Paracheilinus Fourmanoir, 1955

Tea, Yi-Kai & Walsh, Fenton, 2023, Review of Australian Species of Paracheilinus Fourmanoir (Teleostei: Labridae), with Description of a New Species from the Great Barrier Reef and Coral Sea, Ichthyology & Herpetology 111 (3), pp. 397-415 : 400-402

Genus Paracheilinus Fourmanoir, 1955

Paracheilinus Fourmanoir in Roux-Estève and Fourmanoir, 1955: 100 (type species Paracheilinus octotaenia Fourmanoir , by original designation).

Diagnosis.— The following synapomorphy and combination of characters diagnose Paracheilinus from all other labrid genera.

Shape of pelvic girdle: Paracheilinus possesses a distinct pelvic girdle characterized by anterior narrowing of the central processes with the external ventral wings curling medially along the mid-line. This curling forms a shallow canal that extends along the anterior half to two-thirds the length of the pelvic girdle (described and illustrated in Tea et al., 2021). We consider this character a synapomorphy diagnosing Paracheilinus .

In addition to the aforementioned character, the following combination of additional characters distinguishes Paracheilinus from all other labrid genera: dorsal-fin rays IX (rarely VIII or X),11; anal-fin rays III,9 (rarely 8 or 10); pectoral-fin rays 14 (rarely 13 or 15); principal caudal-fin rays 13, the median 11 branched; lateral line interrupted, pored scales in the dorso-anterior series 11–17, pored scales in the midlateral posterior peduncular series 3–10; median predorsal scales 5 (rarely 4 or 6); rows of scales on cheek 2; total gill rakers 11–18; branchiostegal rays 5; vertebrate 9 þ 16; scleral cornea of orbit over pupil bisected into two foci; lips small, without plicate folds, barely visible when mouth closed; three pairs of recurved canines anteriorly on upper jaw, third pair largest; single pair of canines anteriorly on lower jaw; sides of jaw with single row of small, closely set conical teeth; no canines at corner of mouth; palate without teeth; ventral margin and corner of preopercle thin and membranous, posterior bony edge smooth (sometimes very weakly serrated); snout, chin, and interorbital space naked; pelvic fin short, longest ray not reaching anal-fin origin; dorsal scleral surface of orbit and orbital rim of juveniles and initial phase (IP) specimens with white “eyebrow” markings.

Description.— Dorsal-fin rays IX (rarely VIII or X),11, segmented rays variably branched (see below); anal-fin rays III,9 (rarely 8 or 10), segmented rays variably branched (see below); pectoral-fin rays 14 (rarely 13 or 15), upper two unbranched; pelvic-fin rays I,5; principal caudal-fin rays 7 þ 6, uppermost and lowermost unbranched; upper procurrent caudal-fin rays 4–5; lower procurrent caudal-fin rays 4–6; lateral line interrupted, with dorso-anterior series of pored scales 11–17 and midlateral posterior peduncular series 3– 10; first pored scale on posterior peduncular series often pitted; last pored scale on posterior peduncular series enlarged and overlapping hypural crease; scales above lateral line to origin of dorsal fin 2; scales below lateral line to origin of anal fin 6; median predorsal scales 5 (rarely 4 or 6); circumpeduncular scales 14–16; total gill rakers 11–18; branchiostegal rays 5; vertebrae 9 þ 16.

Mouth small, oblique, maxilla not reaching vertical at anterior edge of orbit; dentition typical of genus (see diagnosis); lips small, without plicate folds, barely visible when mouth closed; gill rakers short, longest about a third length of longest filament on first gill arch; posterior nostril an oval opening about 2–3 times larger than cephalic sensory pores, about level with fleshy upper edge of orbit and slightly anterior to vertical at anterior bony rim of orbit; anterior nostril smaller, with a short fleshy rim anterior and slightly ventral to posterior nostril.

Head scaled except for anterior occipital region, interorbital space, snout, and chin; a row of elongate scales on dorsal- and anal-fin bases; basal half of caudal fin with large scales; axillary scale of pelvic fin slightly shorter than pelvic spine; midventral scaly process of pelvic fins slightly longer than pelvic spine; free ventral margin of preopercle extending forward to vertical at center of orbit, vertical posterior margin to level of lower edge of pupil; exposed bony edge of preopercle smooth without serrations (sometimes very weakly serrated on ventral bony edge).

Origin of dorsal fin above third lateral-line scale; dorsal-fin spines progressively longer; posterior soft-portion of dorsal fin with or without filaments, branching pattern variable (see below); origin of anal fin below base of first dorsal-fin soft ray; pelvic fins short, longest ray barely reaching anal-fin origin; caudal fin varying from truncate, rounded, emarginate (with or without lobes bearing filamentous extensions), or lanceolate (in one species).

Variable branching of dorsal- and anal-fin rays.— Paracheilinus is one of several labrid genera to possess filamentous dorsal-fin rays. The term “filament” is loosely defined, but generally refers to any filamentous prolongation of spinous or radial elements in the fins. In most filament-bearing labrid genera, those borne on the dorsal fin occur only in the unsegmented, spinous portion of the fin. These are, however, usually fibrous extensions of the cirri or flexible extensions of membranous tissue distal to the spinous element. Paracheilinus is unusual in having dorsal-fin filaments only in the segmented rays in the posterior portion of the fin. In Paracheilinus , the filaments are always prolongations of the radial elements and not fibrous or membranous extensions. Filaments can consist of a single segmented ray, or multiple adjacent rays bounded by membranous tissue. In the former condition, it is not uncommon for several species to develop more than one filament, but the filaments are usually separated from each other by deep incisions of the interradial membrane. The filaments in some species can be very long (up to 1.8 in SL in P. nursalim ) and make for exceptionally spectacular displays when fully raised.

Within the genus, the following western Indian Ocean species form a monophyletic sister group to all remaining species of Paracheilinus . They are P. attenuatus , P. octotaenia , P. hemitaeniatus , and P. piscilineatus . This relationship is supported based on molecular sequence data ( Allen et al., 2016). Except for P. attenuatus , which is unusual in possessing a single hair-like “naked” ray with no surrounding membranous tissue, the remaining species lack filaments entirely. No other cirrhilabrin genera possess segmented dorsal-fin filaments. The character therefore appears to be a derived condition unique to Paracheilinus , but not a synapomorphy diagnosing it. Given that there are several other non-filament bearing species nested within the genus, we consider the presence of segmented dorsal-fin filaments homoplasious within Paracheilinus . The only other labrids to somewhat approach this morphological condition are those in the hypsigenyin genera Bodianus , Clepticus , and Semicossyphus , where large males may develop pronounced or slightly filamentous segmented dorsal-fin rays, though never as dramatically as in Paracheilinus .

The degree of segmented dorsal-fin ray branching is further unusual in Paracheilinus and is highly variable within and between species. For species that possess filaments, the filamentous rays are usually unbranched, but those situated more posteriorly (in species bearing more than one filament) may exhibit weak primary or, rarely, secondary and tertiary branching. The last segmented dorsal-fin ray is always split to base regardless. If branching occurs in the filamentous rays, it is usually near the base, with the branched portions rarely extending the full length of the filament. This condition does not appear to be ontogenetic, as juveniles and IP males can also display variable branching of segmented dorsal-fin rays.

For species that lack filaments, segmented rays exhibit branching patterns typical of other labrids. In Paracheilinus , however, it is not uncommon for some of the anterior segmented rays to be completely unbranched, the number and positioning of which is variable. For example, in the holotype of the non-filament bearing P. togeansis , only the first segmented ray is unbranched, followed by branching of all proceeding rays ( Kuiter and Allen, 1999). Underwater images of three separate individuals of P. togeansis published in Allen et al. (2016) demonstrate unbranching of the anteriormost three, four, and five segmented rays, respectively ( Allen et al., 2016: figs. 49–50). An unpublished photograph (examined by the authors of this study) of P. togeansis photographed by Ned DeLoach shows yet a specimen with branching of all segmented dorsal-fin rays. More uncommonly, unbranched rays may occur in between branched rays ( Allen et al., 2016: fig. 52). Rarely, filaments may develop on the anal fin, though the presence and number of anal-fin filaments are aberrant and are never diagnostic for any of the known species ( Fig. 2 ). These conditions become increasingly prevalent in hybrids (see fig. 5B in Allen et al., 2016).

While none of these conditions in isolation are unique among teleost fishes, the degree of variation displayed in ray branching pattern within a single genus is unusual. No other labrid genus displays such variability in the positioning, number, and extent of branched dorsal- and anal-fin rays in any given species. Given the labile nature of these characters, however, we do not at this time consider this a synapomorphy diagnosing the genus, though we acknowledge its potential usefulness in separating certain species from other labrid genera.

Etymology.— Combination of the Greek para meaning near or proximal to, and the labrid genus Cheilinus , in reference to its superficial resemblance to the genera Cheilinus and Pseudocheilinus ( Roux-Estève, 1956) ; to the former in having the second anal-fin spine shorter than the third, and to the latter in having recurved outward pointing canines. Paracheilinus is, however, most closely related to Cirrhilabrus . Genus is masculine. Species of Paracheilinus are commonly known as flasher wrasses after their spectacular courtship displays.

Habitat and biology.— Small to medium (usually under 70 mm SL) brightly colored labrids frequently found swimming above rubble pans with Halimeda or Padina growth, in groups consisting anywhere between tens to hundreds of individuals with females greatly outnumbering males. Occurs between 5–70 m, but with most species inhabiting 15–40 m ( Allen et al., 2016). Diet primarily zooplankton which they pick off the water column. Males of all species are known for flashing bright iridescent colors during acts of aggression or nuptial display. This display is often accompanied by rapid swimming and the erection of all median fins. When not displaying, the colors are muted (though still very striking) and the fins are folded against the body.

KEY TO THE SPECIES OF AUSTRALIAN PARACHEILINUS

1a. Body with stripe pattern A or A’; caudal fin truncate to slightly emarginate and with pronounced filamentous lobes; dorsal fin with four or more yellow to reddish orange filaments ------------------------------------------------------------------------------------------------------------- 2

1b. Body with stripe pattern B; caudal fin rounded and without filaments; dorsal fin with three or fewer red filaments (usually one) ------------------------------------------------------------------------------------------------------- 3

2a. Body with stripe pattern A; ground color of body red to maroon in life; dorsal fin and filaments reddish orange at rest, richly yellow when in display; central portion of caudal fin with triangular hyaline region, upper and lower lobes red with metallic blue margins dorsally and ventrally (in life); spines and rays of median fins purple in preservation (northern Great Barrier Reef) ---------------------------- P. filamentosus 2b. Body with stripe pattern A’; body with two black rectangular epaulettes, one below spinous portion of dorsal fin, one along lower caudal peduncle (dusky in preservation); ground color of body yellow orange in life; dorsal fin and filaments yellow at rest, filaments bright white when in display; central portion of caudal fin with intricate blue markings (in life); spines and rays of median fins translucent and without purple pigment in preservation (Timor Sea) --------------------------------------------------------------------------------------- P. nursalim

3a. Anal fin uniformly yellow or orangey yellow; dorsal fin with one to four filaments (usually one; Timor Sea) --------------------------------------------------------------------------------------------------------------------------------------------- P. flavianalis

3b. Anal fin sharply bicolored, yellow basally, red distally; dorsal fin with one filament (Coral Sea and Great Barrier Reef) ------------------------------- P. amanda , new species

Figures

FIG. 2. Paracheilinus paineorum (non-Australian species) demonstrating filamentous prolongation of segmented dorsal- and anal-fin rays. In this specimen, nearly all dorsal-fin rays are unbranched. Note that the bifurcation at the tip of the first dorsal filament is not supported by branching of the segmented ray (it appears to be a result of a tear in the surrounding membrane). Note the presence of aberrant anal-fin filaments. Underwater photograph taken in Lembeh Strait, Indonesia, by N. DeLoach.