Aegla chilota, Crandall, 2018

Aegla chilota View in CoL , new species

Figure 2 View Figure 2 (a–g)

Diagnosis. Aegla chilota , new species, is distinguished from the remaining species of Chilean Aegla by having the ensuing character combination: rostrum neatly triangular, short, scarcely surpassing eyes; orbital sinus wide, shallow, limited by tiny extra-orbital spine and extra-orbital sinus; carpal lobe prominent, triangular, tipped by at least two coalescent acute conical scales; second abdominal epimeron little produced, tipped by acute scale; telson plate roughly pentagonal, with functional median suture; presence of the rectangular palmar crest.

Typematerial. Holotype,male 20.3mm CL(carapace length), MNHNCL DEC-15104 . Allotype, female, 16.8 mm CL, MNHNCL DEC-15105 . Paratypes: two males, (P1M) 16.7, and (P2M) 15.5 mm CL; three females, (P3F) 17.2 (P4F, ovigerous) 15.0 and (P5F) 14.3 mm CL, respectively, MNHNCL DEC-15106 . The type series was collected on November 05, 2008, under a bridge over the Incopulli stream, which finally drains into Yaldad Bay , at 43º06’02” S; 73º41’47” W, 21 m above sea level, 2 km to East from Yaldad town, Chiloé Island, Chile ( Fig. 3 View Figure 3 ) GoogleMaps .

Additional material examined. Five males, labeled as M1 to M5, (CL 17, 16.7, 15.8, 15.6, 14.4 mm, respectively), and one female, F1, (CL 14.2 mm), MNHNCL DEC-15107 , collected on November 06, 2008, from Yeco or Yecuitá stream that drains into Yaldad Bay, at 43º05’06” S; 73º43’07” W, 37 m above sea level, 2.44 km straight line NW from type locality GoogleMaps .

Description (based on male holotype). Body almond-shaped. Margins of carapace smooth.Rostrum short (CL/RL ratio 6,8), rather flat, neatly triangular, scarcely surpassing eyestalks corneae. Rostral margins with row of tiny acute scales extended between orbital sinus and rostral tip; scales increasing in size toward rostral tip. Rostral carina low, almost merged with rostral body, with diffuse row of scales along its longitudinal axis; close to rear end between epigastric lobes, profile becomes concave. Tip of rostrum with blunt apical scale surrounded by “crown” of smaller scales and very short setae. Both sides of rostral carina with flat, slightly concave area limited by margin of rostrum and epigastric eminence. Epigastric eminences as arquate, low, blunt crest extended between most prominent portion, just behind deepest part of orbit, and fronto-lateral part of gastric area where it fades out. Protogastric lobes inconspicuous.Anterolateral lobe of carapace wide, with prominent acute anterolateral spine separated from orbital sinus by shallow extraorbital notch. Limit between orbital and extraorbital sinus marked by small acute scale mounted on edge of orbital ridge; below it another small scale on margin of orbital wall. Orbital sinus amply wide, not particularly deep. Gastric area wide, markedly convex, somewhat bulbous just behind protogastric lobes; lateral margins clearly delimited from hepatic areas by irregular semicircular crease. Hepatic lobes well defined, blunt margins with row of small conical scales. First hepatic lobe separated from anterolateral lobe of carapace by wide deep indentation.

Branchial areas rather narrow compared with wide expanded cardiac area. Cervical groove moderately incised at limit between gastric and cardiac areas, and between third hepatic lobe and interior branchial area. “Bar” linea, at junction of interior, anterior and posterior branchial areas and cardiac area, diverging from carapace midline in 45º. Cardiac area almost square, little longer than wide, with broad areola and large button-like swellings both sides anterior end of it. Cardiac area as wide as posterior branchial area. Margin of branchial areas smooth, without teeth or spines, only with irregular row of small acute conical scales atop tiny tubercles more marked along anterior branchial margin. Margin of posterior branchial area slightly recurved, as continuation of thick carapace rear end margin. Anterior branchial lobe pyramidal, little protuberant; tip does not surpass the level of branchial margin behind it, bearing a conical scale little larger than those along branchial margins.

Abdomen normal, with dorso-latero-external angle of second epimeron produced as conical acute tubercle tipped by conical scale; behind it a blunt lateral ridge that fades out on epimeron rear end; tip of latero-external angle does not surpass level of posterior branchial margin. Ventro-lateral angle of second epimeron (seen from ventral side) blunt, with irregular line of stiff, long setae extending along ventral border to the tip of dorso-latero-external angle; ventral inner margin of same epimeron with dense fringe of long plumose setae. Lateral angle of third and fourth epimera tipped with minute conical scale. Same angle on fifth and sixth epimera blunt, unarmed. Telson plate sub-pentagonal, little wider than long, with functional median suture.

Chelipeds large, moderately massive at propodus of chelae; left larger than right. Coxae without ornamentation. Basi-ischium with blunt tubercle on dorso-external edge; ventro-external border unornamented; ventro-internal margin with three, low crater-like tubercles, each bearing a bunch of stiff long setae; one of them at proximal end; one at the limit between the proximal and the middle third; and, one at the distal end which is the largest; that one on left ischium with minute apical scale. Ventro-internal margin of merus with row of equidistant pits from which bunches of 3 to 5 long, stiff, setae arise. Small acute scale on rear part of two of the pits (right cheliped). Distal end of ventrolateral margin with large conical, acute tubercle. Ventro-external margin smooth; distal end with two small conical tubercles tipped with one small sub-acute scale. Sub-articular tubercle on distal end of same margin with 2 (left), 3 (right cheliped) small scales in a dorso-ventral row. Dorsal margin of ischium rather sharp edged, with row of low tubercles tipped by small conical scales increasing in size from proximal to distal; distal largest. Dorso-distal swelling above ischio-carpal joint little developed, its free border with 7 (left) and 9 (right) minute scales in a row.Carpus not particularly ornamented. Dorso-internal border with 3 large conical spines, tipped with acute scale, in a row increasing in size from proximal to distal. Carpal lobe large but not particularly prominent, summit frontally displaced so that it is aligned with distal border of carpus, close to dorsal carpus-propodus articular knob. Apex of carpal lobe with 3 (left) and 2 (right) large conical scales, flanked by scales of lesser size and minute stiff setae. Frontal margin of carpus with fringe of small, equidistant, conical scales. Dorsum with two tuberculate ridges; larger one arquate, parallel to base of spines of dorso-internal margin, thick, prominent, formed by 7 (left) and 6 (right) knob-like tubercles bearing irregular oblique row of two to six minute rod-like scales; lesser one formed by 3 or 4 low flat tubercles bearing 2 or 3 minute scales and stiff setae, situated on external half of dorsum, proximal to meruscarpus joint. Ventral face of left carpus smooth, only with some scabrosities and long, stiff, simple setae; right carpus with a broad-based conical tubercle tipped by acute, short, scale surrounded by long simple setae. Left propodus larger than right, their surface rough due to minute acute scales pointing frontally. Palmar crest moderately expanded; margin of left one with 3 serrated teeth, margin of right with 4 teeth, tipped by acute scale. Disto-dorsal margin above dactylar joint with row of small scales; upper angle with a scale larger than those in adjacent row. Ventral face with welldefined sub-marginal ridge behind fixed finger; row of pits from which bundles of long simple setae arise; each pit adjacent to small tubercle tipped by scale. Cutting edge of left propodus with large angular tooth at about midpoint. Dactylus regularly curved, dorsal margin near propodus joint with low pyramidal lobe tipped by one or two large conical scales.Distal half of ventral face of dactylus markedly excavate, forming with opposite and equally excavate propodal finger a deep concavity. Distal tip of dactylus at closing border of chela with large canine-like corneous teeth. Cutting edge of left dactylus with moderately thick molar process at proximal end. Pereopods with fringe of plumose setae along dorsal margin of merus; opposite margin with row of acute scales intermingled with short stiff setae; scales on margin’s distal end larger and regularly spaced forming a palisade. Margins of remaining articles with band of short, stiff setae mixed with scattered minute scales. Disto-dorsal angle of carpus of second and third pair of pereopods produced as conical tubercle tipped by acute scale. Dactylus as long as propodus, tip with curved acute, long, conical scale; postero-ventral margin, adjacent to tip, with longitudinal row of 6 or 7 acute rod-like scales increasing in size from proximal to distal end. Thoracic sterna flat, their surface punctuated by shallow pits bearing 2 or 3 short simple setae.

Allotype. It differs from holotype by having slightly longer rostrum (CL/ RL ratio 5.6), with acute apical scale; sub-apical “crown” of short stiff setae and minute scales absent (probably worn out). Gastric area apparently more elevated, summit almost flat, deeply punctate. Antero-lateral angle of second abdominal epimeron less protruding; same angle of third and fourth epimera blunt, without apical scale. Chelipeds slender; homochelic. Tubercles on dorsal border of merus very low, blunt. Inner margin of carpus with only two large spines; ventral face with low, blunt, tubercle; carpal lobe with three apical acute scales of similar size in a row.

Paratypes. No morphological variations with respect to the holotype were observed, except for the absence, in both chelipeds of P3F, of the broad-based conical acute tubercle present on the ventral face of the carpus of the right cheliped of the holotype. Both male paratypes had injuries of unknown origin that left notorious scars. Male P1M has a deep scratch on the upper part of the gastric area, oblique to the longitudinal median line, about 3.8 mm long; furthermore, the right third maxilliped is completely lacking except its coxa, and from the left maxilliped only remains the exopod. Male P2M lacks the right uropod completely, and the right half of the telson, including the anus orifice; the healing process produced the deformation of the remaining telson plate and the obliteration of its median suture; the anus orifice opens without protection from proctal plate and sphincter, which were destroyed.

Additional material. Diagnostic characters are well expressed in all six specimens except the absence of spine, and the coalescent acute scales on its tip, on the carpal lobe of the right cheliped of M1. Variation is also observed in relation with the broad-based conical acute tubercle that is present on the ventral face of the carpus of the right cheliped of the holotype.Among the additional specimens, that particular conical tubercle is present on the right carpus of M1 and M4, on both carpuses of M2, M3, and M5 but absent from both carpuses of F1.

Morphological variation. Examination of the whole sample of A. chilota n. sp. collected at Iñipulli stream (53 specimens) led to find one male (9 mm CL) with partially, and one female (15.8 mm CL) with completely obliterated telson median suture.

Morphometry. Table1 summarizesthemorphometric data related to the type series specimens. Table 2 summarizes the same measurements for the additionally examined material. No significant morphometric differences (Student’s t-test for independent samples) were found when comparing the mean value of CL/RL, PCW/FW, and AL/AW ratios of both populations. A. chilota n. sp. has short rostrum (CL/RL mean value for type series 5.67 ± 0.53, n = 6), narrow front (PCW/ FW 1.92 ± 0.14), and square areola (AL/AW 1.27 ± 0.05) (see Bond-Buckup and Buckup, 1994).

Biology. The ovigerous female (P4F) had 104 eggs attached to its pleopods, all of them in moderate state of development, equivalent to stage 7, early zoea, described by Lizardo-Daudt and Bond-Buckup (2003) in A. platensis Schmitt, 1942 .

Etymology. Specific epithet, i.e., chilota , from Latin

(Spanish), inhabitant of (endemic to) Chiloé Island.

Comparison. Aegla chilota n. sp., at first glance resembles A. alacalufi in having short,neatly triangular, rather flat rostrum, flanked by wide orbital sinus; little pronounced rostral carina; wide, protuberant, gastric area with thick, nodulose, epigastric prominences, and scarcely marked protogastric lobes; epibranchial tooth little protuberant; branchial margins smooth; carpal lobe pyramidal, its apex close to the distal end of carpus; and, palmar crest rectangular, little expanded, its free border denticulate or nodulate. A. chilota differs from A. alacalufi in having an irregular row of tiny scales along the rostral carina; latero-external margin of the antero-lateral lobe of carapace slightly sinuose but not markedly sigmoid; antero-lateral angle of second abdominal epimeron produced, bearing conical sharp scale; telson plate with well-marked median suture; and sternum of fourth thoracic segment flat, without broad, low anteromedial tubercle. A. chilota n. sp. shares with A. hueicollensis Jara and Palacios, 1999 all the latter diagnostic characters, differing from it solely by consistently having the carpal lobe tipped by two to four acuminate scales, a character that sporadically appears in A. hueicollensis .

Systematics. The 15 A. chilota n. sp. specimens formed a clade ( Fig. 1) in our maximum likelihood tree sister related to A. hueicollensis (bp = 71%). Both species belong to clade A in Pérez-Losada et al. (2004) together with A. affinis Schmitt, 1942 , A. bahamondei Jara, 1982 , A. occidentalis , A. alacalufi , A. manni Jara, 1980 , and A. denticulate, Nicolet, 1849 . It is also interesting to highlight that of all the Aegla species in this clade A, only A. alacalufi and A. denticulata currently occur on the island of Chiloé.

Conservation. Since the taxon is new, a conservation status has not been assigned. However, field observations by C. Jara (pers. obs., October 2014) suggest that A. chilota n. sp. populations are neither threatened by human activities nor by foreign invasive species such as the American mink Neovison vison . However, the known extent of occurrence (as defined in the IUCN, 2017) is limited and estimated to be <100 km 2; consequently, the conservation status of A. chilota can be considered Vulnerable ( IUCN, 2017).

Remarks. Obliterated telson median suture is a morphological feature found, as a norm, in two Chilean species, i.e., A. papudo Schmitt, 1942 , and A. alacalufi . However, molecular data ( Pérez-Losada et al., 2002; 2004) indicate that those two species do not share a recent common ancestor; therefore, the obliterated telson median suture appears as an apomorphic character acquired independently by them. In the case of A. chilota n. sp., the cause of the obliteration of the telson median suture in a small fraction of the population is an open question, but it seems relevant to note that A. chilota n. sp. resembles A. alacalufi , and that its micro-endemic distribution is included in the much wider geographic range of A. alacalufi , implying perhaps occasional gene flow between populations of both species.