Tanystylum isthmiacum Stock 1955
Creators: name: Müller, Hans-Georg
name: Krapp, Franz
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Pycnogonida
Pantopoda
Ammotheidae
Tanystylum
Tanystylum isthmiacum

description: Tanystylum isthmiacum Stock, 1955   
Fig. 23  
 Tanystylum isthmiacum Stock, 1955: 247.—Müller 1990: 280.   
 Tanystylum isthmiacum difficile —Fage & Stock, 1966: 318. Stock: 389. Stock 1975: 74. Child 1979: 29. Stock 1979: 11. Stock 1986: 402.   
 Tanystylum isthmiacum isthmiacum — Child 1979: 29.   
 Material: 4.— 1 male, 1 juv. (SMF 1399), algal growth on rocks, mesolittoral, 24.V.1985.   
 16.— 3 males (SMF 1400), brown and red algae on rocks, mesolittoral, 15.VII.1985.   
 17.— 1 male (ov.) (ZFMK), from Cnidoscyphus on rocks, mesolittoral, 8.XI.1985.   
 20.— 1 juv. (SMF 1401), from Sargassum cymosum, 5 l substratum, 0–0.5 m, 2.X.1985. 1 fem. (gravid) (SMF 1402), from Sargassum cymosum, 5 l substratum, 8.XI.1985. 2 males (SMF 1403), from Sargassum cymosum, 5 l substratum, 3.III.1986.   
 21.— 1 male (ZMA 3381), from Digenia simplex, 5 l substratum, mesolittoral, 8.XI.1985.   
 Description of male: Dorsal trunk outline circular, crurigers touching along their entire length; crurigers 1–3 with short, dorso-distal spines, mostly on flat-rounded antero-lateral tubercle; all trunk segments fused. Anterior rim of cephalon with two short lateral spines. Ocular process higher than broad, with a distal pointed tip. Eyes relatively large, distinctly pigmented. Abdomen rather short and directed obliquely dorsally, with 5 short spines in distal half, abdomen surpasses the 4 th crurigers by ca. 1/4 of its length. Proboscis rather robust, bottle-shaped, somewhat narrowed in distal third only.   
 Cheliphores 1/4–3/5 length of proboscis, distally rounded, with 3–4 short setae. Palp 6-articled, 4 th article distinctly elongate, 3 rd article very short; terminal article twice as long as penultimate, with about 16 spines on lateral, ventral and distal aspect. Oviger 10-articled, robust; articles 4 and 5 elongate, the fifth slightly longer than the fourth; 7 th article with a pronounced roundish tubercle which bears ca. 5 short spines; terminal article the shortest and bearing a pair of denticulate flat spines.   
Legs robust, articles with relatively few short spines and setae; coxae 1 of all legs on distal rim with an antero-lateral, a dorsal and frequently a postero-lateral round tubercle; these tubercles armed with 1 to 3 short setae; coxae 1 and coxae 3 of equal length, coxae 2 slightly longer; cement gland tube of femur dorso-distal, with a short and nearly straight terminal region; tibia 1 and tibia 2 of equal length, barely longer than femur, with two dorsal flat tubercles; tarsus as long as broad, with 5 short ventral setae; propodus moderately curved and without pronounced heel; proximal third of sole armed with 3 robust spines; distally with ca. 5 short setae; main claw moderately curved of 1/2 length of propodus; auxiliary claws feebly curved, 1/4 of propodus length.  
 Measurements: Length 0.61; width (across 2 nd crurigers) 0.63; abdomen 0.17; proboscis 0.36. Leg 3: coxa 1, 0.18; coxa 2, 0.19; coxa 3, 0.18; femur 0.41; tibia 1, 0.39; tibia 2, 0.39; tarsus 0.04; propodus 0.35; main claw 0.17; auxiliary 0.09.   
 Female: In contrast to to the previously decribed species without any apparent salient sexual dimorphism. Oviger conspicuously shorter and slenderer than in male; terminal article tiny, with one pair of denticulated foliose spines which are longer than the article itself.   
 Remarks: T. isthmiacum is morphologically very variable, which induced Fage & Stock (1966: 318) to split it into 2 subspecies, T. isthmiacum isthmiacum and T. isthmiacum difficile. Here we do not follow this procedure as a clear separation is too difficult. The first author is convinced that an erection of subspecies is not helpful while even the distinction of species in this genus is problematical.   
 Closer relations may exist with Tanystylum oculospinosum Hilton, 1942 from Baja California and the Galápagos Archipelago (see Child & Hedgpeth 1971: 619, fig.5). Based on the figures of Child & Hedgpeth, T. isthmiacum is differentiated from T. oculospinosum by more feebly developed tubercles on coxae 1 of legs and by more robust femora and tibiae.   
 In the research area T. isthmiacum belongs among the more rarely found species. Mostly diverse algal stands from the mesolittoral to ca. 0.5m depth were colonized. This comes as a surprise, as almost all data from the literature report this species from deeper water layers.   
 Distribution: From the Pacific there are records from Costa Rica and Mexico (Child 1979: 29), from Panamá (Stock 1955b: 247) and Ecuador (Stock 1975c: 74). In the western Atlantic the species was recorded from Panamá (Child 1979: 29), Brazil (Stock 1975a: 984), Curaçao (Stock 1979: 11) and Martinique (Müller 1990d: 280). From the eastern Atlantic there is one find from the Islands of Cape Verde only (Stock 1966: 389).
description: Published as part of 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, pp. 1-138 in Zootaxa 2319 (1) on pages 49-51, DOI: 10.11646/zootaxa.2319.1.1, http://zenodo.org/record/5317868