ADDENDUM (19 October 2003)

When I wrote these short notes, at the end of May 2003, I only had photos of some specimens (see photo 1-3) with very different physical characteristics compared to H. bargibanti.  In June and July I had the chance to see and photograph some specimens with different body texture (see photo 4-6) which surprisingly had bumps similar to those of H. bargibanti.  Physical differences between these specimens of the same specie H. denise  are obviuos. While the subjects of the first three photos have smooth bodies, with few light round speckles, subjects of the following photos have prominent bumps and a brighter, less regular colour. It was the first time I could see this kind of H. denise  and these differences made me curious.

I asked advice from a friend of mine, the biologist Massimo Boyer, an expert on Indonesian species. I was really surprised to learn that those subjects I had recently photographed were the common ones for him, while he had not yet seen the 'smooth' ones in the Manado area (North Sulawesi), where he works. This morphological difference may possibly depend on the guest gorgonians:

1. Specimens of photos 1-3 are on Annella sp.,  a gorgonian with short, fully retractile polyps and with thin branches. When its polyps are completely drawn back, only dark speckles can be seen (see photos 1 and 2). So H. denise,  living on this gorgonian, has physically modified his appearance consistently with the guest to improve his mimicry;
2. Specimens of photos 4-5 are on Acanthogorgia sp.,  a gorgonian with thicker polyps, often open even in day light, which cannot be fully drawn back. So, when not extended, the polyps look like small and round excrescences and the gorgonian branches are never smooth (see photo 5 and 6). That's why the H. denise,  living on this host, needs a less regular colour and bumps, which are not so different from the H. bargibanti  ones.

Obviously this is only a hypothesis. What is sure is that there are two different kinds of H. denise : the smooth one and the bumpy one.
The existence of this bumpy specimen could also explain why for few years he has been considered a juvenile form of H. bargibanti.

Therefore, what follows should be read keeping in mind this 'addendum' and that this specie can have two different textures.

This pygmy seahorse has already been known to exist for a few years, but until the first months of 2003 nobody knew his exact classification and there were many unanswered questions about him. Many people thought he belonged to the bargibanti species, although his obvious physical variations (see photos), like his different color, lack of typical bumps (or tubercles) normally red and his smaller size would suggest otherwise. He also lives on a different species of gorgonian. Hippocampus bargibanti lives on two species of Muricella,  with bulbous red polyps which are commonly open during the day, while this second species lives on gorgonians of light yellow color, with small polyps rarely open and of the same pale color.

Two expert biologists, Sara A. Lourie (Project Seahorse, Department of Biology, McGill University, Montreal) and John E. Randall (Bishop Museum, Honolulu) have now resolved this matter. After careful analysis they came to the conclusion that this seahorse is indeed a different species from H. bargibanti.

The name of Hippocampus denise  was given to this new species in honor of Denise Tackett, who was the first to bring him to the attention of the scientific community and shared her knowledge about pygmy seahorses. The name 'Denise' also comes from Dionysus, the Greek god of wine, which makes people 'lively'. It seems, in fact, that this new species is indeed more active (I have never noticed this characteristic).

The aptitude of H. bargibanti  to adapt his color, consistent with his hosts gorgonian color (see photo 7-9), was the main reason for people to believe H. denise to be a juvenile form of H. bargibanti,  with still undeveloped colored bumps which would improve his camouflage. This theory was abandoned only when some H. Denise specimens were found with fertilized eggs in their trunk region (and so adults).

Characteristics of Hippocampus denise

Reports made by the two biologists include full detailed information about this new species of seahorse. I'll list only the most obvious ones, those that can easily be appreciated by simply observing a live specimen. All comparisons are in reference to H. Bargibanti:

1. the body doesn't have the obvious rounded bumps, on the contrary it looks almost smooth, and as an adult may have small darker spots all over it; (see addendum)
2. color leans towards yellow, more or less strong, depending on the host gorgonian. Tail can have a few darker rings;
3. he has a smaller size. The average total length, calculated on ten specimens, is only 16.2 millimeters, including the tail;
4. difference between the two sexes is more obvious: the female has a slender body, with an abdominal bulge opposite the small dorsal fin (see photo 1), while in males this bulge encompasses the whole trunk;
5. data available to date shows he lives on three different species of gorgonians (four - see addendum):
   Annella reticulata, Muricella sp., Echinogorgia sp. (and Acanthogorgia sp. - see addendum).
   H. bargibanti  has been reported on only two different species of gorgonians, typically with open polyps even in the daytime: Muricella plectana  for red or pink specimens (see photo 7) and Muricella paraplectana  for yellow or orange specimens (see photo 8 - 9).

There are many other differences between the two species but they need laboratory analysis to be seen, for example, the different number of rings in the tail and the different spatial ratios between some parts of the body and the head. Basically these two species are very similar. Among the characteristics they share, they are both lacking the separate pouch structure for brooding. The eggs or developing embryos are housed entirely within the trunk region. This variation may be related to their smaller size.
Just as a curiosity, Hippocampus denise  is the smallest seashore described to date. He reaches his maturity at one of the smallest sizes among the teleost fishes: only 13.3 millimeters (record belongs to Trimmatom nanus  - a small goby - only 10 millimeters!)