Rhopalorhynchus magdalena, Staples, David A., 2009

Staples, David A., 2009, A new species of Rhopalorhynchus (Pycnogonida: Colossendeidae) from Lizard Island, North Queensland, Australia, Zootaxa 2051, pp. 62-68 : 62-67

publication ID	https://doi.org/ 10.5281/zenodo.186599
DOI	https://doi.org/10.5281/zenodo.5694033
persistent identifier	https://treatment.plazi.org/id/03E48F65-D64E-5165-FF7E-F8A4FAD9FA4E
treatment provided by	Plazi
scientific name	Rhopalorhynchus magdalena
status	sp. nov.

Treatment

Rhopalorhynchus magdalena View in CoL sp. nov.

Figures 1 View FIGURE 1 , 2 View FIGURE 2 .

Material examined. Holotype: North Qld., Lizard I. (14˚ 6₁.061˝S, 145˚ ₁5.365˝E), 15 m, amongst coral rubble, sand, collected from crevices, hand dredge, M. Blazewicz-Paszkowycz, 18 Apr 2008, QM S83741 View Materials (female).

Paratypes: Lizard I. (14˚ 6₁.567˝S, 145˚15•325˝E), 10 m, amongst coral rubble, sand, collected from crevices, hand dredge, M. Blazewicz-Paszkowycz, 4 Apr 0 8, QM S83740 View Materials (1 male). Same collection data NMV J58389 View Materials (1 male).

Diagnosis. A small species compared to its congeners, leg span about 20 mm. Lateral processes 2 and 3 separated by about 6 times their basal diameter, ocular tubercle bearing tall, finger-like process about threequarters of total height. Inflated part of proboscis about 3 times as long as maximum width, tooth prominent, positioned at about 30% along the inflated part, height almost one-fifth proboscis width, basal stalk about 40% of total length of proboscis. Palp segment 10, 3.9 times as long as wide. Legs brevitarsal, tarsal ratio about 55%; tarsus 34–37 % of propodus length; propodus marginally wider distally, claw about one-third length of propodus.

Description of holotype. Leg span about 20mm. Trunk segmented, segment 1 about 0.53 times as long as segment 2, segment 3 about 0.82 times as long as segment 2, segment 4 half length segment of 3; lateral processes short, constricted at bases, processes 1 and 2 separated by almost 6 times their own basal diameter, processes 2 and 3 separated by about 5 times their basal width., processes 3 and 4 separated by about twice their own width. Ocular tubercle with tall, finger-like apical process (about three-quarters height of basal part), bluntly rounded at tip, leaning slightly forward, 4 eyes, anterior eyes marginally larger than posterior pair, pigmented, lateral sensory organs present. Abdomen small, oval, widely cleft at tip, articulated at base, placed between the fourth pair of legs, directed ventrally.

Proboscis length a little shorter than trunk, basal stalk 42% of total length; inflated part 3.1 times as long as maximum width, angled down at about 40º to the stalk, tapering distally to rounded tip, tip not bent downwards, dorsal tooth placed at about 32% of inflated part, prominent, height almost one-fifth of maximum proboscis width, proboscis otherwise smooth. Arthrodial membrane broad in ventral view, indicating ability to extend proboscis through wide ventral arc, possibly to vertical position.

Palp ( Figure 2 View FIGURE 2 C) 10–segmented, attached to anterior margin of cephalon, first segment inflated dorsally; segment 2 very short, less than half segment 1, bearing single ventral seta; segment 3, 1.6 times length of segment 5; segment 6 about two-thirds length of segment of 7; segments 7–9 subequal; segment 10 slightly shorter, 3.9 times as long as wide; segments 6 to 10 with long ventral setae.

Oviger ( Figure 2 View FIGURE 2 A) attached to ventrolateral surface near anterior margin of cephalon; 3 basal segments short; segment 4 longest, about 1.1 times as long as segment 6, strigilis tightly curled, laying over segment 7, segments 7 to 10 bearing long, fine spines in several irregular rows, distal spine on segment 10 robust, much larger than preceding spines but not forming obvious subchelate structure with the terminal claw, crenulations on spine margins not evident, claw gently curved, stout, width about 75% of length.

Legs ( Figure 1 View FIGURE 1 F, G) brevitarsal (tarsal ratio of third leg 56%). Coxae short, coxa 2 longer than coxae 1 or 3; femur clearly the longest segment, gently curved throughout, conspicuously swollen distally, club-like with few, very fine filamentous setae dorsally, one or more longer setae on distodorsal surface; tibia 1 swollen distally but much less so than femur, size and arrangement of setae similar to femur, longest seta dorsodistal, equal to segment width; tibia 2 slightly longer than tibia 1, gently curved, few dorsodistal setae longer than twice segment width; length of tarsus slightly variable between legs, 34–37% of propodus length, proportionally longest on leg 1; propodus gently curved, marginally wider distally; soles of tarsus and propodus densely setose. Terminal claw, 31–36% propodus length. Auxiliary claws absent. Gonopores conspicuous on ventral surface of coxa 2 of all legs, not evident in males.

Measurements (female holotype, mm). Trunk length (frontal margin of cephalic segment to tip of fourth lateral process), 2.35; trunk segment 1, 0.45; trunk segment 2, 0.85; trunk segment 3, 0.70; trunk segment 4 (to tip of lateral process) 0.35; width across second lateral processes 0.63.

Proboscis (using notation of Stock 1958): α 1.60; β.88; γ 1.40; ε 0.44; ξ 0.15; δ 0.98; height of tooth, 0.09.

Third leg: coxa 1, 0.13; coxa 2, 0.20; coxa 3, 0.15; femur, 2.78; tibia 1, 2.50; tibia 2, 2.40; tarsus, 0.25; propodus, 0.83; claw 0.28.

Oviger: seg.2, 0.14; seg. 3, 0.12; seg. 4, 1.29; seg. 5, 0.14; seg. 6, 1.18; seg. 7, 0.24; seg. 8, 0.20; seg. 9, 0.20; seg. 10, 0.14; claw, 0.04.

Palp: seg. 3, 1.62; seg. 4, 0.05; seg. 5, 0.98; seg. 6, 0.12; seg. 7, 0.18; seg. 8, 0.18; seg. 9, 0.18; seg. 10, 0.15.

Etymology. This species is named for its collector, Dr. Magdalena Blazewicz-Paszkowycz, University of Łódź, Poland; a noun in apposition.

Remarks. The new species is another delicate, almost transparent form similar to R. gracillimus ( Carpenter 1907: 100) and the smallest known species in the genus.

One of the third pair of legs of the holotype is missing, otherwise the specimen is complete. The dorsal process on the ocular tubercle is angled slightly more forward than those of the paratypes suggesting it may be bent. Most long setae on the legs and palps of all specimens are slightly reflexed distally. Based on the shape of the femora and the absence of genital pores, the smaller paratypes (about half the size of the holotype) are judged to be subadult males. The paratypes exhibit the characteristic male femora which are less inflated distally than those of the female but otherwise conform to the species diagnosis generally. In a family where allometry is well documented, any variation in ratios and proportions of those specimens was not investigated.

Compared to the new species, Rhopalorhynchus pedunculatum has a proboscis stalk that is clearly longer than the inflated part (ca 1.5 times), the more widely spaced lateral processes (about 8 times) and a very short first trunk segment relative to segment 2 (25%). Geographically, the closest brevitarsal relatives are R. clavipes and R. mortenseni , which are sympatric in the Coral Sea. Rhopalorhynchus clavipes is distinguished by a longer tarsus and claw, a lower conical ocular tubercle, possession of a ‘minute’ or a ‘not very prominent’ dorsal tooth on the proboscis ( Stock, 1958:127) and a much shorter first trunk segment (41% of segment 2). Clark (1970) provisionally assigned a specimen collected from east of Jumpin Pin Bar, Qld, to R. clavipes . Compared to the new species, Clark’s specimen is very much larger and differs in proportions of the proboscis and leg segments. Rhopalorhynchus mortenseni was only briefly and incompletely described, but differs in the lower terminal process on the ocular tubercle, in the longer tarsus (longer than propodus), longer terminal claw (about 50% of propodus) and the more slender distal palp segments. Rhopalorhynchus filipes is another much larger species (trunk length more than 2.5 times that of R. magdalena sp. nov.) and is further distinguished by the very thin, almost filiform distal palp segments; the pointed ocular tubercle; a longer tarsus (subequal to the propodus), and longer claw (about half the propodus length). Rhopalorhynchus claudus (based on a damaged specimen) can also be distinguished by the longer tarsus and terminal claw (about half the length of the propodus) and a longer neck region of the cephalon (66% of segment 2).

The new species is morphologically closest to R. gracillimus in as much as this species is defined by its lectotype. Both share the finger-shaped apical point on the ocular tubercle and similar proportions of the distal palp segments which were recorded by Carpenter (1907) as 5:8:8:8:7. Stock (1958) described palp segment 6 as being relatively long, measuring slightly shorter to slightly longer than segment 7 and did not comment on Carpenter’s description. Palp segment 6 in the new species is clearly shorter (by one-third) than segment 7. The new species otherwise differs in several respects: its overall size is only two-thirds that of R. gracillimus (trunk length 2.35 mm v 3.71 mm); the tarsus and terminal claw are one-third or less than the propodus compared to the tarsus of R. gracillimus being half the length of the propodus and the terminal claw a little less than half, and in the shape and proportions of the proboscis ( Table 1 View TABLE 1 ). A distally expanded propodus has not been described or figured previously and may be an additional distinguishing character.

Carpenter’s material of R. gracillimus consisted of eight specimens collected from three locations in the Maldive Islands and a single male from the Saya de Malha Bank which he noted differed in several respects. Stock (1958) reviewed Carpenter’s material and assigned the Saya de Malha Bank specimen to R. lomani , at the same time designating one female from South Nilandu as the lectotype of R. gracillimus . Stock (1958: figure 44) illustrated a “female syntype ” but his illustration of a leg (un-numbered) with moderately swollen distal part, is consistent with male morphology and similar to the male specimen figured by Carpenter (1907: Figure 26). It is not certain therefore, whether the illustrated syntype is the male of the ‘one male and one female’ recorded by Carpenter from S. Nilandu or whether it is the female lectotype or another specimen altogether. Stock also assigned one female from Sapeh Bay, Sumbawa I. (Siboga stn 310) and 2 males, one female, from off Durban, South Africa to this species. In his key, Stock (1958, couplet B b.2), described the distal part of the proboscis as “narrowly produced, bent downward”, and used this character to distinguish R. gracillimus from its congeners. However, Stock’s (1958: Figure 42) illustration of a “female syntype ” does not show a distal downturn, nor does he refer to a downturn in his species diagnosis ( Stock, 1958: p 129). Although not discussed by Carpenter, a distal downturn of the proboscis is evident in his Figure 26, so whether Stock relied solely on Carpenter’s figure or observed the downturn in other specimens, is not clear.

PROBOSCIS LEGS

The proboscis of the Durban specimen illustrated by Stock (1958: Figure 56) is closest to that figured by Carpenter (1907: Figure 26), but the specimen is otherwise distinguished by the significantly shorter basal stalk and the downward orientation of the entire inflated part. The inflated part of the proboscis in the Durban specimen is orientated at about 40° to the basal stalk ( Figure 2 View FIGURE 2 H) compared to about 30° in the Maldive Is. syntype ( Figure 2 View FIGURE 2 J) and 50° for the Sumbawa I. specimen ( Figure 2 View FIGURE 2 L). When comparing the Durban specimens, Stock cited the length of the tarsus as a distinguishing character and regarded the long seventh palp joint and finger-shaped tip of eye tubercle as “somewhat aberrant”. The Sumbawa I. specimen also differs in the proportions of the distal leg segments and in the shape and proportions of the proboscis. Arnaud & Child (1988) contributed to the confusion by assigning a longitarsal specimen from East London ( South Africa) to this species. Their observation that the specimen had abnormally short distal palp segments is a further indication that it represented a distinct species. It is puzzling that Stock attributed the diverse and sometimes aberrant morphology evident in his Rhopalorhynchus material to intraspecific variability, particularly in light of his observation that “speciation through geographic isolation is of outstanding importance in marine organisms such as the Pycnogonida” ( Stock, 1958: 113). Differences in general morphology and variation in ratios ( Table 1 View TABLE 1 ) suggest that the wide variability attributed to R. gracillimus is not justified and that the specimens from Sumbawa I. and South Africa may belong to other species.