Nine pycnogonid species from four different families were collected. Propallene socotrana n. sp. and Anoplodactylus erythraeus n. sp. are described. Callipallene cf. dubiosaHedgpeth, 1949 is figured and its systematic position discussed. The Pycnogonida fauna around the Socotra Archipelago (Yemen) supports the hypothesis the Socotra Archipelago represents an important transient zoogeographic region between the Red Sea and the Indian Ocean.
The Socotra Archipelago lies at a unique zoogeographical location in the northwestern Indian Ocean, at the transition between the Arabian and the Red Sea and East African shores at about 12°29’N and 53°51’E. This places it approximately 350 km south of Ras Fartak on the Yemeni mainland, 700 km to the southeast of Aden and 225 km off the ‘Horn of Africa’ (Cape Guardafui). The archipelago was once part of the supercontinent of Gondwana and detached during the Middle Pliocene, so it is not of volcanic origin. Very little information exists concerning the marine biodiversity of the Socotra Archipelago.
Pycnogonida are among the many unknown taxa from Socotra waters; no specimens have been recorded from Socotra to date and very few in the northwestern and western Indian Ocean. This is also reflected by the few papers that have been published on this wide biogeographic area: Gulf of Suez and Gulf of Aqaba (Stock, 1957, 1958), Oman (Stock, 1992), Ethiopia (Stock, 1964), Somalia (Stock, 1982), Kenya (Arnaud, 1973; Müller, 1990), Tanzania (Stock, 1975a) and farther away by Child (2002).
The marine zoogeographic region along the southern coast of Oman has been identified as a center of marine endemism in the region (Randall and Hoover, 1995; Randall, 1996) that probably extends westwards into Yemen, Socotra and the north coast of Somalia (Kemp, 1998).
Shallow-water pycnogonids collected in the Socotra Archipelago support the hypothesis that this is a transitional marine zoogeographic region where species from the Red Sea, the Gulf of Aden, the Indian Ocean and endemisms meet.
Specimens were collected from the northern and western coast of Socotra and from the islands of Abd-el-Kuri, Samha and Darsa during summer 2004 and in spring 2005.
Nine species from four families have been hand-sampled by snorkeling and scuba-diving.
All holotypes and voucher specimens are deposited in the Zoological Museum of Berlin Humboldt University (ZMB repository numbers), while paratypes and other voucher specimens are submitted to the Zoological Museum Amsterdam (ZMA Pa).
Material: Hadibo, 11-19 June 2004, 1-2 m, 2 juv. On macro-algae on rocks and small rock boulders. ZMB 345 1 juv., Hadibo (Socotra), 11 June 2004, 1-2 m, Bartolino leg. ZMB 346 1 juv., Hadibo (Socotra), 19 June 2004, 1-2 m, Bartolino leg.
Our specimens substantially agree with Müller’s description. The differences are probably age-related: the trunk segments are fused and the spines on the dorso-distal lateral processes are lacking. Relative proportions resemble the holotype: proboscis is about 1,6 times longer than wide and 3/4 of the trunk length. The abdomen is as long as in adults. Palps are 8-articulated, with the 6th and 7th articles distally enlarged. Ovigers are incompletely developed. Another difference is in the propodus, slender and with auxiliary claws in juveniles too, but the sole has only one large spine in proximal third instead of two, a distinctly juvenile character.
Material: Hadibo, 11 June 2004, 1-2 m, 1 male bearing eggs, 2 juv. ZMB 347; 7 July 2004, 1-2 m, 1 juv. ZMB 348; 24 September 2004, 1-3 m, 1 juv. ZMA Pa. 205980; 20 March 2005, 1-3 m, 2 females, 1 juv., ZMB 349; 21 March 2005, 1 m, 2 ovigerous males, 1 female ZMA Pa 205979; 21 March 2005, 1 m, 2 subadults ZMB 350. Dihamri (N 12°40’19’’- E 54°11’46’’), 9 September 2004, 1-3 m, 1 female ZMB 351. 23 September 2004, 1-3 m, 2 females ZMB 351; Qadamah-Bashorah, 26 September 2004, 1 m, 1 juv. ZMA Pa 205977 ; Qalansiya, 10 October 2004, 1-2 m, 1 male bearing eggs, 2 females with eggs, 3 females ZMB 352; Shassara (12°37’40’’ N - 54°16’06’’ E), 8 September 2004, 1-2 m, 2 females ZMA Pa 205981. Shassara 31 March 2005, 0-2 m, 1 male bearing eggs, 1 female, 1 juv. ZMA Pa. 205978 + 205979; Shuab, 7 October 2004, 1-2 m, 1 juv.
Among mixed hard coral communities, small encrusting and sub-massive corals. ZMB 352 Bartolino and Tabet leg., all others Bartolino leg.
Ammothella omanensis is the only species collected from most sampling stations, along the north coast of the island, from Shuab to Shassara. Occurs in a variety of environments and on most diverse substrata. Macroalgal assemblages, both on sand-inundated rock platform and rock boulders, dominated by Padina, Dictyota, Ulva, Codium, Caulerpa and Udotea.
The juvenile stage is in this species quite long and large specimens still with juvenile characters, as chelate chelifore and lack of ovigers, have been found. No significant differences have been noticed between our material and the topotypes from Oman.
This is the second record for this species, before it was known from the type locality in Oman only (Stock, 1992).
Material: Hadibo, 20 July 2004, 1-2 m, 1 male, from macro-algae and sparse hard coral community on small rock boulders. ZMB 355 1 male. Hadibo (Socotra), 20 July 2004, 1-2 m, Davis and Bartolino leg.
Müller (1989a, 1990) examined the variability of T. bredini by comparing specimens from Kenya, Sri Lanka, Malaysia and Polynesia. The male we collected in Socotra doesn’t have the particularly long tubercles on the first coxae as the specimen reported from Kenya by Müller (1990). The shape of these spiny tubercles is in good agreement with the material from French Polynesia.
Material: Shassara (12°32‘11“N - 54°15‘43“E), 31 March 2005, 0-2 m, 1 female with ripe ova. Found on mixed hard coral communities on a relict reef separated by sand channels. ZMB 356 1 female-ovigerous, Shassara (Socotra), 31 March 2005, 0-2 m, Bartolino leg.
Nymphon adenense was known previously from the type locality only, the Gulf of Aden. Both holotype and paratypes were collected by the research-ship ‘Meteor’ at 76 m depth (Müller, 1989b) and this new record suggests a bathymetric distribution that reaches very shallow water.
Material: Abd-el-Kuri, Ras Anjro (12°09‘6“N - 52°22‘09“E), 24 March 2005, 2-3 m, 1 subadult taken on macro-algae and sparse hard coral communities on small rock boulders and outcrops. ZMB 357 1 subadult, Ras Anjero (Abd-Al-Kuri Is.), 24 March 2005, 2-3 m, Bartolino leg.
The distinctive pigment pattern represented by a narrow mid-dorsal band on the trunk between ocular tubercle and abdomen distinguishes N. setimanus from most of the other species of the genus.
This species has previously been reported from South Africa, Madagascar and the Gulf of Aden; Müller (1989b) thinks that also two specimens from the Andaman Islands identified by Calman as N. andamanense could belong to N. setimanus.
Material: Hadibo, 17 June 2004, 1-2 m, 1 juv., ZMA Pa 205988; 25 June 2004, 1-2 m, 1 female with ripe ova ZMA Pa 205986; 2 females, 1 male, 2 juv., Hadibo (Socotra), 27 June 2004, 1-3 m, ZMB 360. 2 July 2004, 1-4 m, 3 males bearing eggs and larvae, 2 males, 1 female with ripe ova ZMB 359; 19 July 2004, 2-3 m, 1 male and 1 juv., ZMB 362; 20 July 2004, 1-2 m, 8 males bearing eggs and larvae, 2 females with eggs, 4 juv., ZMB 358; 22 July 2004, 1-3 m, 1 male bearing eggs and larvae ZMA Pa 205985; 9 August 2004, 1-2 m, 2 females with eggs, 1 female, 2 males, 1 juv., ZMA Pa 205984; 6 September 2004, 1-2 m, 2 females with eggs and 1 juv., ZMA Pa 205983; Hadibo-Qadheb, 24 September 2004, 1-2 m, 1 male bearing eggs ZMA Pa 205983; Qadamah-Bashorah, 26 September 2004, 1 m, 1 female with eggs and 2 juv., ZMB 361; Abd-el-Kuri, Ras Anjra, 24 March 2005, 2-3 m, 1 female ZMB 363; Darsa, 27 March 2005, 5-7 m, 1 female with eggs ZMB 364.
Material was collected both on macro-algae and coral dominated substrata. Macro-algae and sparse massive hard corals on rock outcrops parallel to shore, but also on small and large rock boulders (ZMB 358 Davis and Bartolino leg., all the rest Bartolino leg.).
Measurements of one male specimen: total length 0.67, length of body segments 2-4: 0.12, 0.11, 0.07; length of proboscis 0.22, width of proboscis 0.16; lengths of articles in leg 3: coxa 1 = 0.11, coxa 2 = 0.36, coxa 3 = 0.19; femur 0.67, tibia 1 = 0.65, tibia 2 = 0.74, tarsus 0.06, propodus 0.34; lengths of oviger articles: 0.05, 0.10, 0.11, 0.18, 0.30, 0.09, 0.08, 0.10, 0.10, 0.07, diameter of 2nd trunk segment 0.16.
Although several differences have been observed between our specimens from Socotra and C. dubiosaHedgpeth, 1949, they appeared to be too small to dare the description of a new species within the still confuse taxonomy of the genus Callipallene. Thus, we prefer to stress the strong relation with C. dubiosa, assigning the provisional status of affinis dubiosa and postponing the discussion of the value to assign to the differences found.
As Stock himself suggested (1954) C. dubiosa is not well distinguished from C. brevirostris and C. emaciata. Referring to Stock’s drawings (1952), it has a cephalon with a shorter neck and a more curved and larger propodus than C. brevirostris. Its similarities are still stronger with C. emaciata. The proboscis of C. dubiosa that resembles ‘somewhat ... the small end of an egg’ (Hedgpeth, 1949) doesn’t seem a stable character considering Stock’s specimens from Indo-Pacific (1954) and our samples from Socotra. Furthermore our material differed by a more variable number of leaflike spines on strigilis articles and no suture line between third and fourth body segment (see Table 1).
Our specimens can be well distinguished from C. kenyensisMüller, 1990 by the presence of 7 and 11 teeth respectively on the movable and immovable chelifore fingers and by strigilis articles with leaflike spines in the formula: 6-8 spines on the seventh articles, 5-7 on the eighth, 5-7 on the ninth and 7-8 on the tenth. Propodus is sligthly curved in both C. dubiosa and C. kenyensis without a distinct heel, but C. kenyensis has the sole armed with 3 strong spines in the proximal third organized in a single row, 4 smaller spines in the two distal thirds and no row of setae, while specimens from Socotra have respectively 6-7 strong spines arranged in two rows, 6-7 small spines and several setae (see Table 1).
Most of the bibliography around C. dubiosa and C. kenyensis refers to their resemblance to C. emaciata and different authors look for small characters to distinguish several Callipallene specimens found in the Indo-Pacific. We don’t want to discuss here the taxonomic value of these characters, as we are conscious of the urgence of a revision of this genus.
Together with Ammothella omanensis, this is the most abundant species in our samplings, found also in the islands of Abd-el-Kuri and Darsa. Specimens at any developmental stage have been collected, also males and females with eggs and larvigerous males, too. Some male specimens bore simultaneously eggs and larvae. As typical for Callipallenidae, rather advanced larvae (with three pairs of legs) have been found still attached to ovigers (fig. 1).
Although the sampling effort has not been the same during our two visits on the archipelago, all 13 ovigerous males found have been collected during the monsoon season and no one during spring time.
Callipallene dubiosa is a shallow-water species distributed in the Indo-West Pacific found by Müller (1990) along the Kenya coasts.
Genus Propallene Schimkewitsch, 1909
Propallene socotrana n. sp.
Material: Hadibo, Socotra, 12°38’50’’N - 53°59’40’’E, 21 March 2005 - 19 July 2004. Distributed to Berlin and Amsterdam museums as follows: 21 March 2005, 1 m, 1 male (holotype) ZMB 341. 17 June 2004, 1-2 m, 1 female (paratype) ZMB 342, 3 juv. ZMB 343; 19 July 2004, 2-3 m, 3 females (paratypes), 1 juv. ZMA Pa 205982.
Table 1. Some important characters distinguishing C. dubiosa from C. kenyensis, and the same characters found in specimens from Socotra.
Fig.1. Callipallene aff. dubiosaHedgpeth, 1949. Male a) trunk (dorsal view); b) chela; c) leg 2; d) distal articles leg 2; e) oviger with egg; f) spine of oviger article 10; g) larva; h) leg 3 of larva.
Fig. 2. Propallene socotrana n. sp. Male (holotype) a) trunk (dorsal view); b) chelifore; c) chela; d) palp; e) leg 3; f) cement gland ducts of leg 1; g) distal articles leg 2; h) spines on the propodus heel; i) oviger; l) spine 8 of oviger article 8; m) spine 9 of oviger article 9; n) spine 8 of oviger article 10.
Fig. 3. Propallene socotrana n. sp. Female (paratype) a) trunk and leg 3 with eggs (dorsal view); b) chela; c) distal segments leg 2; d) spines on the propodal heel; e) oviger; f) distal articles of oviger; g) spine of oviger article 8.
From macro-algae (i.e. Padina and Dictyota) and sparse hard coral community on small rock boulders. Bartolino leg.
The holotype is the only male among five mature specimens identified as this new taxon from Socotra island. Propallene is a well defined Callipallenidae genus characterised by the presence of 2-articulated palps in the male sex only. At the moment twelve species are ascribed to Propallene, all from the Indo-Pacific region, with the exception of P. stocki Fage, 1956 found in Sierra Leone. The species identification is rather difficult as mentioned by Stock (1975b), several taxa sharing a similar habitus. Diagnostic characters refer to morphology of palps and chelae, to the structure of male ovigers and shape and number of cement gland apertures, mainly.
Description: This species is discriminated from most other Propallene species by a fully segmented concentrated body, further characterised by lateral processes separated by less than half their diameter (figs. 2 and 3). Neck short, ventrally bent, proboscis very short.
It is distinguished by P. ardua Stock, 1975 by:
wider and more compact propodus;
second spine on the propodus heel longer than the first;
more numerous teeth on the movable chela finger;
more compact tibiae, with a length-width ratio of 2.8-3.2
less numerous cement gland openings;
cone-shape ocular tubercle much less rounded.
It differs from P. crassimanusStock, 1959 by the following characters:
neck progressively enlarging to the origin of chelae;
10th article of oviger sligthly shorter than 9th;
propodus more slender without evident sexual dimorphism;
cheliphore scape not longer than chela.
Eye cone moderately high, four feebly pigmented eyes sitting near base of eye cone, slightly enlarging towards its midlength, from there tapering to a bluntly rounded tip. Cheliphore scape longer than proboscis, chelae overhanging the mouth. Chela with single setae on all aspects, both fingers slightly longer than palm, bearing five denticulate teeth on immobile and 7 on the movable finger.
Palps bi-articulate, basal article short, terminal one long, of a flattened rod-like shape, terminally bearing 3+3-4 setae.
Oviger origin barely discernible from above, on anterior margin of first cruriger. Oviger 10-articulated, the 5th article the longest, the thickened 4th and the short 6th form the ‘knee’; they bear 2 and 1 longer setae, respectively. Strigilis with leaf-shaped special spines in the formula 13:12:10:9 (in male holotype); spines slender and with 5 serrations on both flanks; no terminal claw (see genus definition).
Abdomen a tiny knob, curved ventrally, its extremity almost level with 4th lateral process.
Legs rather short, coxae 1 and 3 subequal, barely longer than wide, coxa 2 longer (see measurements), femur the longest article, tibiae of subequal length, tarsus very short, propodus about 1/4 shorter than tibia 2, heel not distinctly set off, bearing two short spines, sole with about 8-10 setae. Terminal claw long, moderately curved, no auxiliaries.
All leg articles sparsely beset with setae, the longest of them on dorsal face of both tibiae.
Measurements im mm: total length 1.05; lengths of body segments: 2nd 0.13; 3rd 0.15; 4th 0.16, length of proboscis 0.4, width of proboscis 0.36; lengths of all articles of 3rd leg: coxa1 0.26; coxa2 0.41; coxa3 0.26; femur 0.78; tibia1 0.62; tibia2 0.66; propodus 0.08; tarsus 0.58. Lengths of palp articles: 1st 0.04; 2nd 0.33. Lengths of oviger articles: 0.23 - 0.24 - 0.46 - 0.60 - 0.10 - 0.19 - 0.21 - 0.15 - 0.13.
Propallene socotrana n. sp. enriches the zoogeographical scenario depicted by this genus along the African coasts, filling the gap between P. ardua Stock, 1975 found in Tanzania (Stock, 1975a) and P. crassimanusStock, 1959 recorded from South Africa (Stock, 1959) and Oman (Stock, 1992) (see Table 2).
Etymology: The species is named after its type locality, Socotra Island, Yemen.
Table 2. Main characters distinguishing Propallene socotrana n. sp. from P. crassimanus and P. ardua:
Family Phoxichilidiidae Sars, 1891
Genus Anoplodactylus Wilson, 1878
Anoplodactylus erythraeus n. sp.
Material: Shassara, Socotra (12°38’11”N - 54°15’43”E), 31 March 2005, 0-2 m, 1 male (holotype) ZMB 344 comes from macro-algae (i.e. Padina and Dictyota) and sparse hard coral community on small rock boulders. Bartolino leg.
Remarks: This newly found species belongs to a group of closely related Anoplodactylus-species of an extremely attenuated habitus. A fourth species in this complex was described after the submission of the present paper based on the specimens referred by Arango (2003) to A. tenuicorpus. A review of that tenuicorpus-complex is given in Arango and Krapp (2007). Anoplodactylus typhloides is a blind species - from deeper waters - of a roughly similar body shape but otherwise very different from these shallow water species belonging to the tenuicorpus group from coral habitats.
Description: Body extremely slender, segments of about the same diameter as crurigers 2 and 3, separated by nearly 5 times their width. Only few short setae on body surface. Eye cone lowly rounded, placed close to the anterior margin of cephalon, with 4 distinct eyes. Cephalon shortest segment, its crurigers anteriorly bent at an angle of about 60°. Body segments 2 and 3 of subequal length, extremely attenuated, elongated towards their anterior sutures. 4th segment shorter, bent backwards at an angle of about 135°. Abdomen tiny, reaching to about half length of 4th crurigers.
Proboscis long (shorter than either body segments 2 or 3), narrowing at base, with a slight expansion at mid-length and after little narrower stretch follows a subterminal swelling, mouth opening with three distinct lips = the antimere tips.
Chelifore scape extremely slender, longer than proboscis, movable finger distinctly longer than hand. Chela gaping, both finger tips crossing at their extremities, on their ‘cutting’ edge fitted with about 5 needle-like teeth.
Ovigera originating on a swelling ventrally at mid-length of first crurigers, 6-articulated, slightly spinose, 3rd article the longest, its articulation with 4th article forming the most apparent ‘knee’, less so between articles 5 and 6; this terminal article bearing about 7 strong endal setae, which are bent backwards.
Legs extremely slender, coxae 1 and 3 short, coxa 2 around 3 times longer than 3rd one; femur the longest article, tibia 2 almost as long, tibia 1 somewhat shorter (see measurements). All leg articles bearing a few short setae. Cement gland opening slit-like, on the dorsal face of femur of male holotype, slit length almost one sixth of femur length. Tarsus shorter than broad, ventrally bearing one subterminal spine and 3-4 setae. Propodus slender, heel region almost imperceptibly merging into sole, but in this basal region three heavy spines, the third one the longest and with 9 serrations on distal side. Propodal sole bearing about 8 spines which are flanked on both sides by setae, no cutting lamina. Main claw very long, moderately curved, reaching almost to base of serrated spine. Auxiliary claw absent.
Anoplodactylus erythraeus is distinguished from tenui-corpus Child, 1991 by the following characters:
lack of tiny cutting lamina distally on propodal sole;
greater number (about 9 instead of about 5) of spines on sole of propodus;
only one slit-like expanded cement gland opening on dorsal aspect of femur instead of two tiny ones (this seems the most important among those characters);
tibia 2 instead of femur is the longest leg article.
Fig. 4. Anoplodactylus erythraeus n. sp. Male (holotype) a) trunk (dorsal view); b) body segment 1; c) proboscis (ventral view); d) chelifore; e) leg 3; f) femur of leg 4; g) distal articles leg 3; h) oviger.
Measurements in mm: total length 2.17, length of body segments 1 - 4: 0.36, 0.63, 0.65, 0.53; length of proboscis 0.64, width of proboscis 0.22; lengths of articles of leg 3: coxa 1 = 0.31, coxa 2 = 0.77, coxa 3 = 0.25; femur 1.51, tibia 1 = 1.27, tibia 2 = 1.49; tarsus 0.06, propodus 0.53, lengths of the palp articles: basal 0.04, distal 0.33; lengths of the oviger articles 0.21, 0.47, 0.73, 0.25, 0.14, 0.18; width across 2nd lateral processes 1.13; distance between lateral processes 2 and 3: 0.45.
Members of this species group were recorded also from Aldabra Atoll and the Seychelles Islands by Child (1988b) and Arango (2003) from the Australian Great Barrier Reef. Child (1988b) identified some females as A. attenuatus based on habitus alone, this species was originally described by Child under that preoccupied name in his 1988a paper from the Philippines. In 1991 he had to change it to tenuicorpus. Arango (2003) applied this name also to her Great Barriere Reef material even if depicting clearly deviating characters. Evidently both authors relied mostly on the slender build and were not aware of Stock’s (1994) paper in which he described A. exaggeratus as another related species.
Etymology: The species epithet is derived from the classical Greek erythros = red, and refers to the nearness of Socotra to the Red Sea, but mainly to the fact that the old Greeks called the sea region off the actual Eritrea the ‘Red Sea’; only afterwards this denomination was extended to cover the entire present-day Red Sea. Needless to add that the country Eritrea derives its name from the same Greek word.
Material: Shassara (12°37’40’’N - 54°16’06”E), 8 September 2004, 1-2 m, 1 female with eggs ZMB 366 Bartolino and Mohammed Kaed leg.; Hadibo-Qadheb, 24 September 2004, 1-3 m, 1 female ZMB 365 Bartolino leg. Both from macro-algae and sparse massive hard corals and on rocks, relict reefs and large boulders.
Many small Anoplodactylus-species are ascribed to the Anoplodactylus pygmaeus-complex. It clusters closely similar species whose taxonomic identity is still uncertain. Among all these taxa we can roughly identify two groups on the presence or absence of auxiliary claws. The main species with auxiliaries are: A. minutissimusStock, 1954, A. micros Bourdillon, 1955, A. trispinosusStock, 1951 and A. turbidus Stock, 1975. The differences between these species are minute and easier to identify in males than females because their ovigers and the length and position of the cement gland are important identification characters. The toothed finger of chela and the presence of two spines in front of a long lamina on the propodal sole have brought us to the present identification. A certain degree of variability of several diagnostic characters has been previously observed for some species of the A. pygmaeus complex (Stock, 1951; Stock, 1964; Stock, 1975c). The presence of two strong spines on the propodal heel, sometimes reduced to only a single (unpaired) one, is for the first time mentioned for this species, as it was also recorded by Stock (1964) for A. trispinosus.
Several specimens from the Dahlak Archipelago (South Red Sea), previously identified as A. trispinosus, have been assigned to this species together with Ethiopian material after its description by Stock (1975). The same author reported 3 specimens from Madagascar in 1974.
Table 3. Some important characters distinguishing three attenuated Anoplodactylus-species in this complex (for the fourth one see Arango and Krapp, 2007).
The authors would like to thank the Environmental Protection Authority of Yemen for releasing the authorizations for the collection of samples. We are grateful to the Socotra Conservation and Development Programme for logistics and to Miles Davis and Mohammed Kaed Hassan Ali for their valuable help in the fieldwork. We thank the reviewers for their very helpful comments.
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