Phimochirus tunnelli, Felder & Lemaitre & Craig, 2019

Felder, Darryl L., Lemaitre, Rafael & Craig, Catherine, 2019, Two new species of the Phimochirus holthuisi complex from the Gulf of Mexico supported by morphology, color, and genetics (Crustacea: Anomura: Paguridae), Zootaxa 4683 (4), pp. 531-551 : 544-548

Phimochirus tunnelli nov. sp.

( Figs 1 ; 2E, F ; 7 A–J; 8A–H; Tab. 1 )

Phimochirus holthuisi .— McLaughlin, 1981a: 5; McLaughlin, 1981b: 342, figs 4c, 6a-c, 7c (in part; see Remarks under P. holthuisi s.s. and P. formani nov. sp.)

Phimochirus sp.— Felder et al., 2014: 813, fig. 7b.

Type material. Holotype: male sl 6.3 mm ( USNM 1547302 = ULLZ 13837 ) northwestern Gulf of Mexico, 28° 05.684’ N, 91° 05.22’ W, 55 m, Louisiana shelf bank, 29 Aug 2011.

Paratypes: Northeastern Gulf of Mexico . 1 juvenile male, sl 1.9 mm ( USNM 1543319 = ULLZ 7973 ) 28° 50.74’ N, 85° 02.11’ W, 52 m, northwestern Florida shelf ; 1 female, sl 3.1 mm ( USNM 1543432 = ULLZ 8164 ) 29° 43.32’ N, 85° 54.84’ W, 38 m, northwestern Florida shelf, 2 Jul 2006 . Northwestern Gulf of Mexico . 2 males, sl 3.0, 4.7 mm, 1 ov female, sl 3.9 mm ( USNM 1541146 = ULLZ 5789 ) 28° 06.3’ N, 29° 01.6’ W, 66 m, Ewing Bank , Louisiana shelf, 1 Aug 2002 ; 2 males, sl 2.5, 3.3 mm, 1 ov female, sl 3.9 mm ( USNM 1543233 = ULLZ 7825 ) 27° 56.46’ N, 92° 00.03’ W, 70 m, off Louisiana , 9 Jul 2006 ; 1 male, sl 4.1 mm ( USNM 1545269 = ULLZ 10611 ) 27° 59.141’ N, 91° 38.382’ W, 68 m, Louisiana shelf deep bank, 1 Jul 2001 ; 1 male, sl 4.4 mm, ( USNM 1558304 = ULLZ 17898 ) 27° 54.961’ N, 92° 23.01’ W, 80 m, Louisiana shelf bank, 9 May 2018 ; 1 female, sl 2.1 mm ( USNM 1558291 = ULLZ 17909 ) 27° 58.925’ N, 91° 39.779’ W, 72 m, Louisiana shelf bank, 6 May 2018 . Southwestern Gulf of Mexico . 1 male, sl 2.8 mm ( USNM 1544265 = ULLZ 9359 ) 22° 16.08’ N, 90° 42.89’ W, 55 m, western Campeche shelf, Mexico, 18 Jun 2005 ; 1 juvenile male, sl 2.1 mm ( USNM 1541878 = ULLZ 7021 ) 22° 07.98’ N, 91° 23.75’ W, 49 m, western Campeche shelf, Mexico, 17 Jun 2005 ; 1 ov female, sl 3.2 mm ( USNM 1544260 = ULLZ 9354 ) 21° 06.64’ N, 92° 08.72’ W, 47 m, western Campeche shelf, Mexico, 9 Jun 2005 . Southeastern Gulf of Mexico. 1 ov female sl 5.7 mm, ( USNM 1541669 = ULLZ 5814 ) 24° 38.27’ N, 83° 36.36’ W, 65 m, off Dry Tortugas, Florida, 3 Jun 2004 ; 1 male, sl 3.7 mm ( USNM 1544363 = ULLZ 8954 ) 24° 41.73’ N, 83° 36.48’ W, 64 m, off Florida Keys , 1 Jun 2004 .

Other material. Northeastern Gulf of Mexico. 3 females (1 ov), sl 3.4–3.7 mm ( USNM 1549242 = ULLZ 16182 ) 25° 03.354’ N, 83° 43.559’ W, 83 m, southwestern Florida shelf, 9 Sep 2014 ; 1 male, sl 2.8 mm ( USNM 1549449 = ULLZ 16244 ) 24° 48.929’ N, 83° 40.609’ W, 66 m, off Florida Keys , 10 Sep 2014 ; 1 male, sl 5.1 mm ( USNM 1549196 = ULLZ 16088 ) 24° 45.723’ N, 83° 35.305’ W, 67 m, off Florida Keys , 10 Sep 2014 ; 1 male, sl 3.6 mm ( USNM 103706 ) 29° 28’ N, 85° 31’ W, 21.9 m, northwestern Florida shelf, 1 Feb 1956 ; 2 males, sl 4.8, 6.6 mm ( USNM 1253344 ) 25° 16’54” N, 83° 37’48” W, 73 m, southwestern Florida shelf, 5 Mar 1984 . Northwestern Gulf of Mexico. 2 males, sl 4.0, 4.5 mm ( USNM 1549372 = ULLZ 16123 ) 28° 05.542’ N, 91° 01.697’ W, 58 m, off Louisiana , 14 Sep 2014 ; 1 male, sl 6.0 mm, 3 females, sl 2.1–3.9 mm ( USNM 1549147 = ULLZ 16113 ) 28° 05.382’ N, 91° 06.742’ W, 58 m, off Louisiana , 14 Sep 2014 ; 1 ov female, sl 4.6 mm ( USNM 1549102 = ULLZ 16106 ) 28° 05.542’ N, 91° 01.697’ W, 58 m, off Louisiana , 14 Sep 2014 ; 1 male, sl 5.2 mm ( USNM 1548210 = ULLZ 15181 ) 28° 05.552’ N, 91° 01.825’ W, 57 m, Ewing Bank , off Louisiana, 19 Oct 2013 .

Diagnosis. Carapace shield approximately 1.1 times longer than broad; rostrum acutely triangular, reaching distally beyond lateral projections, terminating in strong spine. Antennular peduncles reaching to distal margins of corneas when fully extended. Antennal peduncles reaching to approximately midlevel of corneas when fully extended; flagellum with short setae 1 to <1 flagellar articles in length. Right chela with dorsal surface of fixed finger covered with well-spaced low tubercles; palm with numerous well-spaced tubercles or blunt spines on distal half, dorsomesial margin sharply defined as straight (in mesial view) crenulate or bluntly spinulose ridge terminating in rounded or spine-like angle; carpus with dorsomesial margin sharply defined by ridge with 3 or 4 sharp proximal spines and 2 or 3 smaller blunt distal spines. Dactyls of second and third pereopods with 3 rows of corneous spinules, one dorsomesial with 10 or 11, one ventromesial with 5–10, and one ventral with 9–11. Anterior lobe of sternite between third pereopods semisubovate, distal margin with simple and often capsulate setae; sternites between fourth and fifth pereopods with simple setae and often short capsulate setae. GenBank sequence accession numbers for holotype (USNM 1547302 = ULLZ 13837): (12s) MK848209 ; (16s) MK848226 .

Description. Carapace shield ( Fig. 7A ) subtriangular, approximately 1.1 times longer than broad; dorsal surface glabrous except for scattered short setae medially on each side and near anterior margin, lacking linea or groves except for weakly visible short linea-d and grooves separating narrow lateral lobe on each side; anterior margin between rostrum and lateral projections concave; anterolateral margins sloping; posterior margin roundly truncate. Rostrum acutely triangular, reaching distally beyond tip of lateral projections, terminating in spine. Lateral projections subtriangular, terminating bluntly or in small marginal spine.

Ocular peduncles ( Fig. 7A ) relatively long, about 0.7 length of shield, width near equal throughout; surfaces naked except tuft of short setae medially on mesial and lateral faces; corneas weakly dilated. Ocular acicles ( Fig. 7B ) narrow (approximately 2.3 times longer than basal width), acutely subtriangular, with dorsal surface concave, each terminating in small submarginal spine.

Antennular peduncles reaching to distal margins of corneas when fully extended. Segments naked or with scattered short setae; basal segment with blunt ventromesial distal angle, and small spine on lateral face.

Antennal peduncles reaching to approximately midlevel of corneas when fully extended. Fifth segment slender, with few short setae on lateral and mesial margins. Fourth segment unarmed. Third segment with small sine on ventrodistal angle. Second segment with dorsolateral distal angle produced into strong spine-like process with few short distolateral setae; dorsomesial distal angle with small spine. First segment unarmed laterally. Antennal acicles not reaching proximal margin of corneas, broadly curving outward, terminating in strong spine, with few tufts of setae on mesial margin and tuft of setae distally. Flagellum long, exceeding extended right cheliped, with short setae 1 to <1 flagellar articles in length.

Third maxilliped ( Fig. 7D ) ischium with crista dentata consisting of approximately 18–20 small, sharp teeth slightly diminishing in length distally, and accessory tooth.

Chelipeds ( Fig. 7 E–J) strongly dissimilar in robustness and shape, right massive and distinctly larger and stronger than left; articular membrane between chela and carpus often with fleshy protuberance (see Remarks under P. formani nov. sp.). Right (major) cheliped ( Fig. 7 G–J) operculate, virtually naked on all surfaces except for few scattered short setae. Chela subcircular in outline; cutting edges of dactyl and fixed finger each with row of slightly unequal calcareous teeth and terminating in blunt, inwardly curved calcareous tips overlapping when closed. Dactyl slightly shorter than palm; mesial margin sharply defined by bluntly spinulose ridge; dorsal surface with distinct median ridge, dorsomesial surface concave. Fixed finger broad basally; dorsal surface with few well-spaced low tubercles or blunt spines; lateral margin sharply defined by bluntly spinulose ridge. Palm with numerous well-spaced tubercles or blunt spines on distal half; ventrolateral margin sharply defined by weakly spinose ridge; dorsomesial margin sharply defined as straight crenulate or bluntly spinulose ridge terminating in rounded or spine-like angle; ventromesial surface smooth. Carpus approximately as long or slightly shorter than merus; dorsal and lateral surfaces smooth, rounded, with weakly defined ridge on dorsolateral margin distally; dorsodistal margin with row of minute tubercles; dorsomesial margin sharply defined by ridge of 3 or 4 sharp proximal spines and 2 or 3 smaller blunt distal spines; mesial surface nearly vertical, distal portion somewhat flaring and armed with 3 small spines; ventral surface smooth. Merus subtriangular in cross-section, surfaces smooth, unarmed except for row sharp spines on dorsodistal margin and spine on ventrolateral distal angle. Ischium unarmed. Coxa with ventrolateral margin bluntly spinulose, row of setae on ventromesial distal angle.

Left (minor) cheliped ( Fig. 7E, F ) slender, reaching to approximately mid-level of right palm, surfaces smooth, with scattered short setae; fingers terminating in inwardly curved corneous tips crossed when closed and ventrally forming spoon-like surface. Dactyl slightly longer than palm; cutting edge with row of fused minute corneous spinules. Fixed finger broader than dactyl; cutting edge with row of minute calcareous teeth and row of fused corneous spinules; dorsal surface smooth or with scattered small low tubercles. Palm dorsal surface with weak median minutely spinulose ridge proximally, and small median spine distally near cutting edges of fixed finger and dactyl. Carpus approximately as long as merus; dorsomesial margin with row of 5 spines, dorsolateral margin with 2 spines distally; lateral surface with small ventrodistal spine. Merus subtriangular in cross-section; lateral surface with small ventrodistal spine. Ischium and coxa unarmed, latter with row of setae on ventromesial margin.

Ambulatory pereopod 2 and 3 sparsely setose ( Fig. 8 A–E), left and right subequal. Each with dactyl broadly curved, approximately 1.3 times longer than propodus, terminating in sharp corneous claw curving ventrally; dorsal margins with well-spaced long setae; with 3 rows of corneous spinules, one dorsomesial with 10 or 11, one ventromesial with 5–10, and one ventral with 9–11. Propodus nearly straight, subequal in length to carpus, with few tufts of setae dorsally; ventral margin with row of 4 corneous spinules in addition to 2 corneous spinules near articulation with dactyl. Carpus with small dorsodistal spine, with few setae or tufts of setae dorsally. Merus and ischium unarmed. Anterior lobe of sternite between third pereopods semisubovate ( Fig. 7C ), distal margin often with capsulate, in addition to simple, setae.

Pereopod 4 ( Fig. 8F ) semichelate, sparsely setose. Dactyl stout, slender, terminating in inwardly curved corneous claw; dorsal margin with tuft of long setae distally; ventral margin with ventrolateral row of minute, closely-set corneous teeth, and distinctly developed brush-like preungual process at base of corneous claw. Propodal rasp with 1 row of ovate corneous scales. Carpus unarmed except for few long setae dorsally. Merus unarmed, nearly naked. Sternite between coxae ( Fig. 7C ) rod-like, with simple setae and often short capsulate setae.

Pereopod 5 chelate. Propodal rasp extending for about half length lateral surface of propodus, with long curved setae on ventrodistal angle. Anterior lobe of sternite between coxae subdivided ( Fig. 7C ), with simple setae and often capsulate setae distally.

Uropods markedly asymmetrical, left largest, exopods each with row of long setae dorsally; ventral margin of left and right exopods with long setae distally. Telson ( Fig. 8G, H ) weakly asymmetrical, longer than broad, with distinct lateral indentations; posterior lobes with corneous lateral margins, lobes separated by narrow U-shaped median cleft, terminal margins oblique, each armed with row of 4 strong, slender spines (including spine at distolateral angle) interspersed with 1 or 2 small spines.

Color. In life ( Fig. 2E, F ), ocular peduncle with usually complete band of lavender near midlength, abutted by narrower band of dark orange proximally; carapace shield lacking light “trident” pattern, near uniformly orange or marked by large spot or subquadrate area of dark orange anteriorly; distal margins of cheliped and anterior walking leg meri marked by lavender patches.

Etymology. The specific name is assigned in recognition of the late John W. (Wes) Tunnell, formerly of Texas A&M University–Corpus Christi, whose deep appreciation for, and professional understanding of, coastal and marine biodiversity in the Gulf of Mexico region is reflected in many books and other publications that he authored or orchestrated over his long and productive career.

Habitat. Occupying varied medium sized gastropod shells, especially faciolariids, turbinids, and muricids; offshore rhodolith and other calcareous banks, especially where richly covered by macroalgae and epifaunal communities; inner to middle continental shelf; 38– 72 m.

Distribution. Western Atlantic: northeastern, northwestern, and southeastern Gulf of Mexico.

Remarks. Phimochirus tunnelli nov. sp., corresponding to Clade II in our molecular genetic analyses ( Fig. 1 ), was long confused under the name P. holthuisi , as was P. formani nov. sp. Available collections of P. tunnelli suggest this species averages slightly larger sizes than does P. formani nov. sp., but both species can exceed 6.0 mm in shield length, somewhat larger than any known specimen of P. holthuisi s.s. P. tunnelli nov. sp. is among the most common of benthic decapods on deep banks of the northern Gulf of Mexico, especially on rhodolith-covered calcareous banks of the northwestern Gulf. Following marked declines in other benthic decapod species on such banks after the Deepwater Horizon oil spill, populations of this new species recovered to dominate decapod abundances in those habitats ( Felder et al. 2014: fig. 7b).

A noteworthy setal type and some morphological variations were observed in Phimochirus tunnelli nov. sp. The sternites between the third to fifth pereopods frequently bear tear-shaped capsulate setae, though these are more frequently seen in males than in females. The anterior lobe of the sternite between the third pereopods is semisubovate but in larger specimens such as in an ovigerous female (sl 5.7 mm, USNM 1541669 = ULLZ 5814), it is noticeably narrow and more elongated. In that same ovigerous female, the armature of the terminal margins of the posterior lobes of the telson ( Fig. 8G, H ) is visibly stronger, with more numerous interspersed spines in between the larger ones than in other specimens, and with the anterolateral angles each having a strong, curved terminal spine and 2 additional spines laterally.

Figures

FIGURE 1. Maximum Likelihood phylogeny inferred in RAxML based on H3 nuclear DNA, 12s mtDNA, and 16s mtDNA. Bootstrap support values (bs) and Bayesian posterior probabilities (bp) with values greater than 50 are displayed above branches at tree nodes with the notation bs/bp. Clades I and II, assigned a priori to Phimochirus cf. holthuisi, are delimited by vertical black bars and correspond to two new species herein described. For branch labels, taxon name is followed by voucher catalog number (see Table 1) and collection locality. Abbreviations: eGMx = eastern Gulf of Mexico, ePac = eastern Pacific, neGMx = northeastern Gulf of Mexico, nwGMx = northwestern Gulf of Mexico, seGMx = southeastern Gulf of Mexico, swGMx = southwestern Gulf of Mexico.

FIGURE 2. Phimochirus holthuisi (Provenzano, 1961) s.s.: A, male, sl 3.3 mm (USNM 1542650 = ULLZ 3564), Belize; B, male, sl 2.9 mm (USNM 1558313 = ULLZ 16588), Belize. Phimochirus formani nov. sp.: C, male paratype, sl 3.1 mm (USNM 1547566 = ULLZ 14352), northeastern Gulf of Mexico; D, male paratype, sl 2.8 mm (USNM 1543170 = ULLZ 7711), northeastern Gulf of Mexico. Phimochirus tunnelli nov. sp.: E, male paratype, sl 4.1 mm (USNM 1545269 = ULLZ 10611), northwestern Gulf of Mexico; F, ov female paratype, sl 3.9 mm (USNM 1541146 = ULLZ 5789), northwestern Gulf of Mexico.

FIGURE 7. Phimochirus tunnelli nov. sp. A–I, male holotype, sl 6.3 mm (USNM 1547302 = ULLZ 13837), northwestern Gulf of Mexico; J, ovigerous female paratype, sl 5.7 mm (USNM 1541669 = ULLZ 5814), southeastern Gulf of Mexico. A, cephalothorax, eyes, and frontal appendages, dorsal surface; B, left ocular acicle, dorsal surface; C, thoracic sternites and coxae, ventral surface; D, right third maxilliped, external surface; E, minor (left) cheliped, dorsal surface; F, minor (left) cheliped, lateral surface; G, major (right) cheliped, dorsal surface; H, major (right) cheliped, mesial surface; I, major (right) cheliped, ventral surface; J, major (right) cheliped, dorsal surface. Scale bars = 2.0 (A, C–J); 0.5 (B).

FIGURE 8. Phimochirus tunnelli nov. sp. A–G, male holotype, sl 6.3 mm (USNM 1547302 = ULLZ 13837), northwestern Gulf of Mexico; H, ov female paratype, sl 5.7 mm (USNM 1541669 = ULLZ 5814), southeastern Gulf of Mexico. A, right second pereopod, lateral surface; B, right second pereopod terminal articles, mesial surface; C, right third pereopod, lateral surface; D, right third pereopod terminal articles, mesial surface; E, left third pereopod, lateral surface; F, right fourth pereopod terminal articles, lateral surface; G, H, telson, dorsal surface. Scale bars = 2.0 mm (A–E); 1.0 mm (F, H); 1.5 mm (G).