Chthamalus southwardorum, Pitombo & Burton, 2007

Pitombo, Fábio Bettini & Burton, Ron, 2007, Systematics and biogeography of Tropical Eastern Pacific Chthamalus with descriptions of two new species (Cirripedia, Thoracica), Zootaxa 1574 (1), pp. 1-30 : 9-14

Chthamalus southwardorum sp. nov.

( Figures 9–14 )

Type Materia l. Holotype: Adult , 7.4mm, cirri and mouthparts dissected and mounted on one slide opercular plates and parietes dried. San Cristovan river estuary, San Blas, Nayarit, Mexico (21 0 30’54’’N 105 0 15’53’’W) [MNRJ-19713], collected by F. B. Pitombo, 17 February 2002, attached to oyster shell, on low midlittoral zone.

Paratypes: same locality, collector and collection date as holotype. One adult, cirri and mouthparts dissected and mounted on one slide, opercular plates and parietes dried, CO1 gene sequenced [MNRJ-19714]; three adults, with cirri and mouthparts dissected and mounted on one slide each, opercular plates and parietes dried [MNRJ-19715]; seven adults, specimens not dissected [SIO-BIC C-10940]; seven adults, specimens not dissected [EMU-6841] .

Description. Based on holotype, supplemented with some measurements made of 4 paratypes [MNRJ- 19714 and MNRJ-19715].

Shell: externally white, folded in lower half; internally white, smooth, sheath white, orifice wide; articula- tion between scutum and tergum presenting marked angle; rostro-carinal and orifice aperture diameters 7.4mm and 2.6mm, respectively.

Scutum: both plates corroded in upper half, growth lines present only in lower half; length/width ratio 1.9 for both plates [avg. of 4 paratypes = 1.7 ±0.1]; plates weakly asymmetric, left with tergal margin 7% wider [avg. of 4 paratypes = 8% ±4 of asymmetry, 2 wider on left plates, 2 wider on right]; occludent margin of left scutum with growth lines on inner face occupying 17% its height (right scutum not showing this inward growth) [avg. of 4 paratypes = 16% ±1.2]; articular furrow wide, articular ridge developed, extending to or beyond tergal margin; adductor muscle ridge weak, not reaching basal margin; lateral depressor muscle pit deep, smooth [paratypes: all lateral depressor muscle with septa on at least 1 plate]; sum of occludent angles 143 0 [avg. of 4 paratypes = 138 0 ±3.3 0]; the ratio between width of adductor muscle insertion and width of scutum at tlevel of adductor muscle 0.37 for both plates [avg. of 4 paratypes = 0.33 ±0.06].

Tergum: wide, ratio between scutal and carinal margins 0.79 for both plates [avg. of 4 paratypes = 0.83 ±0.06]; scutal margin of left tergum 9% higher than right [avg. of 4 paratypes = 10% ±2, 3 higher on right plates 1 higher on left]; spur long with indented margin near basicarinal angle, 4 tergal depressor muscle crests, major length extending about 1/2 of carinal margin; outer face without longitudinal furrow.

Labrum: with upper margin concave, bearing row of short conical teeth.

Palps: with upper margin covered by single row of short, smooth setae proximally and distally towards supero-distal angle, setae lengthening to form clump; very long, pinnate setae on distal margin, lengthening toward infero-distal angle.

Mandible: quadridentoid, fourth tooth double, row of approximately 20 closely spaced, fine spines below; lower angle of both mandibles with 2 strong spines.

Maxilla I: cutting edge straight; upper angle with pair of developed spines and 1 shorter, marginal spine, 2 and 5 slender spines below on right and left maxillae, respectively; notch weak, row of 8 subequal spines below in both maxillae, the lowest spine short, thick, bifid; inferior angle protuberant, covered with row of slender spines, strong spine centrally placed.

Maxilla II, posterior margin of distal lobe covered with long, acuminate, finely pinnate setae becoming shorter, smooth, acuminate setae on anterior margin; outer face with patch of very fine setae near distal margin; anterior margin of proximal lobe covered with short setae.

Cirrus I: right and left cirri composed of 8 (outer) and 7(inner) articles; inner faces of articles covered with long, acuminate, pinnate setae; outer faces of outer rami with longitudinal row of long setae; inner rami with bidenticulate setae with and without basal guard on distal articles on right and left rami, respectively.

Cirrus II: right cirrus composed of 7 (outer) and 6 (inner) articles; left cirrus formed by 7 articles on both rami; bidenticulate setae with basal guards (complex setae) present on inner face of distal articles of both cirri; right outer ramus with 5 and 2 complex setae on 2 distal articles, left outer ramus with 7 and 3 complex setae on 2 distal articles; right inner ramus with 6 and 3 complex setae on 2 distal articles; left inner ramus with 3, 7 and 1 complex setae on 3 distal articles; inner faces of articles covered with long, acuminate, pinnate setae.

Cirrus III: right cirrus antenniform, composed of 19 (outer) and 15 (inner) articles; left cirrus formed by 19 (outer) and 16 (inner) articles; inner faces of both outer rami with 4 pairs of long setae on 8 (right) and 6 (left) medial articles; inner faces of both inner rami with 4 pairs of long setae on 9 medial articles; short setae on protuberance between each pair of long setae; most distal article of each ramus with group of 3 stout setae distally, feature repeating from cirri IV to VI.

Cirrus IV: right cirrus composed of 19 articles on both rami; left cirrus formed by 17 (outer) and 18 (inner) articles; inner face of right outer ramus with 5 pairs of long setae on 1 medial article; inner faces of left outer ramus with 4 pairs of long setae on 12 medial articles; inner face of inner ramus with 5 pairs of long setae on 4 (right) and 2 (left) medial articles.

Cirrus V: right cirrus composed of 19 articles in both rami; left cirrus with 20 (outer) and 19 (inner) articles; inner face of right outer ramus with 4 pairs of long setae on 12 medial articles, inner face of left inner ramus with 5 pairs of long setae on 1 medial article; inner face of right inner ramus with 5 pairs of long setae on 6 medial articles, inner face of left inner ramus with 4 pairs of long setae on 15 medial articles.

Cirrus VI: right cirrus composed of 21 articles on both rami; left cirrus formed by 21 (outer) and 20 (inner) articles; inner face of right outer ramus with 5 pairs of long setae on 10 medial articles, inner face of left outer ramus with 4 pairs of long setae on 16 medial articles; inner face of right inner ramus with 5 pairs of long setae on 1 medial articles, inner face of left inner ramus with 4 pairs of long setae on 16 medial articles.

Penis: with genital aperture surrounded by tuft oflong setae, 4 longitudinal rows of long setae radially placed on distal third.

Distribution. Bahía Magdalena, Baja California Sur, Mexico to Puerto Chicama, Peru ( Fig. 15 ).

Habitat. Chthamalus southwardorum is found from the lower midlittoral zone to the littoral fringe on wave protected shores. On exposed rocky shores, it can be found in crevices, tide pools and on protected faces. In Mazatlan, at Punta Camarón, C. southwardorum was found in a tide pool with C. hedgecocki living outside the pool in more exposed conditions. Also in Mazatlan, at the Astilero estuary, C. southwardorum was found on harbor buoys growing on top of Megabalanus coccopoma and on pilings, in an almost sub littoral condition. On inner sites of the Panama channel estuary, only C. southwardorum was found on rocky shores, while on exposed shores at the mouth of the channel, C. panamensis was dominant, but C. southwardorum can also be found in particular sheltered conditions. Although in many places these species are ecologically segregated, they can be found co-habiting in intermediate conditions. For instance, both species C. panamensis and C. southwardorum were found attached to a single rock in Punta Paitilla, Panama [SIO-BIC C-7937] and, at Punta da Mita, on the leeward side of Banderas Bay, C. southwardorum , C. panamensis and C. hedgecocki cooccurred.

Remarks. Chthamalus southwardorum belongs to the C. fissus group as it has bidenticulate setae with basal guards on cirrus II and lacks conical spines on the outer ramus of cirrus I. The pronounced spur distinguishes this species from C. fissus and the absence of the longitudinal furrow on the outer face of the tergum and the projected articular ridge of the scutum separates this species from C. hedgecocki and C. panamensis . Chthamalus southwardorum also can be distinguished from C. anisopoma by the strong asymmetry of the opercular plates of the latter. Chthamalus southwardorum has bidenticulate setae with basal guards limited to the second and third distal articles of the inner ramus of cirrus II, whereas in C. anisopoma they occur down to the fourth or fifth, in C. fragilis to the fifth and in C. proteus to the third and fourth. The presence of inward growth lines on the inner face of the scutum of C. southwardorum also distinguishes it from C. proteus . Chthamalus southwardorum has a long distributional range, occurring in sympatry with C. panamensis , C. hedgecocki and C. fissus along the western coast of the Americas.

Etymology. The name is in honor of Dr. A. J. Southward for his extensive contribution to the knowledge of the chthamalids and his careful collecting during the “Tropical Eastern Pacific Expedition”.

Figures

FIGURE 9. Chthamalus southwardorum sp. nov., holotype MNRJ-19713. Shell with opercular plates not removed. Scale bar = 1mm.

FIGURE 10. Chthamalus southwardorum sp. nov., holotype MNRJ-19713. Opercular plates. A–D scuta; E–H terga; A, C, E, F left plates; B, D, G, H right plates; A, B, F, G outer face; C, D, E, H inner face. Scale bar = 1mm.

FIGURE 11. Chthamalus southwardorum sp. nov., holotype MNRJ-19713. Left mandible. A- schematic (setae omitted); B- photo of lower angle. Scale bar = 0.05 mm

FIGURE 12. Chthamalus southwardorum sp. nov., holotype MNRJ-19713. Right maxilla I. A- schematic (setae omitted); B- photo of lower angle. Scale bar = 0.05 mm.

FIGURE 13. Chthamalus southwardorum sp. nov., holotype MNRJ-19713. Left cirrus II. A- schematic (setae omitted); B- schematic of inner ramus distal segment showing only the bidenticulate setae; C- photo of inner ramus distal segments. Scale bar: A = 0.2 mm; B and C = 0.05 mm.

FIGURE 14. Chthamalus southwardorum sp. nov., holotype MNRJ-19713. Cirri III and VI. A- schematic of cirrus III, right (setae omitted); B- schematic of cirrus VI, right (setae omitted); C- schematic draw of ninth and tenth segments of cirrus VI, outer ramus. Scale bars: A and B = 0.1 mm; C = 0.05 mm.

FIGURE 15. Distribution of Chthamalus fissus Darwin, C. anisopoma Pilsbry and C. southwardorum sp. nov. along the western coast of the Americas. Symbols mark the localities from where specimens were examined; encircled symbols indicate localities where the COI gene was sequenced.