Paragiopagurus atkinsonae, Landschoff, Jannes & Lemaitre, Rafael, 2017

Landschoff, Jannes & Lemaitre, Rafael, 2017, Differentiation of three common deep-water hermit crabs (Crustacea, Decapoda, Anomura, Parapaguridae) from the South African demersal abundance surveys, including the description of a new species of Paragiopagurus Lemaitre, 1996, ZooKeys 676, pp. 21-45 : 22-28

Paragiopagurus atkinsonae sp. n. Figs 2, 3, 4, 5, 6

Type material.

Holotype: male 7.0 mm, South Africa, West Coast, WCDSS2016, CCH008, sta D00723-3243, S31°52.81', E16°57.12', 265 m, 11 Mar 2016 (USNM 1292083).

Paratypes: South Africa, West Coast. WCDSS2012, AFR279: 1 male 7.6 mm [with zoanthid symbionts], sta A32208-3233, S31°39.79', E17°02.79', 259 m, 24 Jan 2012, coll. L. Atkinson (USNM 1292086). WCDSS2015, AND004: 1 male 7.6 mm, sta C0416-3258, S32°08.05', E17°08.52', 230 m, 26 Feb 2015 (USNM 1292080); 1 male 7.0 mm (USNM 1292084), 1 male 6.2 mm (SAMC MB-A066814), sta C430-3237, S31°42.07', E16°58.53', 277 m, 1 Mar 2015. WCDSS2016, CCH008: 1 male 6.8 mm, sta D00724, S32°03.18', E17°03.11', 243 m, 11 Mar 2016 (SAMC MB-A066815); 1 male 7.8 mm (USNM 1292082), 3 females 6.4-7.0 mm (USNM 1292081), 4 females 5.9-7.1 (USNM 1292085), 1 ovig. female 6.8 mm (SAMC MB-A066809), 1 ovig. female 5.9 mm (SAMC MB-A066810), 1 ovig. female (SAMC MB-A066811), 3 ovig. females 6.6-7.2 mm, 7 females 7.2-8.0 mm (SAMC MB-A066812), 2 ovig. females 6.7-7.3 mm (SAMC MB-A066813), 1 ovig. female 6.4 mm (SAMC MB-A066816), sta D00726-2446, S32°22.98', E17°27.78', 199 m, 11 Mar 2016.

Description.

Eleven pairs of biserial (Fig. 2A), or at most weakly divided quadriserial gills. Shield (Fig. 2B, 6C) about as broad as long; dorsal surface nearly naked or with scattered short setae, with weakly- to moderately-calcified median region extending from anterior margins of rostrum, anterior and lateral projections, to about proximal 0.2 length of shield; anterior, lateral and posterior margins with short setae. Rostrum broadly rounded, with short mid-dorsal ridge. Anterior margins weakly concave. Lateral projections subtriangular, armed with short terminal spine. Anterolateral margins sloping. Ventrolateral margin usually with small spine. Posterior margin broadly rounded. Anterodistal margin of branchiostegite rounded, unarmed, setose.

Ocular peduncles (Fig. 2B) about half, or slightly more than half, length of shield, each with longitudinal row of short setae on dorsal surface. Corneas weakly dilated. Ocular acicles subtriangular, about 0.3 as long as ocular peduncles, each terminating in strong, simple spine; separated basally by about 0.6 the width of 1 acicle.

Antennular peduncles exceeding distal margin of corneas by 0.8-0.9 length of ultimate segment; ventral flagellum with 5-7 articles. Ultimate segment twice, or more than twice, as long as penultimate, with scattered setae dorsally. Basal segment with strong ventromesial spine; lateral face with distal subrectangular lobe armed with 1 or 2 spines, and strong spine proximally.

Antennal peduncles (Fig. 2C) reaching to about distal margin of corneas. Fifth segment unarmed, with longitudinal row of setae on lateral and mesial margins. Fourth segment with strong spine on dorsolateral distal angle. Third segment with strong ventromesial distal spine. Second segment with dorsolateral distal angle produced, terminating in strong, simple spine extending to about half length of acicle and having 2 or 3 small spines dorsally; mesial margin with spine on dorsodistal angle. First segment with lateral surface armed with small spine; ventromesial angle not strongly produced, armed with 1-3 small, blunt spines. Antennal acicle slightly curved outward (dorsal view), overreaching proximal margin of cornea, but not exceeding distal margin of cornea, terminating in strong spine; mesial margin with row of about 10 strong spines of similar size and set at about 450 to longitudinal axis of acicle. Flagellum exceeding distal margin of extended right cheliped, nearly naked, or with scattered, short setae less than 1 flagellar article in length.

Mandible (Fig. 3A) with 3-segmented palp. Maxillule (Fig. 3B) with external lobe of endopod moderately-well developed, internal lobe with 1 long setae. Maxilla (Fig. 3C) with endopod well exceeding distal margin of scaphognathite. First maxilliped (Fig. 3D) with endopod exceeding distal margin of exopod. Second maxilliped (Fig. 3E) without distinguishing characters. Third maxilliped (Fig. 3F) with crista dentate with about 10 corneous teeth, decreasing in size distally; basis with 1 dorsomesial corneous tooth; coxa with 1 or 2 mesial teeth.

Chelipeds markedly dissimilar, proportions strongly affected by size and sexual dimorphism, males growing distinctly longer right chelipeds with narrower chela, than females. Right cheliped (Figs 4, 6A, B) massive; in males, about 1.5 times as long as left cheliped and 4.3 times as long as SL; in females, about 1.3 times as long as left cheliped and 3 times as SL; dorsal surfaces covered with sparse or inconspicuous short, simple or plumose setae. Chela operculate, somewhat dorsoventrally flattened, less so in males; males about twice as long as wide, or in females about 1.3 times as long as wide. Fingers moderately curving mesioventrally, each terminating in small corneous claw, dorsal surfaces covered with numerous small, blunt to sharp tubercles or spines, ventral surfaces covered with small tubercles; cutting edge of dactyl with 2 larger calcareous teeth and several small teeth in between, distal row of small fused corneous teeth; cutting edge of fixed finger with 2 large, rounded calcareous teeth and several small calcareous teeth distally and proximally. Dactyl longer (female), or shorter (male), than mesial margin of palm, set at oblique angle to longitudinal axis of palm; mesial margin well defined by longitudinal row of spines or tubercles; proximal half of ventromesial face strongly concave. Fixed finger basally much broader in females than in males. Palm distinctly broader than long in females, or usually distinctly longer than broad in males; dorsal surface covered with numerous small tubercles or spines; lateral margin well defined by row of small tubercles or spines; dorsomesial margin with row of irregular spines (less strong in males); mesial face strongly sloping, slightly concave (less so in males), covered with small tubercles; ventromesial margin weakly delimited (less so in males) by row of low tubercles or spines; ventral surface nearly flat or weakly convex, with small tubercles or spines less numerous than on dorsal surface. Carpus similar to chela in general armature and setation, subtriangular in cross-section, longer in males than in females; dorsal surface covered with numerous small tubercles or spines, generally spines sharper in females than in males; dorsal margin with irregular row of spines, dorsodistal margin armed with strong (females) or weak (males) spines, increasing in size mesially; ventrolateral margin well defined (more so in females) by row of spines increasing in size distally; ventromesial distal margin somewhat expanded, wing-like, armed with row of strong spines. Merus subtriangular in cross-section, dorsal margin unarmed, or with low tubercles and row of short setae, and strong dorsodistal spine; lateral surface with minute tubercles; ventrolateral margin with row of blunt spines distally; mesial surface flat, unarmed, ventromesial margin with row of strong, mostly blunt spines; ventral surface smooth or with very low tubercles. Ischium with ventrolateral row of small spines, and moderately long setae mesioventrally. Coxa with row of small spines on ventrolateral distal margin and ventrodistal row of long setae.

Left cheliped (Figs 4E, 6A, B) generally well calcified, reaching to base of dactyl (females), or mid-length of palm (males), of right cheliped. Fingers weakly bent lateroventrally, gaping slightly when closed, each terminating in sharp corneous claw; dorsal and ventral surfaces unarmed, except for few tufts of short setae; cutting edges each with closely-set small, corneous teeth. Dactyl slightly longer than palm; proximal half of ventromesial face slightly concave. Palm longer than wide; dorsal surface with 2 median rows of small, low tubercles, and sparse tufts of short setae, somewhat depressed medially; dorsomesial margin with row of small tubercles or spines; dorsolateral margin rounded; ventral surface unarmed except for scattered setae. Carpus with moderately dense setation on dorsal, lateral and mesial surfaces; dorsal margin with irregular row of small tubercles or spines, and strong dorsodistal spine; lateral and mesial faces unarmed except for setae, and strong spine on lateroventral distal angle; ventral surface smooth, at most with tufts of sparse setae. Merus unarmed except for minute tubercles on lateral, mesial and ventral faces, and dense setation on dorsal ventromesial margins. Ischium unarmed and smooth except for dense setae on ventral surface. Coxa at most with minute spines on ventromesial distal margin and row of setae on ventrodistal margin.

Ambulatory legs or pereopods 2 and 3 (Figs 5 A–D, 6A, B) similar from right to left, except for slightly longer meri on right; usually exceeding right cheliped by about 0.2 length of dactyl of legs when fully extended. Dactyl about 1.5-1.9 as long as propodus, broadly curved, terminating in sharp corneous claw; dorsal margin mostly with short setae, except for distal row of bristle-like setae; ventromesial margin (Fig. 5B, D) armed with 2 or 3 irregular rows of short, corneous spinules and usually terminat ing as single row near claw; lateral and mesial face with shallow, longitudinal sulcus on proximal half, deeper on mesial face. Propodus nearly naked; dorsal margin with setae usually arising from low tubercles. Carpus nearly naked, or with sparse short setae; dorsal margin armed with row of distinct, well-spaced small spines (stronger on pereopod 2) increasing slightly in size distally, and small dorsodistal spine. Merus unarmed except for scattered setae on dorsal margin. Ischium with dorsal and ventral row of setae. Coxa unarmed except for 1 or 2 minute spines on ventromesial proximal angle (pereopod 2 only) and ventromesial row of setae. Anterior lobe of sternite XII (of pereopods 3; Fig. 5E) subtriangular, setose, and terminating in simple or more frequently bifid spine.

Pereopod 4 (Fig. 5D) subchelate. Dactyl broadly curved, terminating in sharp, corneous claw, with ventrolateral row of small corneous teeth increasing in size distally. Propodus longer than wide; rasp consisting of 2 or 3 rows of rounded scales. Carpus with long setae on dorsal margin. Merus with rows of long setae on dorsal, ventromesial and ventrolateral margins.

Pereopod 5 (Fig. 5F) chelate. Propodal rasp extending slightly beyond mid-length of segment. Dactyl with row of minute, rounded scales on ventrolateral surface.

Uropods and telson asymmetrical. Telson (Fig. 2D) lacking transverse sutures separating anterior and posterior lobes; dorsal surface with scattered short setae; lateral margins with moderately long (left) and short (right) setae; posterior lobes separated by narrow, median cleft, terminal margins rounded, armed with row of 15-8 (left lobe) or 10-12 (right lobe) short corneous spines, some slightly curved.

Males lacking first gonopods; with unpaired left pleopods 2-5, of which pleopod 2 (Fig. 2E) is 2-segmented, uniramous, and other pleopods biramous. Females with unpaired pleopods 2-5, with well-developed rami on pleopods 2-4, and short endopod on pleopod 5.

Colour (in life; Figs 4C, D, 6 A–C). Shield and cephalic appendages mottled orange and cream to white. Ocular peduncles white with basally and distally broadened dorsomedian orange stripe; orange pattern extending to ventromesial face just below midlength of ocular peduncle. Corneas usually green. Ocular acicles mottled orange with white spines. Chelipeds orange-red, with white tubercles and spines. Right chela often with dactyl and fixed finger each with cream patch proximally at about midline, fingertips white; propodus, merus and carpus with distinct cream to white spot on dorsomesial distal angle. Left chela with cream patches of different size, fingertips white. Ambulatory legs orange overall; dactyl light orange, distally cream; propodus with cream patch on distolateral and distomesial angles, lateral face with dark orange stripe; carpus orange overall, with lighter orange medially on lateral face. Merus with white band distally, large white patch on proximal half of lateral face, and darker orange on dorsodistal margin. Uropods and telson mottled orange and cream. Pleon orange, in some females dark red ventrally due to gonads with unspawned eggs. Eggs bright red.

Habitat.

Occupying shells created by colonies of Epizoanthus sp. that incorporate sand grains in their tissue and form a carcinoecia that completely covers a minute gastropod shell. This Epizoanthus sp. appears the same to that frequently used by Sympagurus dimorphus in the South African region.

Distribution

(Fig. 8). Known so far only from a small portion of the west coast of South Africa, between 31°42'S and 32°23'S, in a depth range of 199-277 m.

Etymology.

This species is named after Dr. Lara Atkinson, a researcher from the South African Environmental Observation Network (SAEON), Egagasini Node for marine-offshore systems, who first noticed the presence of this new species and collected the first specimen. The name honours her research efforts to understand the benthic marine fauna of South Africa, and acknowledges the major role she played in organizing sampling of additional material of this new species.

Common name.

"Green-eyed hermit crab".

Genetic data.

Sta D00723-3243, S31°52.81', E16°57.12', 265 m, male 7.0 mm (holotype), BOLD: SEAKY1181-17 (USNM 1292083). Sta D00726-2446, S32°22.98', E17°27.78', 199 m, ovig. female 6.8 mm, BOLD: SEAKY1181-17 (MB-A066809); ovig. female 5.9 mm, BOLD: SEAKY1183-17 (MB-A066810); male 6.8 mm, BOLD: SEAKY1180-17 (MB-A066815).

Variations.

In males with SL> 7.0 mm, the right cheliped (merus to dactyl) ranges from 3.6-4.8 times as long as the shield, and the chela varies from 1.7-2.4 as long as wide. In females with SL> 5.9 mm, the right cheliped (merus to dactyl) ranges from 2.6-3.2 times as long as the shield, and the chela varies from 1.3-1.6 as long as wide. The spination of both right and left chelae tends to be sharper, and stronger in females.

Remarks.

Three characters present in Paragiopagurus atkinsonae sp. n. exemplify the morphological evolutionary tendencies that in general are observed ( Lemaitre 2013) in species of Paragiopagurus . These three characters are: biserial gills that are, at most, weakly divided distally; the drastic sexual dimorphism exhibited on the right cheliped; and in males, the complete loss of paired first and second pleopods modified as gonopods. In sharing these three characters, this new species is most similar to P. ventilatus Lemaitre, 2004c, a northwestern Pacific species that is known to associate with hydrothermal vents in the northeastern coast of Taiwan and the Mariana Trough ( Lemaitre 2004c; Komai et al. 2010). Additionally, both species share a rare armature condition in parapagurids for the ventromesial margin of the dactyls of the ambulatory legs, being armed in this new species with two or three irregular rows of numerous corneous spinules instead of a single regular row of relatively few spines, as in other species of this genus. In other respects, however, these two species are markedly different. In P. atkinsonae sp. n. the fourth antennal segment is armed with a spine on the dorsolateral distal angle, whereas in P. ventilatus the fourth segment is unarmed; the antennal flagella is nearly naked or with scattered short setae, whereas in P. ventilatus the flagella are densely covered with long setae; the third maxillipeds and basal segments of the chelipeds lack dense plumose setae, whereas in P. ventilatus these are present; the propodal rasp of pereopod 4 has two or three rows of ovate scales, whereas in P. ventilatus the rasp has only one row of ovate scales; the telson is weakly asymmetrical, whereas in P. ventilatus the telson is strongly asymmetrical. Furthermore, P. atkinsonae sp. n. is not associated with hydrothermal vent habitats, whereas P. ventilatus has been found exclusively in or close to vent habitats ( Lemaitre 2004c; Komai et al. 2010).

In addition to Paragiopagurus atkinsonae sp. n., there are seven other species of Paragiopagurus in which the male lacks paired first and second gonopods: P. trilineatus Lemaitre, 2013, P. bicarinatus (de Saint Laurent, 1972), P. hirsutus (de Saint Laurent, 1972), P. acutus (de Saint Laurent, 1972), P. ruticheles (A. Milne-Edwards, 1891), P. hobbiti (Macpherson, 1983), and P. ventilatus . The complete pleopod condition in the male for all these species is the same, i.e., presence of left unpaired pleopods 2-5. Pleopod 2 is uniramous, 2-segmented, with a short distal segment, and pleopods 3-5 are biramous. In both sexes of P. atkinsonae sp. n., the propodal rasp of pereopod 4 has two or three rows of ovate scales, a condition similar to that of three other congenerics: P. trilineatus , P. pilimanus (A. Milne-Edwards, 1880), and P. tuberculosus (de Saint Laurent, 1972). Other than the development of pleopods in the male, and the number of rows of scales on the propodal rasp of the pereopod 4, P. atkinsonae sp. n. differs significantly from all those species (see Lemaitre 2013).

When using Lemaitre’s (2013) species identification key for specimens of Paragiopagurus atkinsonae sp. n., the user will reach couplet 19. To accommodate this new species to that key, couplet 19 can be replaced with the following two new couplets 19 and 20 (and changing the numbers of Lemaitre’s couplets 20-23 by +1):