Rhynchothorax philopsammum Hedgpeth, 1951

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 : 126-128

Rhynchothorax philopsammum Hedgpeth, 1951

Fig. 66

Rhynchothorax philopsammum Hedgpeth, 1951:111 . Child 1979: 72. Child 1990: 311. Müller 1990: 197.

Material: 9.— 2 males, 1 juv. ( SMF 1538 ), under stones on sandy bottom, 0–0.5 m, 31.XII.1985 .

42.— 1 male, 3 juv. ( SMF 1539 ), coral rubble, 13 m, 28.II.1986 .

Description of male: Trunk in dorsal view oval, robust, all segments separated by furrow, dorso-medially without tubercles; crurigers close together, with short lateral outgrowths, which are normally unforked. Eyes absent, 5 small tubercles in place of an ocular process; first trunk segment bearing antero-lateral outgrowths directed obliquely anteriorly, which serve as origins for the palps; these outgrowths longer than broad without any tubercles. Abdomen horizontal, surpassing first coxae of fourth legs by about half of its length.

Proboscis oval, robust, longer than half length of trunk, with small dorsal tubercle. Palp 4-articled; articles 1–3 with small round tubercles, most distinctly on terminal article; first article the longest, 5.5 times as long as second; third article 3 times as long as second, with an oval dorso-distal outgrowth bearing 2–3 spines and about as long as second article; terminal article curved dorsally, its anteriorly directed (= ventral) aspect armed with about 15 short spines. Oviger 10-articled; articles 1–2 and 8–10 the shortest, their lengths about equal to their diameter; 4 th article the longest, just longer than 6 th; articles 7–10 on their inner aspect with some short, mostly forked spines; terminal article with a curved robust claw, on its inner face with a finely serrated membrane.

Legs moderately robust, sparsely clad with setae; coxae 1 in legs 1–3 with short and mostly unforked lateral tubercles; coxae 1 and 3 of almost equal length, about 3/4 length of coxa 2; coxa 2 with irregularly formed ventro-lateral flat; femur and tibia 1 of equal length, tibia 2 slightly shorter; each of these three articles dorso-distally with a longer seta, especially long on both tibiae; cement gland duct on ventral side of femur, marked by tiny conical tubercle centrally; tarsus about as long as its diameter; propodus feebly curved, without heel; sole with 5 short setae; terminal claw robust and curved, about 2/5 of propodus length; auxiliary claw slender and feebly curved, 2/3 of length of main claw.

Measurements: Trunk length 0.75; width 0.38 (across first crurigers); length of abdomen 0.14; length of proboscis 0.42; lengths of articles of leg 3: coxa 1—0.08; coxa 2—0.10; coxa 3—0.07; femur 0.17; tibia 1 0.17; tibia 2, 0.15; tarsus 0.04; propodus 0.17; main claw 0.07; auxiliary claw 0.05.

Female: no material available from the Caribbean coast of Colombia.

Subadult (or juvenile, fig. 66): Trunk segments 3 and 4 fused; segments 2–4 dorso-medially with a small tubercle. Ovigers present as stumps, without articulation. Total length 0.52.

Postlarva: Body outline oval, with small pyriform proboscis. Palps very small and three-articled. First trunk segment separated by a dorsal furrow from caudal part. Fourth legs mere stumps and without articulation, not overreaching abdomen.

Remarks: The species was re-described by Müller (1990b: 197) based on material from the Society Islands. R. philopsammum is closely related to Rhynchothorax vallatus Child, 1990 from the Australian Barrier Reef. Rhynchothorax vallatus is known from a single female and, compared to Rhynchothorax philopsammum , shows a more protracted body and smaller tubercles on the crurigers, and the femur is longer than tibia 1. In Rhynchothorax philopsammum both of these articles are of equal length.

In comparison with the material from the Society Islands (Bora Bora) the specimens from Colombia show small differences, mostly regarding the development and number of tubercles on trunk segments. A salient feature is the small size of males from Bora Bora (0.54).

From the Santa Marta region 6 specimens were collected from 2 localities in 0–13m depth only.

After completion of the present study, the first author detected a mature specimen of R. philopsammum in a sorted sample from Martinique. This specimen therefore was not included in his study from that Island ( Müller 1990d). It was found near Madras, Baie de Tartane, among dead corals in moderately wave exposed seagrass beds (1–2m) and is deposited at ZSM.

Distribution: California, Pacific coast of Mexico ( Child 1979: 72), Bora Bora, Society Islands ( Müller 1990b: 197), Martinique ( Müller 1990d) and Caribbean coast of Colombia.

Figures

FIGURE 66. Rhynchothorax philopsammum Hedgpeth, 1951: A male dorsal, B juvenile dorsal, C postlarva dorsal, D postlarva ventral, E male palp, F male oviger, G male leg 3, detail cement gland pore, H tarsus and propodus of male leg 3.