Tanystylum acuminatum Stock, 1954

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 : 39-41

Tanystylum acuminatum Stock, 1954

Fig. 17

Tanystylum acuminatum Stock 1954: 125 . Stock 1979: 11. Stock 1986: 401. Müller 1990: 278.

Material: 16.— 2 males (1ov.), 1 fem. ( SMF 1477 ), from brown and red algae on rock, mesolittoral, 15.VII.1985 .

17.— 1 male (ov.), 1 fem. ( SMF 1478 ), on blocks of stone, covered with short growth of algae, 0–0.5 m, 7.I.1986 .

20.— 3 males, 4 fem. ( ZFMK), Sargassum cymosum on rock, 5 l substrate, 0–0.5 m, 7.VI.1985 . 1 male ( MNHN), Sargassum cymosum on rock, 0–0.5 m, 13.VIII.1985 . 1 male, 2 fem. ( INVEMAR), Sargassum cymosum on rock, 0–0.5 m, 9.IX.1985 . 1 fem. ( USNM), Sargassum cymosum on rock, 0–0.5 m, 2.X.1985 . 1 male ( ZSM), Sargassum cymosum on rock, 0–0.5 m, 8.XI.1985 . 17 males (10 ov.), 19 fem., 4 juv. ( SMF 1479 ), Sargassum cymosum on rock, 7.XII.1985 . 51 males (34 ov.), 43 fem., 12 juv. ( SMF 1480 ), Sargassum cymosum on rock, 7.I.1986 . 9 males (5 ov.), 7 fem., 1 juv. ( ZSM), Sargassum cymosum on rock, 12. II.1986 . 4 males (1 ov.), 3 fem. ( SMF 1481 ), Sargassum cymosum on rock, 3.III.1986 . 10 males (9 ov.), 10 fem. (9 gravid), 1 juv. ( SMF 1482 ), Sargassum cymosum on rock, 3.IV.1986 . 2 males, 3 fem. ( INVEMAR), Sargassum cymosum on rock, 2.V.1986 .

21.— 1 fem. ( SMF 1483 ), Digenia simplex on rock, 5 l substratum, mesolittoral, 7.VI.1985. 1 male , 1 fem. ( SMF 1484 ), Digenia simplex on rock, 3.IV.1986 .

Description of male: Dorsal trunk outline circular, crurigers touching each other in their entire length; all trunk segments coalesced. Cephalon bearing tiny tubercle with short apical seta antero-laterally above palp origin. Ocular process as high as broad, eyes large and distinctly pigmented. Cruriger 1 with small rounded dorso-distal tubercle bearing short seta; cruriger 2 with pair of dorso-lateral tubercles; crurigers 3 and 4 with single antero-lateral distal tubercle. Abdomen relatively short, directed obliquely dorsally, with about 6 short setae in distal half; about 1/6 of abdomen length surpassing cruriger 4. Proboscis flask-haped; strongly narrowed in its distal fourth, distally slender and tube-like.

Cheliphores very short, stump-like, with one short seta, barely visible at anterior margin of the cephalon. Palp 6-articled; partition between 3 rd and 4 th article indistinct; these articles with short lateral setae; articles 5 and 6 short, of nearly same length and with additional set of short setae. Oviger 10-articled; articles 4 and 5 elongate, subequal in length; 7 th article with distal rounded tubercle bearing group of 6 spines; 8th article with 3 spines, 9th article with about 4 spines; terminal article with pair of short spines ending in three points.

Legs robust, all articles with numerous sparsely arranged spines and setae; coxae 1 distally with a roundish tubercle in antero-lateral, dorsal and postero-lateral position, each with short apical seta; coxae 3 of same length; cement gland on femur terminating in short dorsodistal tube; tibia 1 and tibia 2 of same length, dorsally with 2 flat round tubercles; tarsus as long broad, with robust ventral spine and 4–5 setae; propodus feebly curved, without distinct heel; sole armed with 3 robust spines in proximal third and distally with 3–4 short spines and some setae; main claw moderately curved, half length of propodus; auxiliary claws feebly curved, about half length of main claw.

Measurements: Trunk length 0.52; width 0.49 (across 2 nd crurigers); length of abdomen 0.14; length of proboscis 0.45. Leg 3: coxa 1—0.17; coxa 2—0.18; coxa 3—0.16; femur 0.40; tibia 1—0.35; tibia 2—0.36; tarsus 0.09; propodus 0.36; main claw 0.18; auxiliary claw 0.10.

Female: In habitus similar to male, but tubercles on crurigers and 1 st coxae of all legs more feeble; oviger shorter than in male, 7 th article without tubercle; 5 distal articles spinose; articles 6 and 7 with a robust simple spine; articles 8 and 9 with a single, terminal article with a pair of denticulated spines.

Remarks: T. acuminatum is strongly characterized by its proboscis, which is narrowed in its distal fourth only. As Stock (1954a: 125) remarked T. acuminatum shows relations to Tanystylum isabellae Marcus, 1940 , which we found in the region of Santa Marta , too (see below). The easiest way to differentiate between both species without dissecting them is the proboscis shape. In T. acuminatum the proboscis is narrowing abruptly in its distal fourth to a slender tube—whereas in T. isabellae the central region narrows continuously and is tubiform in its distal third—but broader in this part than in T. acuminatum .

In the study region, T. acuminatum was exclusivley associated with algae as a substratum, from the tidemark to maximally 0.5 m depth. As we collected this species at all stations during an entire year in about monthly intervals, and ovigerous males were encountered during XII and I–IV only, a restricted reproduction period seems probable. It begins at the end of the rain period in XII and ends before the onset of the next rainy period (VI/VII) in IV. As the femora of legs were not transparent enough to allow an inspection we could not distinguish during which period the ova developed in the female ovaries.

Distribution: St. Barthélémy and Anguilla, Lesser Antilles (Stock 1954a: 125; 1979: 11), Martinique

( Müller 1990d: 278) and Caribbean coast of Colombia

Figures

FIGURE 17. Tanystylum acuminatum Stock, 1954: A male dorsal, B female dorsal, C male lateral, D proboscis ventral, E palp, F male oviger, G distal article of male oviger, H male leg 3, I cement gland duct of male leg 3, J female leg 3.