Achelia gracilis Verrill, 1900

Müller, Hans-Georg & Krapp, Franz, 2009, The pycnogonid fauna (Pycnogonida, Arthropoda) of the Tayrona National Park and adjoining areas on the Caribbean coast of Colombia 2319, Zootaxa 2319 (1), pp. 1-138 : 14-17

Achelia gracilis Verrill, 1900

Figs. 2–3

Achelia ? gracilis Verrill, 1900: 582 .

Achelia (Pigrolavatus) gracilis ,—Fry & Hedgpeth 1969:104; (literature).

Achelia gracilis ,—Stock 1975: 983.— Stock 1979: 10. Stock 1986: 400. Müller 1992: 43

Material: 8.— 2 males, 2 fem. (2 gravid), 2 juv. ( SMF 1377 ); shaded piles at jetty, from poriferans and hydroids, 0–1 m, 24.IV.1985 . 8 males (2ov.), 1 fem. (gravid) ( SMF 1378 ), same locality, 25.IV.1985 . 3 males (1 ov.), 1 fem., 2 juv. ( ZFMK), same locality, 4.V.1985 . 3 fem. (gravid) ( SMF 1379 ), piles at jetty exposed to light, 0–1 m, 10.V.1985 . 7 males (3 ov.), 4 fem. (gravid) ( ZMA 3386 ), shaded piles at jetty, from poriferans and hydroids, 0–1 m, 14.V.1985 . 1 male, 4 fem. (3 gravid) ( MNHN), piles at jetty exposed to light, from porifera and hydroids, 0–1 m, 14.V.1985 . 1 male (ov.) ( SMF 1380 ), shaded piles at jetty, from poriferans and hydroids, 0–1 m, 16.V.1985 . 5 males, 4 fem. (gravid) ( SMF 1381 ), same locality, 18.V.1985 . 3 males, 2 fem. (gravid) ( INVEMAR), same locality, 0–1 m, 19.V.1985 . 1 fem. (gravid) ( SMF 1382 ), from poriferans and hydroids, 5–7 m, 27.V.1985 . 1 male ( SMF 1383 ), same locality, from hydroids and bryozoans, 1–3 m, 17.VI.1985 . 1 male, 1 fem. (gravid) ( SMF 1384 ), piles at jetty exposed to light, from different encrusting taxa on ropes and fishing lines, 0.5–6 m, 2.VIII.1985 . 8 males (1 ov.), 3 fem. (gravid) ( SMF 1385 ), shaded piles at jetty, from Cnidoscyphus , 0–1m, 10.V.1985 . 3 males (ov.), 6 fem. (5 gravid) ( SMF 1386 ), same locality, 24.XI.1985 . 3 males (1ov.) ( ZSM), same locality, different encrusting taxa, 0–1 m, 17.XII.1985 . 2 fem. (gravid gravid) ( SMF 1387 ), same locality, hydroids, 0–2m, 1.II.1986 . 3 males, 1 fem. ( USNM), same locality, from poriferans and hydroids, 0–1 m, 14.III.1986 .

12.— 1 fem. (gravid), 1 juv. ( SMF 1388 ), from hydroids and octocorals, 16–18 m, 16.IX.1985 . 2 fem., 1 juv. ( SMF 1389 ), from hydroids and bryozoans, 11–15 m, 2.X.1985 . 1 male, 1 fem. (gravid) ( SMF 1390 ), coral rubble, 18 m, 2.X.1985 .

13.— 3 males (1 ov.) ( SMF 1391 ), coral rubble, 18 m, 2.X.1985 .

Description of male: Trunk oval in dorsal view, compact, crurigers touching. Cephalon antero-laterally with small tubercle bearing one short apical seta. Ocular process higher than its diameter, distally rounded, with distinctly pigmented eyes. Crurigers 1–3 with dorso-distal tubercle terminating in single seta. Abdomen sloping backwards and narrowing distally, armed with some short setae; abdomen overreaching crurigers 4 by half of its length. Proboscis a protracted oval, about as long as trunk and widest in its middle part.

Scape of cheliphores about 3 times as long as broad, distally with 2 short setae. Chela rudimentary, a mere stump, exteriorly with one short seta. Palp 7-articled; 2 nd article longest, 4 th just shorter; characteristically long 6 th article (possibly the fusion of two shorter articles); 6 th and 7 th articles ventrally and distally with numerous setae. Oviger of 10 articles; 4 th and 5 th articles elongated, about equal in length; the shortened articles 8–10 bearing pairs of specialized spines (flattened with serrated edges). Legs robust; coxa 1 of legs 1–2 with 4 dorso-lateral spinose tubercles, coxa 1 of leg 3 with 3 dorso-lateral spinose tubercles and of leg 4 with only 2 dorso-lateral spinose tubercles. Coxa 2 of legs 1–4 generally with 2, rarely 3 lateral spinose tubercles in their distal area; coxa 3 of legs 1–4 without tubercles or setae; cement duct a dorso-distal prolonged cone-shaped process on femur, apically ending in a short tube-shaped section; tibiae 1 and 2 bearing numerous setae, as well as one short proximal and one longer distal spine. Tarsus slightly longer than broad, mostly with one short vetral spine and 2 short setae. Propodus slightly curved, no heel; sole with 3 short spines in basal third, distally with about 7 short setae; main claws feebly curved and of half length of propodus; auxiliary claws about 4/5 as long as main claw.

Measurements (mm): Length 0.63; width 0.53 (across 2 nd crurigers); length of abdomen 0.21; length of proboscis 0.52; length of cheliphore 0.18; 3 rd leg: coxa 1, 0.13; coxa 2, 0.28; coxa 3, 0.13; femur 0.61; tibia 1, 0.55; tibia2, 0.61; tarsus 0.07; propodus 0.36; main claw 0.18; auxiliary claw 0.13.

Female: Habitus similar to male, but numbers of tubercles on crurigers fewer and the tubercles feebler. Coxa 1 of all legs with 1 pair of small dorso-distal tubercles only. Ovigers shorter than in males; 7 th article of oviger shorter, articles 7–10 with pairs of flat serrated spines.

Remarks: After the original description by Verrill (1990: 582) the species was figured by Cole (1904b: 317) and Hedgpeth (1948: 244) only, but in little detail and without regard to the sexual dimorphism. A. gracilis is in habitus similar to Achelia sawayai Marcus 1940b (q.v.) and may be easily confused with that species without closer examination. The dorso-distal tubercles on the crurigers in the males of A. gracilis are stronger and the coxae of legs 1–2 show 4 tubercles as opposed to 3 with A. sawayai . A clear differentiating character—also in the females—is the number and shape of palp articles of both species ( A. gracilis : 7, A. sawayai : 8).

The preferred substrata of both species are also different: While A. gracilis extends to deeper water (maximally 18 m in our research area) and was sampled mainly on the piles of the jetty in the Santa Marta harbour, A. sawayai shows a preference to stands of algae and seagrass in shallow water. A circumscribed reproduction period is not recognizable. Ovigerous males were found in months IV–V and X–XII, females with ripe ova in II, IV–V and VIII–IX, juveniles in IV–V.

Distribution: Tropical and subtropical western Atlantic.— Bermuda (Cole 1904b: 317), Hedgpeth (1948: 244) and Verrill (1900: 582); Bahamas (Giltay 1934b: 5); Martinique Bourdillon (1955: 597); Barbados ( Müller 1992: 43); Florida, Puerto Rico and Virgin Islands (Stock 1975a: 983); Curaçao ( Stock 1979: 10); Channel of Yucatán ( Stock 1986: 416) and Caribbean Coast of Colombia.

Figures

FIGURE 2. Achelia gracilis Verrill, 1900. A, male dorsal, B, female dorsal, C, male lateral, D, male cheliphore, E, female oviger, F, male oviger. Scale 200 mm for A–C, 50 mm for D–E, 100 mm for F.

FIGURE 3. Achelia gracilis Verrill, 1900. A, male palp, B, leg 3 of male, C, leg 3 of female, D, cement gland duct, E, tarsus and propodus of male leg 3.