Phaeoptyx

Baldwin, Carole C., Mounts, Julie H., Smith, David G. & Weigt, Lee A., 2009, Genetic identification and color descriptions of early life-history stages of Belizean Phaeoptyx and Astrapogon (Teleostei: Apogonidae) with Comments on identification of adult Phaeoptyx, Zootaxa 2008, pp. 1-22 : 6-15

Phaeoptyx

Identification. Our Phaeoptyx specimens form three distinct genetic lineages, corresponding to the three known species ( Fig. 1 ). Intraspecific variation ranges from 0.00–2.19% nucleotide substitutions per site as opposed to 15.20–20.80% for interspecific variation ( Table 2). See “Comments on Identification of Adult Phaeoptyx ,” below, for a discussion of morphological identification of adult Phaeoptyx .

P. p i g m e n t a r i a N= 44 P. conklini N= 26 P. xenus N= 6 P. p i g m e n t a r i a 0.56% (0.00–2.19)

P. conklini 16.79% (15.65–19.02) 0.78% (0.00–5.81) P. xenus 16.03% (15.20–20.80) 18.10% (16.71–20.80) 0.43% (0.00–0.93) Larvae ( Fig. 2 ). Phaeoptyx larvae are easily distinguished from other apogonids by the presence of yellow chromatophores on the first dorsal and pelvic fins and usually melanophores on some portion of the pelvic fin. The yellow fin pigment typically disappears about the same time as the blotch of melanophores appears on the caudal peduncle, and here we separate larval and juvenile stages based on this transition in pigment. This also corresponds well with settlement from the plankton, as most of our net-collected larvae that have caudalpeduncle pigment do not have the pigment well defined as it is in juveniles and adults. Diagnostic features of the species are given below.

Phaeoptyx conklini: Size range 10–13.5 mm SL. First dorsal fin yellow; no melanophores. Second dorsal fin clear. Pelvic fin yellow, usually more strongly so proximally, with a prominent melanophore at the base and linear series of melanophores along the fin rays to the distal tip of the fin. Anal fin mostly clear; orange, if present, restricted to base. Posterior end of caudal peduncle with two dense, vertical crescent-shaped bands of orange chromatophores overlying posterior margin of hypural plate, the dorsal one only partially formed in small specimens. Caudal fin with orange chromatophores on bases of central rays; remainder of fin without pigment. Head mostly orange, some specimens with yellow chromatophores over posterior portion of brain; scattered melanophores present on top of head, a couple sometimes present on cheek, and heavy pigment developing in temporal region by approximately 12 mm. Scattered melanophores present on gut and a cap of melanophores usually visible over swimbladder in all larvae, and a series of internal melanophores usually developing along anterior portion of vertebral column by 12 mm.

Phaeoptyx pigmentaria: Size range 13–18 mm SL. First dorsal fin usually yellow, last two elements sometimes orange; melanophores, if present, restricted to the distal half of anterior spines. Second dorsal fin with orange stripe along proximal one fifth to one third of fin rays. Pelvic fin yellow; melanophores, if present, restricted to distal half of fin (or distal tips of fin rays). Anal fin mostly orange. Posterior end of caudal peduncle with two dense, vertical crescent-shaped bands of orange chromatophores overlying posterior margin of hypural plate; caudal fin mostly orange, melanophores usually present at distal ends of outer branched rays of dorsal and ventral lobes. Head mostly orange, some specimens with yellow chromatophores over posterior portion of brain; scattered melanophores present on top of head and a few present on cheek/ temporal region by 13 mm; larger larvae usually also with melanophores on distal margins of premaxilla and dentary. Scattered melanophores present on gut, and a cap of melanophores visible over swimbladder in all larvae; a series of internal melanophores developing along anterior portion of vertebral column by 15 mm.

Phaeoptyx xenus: Size range 8–10 mm SL. First dorsal fin primarily yellow, last two fin elements clear; no melanophores. Second dorsal-fin spine elongate, extending when depressed beyond posterior base of second dorsal fin in 8-mm SL specimen, to middle of second dorsal fin in 10-mm SL specimen. Second dorsal fin clear. Pelvic fin orange at base; the remainder of fin yellow with scattered melanophores on the distal three quarters. Anal fin primarily clear. Posterior end of caudal peduncle with two vertical crescent-shaped bands of orange chromatophores overlying posterior margin of hypural plate, the dorsal one only partially formed in 10 mm specimen, absent in 8 mm specimen. Caudal fin with a few scattered chromatophores on anterior portion of central rays; remainder of fin clear. Head mostly orange, with bright yellow chromatophores over posterior portion of brain; a few melanophores present on top of head and two to several present on temporal region. Lateral surface of gut yellow in 8-mm specimen, pale yellow and with a few melanophores in 10 mm specimen. A cap of melanophores developing over swimbladder in 8 mm specimen, well developed and prominent at 10 mm. The 10 mm specimen also with a well-developed series of internal melanophores on anterior portion of vertebral column.

Comparisons ( Table 3 ): The patterns of chromatophores and melanophores on the fins usually distinguish larvae of the three species. Phaeoptyx pigmentaria is unique in typically having melanophores on the first dorsal and caudal fins, a wide orange stripe at the base of the second dorsal fin and a mostly orange caudal fin. Phaeoptyx conklini is distinctive in having a prominent melanophore at the base of (and usually spots along the entire length of) the pelvic fin; in the other species, melanophores are restricted to the distal half (P. p i g m e n t a r i a, if present) to three quarters (P. x e n u s) of the fin. Phaeoptyx xenus is distinctive in having the second dorsal-fin spine elongate. Some of the differences noted above may be related to developmental stage and size: although P. pigmentaria is the most common larval Phaeoptyx species in our samples, we have not obtained larvae smaller than 13 mm, whereas the largest larvae of P. xenus and P. conklini we have collected are 10 and 13.5 mm, respectively.

Species Second D1 Melanophores: D1 Melanophores: P2 Melanophores: Caudal Fin

Element

Elongate

Species Chromatophores: D1 Chromatophores: D2 Chromatophores: Caudal Fin Juveniles ( Fig. 3 ). Phaeoptyx juveniles can be distinguished from other juvenile apogonids by the pattern of pigment – from Astrapogon in lacking heavily pigmented first dorsal and pelvic fins, and from Apogon in always having a blotch of pigment on the caudal peduncle (vs. caudal-peduncle spot present only in some species), trunk beginning to develop uniform covering of melanophores (vs. melanophores only in discrete spots or bars), and in having a pale pink color (vs. having bright orange chromatophores covering most of trunk).

Phaeoptyx conklini: Size range 14–22 mm SL. Snout and upper and lower jaws with orange chromatophores, never yellow. Tip of snout blunt, forming almost a 90o angle with dorsal profile. Second dorsal and anal fins lacking distinct stripes of orange pigment but entire fin may be orange. Specimens 15 mm SL and smaller lacking melanophores on second dorsal and anal fins. Specimens 17 mm SL and larger with distinct stripes of melanophores forming at bases or slightly apart from bases of second dorsal and anal fins. Posterior end of caudal peduncle with vertical, dark bar spanning most of peduncle; anterior edge of bar irregular, the central portion usually extending further anteriorly than rest of bar. Posterior end of peduncle retaining the two vertical crescent-shaped bands of orange chromatophores of larvae. Caudal fin orange and with numerous melanophores in wildcaught juveniles, usually pale and with fewer melanophores in reared specimens. Teeth, when developed, small (see Fig. 5 ).

Phaeoptyx pigmentaria: Size range 17–21 mm SL. Snout and upper and lower jaws usually with yellow chromatophores. Tip of snout rounded. No stripe of melanophores along bases of second dorsal and anal fins. Second dorsal fin with orange stripe along proximal one fifth to one third of fin rays. Anal fin with similar orange stripe in wildcaught specimens (lacking in some reared juveniles). Caudal peduncle with dark bar usually spanning entire peduncle; anterior edge of bar relatively straight and uniform. Posterior end of peduncle retaining the two vertical crescent-shaped bands of orange chromatophores of larvae. Caudal fin mostly pale orange, with numerous scattered melanophores. Teeth, when developed, enlarged (see Fig. 5 ).

Phaeoptyx xenus: Presumably juveniles are typically larger than our largest larva, 10 mm SL, and smaller than our smallest adult, 28 mm SL; our description here is based on one reared larva measuring 11 mm SL and a wild-caught juvenile of 21 mm SL. Snout and upper and lower jaws pale yellow; tip of snout rounded. Second dorsal and anal fins lacking distinct stripes of pigment in 11 mm specimen, with well-developed stripes of pigment in 21 mm specimen. First dorsal and caudal fins with scattered melanophores in 21 mm specimen. Center of caudal peduncle with vertical oval of melanophores, oval not reaching dorsal and ventral body margins. Posterior end of caudal peduncle with two crescent-shaped lines of orange chromatophores as in larvae. Teeth small.

Species Yellow Snout Tip of Snout Enlarged Teeth in Melanophores: Stripes at Bases of D2 and A

and Jaws Jaws

Species Melanophores: Caudal Peduncle Chromatophores: D2 P1 Rays Comparisons ( Table 4 ): Juveniles typically can be separated by the following: size and shape of the blotch of pigment on the caudal peduncle (spanning entire depth of peduncle and with a relatively uniform anterior margin in P. pigmentaria , usually spanning entire depth of peduncle and with irregular anterior margin in P. conklini , more oval shaped and not reaching dorsal and ventral body margins in P. xenus ); presence or absence of yellow pigment on the snout and tip of lower jaw (usually present in P. pigmentaria and P. xenus , absent in P. conklini ); shape of the tip of the snout (blunt in P. conklini , rounded in P. pigmentaria and P. x e n u s); presence or absence of basal stripes of melanophores on the second dorsal and anal fins (absent in P. pigmentaria , present and set slightly apart from bases of fins in P. conklini , present and covering bases of fins in P. xenus ); and presence or absence of orange pigment proximally on second dorsal (and usually anal) fin (present in P. pigmentaria , absent in P. c o n k l i n i and P. xenus ). Larger juveniles of P. pigmentaria differ from the others in having enlarged teeth. Additionally, Phaeoptyx xenus , which is not common in our samples at any life-history stage, has 10 pectoral-fin rays vs. 11–13 in the other two species.

Comments on Identification of Adult Phaeoptyx ( Fig. 4 , Table 5 ). Adult P. p i g m e n t a r i a is easily identified by the absence of a well-developed pigment stripe along the bases of the second dorsal and anal fins (although there may be a small stripe comprising one or two rows of melanophores as well as numerous scattered spots on both fins – Fig. 4 D); presence of enlarged teeth in the upper and lower jaws ( Fig. 5 ); and by having 11–13 (rarely 13) lower-limb gill rakers (vs. 13–15, usually 14, in P. x e n u s, 14–16, usually 15, in P. conklini—Böhlke and Chaplin 1968). Phaeoptyx conklini has traditionally been separated from P. xenus by the presence of wide, dark stripes of pigment along the bases of the second dorsal and anal fins, a larger eye, and modally one more gill raker (15 vs. 14) on the lower limb ( Böhlke & Chaplin 1968; Gon 2002). There is overlap in extremes of eye diameter ( Fig. 6), the stripe of fin pigment may be wider in P. xenus than in P. conklini , and accurate gill-raker counts are sometimes difficult to make in small adults, especially in the field. As noted by Böhlke and Chaplin (1968), the fin stripes in P. conklini are usually darker and more prominent than in P. xenus and set slightly apart from the bases vs. directly along the bases. However, the intensity of the stripes is most informative when both species are available for comparison, and several of our P. conklini adults lack the pale streaks or gaps between the stripes of fin pigment and fin bases. The stripe of pigment on the anal fin does not extend anteriorly to the first and second anal-fin elements in P. xenus , whereas it does extend to the first two elements in P. conklini . Additionally, adult P. conklini retain the very blunt snout of juveniles, and it is not yellow as it is in adult P. pigmentaria and P. x e n u s. If the mouth is closed, the morphology of the snout is often the most distinctive diagnostic character of P. conklini . Phaeoptyx conklini usually has the pigment spot on the caudal peduncle extending to or near the dorsal and ventral body margins, whereas this spot is typically restricted to the center of the caudal peduncle in P. xenus . Finally, adults of all three species can usually be separated by the size, number, and distribution of melanophores on the trunk: in P. pigmentaria , there is usually one melanophore per scale, and the pigment forms uniform rows of spots from anterior to posterior ( Fig. 4 C); in P. conklini , there are usually two or more melanophores per scale posteriorly, and the pigment spots are uniformly spaced on the trunk ( Fig. 4 B); in P. xenus , the trunk pigment is irregular, with larger melanophores scattered along the center and smaller, more densely clustered melanophores dorsally and ventrally ( Fig. 4 E, F). As with most other characters of Phaeoptyx , however, there is variation within species, and one specimen of P. pigmentaria , for example, has a pattern of trunk melanophores more like that of P. xenus than other P. pigmentaria ( Fig. 4 D).

Comments on Previous Identifications of Early Life Stages of Phaeoptyx . Lara (2006:1393) provided illustrations of a 12 mm larva and a 16.2 mm late larval or juvenile specimen of P. conklini . The larva has the hallmark P. conklini pelvic-fin pigment—melanophores along the entire length of the fin including a spot at the base. In the description of larvae, however, Lara (2006:1392) did not mention pelvic-fin pigment. The 16.2-mm specimen exhibits the blunt snout, small teeth, and caudal-peduncle pigment spanning entire depth of peduncle and with irregular anterior edge typical of juvenile P. conklini . Lara (2006:1395) provided an illustration of a 17.2-mm SL specimen of P. pigmentaria that resembles our juvenile specimens of that species in having the blotch of melanophores on the caudal peduncle extending the entire depth of the peduncle and lacking a blunt snout, although the snout in that illustration is considerably more pointed than the snout is in any of our larval, juvenile, and adult specimens. Lara (2006:1394) noted that larval P. pigmentaria has little or no pigment on the fins, but most of our specimens have diagnostic melanophores at the distal tips of the first dorsal, pelvic, and caudal fins. Lara (2006: 1397) illustrated 13.9- and 22.1-mm SL specimens of P. x e n u s. The configuration of the blotch of pigment on the caudal peduncle, which, in both specimens does not extend to the dorsal and ventral margins of the body, agrees with our juveniles of P. xenus . The pelvic fin of the 13.9 mm specimen lacks the pigment characteristic of our smaller P. x e n u s larvae. One additional illustration of Phaeoptyx provided by Lara (2006:1399: Figure 3 C) could be P. pigmentaria based on the absence of pelvicfin pigment.

40

35

30

HL 25

%

as Phaeoptyx conklini diameter 20 Phaeoptyx Phaeoptyx xenus pigmentaria Eye 15

10

5

0

0 5 10 15 20 25 30 35 40 45 50

Standard length (mm)

Figures

FIGURE 1. Neighbor-joining tree derived from Cytochrome Oxidase 1 sequences showing three genetically distinct lineages of Belizean Phaeoptyx.

FIGURE 2. Phaeoptyx larvae: (A) Phaeoptyx conklini, 12 mm SL, 5039; (B) Phaeoptyx pigmentaria, USNM 393356, 15 mm SL, 7013, (C) Phaeoptyx pigmentaria, USNM 393358, 15.5 mm SL, 7080; (D) Phaeoptyx xenus, 8 mm SL, 6161.

FIGURE 3. Phaeoptyx juveniles: (A) Phaeoptyx conklini, USNM 393373, 22 mm SL, 5144; (B) Phaeoptyx pigmentaria, USNM 393352, 19 mm SL, 6371; (C) Phaeoptyx xenus, USNM 393399, 21 mm SL, 7741.

FIGURE 4. Phaeoptyx adults: (A) Phaeoptyx conklini, USNM 393372, 40 mm SL, 5143; (B) Phaeoptyx conklini, USNM 393376, 30 mm SL, 5303; (C) Phaeoptyx pigmentaria, USNM 393338, 30 mm SL, 5269; (D) Phaeoptyx pigmentaria, USNM 393327, 38 mm SL, 5052; (E) Phaeoptyx xenus, USNM 393395, 38 mm SL, 6298; (F) Phaeoptyx xenus, USNM 393393, 28 mm SL, 5465.

FIGURE 5. Teeth of Phaeoptyx conklini (A), USNM 365171, 38 mm SL, and Phaeoptyx pigmentaria (B), USNM 347318, 19 mm SL.

Tables

TABLE 3. Diagnostic characters of Phaeoptyx larvae from Belize, Central America.

P. conklini 10–13.5 mm SL	No	No	Yes, at base and along entire length of fin	No
P. p i g m e n t a r i a 13–18 mm SL	No	Usually several near distal tips of anterior spines	Yes, on distal ½ of fin or restricted to distal tips of rays	Yes, numerous on distal tips of outer branched rays
P. xenus 8–10 mm SL	Yes	No	Yes, on distal ¾ of fin	No

TABLE 4. Diagnostic characters of Phaeoptyx juveniles from Belize, Central America.

P. conklini 14-22 mm SL	No	Blunt	No	Developing; pale streak between stripe and base of fin
P. p i g m e n t a r i a 17-21 mm SL	Yes	Rounded	Yes, when developed	No
P. xenus 11, 21 mm SL	Yes	Rounded	No	Developing; no pale streak between stripe and base of fin

TABLE 5. Diagnostic characters of Phaeoptyx adults from Belize, Central America.

Species	Yellow Snout	Tip of Snout	Enlarged Teeth	Melanophores D2 and A	Melanophores Trunk	Melanophores Caudal Peduncle	Lower- Limb Gill Rakers
P. conklini > 22 mm SL	No	Blunt	No	Well-developed dark stripe; usually a pale streak between stripe and base of fin	Multiple per scale; spots usually uniformly spaced	Bar usually spanning entire width; anterior margin usually irregular	14–16, usually 15
P. pigmentaria > 21 mm SL	Yes	Rounded	Yes	No well-developed stripe; may be a single or double row of melanophores and others scattered across fin	One per scale, occasionally two; spots usually uniformly spaced	Bar spanning entire width; anterior margin typically uniform.	11–13, usually 11 or 12
P. xenus > 21 mm SL	Yes	Rounded	No	Well-developedstripe but usually not dark; no pale streak between stripe and base of fin	Multiple per scale; spots irregularly spaced; larger spots in center, smaller spots at periphery	Vertical oval, not reaching dorsal and ventral margins	13 –15, usually 14