backwards from vertical position of anus, not extending to upper half of body; fourth one located below second dorsal fin, in form of a cross band with its anterior edge at fifth to sixth segmented ray of second dorsal fin and posterior edge at posterior end of second dorsal fin base; fifth one located at caudal fin base, in form of a wide transverse cross band, shaping like a barrel. Head with two oblique brown bars, one extending from tip of snout running diagonally backwards, up to posterior edge of orbit, two bars joined with a square shaped blotch; other extending from posterior end of orbit running diagonally backwards, down to posterior end of operculum and interrupted medially. Predorsal region with a wide, square-like brown blotch located at pectoral fin base and connected with postorbital blotch with two short bands ( Fig. 2C ). Papillose flaps with short brown bands arranged in rows. First dorsal fin with a bright yellow spot and white margin in juveniles ( Fig.2A ), gradually changing to a brown spot with orange margin ( Fig. 2B ) then finally a dark brown spot with a white margin scattered with brown specks ( Fig. 1 ). Second dorsal fin brownish white with a medial oblique brown stripe, width about same with orbit, connecting downwards with lateral blotched on body at sixth to seventh segmented ray; fin origin with a small brown blotch; larger individuals with an additional single brown blotch at posterior tip. Pectoral fins brownish white with a brown smear, larger individuals with a thin whitish transparent margin. Pelvic fins white with dark brown specks scattered. Anal fin with a brown stripe located at posterior half, connecting to fourth lateral body blotch, other parts of fin scattered with light brown specks. Caudal fin brownish white at base and dark brown thoroughly, upper edge and lower edges dark brown to black; only upper 2/3 posterior margin white. All bands turn vague or with mottled margins and body color more intensely mottled in larger individuals.

Coloration in preservatives. All colored shades and body color turning grayish white; all bark brown and brown bands turning black.

Etymology

The specific name, aquilus , is derived from the Latin “’aquila”, meaning “eagle”, in allusion to the overall brownish coloration and enlarged, wing-like pectoral fins of the new species.

Distribution and habitat

Callogobius aquilus sp. nov. is so far only known from its type locality of southeastern Taiwan, inhabiting shallow coral reefs surrounded by silty sand or rubble plains.

Remarks

Callogobius aquilus n. sp. can be immediately distinguished from its congeners by having sensory papillae row i in the form of 11 rows of short flaps (vs. row i in 11 rows of short flaps plus one single papilla or in three rows of short flaps plus 8–20 papillae), placing it within the subgeneric hasseltii group “clade” proposed by Akihito and Meguro (1977), Delventhal and Mooi (2018), and Akihito and Ikeda (2021). From the nominal members within this “clade”, Callogobius aquilus sp. nov. can be further distinguished by a combination of having a short, robust body (lateral scale row count <30) and a relatively light, unsoiled coloration (vs. no such characters), making it mostly similar to the congeneric members, including C. plumatus Smith, 1959 , C. amikami Goren, Miroz & Baranes, 1991 , C. sheni Chen, Chen & Fang, 2006 , and C. falx Fujiwara, Suzuki & Motomura, 2021 .

Of the above four closely related species, Callogobius plumatus and C. amikami so far are only distributed in the western Indian Ocean and the Red Sea ( Smith 1959; Goren et al. 1991; Delventhal et al. 2016). The new species Callogobius aquilus sp. nov. shares similarities with C. plumatus in terms of dorsal and anal fin element counts, transverse and predorsal scale counts, and overall cephalic sensory organ arrangements ( Fujiwara et al. 2021: Figs. 7 & 8), however, it can be distinguished from the latter in having lower pectoral fin ray counts (16–17 vs. 19–20), longitudinal scale row counts (27–28 vs. 30–33), and different postorbital cheek bar patterns (interrupted at midpoint vs. continuous). Apart from Callogobius amikami , C. aquilus can be identified by the second dorsal fin having 9 segmented rays (vs. 10 in C. amikami ), anal fin having 7 segmented rays (vs. 8 in C. amikami ), higher longitudinal scale rows (27–28 vs. 24 in C. amikami ) and predorsal scale counts (11–12 vs. 8 in C. amikami ), paired pore ω absent (vs. present in C. amikami ), and different coloration patterns of body (brownish white with large blotches vs. white with 8 narrow brown longitudinal bars), dorsal fin blotches (Brownish vs. orange framed with black margin), and anal fin (white with a medial brown blotch vs. dark brown with a white round blotch).

C. aquilus sp. nov. can be distinguished from the two other western Pacific species, Callogobius sheni and C. falx , by several characteristics. The new species can be differentiated from C. sheni by having shorter pectoral fins (35.9% in SL vs. 40.9 in SL), higher predorsal scale counts (11–12 vs. 9–10), absence of interorbital pore κ (vs. present), presence of preopercular canal and paired pores (vs. absent), different body coloration patterns (brownish white scattered with brown specks vs. white with longitudinal brown stripes at posterior half of body), and different postorbital cheek bar patterns (interrupted at midpoint vs. continuous). C. aquilus can finally be distinguished from C. falx by having fewer segmented pectoral fin ray counts (16–17 vs. 18–19), a higher longitudinal scale row (27–28 vs. 20–22) and predorsal scale counts (11–12 vs. 9), the presence of cephalic canal pores (vs. completely absent), and different blotch patterns of the caudal fin base (barrel-like cross band vs. narrow, sickle-like) and postorbital cheek bar (interrupted at midpoint vs. continuous).

Figures

FIGURE 1. Callogobius aquilus, holotype, NTOUP-2023-11-007, 24.2 mm SL (A) Freshly dead; (B) After preservation for 1 day.

FIGURE 2. Callogobius aquilus (A) NTOUP-2021-08-011, paratype, male, 13.4 mm SL; (B) lateral view and (C) dorsal view of NTOUP-2021-09-024, paratype, female, 17.4 mm SL.

FIGURE 3. Head lateral-line system of Callogobius aquilus (NTOUP-2023-11-007, holotype, 24.2 mm SL), also showing squamation of the predorsal and thoracic regions. AN, anterior nostril; PN, posterior nostril. Arrow indicates the lower edge of the gill slits. Scale bar = 0.1 mm.

FIGURE 4. Pelvic fin morphology of Callogobius aquilus (NTOUP2023-11-007, holotype, 24.2 mm SL). Scale bar = 0.1 mm.

FIGURE 7. Pelvic fin of Callogobius clitellus (NTOUP2003-11-284, 34.6 mm SL). Scale bar = 0.1 mm.

Tables

TABLE 1. Meristic counts and morphometry measurements for types of Callogobius aquilus sp. nov.

Species		Callogobius alilis sp. nov.
	Holotype	Paratypes
Sex	♂	♂	♀
D	VI-I, 9	VI-I, 9	VI-I, 9
A	I, 7	I, 7	I, 7
P1	16	17	17
P2	I, 5	I, 5	I, 5
LR	27	28	27
TR	9	10	9
D-P	5	5	5
Pred	12	12	11
SL (mm)	24.22	13.35	17.44
Percent in standard length (%)
Head length	30.27	32.06	34.40
Predorsal length	39.98	40.40	40.98
Snout to 2nd dorsal origin	60.33	58.77	61.22
Snout to anus	56.40	57.02	58.51
Snout to anal fin origin	59.45	61.24	60.02
Prepelvic length	30.72	31.25	31.92
Caudal peduncle length	24.59	23.19	23.41
Caudal peduncle depth	14.13	14.54	15.06
1st dorsal fin base	16.16	16.75	17.70
2nd dorsal fin base	23.46	23.90	23.58
Anal fin base	17.87	17.96	18.46
Caudal fin length	32.22	32.61	33.81
Pectoral fin length	35.68	35.90	36.12
Pelvic fin length	25.71	25.27	25.64
Body depth at pelvic fin base	22.06	21.82	22.55
Body depth at anal fin base	19.63	19.43	20.36
Body width at anal fin base	14.35	14.82	13.23
Pelvic fin origin to anus	25.05	25.60	25.85
Percent in head length (%)
Head width in maximum	81.16	80.54	82.21
Head width at upper gill opening	55.57	56.52	54.85
Eye diameter	28.26	30.99	29.57
Bony interorbital width	3.66	3.09	2.95
Fleshy interorbital width	45.46	45.22	44.17
Snout length	28.09	27.71	28.47
Lower jaw length	23.92	24.21	22.30
Cheek depth	32.50	31.44	31.95
Postorbital length	52.41	51.35	51.90