Stichopus herrmanni vs Stichopus chloronotus

The identity of the sea cucumber (see post) spotted at Pulau Semakau in August has finally been confirmed as Stichopus herrmanni. Below is the reply from Dr. Claude Massin from the Royal Belgian Institute of Natural Sciences in Belgium.

“Dear Colleague,

At first glance your specimen could be confused with a Stichopus chloronotus. However, if S. chloronotus has large dorsal papillae with orange tips, these papillae are always well aligned on rows. On your specimen, all the dorsal papillae have the same size and are evenly dispersed. This colour pattern is more reminiscent of S. herrmanni. Moreover, you have a lot of rosettes in your preparations. In S. chloronotus the rosettes are said to be absent or very rare. If you check the size of the C-shaped rods, it is also easy to separate S. chloronotus from S. herrmanni.

S. chloronotus: in dorsal body wall, maximum 45 µm long; in ventral body wall maximum 70 µm long.
S. herrmanni: in the dorsal body wall, 35-100 µm long; in the ventral body wall maximum 150 µm long.

I think your specimen is a particularly dark morph of S. herrmanni.”

Stichopus herrmanni (dark form)

Stichopus chloronotus

Stichopus herrmanni (greyish-green form)

In all the previous reference books and papers, pictures of S. herrmanni are always greyish-green or brownish-green in colour. Looks like we have observed a rather rare dark morph of this species.

Several studies on their reproductive cycle have been conducted in various parts of the world. In Iran, S. herrmanni spawn during the peak of summer in July-August while in New Caledonia, they spawn during the months of January-February. In both cases, warmer seawater temperature is the trigger for reproduction. I wonder what is the situation in Singapore where there is no significant seasonal climate differences in tropical Southeast Asia.

I’ve had the opportunity to interact with several echinoderm experts around the world and have gained much knowledge. I certainly look forward to more advice from them.


Pictures taken at: Pulau Semakau, August 2007; S. chloronotus and S. herrmanni (greyish-green form) are from the book Taxonomie des holothuries des Comores.

References:

Massin, C., Y. Zulfigar, A. S. H. Tan & S. Z. Rizal Boss, 2002. ‘The genus Stichopus (Echinodermata: Holothuroidea) from the Johore Marine Park (Malaysia) with the description of two new species’, Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, Biologie, vol. 72, pp. 73-99.

Samyn, Y., D. VandenSpiegel & C. Massin, 2006. Taxonomie des holothuries des Comores, Abc Taxa (Volume 1), Belgium.

Tehranifard, A., S. Uryan, G. Vosoghi, S. M. Fatemy & A. Nikoyan, 2006. ‘Reproductive cycle of Stichopus herrmanni from Kish Island, Iran’, SPC Beche-de-mer Information Bulletin, vol. 24, pp. 22-27.

Sand Star

Sand Stars (Archaster typicus) is one of the more easily seen sea star on our shores. During low tide, they will emerge from the sandy sediments and they could also be located by the star-shaped impressions left on the sand. This is especially so on the sandy shores of Pulau Semakau. We spotted several mating pairs and the Temasek Poly students wondered how copulation takes place.

A. typicus belongs to the family Archasteridae. This is a small family with only one single genus, Archaster. Sand Star males are slightly smaller than females and a mating pair will always involve the male superposed on top of the larger female. However, fertilization occurs externally where both male and female synchronize the release of sperm and eggs. Thus copulation, which infers internal fertilization, is probably the wrong term to use. Pseudocopulation is the term widely used by scientists.

Sand Star is one of only two sea star species currently known to perform male-on-female superposition sexual behaviour. Most other species conduct aggregate spawning. It is not exactly clear why Sand Stars superpose during breeding. It could either be to increase the chances of fertilization when the eggs and sperm are dispersed into the water or it is a mate guarding behaviour.

Pictures taken at: Pulau Semakau, August 2007.

References:

Komatsu, M, 1983. ‘Development of the Sea-star, Archaster typicus, with a Note on Male-on-female Superposition’, Annotationes Zoologicae Japonenses, vol. 56 (3), pp. 187-195.

Lane, D. J. W. & D. VandenSpiegel, 2003. A Guide to Sea Stars and other Echinoderms of Singapore. Singapore Science Centre, Singapore.

Gold-spotted Mudskipper

It has been a while since I stepped into a mangrove and I’m beginning to miss the mudskippers, or as Rachel would affectionately call them the ‘doink-doink-doinks’ because of their locomotion on land. Their movement of pectoral fins pulling and dragging the body forward always leaves a distinctive trail on the mudflat.

Gold-spotted Mudskippers (Periophthalmus chrysospilos) have pretty orange spots along their body and some of them can appear yellowish in colour. They are rather common and easy to identify from afar. One of the diagnostic features separating this species from other mudskippers is their fully fused pelvic fins that form a round disc.

P. chrysospilos has a small gill area compared to other mudskippers. They are thus less efficient in aquatic respiration and so more adapted to land than water. Their breeding period is thought to be between May and July when they’ll become less seen as they spend more time in their burrows. Males will attract females to their burrows with vigorous courtship displays. Once paired, the male will defend his burrow and surrounding territory against all comers including mangrove crabs!


Pictures taken at: A southern offshore island, December 2006; A northern offshore island, May 2006 and western part of Singapore, January 2007.


References:

Ip, Y. K., S. F. Chew, L. L. Lim & W. P. Low, 1990. ‘The Mudskipper’, in Essays In Zoology. Papers Commemorating the 40th Anniversary of the Department of Zoology, National University of Singapore, eds, L. M. Chou & P. K. L. Ng, Department of Zoology, National University of Singapore.

Larson, H. K. & K. K. P. Lim, 2005. A Guide to Gobies of Singapore, Singapore Science Centre, Singapore.

Stichopus cf. herrmanni

Another sea cucumber!! This time its from the family Stichopodidae.

I chanced upon it during a recent seagrass monitoring at Pulau Semakau. It has a thick body wall, a lumpy body surface and is covered with orange papillae which contrast brightly against the black body surface.

Following the advice from Dr. David Lane, I proceeded to obtain some tissue samples from the dorsal tegument before returning the creature back to the sea.

After several failed attempts at ossicles preparation from a different species, I decided to try again. And voilà! The beautiful ossicles appeared as I adjusted the microscope’s focus. Intricate tables, C-shaped, S-shaped and branched rods of various patterns came into view. It’s a real wonder that these microscopic skeletons have, over evolutionary time, been reduced to these beautifully elaborate 3-D structures.

Based on the references, the ossicle shapes and general morphology would identify it as a Stichopus sp. and it most resembles Stichopus herrmanni. However none of the references noted S. herrmanni appearing in black. Looks like I’ll have to search deeper into sea cucumber taxonomy.

Sea cucumber ossicles, the real beauty is within.

Pictures taken at: Pulau Semakau, August 2007.


References:

Clark, A. M. & F. W. E. Rowe, 1971. Monograph of the Shallow-Water Indo-West Pacific Echinoderms, British Museum (Natural History), London.

Colin, P. L. & C. Arneson, 1995. Tropical Pacific Invertebrates. A Field Guide to the Marine Invertebrates Occurring on Tropical Pacific Coral Reefs, Seagrass Beds and Mangroves, Coral Reef Press, U.S.A.

Lane, D. J. W. & D. Vandenspiegel, 2003. A Guide to Sea Stars and other Echinoderms of Singapore, Singapore Science Centre, Singapore.

Ictinogomphus decoratus

Most of the commonly seen dragonfly species belong to the family Libellulidae. Some of them have adapted to urbanisation and are thriving very well in the ponds and canals within our landscaped parks and gardens. Dragonflies from the family Gomphidae are less common. They are more sensitive to environmental degradation and thus in Singapore; they are more easily encountered in natural streams and water bodies.

Gomphids' pair of eyes is well separated and this is one of the features differentiating them from other dragonfly families. There are only about eight recorded gomphid species in Singapore. Yangchen spotted this striking Ictinogomphus decoratus during one of our surveys. Ictinogomphus species are large and they like to breed largely in standing water. I. decoratus in particular inhabits ponds and dams which makes them the most common among Singapore’s gomphid dragonflies.

This year we celebrate National Day at Marina Bay. Not many of the spectators would know that the few sedge ponds existing in the nearby Marina South and Marina East would soon be cleared for development. And so we will lose another location which supports good dragonfly diversity.

Pictures taken at: Western part of Singapore, August 2007.


References:

Orr, A. G., 2003. A Guide to the Dragonflies of Borneo. Their Identification and Biology, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.

Orr, A. G., 2005. Dragonflies of Peninsular Malaysia and Singapore, Natural History Publications (Borneo) Sdn. Bhd, Malaysia.