Tanystylum lamonti, Staples, 2019

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 413-415

Tanystylum lamonti sp. nov.

Figure 7 A–J; Plate 2 E–H

Material examined. Holotype, male with eggs ( NHMUK 2018.13 ), Southwest Indian Ocean, Coral Seamount, 41° 20.71´S, 42° 55.29´E, ROV, 1337 m, specimen JC066-4197, stn 4.2, coral framework/rubble, 12 November 2011.

Paratypes. One female, one subadult ( NHMUK 2018.14 ), Southwest Indian Ocean, Coral Seamount, 41° 20.71´S, 42° 55.29´E, ROV, 1337 m, specimen JC066-4197, stn 4.2, coral framework/rubble, 12 November 2011 . Oviger mounted in Euparal on glass slide. Two males (one ovigerous, one juvenile) ( NHMUK 2018.15 ), Southwest Indian Ocean, Middle of What Seamount, 41˚ 22.3'S, 42° 54.61´E, ROV, 745 m, specimen JC066-3521, stn 6.7, on dead coral in association with yellow and orange parazooanthids, 16 November 2011 .

Other material. One subadult (NHMUK 2018.16), Southwest Indian Ocean, Coral Seamount, 41˚ 22.31'S, 42°54.57'E, ROV, 732 m, specimen JC066-871, parent 2551, stn 4.38, on whale bone rope in association with hydroids, 20 November 2011. One subadult, one juvenile (NHMUK 2018.17), Southwest Indian Ocean, Coral Seamount, 41˚ 22.3138'S, 42˚ 54.57'E, 732 m, specimen JC066-884, stn 4.38, parent 2542, on whale bone rope in association with hydroids, 20 November 2011.

Description. Male holotype. Trunk ( Fig. 7A, B . Plate 2E, F ) discoid, compact, post ocular surface of cephalon steeply inclined upwards from first suture line to base of ocular tubercle, cephalon with two prominent tubercles on anterolateral margins, each about same height as those on lateral process; lateral processes touching, each with two prominent, pointed dorsodistal tubercles, the posterior-most tubercle on the fourth lateral processes is either concealed by the abdomen, much reduced in size or absent. Ocular tubercle placed on mid-region of cephalon, height of anterior margin little less than basal width, with two tiny lateral sense organs; four eyes, large, oval, pigmented.

Proboscis cylindrical, straight, tapering evenly throughout length to rounded tip.

Abdomen slightly up-curved, unarticulated at base, length about 3.5 time’s median width, slightly swollen distally before tapering towards tip.

Chelifore scapes joined at bases, ( Fig. 7B ), one-segmented, cylindrical, inclined strongly upwards, narrowing towards tip, several fine setae at tip ( Fig. 7A, B ). Chelae absent.

Palp ( Fig. 7H ) seven-segmented, segment 4 longest, tapering distally, length about 1.3 times next longest segment 2, segments 5 to 7 with strong ventral setae.

Oviger ( Fig. 7C ) ten-segmented, segment 5 longest, slightly longer than segment 4, segment 4 curved, segment 6 particularly spinous, distal segments tightly folded.

Legs ( Fig. 7D ) first coxa of all legs with pair of dorsodistal spine-tipped processes of equal size, all segments bearing fine setae, those on tibiae longer and more numerous than femur, femur shorter than tibiae, tibia 2 longest, dorsal surface of tibiae uneven, irregular, many slender spines, tibia 1 with two prominent dorsoproximal humps, auxiliary claws present, flared, greater than half length main claw, propodus surface with numerous spinules, without heel, 4 proximal spines of equal size, each about two-thirds width of propodus followed by about five lesser sole spines and many fine lateral spines ( Fig. 7E ); cement gland tube mounted on inflated base at dorsodistal tip of femur, all legs ( Fig. 7F ). Gonopore ventrodistal coxa 2, legs 2, 3 and 4.

Female ( Plate 2G, H ) slightly larger and more robust than male. Anterolateral processes on cephalon shorter than those of male. Chelifore scape in lateral view narrowing abruptly from broad base to upcurved distal part ( Fig. 7I ), no terminal spines. Oviger ( Fig. 7J ) smaller and far less spinous than male, segment 4 longer than segment 5. Gonopore on ventrodistal surface of coxa 2, all legs.

Measurements of holotype (mm). Trunk length (frontal margin of cephalic segment to tip of 4 th lateral process), 1.600; width across 2 nd lateral processes, 1.920; proboscis length (lateral), 1.448 (approx); greatest diameter proboscis, 0.664; abdomen length (lateral), 0.928.

Palp: seg. 1, 0.136; seg. 2, 0.496; seg. 3, 0.160; seg. 4, 0.616; seg. 5, 0.120; seg. 6, 0.200; seg. 7, 0.232. Oviger: seg. 1, 0.344; seg. 2, 0.472; seg. 3, 0.480; seg. 4, 0.800; seg. 5, 0.920; seg. 6, 0.280; seg. 7, 0.272; segment 8-10 not measured. Second leg: coxa 1, 0.400; coxa 2, 0.520; coxa 3, 0.400; femur, 1.344; tibia 1, 1.156; tibia 2, 1.840; tarsus, 0.184; propodus, 0.824; claw, 0.344; auxiliary claws 0.240.

Etymology. Named for Dr Peter Lamont, Scottish Association of Marine Science, Scottish Marine Institute, who together with Dr. Natalia Serpetti was responsible for gathering most material post-voyage.

Remarks. The distal segments of the holotype oviger are so tightly folded that it is not possible to measure the segments without causing damage, consequently only segments 1 to 7 are measured. Individual eggs measure 0.096 µm diameter. The trunk tubercles of subadults in this collection are more conical and tipped with more prominent spines than those of adults of either sex. It is unfortunate that only one adult female is present in order to know whether the shape of the scape is a reliable diagnostic character of the sex or whether it is unique to the specimen. In some specimens the scapes are coalesced for most of their length revealing only a shallow bifid tip on the anterior margin rather than being two distinct appendages.

There are several species of Tanystylum that possess conical processes on the anterolateral surface of the cephalon but these processes are typically low mounds or at most moderately tall; none seemingly as prominent as those on this species. Four species have seven-segmented palps and ten-segmented ovigers in both sexes: T. antipodum Clark, 1977 ; T. grossifemorum ( Hilton, 1942) ; T. neorhetum Marcus, 1940 ; T. styligerum ( Miers, 1875) . Tanystylum antipodum differs from the new species by not having dorsal tubercles on the lateral processes and cephalon margin. Tanystylum grossifemorum differs in having two-segmented chelifores and no dorsal processes but an abundance of hair-like setae on the trunk and legs. Tanystylum neorhetum is described as having six or seven segmented palps but differs in lacking prominent tubercles on anterolateral margin of the cephalon and having a much shorter, erect abdomen. Tanystylum styligerum is the only species listed here with dorsolateral tubercles on the cephalon but it differs by having the longer leg segments of approximate equal length, the tibiae bearing long setae and a broadly ovate proboscis.

Figures

PLATE 2. Nymphon gravidus sp. nov., holotype, female. A, trunk lateral; B, trunk dorsal; C, dorsolateral view showing oocytes in trunk and limbs; D, chelae. Tanystylum lamonti sp. nov., holotype, male. E, trunk lateral; F, trunk ventral showing eggs. Paratype, female. G, trunk dorsal; H, trunk lateral.

FIGURE 7. Tanystylum lamonti sp. nov., holotype, male. A, trunk, lateral view; B, trunk, dorsal view; C, right oviger; D, third leg; E, tarsus and propodus; F, femoral cement gland duct; G, scape; H, palp. Paratype, female. (JC066-4197). I, scape; J, oviger.