Aeolid Nudibranch

Nudibranchs have got to be one of the prettiest and most colourful marine invertebrates. No dives or intertidal walks would be complete without seeing one. I have been very fortunate to see several different species throughout the years. Nudibranchs are classified into four suborders and my personal favourite are nudibranchs from the suborder Aeolidina.

Aeolids are typically longish in body shape and have a pair of cephala tentacles that’s distinct from rhinophores. But what makes them stand out are the rows of cerata on their back. I always thought it gives them a funky and rebellious demeanor.
The cerata are actually respiratory organs. In certain species, a cnidosac occurs at the tip of each ceras. These functions as storage for nematocysts capsules for defence and many aeolids obtain the stinging nematocysts from their food source, for example hydroids.

This aeolid nudibranch spotted at Beting Bronok is an absolute attraction. It most probably is from the family Facelinidae. For exact identification to species, its radula would have to be examined.

A team of University of Queensland researchers studying sea slug pheromones have named the chemicals attractin, enticin, temptin and seductin……..very apt names for an alluring group of animals.

Pictures taken at: Beting Bronok, October 2007.


References:

Behrens, D. W., 2005. Nudibranch Behavior. New World Publications, USA.

Graduate Contact 2007, No. 36. University of Queensland, Australia.

Ceriagrion cerinorubellum; Agriocnemis femina; Lynx Spider

The world of insects is filled with peril as many of them are ferocious predators and it is really a survival of the fittest. A survey at Lorong Halus gave me an exciting insight into their prey-predator relationship.

Agriocnemis femina is a small damselfly measuring up to only about 17mm in body length. This species undergoes colour changes with maturity and mature males have a whitish synthorax. This dainty damselfly is common around ponds and drains and they share the same habitat with another damselfly species, Ceriagrion cerinorubellum.

C. cerinorubellum is about a size bigger than A. femina. They are fierce predators and it was not long before we chanced upon a C. cerinorubellum attacking and consuming an A. femina. The prey’s head had been consumed but we could clearly see that it was an immature male A. femina from the orange tip at the abdomen. The C. cerinorubellum was so engrossed on lunch that it simply ignored me as I approached it really close to get a clear picture.

In nature, it is a case of eat or be eaten. This time the predator became the prey. A Lynx Spider (Oxyopes sp.) had captured a C. cerinorubellum. Lynx Spiders have keen eyesight and they hunt down their prey with very agile movements. This individual must have sprung an ambush on C. cerinorubellum which did not stand a chance once the spider sank in its fangs.

As we were leaving Lorong Halus, C. cerinorubellum reminded us that it is still an awesome predator among the small invertebrates. I managed to record a video of one consuming a fly-like insect. I would imagine the chase prior to capture must be quite a dogfight, a battle for air supremacy on a miniature scale.

These little insects might not have the iconic status of lions or tigers. But they are just are vicious and ruthless when it comes to feeding time. I think back to the movie ‘Honey, I Shrunk the Kids’. With these fearsome insects around, that would be a real nightmare comes true.

Pictures and video taken at: Lorong Halus, November 2007.

References:

Koh, K. H. J., 1989. A Guide to Common Singapore Spiders. Singapore Science Centre.

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

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.