Symbiosis: Entoprocta (comensal)

Ophiuroidea – Entoprocta

• Ophiuroidea: Ophioplinthus gelida: host 
• Entoprocta: Loxosomella sp : commensal

Loxosomella sp. as commensal of Ophioplinthus gelida (Koehler 1900), from which it obtains a substrate that provides its mobility to the food sources, the advantage of not being buried by the sediment as well as certain protection from predators Emschermann (1993). For Ophioplinthus it seems to be no benefits at all.

Loxosomella is mainly located at the edges of dorsal interradii as well as on the lateral plates along the arms, being able to appear with a high density of individuals. They can also appear on the ventral part of the disk, but in a scarce proportion.

Entoprocta (Kamptozoa): colonial or solitary suspensivore lophophorates whith the anus inside of the tentacle crown (lophophore), unlike the bryozoans (Ectoprocta) Loxosomella are solitary entoprocts.

1. Extended lophophorate   2. Bud    3. Contracted lophophorate

Materials studied from Expedition ANTARKTIS- XXlll / 8 Polarstern 2006/2007  in  Joinville Island (3 brittle stars with Loxosomella). They correspond to the same geographical area that the specimens studied by Emschermann to Loxosomella antarctica (Weddell Sea and Bransfield strait).

Specimen conserved in 70% ethanol, all  photographs were made in ethanol.

Collected by Pablo J. González-López.

Identified by Rafael Martín-Ledo.
The study was made using Motic SMZ-168 TL stereo microscope.

References

Emschermann (1993) On antarctic Entoprocta: Nematocyst-like organs in a loxosomatid, adaptive developmental strategies, host specificity, and bipolar occurrence of species. Biol. Bull 184: 153-185

July 2010

Symbiosis: Amphiura - Eulimidae (parasitism)

Amphiura joubini: host

Eulimids: endoparasite

In a Amphiura belgicae specimen, caught in South Georgia, Mortensen (1936) described a gastropod that could belong to the same species as the one from the present study. Mortensen described as a possible mechanism of parasite infestation its entrance through an orifice. He also indicated that the adult looked like a sack and had no visible shell.

In the examined specimens of Amphiura joubini from South Shetland we can  see externally one or two large whitish interradios. When we opened the animals, we saw a bag with numerous white or flesh colored shells inside the coelom, the adult being globular.

There is no observable orifice through which the gastropod entered, so there is a possibility of its regeneration. However, in one of the specimens that had two parasites in contiguous interradios, the other interradios are open ventrally, which leads us to think that this would be an “exit” mechanism for the gastropods.

This parasitism does not necessarily mean the death of the brittle star, possibly due to its great regenerative capacity. Although this is only a supposition, based on the large number of examined specimens of Amphiura joubini with badly damaged interradios due to the process of youth parasitic forms leaving their host.

There have also been numerous open specimens of Ophiolimna antarctica, without most of the aboral disk, it is hard to find a “whole” specimen in our collection. In one of the specimens a pair of juvenile gastropods were found, so it does not seem to be a specific Amphiura genus parasitism.

Although there is a reference in the literature on the presence of internal eulimidae parasites, not yet been identified at specific level (Anders Waren, pers. Comm.)

Live Amphiura jouvini

Symbiosis: Cancerilla - Ophioika (parasitism)

Ophiuroidea – Copepoda

First the ectoparasites copepods of Antarctic ofiuroids were cited by Mortensen (1936), but without identifying the species, it was Heegaard (1951) who identified them. In the taxonomic literature they have also been cited by Madsen (1967).

Ophiacantha antarctica: host

Cancerilla sp: ectoparasite

The copepods are adhered to the dorsal surface of the disc. Females are carrying their bags of eggs like balls, males have not been found.

Ophiacantha antarctica: host

Ophioika sp: endoparasite

Copepods with modified morphology occupy nearly an entire interradius of the disk. In this species very small males are situated inside of females brood-pouch.

In his review of Ophiuroidea reproduction, Hendler (1991), cites a work of Bartsch (1975) in which he described a castration as a consequence of an ectoparasite copepod (Cancerilla oblonga) in Amphiura capensis. This is an issue to investigate whether in Antarctic ofiuroids there are similar consequences.

Specimens conserved in 70% ethanol, all  photographs were made in ethanol.

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8  Polarstern.

Identified by Rafael Martín-Ledo.
The study was made using Motic SMZ-168 TL stereo microscope.

References

Heegaard, P (1951) Antarctic parasitic copepods and an ascothoracid cirriped from brittle-stars. Vidensk. Medd. Dan. Naturhist. Foren. 113, 171-190

Hendler, G (1991) Echinodermata: Ophiuroidea. In: Giese, A.C., 

Pearse, J.S. & Pearse, V.B. (Eds.), Reproduction of marine invertebrates: echinoderms and lophophorates. The Boxwood Press, Pacific Grove, CA, pp. 355–511

Madsen FJ (1967) Ophiuroidea. B.A.N.Z. Antarctic Research Expedition (1929–1931) under the Command of Sir Douglas Mawson Rep Ser B 9:123–145

Mortensen T (1936) Echinoidea and Ophiuroidea. Discovery Reports, National Institute of Oceanography Cambridge 12:199–348

July 2010

Symbiosis: Ophioplinthus - Ascothorax (parasitism)

Ophioplinthus brevirima: Host
Ascothorax sp: endoparasite

Inside there were several parasites (Ascothorax sp) with globose aspect; the smaller ones (probably males) with better distinguished morphology having two valve, while the larger specimens are possibly females. This difference in size, and better conservation of structures in male specimens is a common phenomenon in many parasitic crustaceans.

Ophioplinthus brevirima has short genital  slits, hence its specific epithet. In the studied specimens one of the slits, which coincides with the deformed area of the disc has a deformation making it larger, and the proximate plates look abnormal. It is likely had been caused when the endoparasites were leaving their host.

This is supposedly the first record of endoparasites for Ophioplinthus brevirima.

Materials studied from Expediton ANTARKTIS-XXIII/8 Polarstern 2006/2007 in Snow Hill and Dundee Islands. Specimens conserved in 70% ethanol, all photography were made in ethanol using Motic SMZ-168 TL  stereo microscope.
Collected by Pablo J. González-López
Identified by Rafael Martín-Ledo
July 2010

Live Ophioplinthus brevirima, covered by Iophon sponge

Symbiosis: Hydrozoa (mutualist)

Ophiuroidea – Hydrozoa

Ophioplinthus relegata : mutualist symbiont
Hydractinia sp : mutualist symbiont

Ophioplinthus relegata (Koehler) with Hydractinia sp

One of the most beautiful symbiosis observed in the brittle stars is that of an ophiuroid covered with “flowers” (although they are carnivorous). The colonial hydrozoan Hydractinia vallini Jaederh places its hydrorhiza and polyps between and over the plates of Ophioplinthus relegata (Koehler, 1922).

1. Gastrozooids     2. Gonozooid     3. Hydrorhiza

Polyps, gastrozooids with their tentacles and globose gonozooids are located  mainly in the periphery of the disc and on the side parts of the arms.
The hydrorhizas are situated between interventrales plates, as well as in the characteristic jaw depression of  Ophioplinthus relegata, which also can give a shelter to a polyp. The dorsal part of the disk is generally free.

For Svoboda et al (1997), the ophiuroid transports the hydractinia to the new food resources and keeps it away from the sediment that would collapse it, while the hydractinia defends the brittle star from potential predators, which is similar to the symbiosis of gastropods with cnidarians, a mutualistic type of relationship.

1. Gastrozooid   2. Gonozooid   3. Hydrorhiza

In excavated jaw area of some specimens appear polyps which are larger than the rest of polyps presented in the same ophiuroid. Such specimens have very few polyps in the areas where they normally are, such as the periphery of the disc. The proximity to the mouth of the brittle star induces me to think that hydroids can feed on the remains of the food that fall off when the ophiourid is eating (commensalism), or even that it could be a case of kleptoparasitism.

Specimens conserved in 70% ethanol, all  photographs were made in ethanol.

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8  Polarstern

Identified by Rafael Martín-Ledo.
The study was made using Motic SMZ-168 TL stereo microscope.

References

Svoboda S, Stepanjants S, Smirnov I (1997) Two polar Hydractinia species (Cnidaria), epibiotic on two closely related brittle stars (Echinodermata): an example for a taxonomic and ecological bipolarity. Antarctic communities: species, structure, and survival edit Battaglia B ,Valencia J, Walton DWH Scientific Committee on Antarctic Research 22

July 2010

Symbiosis: Nematoda (parasitism)

Ophioplinthus / Ophionotus - Nematoda

Ophioplinthus gelida (Koehler, 1901): host
Ophionotus victoriae Bell, 1902: host
Nematoda (unidentified): coelomic cavity and bursae endoparasites 

Nematodes identified as parasites of Antarctic ofiuroids belong to Thalassonema genus; they have been found in Ophiocten amitinum, although mentioned in sub-Antarctic waters, and in Ophiacantha antarctica. Mortensen 1936, cites the presence of nematodes, unidentified, in Amphiura microplax disjunta.

  


Nematodes, in some cases, can be seen going out from the openings in the disc and, on opening some ofiuroids, several nematodes can be seen spread all over the body cavity.

References

Jangoux M (1987) Diseases of Echinodermata. II: Agents metazoans (Mesozoa to Bryozoa) Dis aquat org, vol. 2: 205-234

Mortensen T (1936) Echinoidea and Ophiuroidea. Discovery Reports, National Institute of Oceanography Cambridge 12:199–348

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8  Polarstern.
The study was made using Motic SMZ-168 TL stereo microscope.

July 2010