Spondylus morrisoni Damarco, 2015
DAMARCO, P. 2015. A new species of Spondylus from Indonesia. Malacologia Mostra Mondiale, 87: 6-14, figs. 1-6. [p. 6, figs. 1-3, 5, 6]
2015 Spondylus (Rimaespondylus) morrisoni Damarco, 2015
P. Damarco, 2015, figures 1, 2.
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«Type material:
Holotype Height (H): 75 mm, Width (W): 64 mm, Thickness (T): 57 mm, MMM Cupra Marittima Paratype 1 Height 87 mm, Width 71 mm , Thickness 66 mm, B. Briano collection - Savona Paratype 2 Height 89 mm, Width 75 mm, Thickness 60 mm, P. Damarco - Turin Paratype 3 Height 80 mm, Width 70 mm, Thickness 52 mm, P. Damarco - Turin Paratype 4 Height 72 mm, Width 71 mm, Thickness 48 mm, B. Briano collection - Savona Paratype 5 Height 82 mm, Width 72 mm, Thickness 51 mm, B. Briano collection - Savona Paratype 6 Height 99 mm, Width 79 mm, Thickness 68 mm, P. Damarco - Turin Quite rare at the moment. Little more than 40 specimens known, of which 19 available and studied for this publication.
DESCRIPTION
Medium to big sized shells (above 100 mm). strongly inaequivalve, subtriangular and fanshaped, with irregular edges. The noteworthy difference between valves, and especially the umbo extension of the right valve, are the main characteristics that stand out at first sight in these shells. The right valve is generally cup-shaped, showing a big area for shell attachment to substrates, which sometimes is as wide as the 4/5 of the whole valve; this rrregular surface may considerably influence the flnal shape of the shell. The left valve s less developed in height and its central area, close to the umbo, is higher and more curved. Lateral auricles are rather narrow. not very separated from the shell and inclined downwardly. The following characteristics are constant in the specimens, and they allow to distinguish this species from the other similar ones. The left valve is characterized by a sculpture made by principal radial ridges, intercalated by 2/3 minor and thinner ones. The main ridges, ivory-colored in the early developmental stages, often get an irregular appearance; they are sometimes sinuous, becoming darker and forming short and thick black spines. Spines are mainly localized in the right part of the shell, while they are rare or very sparse in the left part. Some specimens are almost completely without spines. Minor ridges tend to disappear towards the edge, becoming less evident and almost deleted by growth lines, which become more strong and increasingly irregular in this area, by adapting to the shape of the right valves attached to surfaces. On the right valve, the sculpture is formed by some radial ridges on the left side, with short, sometimes curved, black spines, corresponding to the spines of the left valve. Starting from the umbo area, tight lamellae are present, which are well evident and developed, representing growth lines. These are only present in the part of the right valve that is free from anchoring to substrates. Cardinal teeth of the right valve are white, with brown-reddish tips, although not always. On the left valve, teeth are white with brown-reddish external edges, connected to the color of the internal edge of the shell,
The lunula (the triangular area below the umbo, towards the cardinal area) of the left valve is well developed in height and very inclined. lt is always whitish, with darker lines, which are grayish and blurred at both edges, as well as in the middle.
The lunula, normally closed, corresponds to the developmental phases of the resilifer. ln the right valve, the lunula is triangular and elongated, the color mirrors the other valve, but in a more accentuated way: it is whitish, with two brown-grayish lines that correspond to the colored area where the cardinal teeth attach to the internal edge. ln younger shells, other brown lines are present in this area, but they disappear with growth. On both sides, two brown-grayish bands are present. ln the lunula of both valves, a closed median line, grayish in color, is visible, corresponding to the growth of the ligament furrow, with traces of the ligament inside (resilifer). The internal color of both valves is white, fading with brown-ocher towards the edges. This color forms a concentric continuous band starting from cardinal teeth, staining them on their external edge, and developing over the entire shell edge, by fading with the color in the center of the valve. ln the right valve, the color is slightly paler, with more orange nuances towards the edge in correspondence to crenulations. The internal edge show 53/55 well incised crenulations. Their color varies from dark brown-violet to deep orange. The number of crenulations in the internal edge of the auricles (between the cardinal plane and periauricolar trenches) ranges from 6 to 11. These are slightly raised and very sparse, almost absent in the left valve. Right in correspondence of the beginning of the auricles, two wider notches for valve are present (periauricolar nicks). These are deeper and more dark colored (blackish outwards) than the neighboring crenulations, and they are localized at the edge of the shell where the auricles start to expand. Such dimples originate two little periauricular apertures, which are evident when the shell is closed. During development, the external edges of the dimples form two black ribs going from the umbo area to the edge of the shell, thus edging the auricles.
Periauricolar apertures are features useful to distinguish some Spondylus species from others, as they are constant morphological and structural characters. For this reason, I here propose the new subgenus Rimaespondylus (from the latin rima. slit, aperture) for shells with this characteristic. Lateral apertures are also present in correspondence of the external tip of the auricles (auricular apertures). ln this case the periauricular lines parallel and strongly replicate the external edge of the auricles. The function of periauricolar apertures is not fully understood, but being a replica of auricular apertures, they probably allow a better and quicker water escape from inside, soon lowering internal water pressure when the mollusk rapidly shut the valves. LOCALITY
SE lndonesia, North-Eastern side of the Palau Sangeang Volcano. HABITAT
This species has a preference for basaltic rocks at a depth comprises between 35 and 55 meters. DISCUSSION
The most recent publication on Spondylus, in which a thoughtfully taxonomic revision is provided and taxonomical misinterpretations on some species were clarified too, is by Kevin Lamprell, 2006 ("Spiny Oysters. A revision of the living Spondylus species of the world"). Since I had the occasion to examine specimens of this new species, I proceeded to compare it to similar species, thus evidencing some substantial differences. The newly described subgenus Rimaespondylus, here proposed and characterized by more or less evident periauricular apertures, needs to be better studied to trace all the species that should be ascribed to this subgenus. ln my opinion, show a certain affinity, the following species: Spondylus Iinguafelis Sowerby, G.B. ll, 1847; Spondylus gloriosus visayensis Poppe & Tagaro, 2010; Spondylus asiaticus Chenu, 1845; Spondylus fauroti Jousseaume, 1888; Spondylus anacanthus Mawe,1823. Among these, a first analysis, only two species of the above have general morphological characters that can lead to confuse them with this form: S. anacanthus and S. fauroti.
S. anacanthus Mawe, 1823
Sinonyms (Lamprell, 2006): Spondylus nudus Sowerby, G.B. ll, 1847 Spondylus flabellum Reeve, 1856 Spondylus sanguineus Dunker, 1852 Shell 52 mm high, solid and fan-shaped. Sculpture formed by numerous thin radial ridges, with spines that are sometimes well developed or more squat, almost becoming nodules. Some little spines develop marginally too. The color is reddish-brown, orange or white, with radial ridges that are more intense in color. The lunula shows two (or more) diverging brown stripes from below the umbo. Shell white internally, the external colors are sometime visible from inside. Anchoring area wide, sometimes occupying the entire right
valve. Commonly glued under dead coral slabs or rocks, in shallow water to about 20 mt, where it is not rare to find many specimens glued together. Less frequent in deep waters. It is different from S. morrisoni for its usually smaller dimension, the generally different and more variable color, the internal color usually whitish, the sculpture of the left valve with more evenly distributed little spines or nodules on the surface, the periauricular ribs and auricular apertures are smaller and slightly evident. Spondylus fauroti Jousseaume, 1 888
Sinonyms (Lamprell, 2006): Spondylus smytheae Lamprell, 'l 998 Spondylus marisrubri Roding in Morris, 19g4 Spondylus gloriandus Melvill & Standen, 1907 This is probably the taxon having the most common features with the new species. However, after a careful observation, difference stands out. This shell may be bigger than 85 mm in height, it is oval, oblique and thick. The right valve is more convex than the left. The sculpture is made by numerous and evident radial ribs, starting from the umbo and becoming wider and a little raised. The main ridges are intercalated with 3 minor ridges, and, from about the half of the shell, they develop little and tight spines, of which only some develop into true spines. These are numerous, short and v-shaped. Some ridges carry spatulashaped spines, which are longer, strongly curved and sometimes superimposed. These are much more developed in the right valve. Spines of the same color of the shell. Two periauricular ribs are present on both valves, the right valve ones being more thick.
The anchoring area is small to wide, depending on substrate type. The color is dark brownish-violet to orange-red, paler in the umbo. The shell is white inside, with brownish-red nuances. Crenulations are whitish in young specimens, while in adults the external edge is dark violet/brown, bordered internally by a yellowishbrown to orange concentric band. This mollusk anchors to substrates (metals, corals or stones) with the umbonal area, and it is rarely attached with the whole valve. lt lives in areas with high tide flows, from 10 to 50 meters deep. The species commonly known as S. smytheae, which is most likely a synonym of this one (World Register of Marine Species, 2010; Huber, 2010), would be, according to some authors, endemic to North Red Sea (Aqaba Gulf). Actually, all the analyzed specimens come from that area. Lamprell (2006) reports specimens from Western lndian Ocean as well, from Solomon and Vanuatu lslands. Actually, the specimens pictured by Lamprell (2006) from these localities are entirely similar to the Red Sea ones, but locality data should be better verified, given the big distance between the two distribution ranges that do not seem in continuity. ln the Red Sea, these shells are often found attached below big Acropora plates, dead but still anchored to the reef, on top or on the vertical walls of the coral reef. ln Solomon lslands they seem to privilege deeper water reefs, as well as wrecks deeper than 30 meters, where they are very rare (Lamprell, 2006). The main differences between these two species may be described as follows:
The shell of S. morrisoni is less oblique and regular. On average its aspect is more elevated in the umbonal area of the left valve.
The sculpture is somehow similar in both species by the presence of spines on the left valve, mainly on the right side of it. However, the sculpture is more strong is S. fauroti, which show more numerous and tight spines, of the same color as the rest of the shell. On the right valve of S. morrisoni, on the right side, well developed lamellae are present, while in S. fauroti these are present in young stages only, in the umbo area or directly in the anchoring aiea, although they are never well detached from the shell surface. Finally, the rest of the valve is adorned with curved spines, ordered in radial lines.
ln S. fauroti, the periauricolar ridges are black and are much more thick and wide in the right valve where they form protruding ribs, marked by growth lines. ln S. morrisoni these ridges are dark brown or black, very little protruding and they are almost equal width on both valves.
The periauricular apertures are more incised, more evident and black in S. fauroti. ln both species they stop the crenulations of the edge in correspondence to the auricles attachment. The number of auricular crenulat¡ons on the internal edge of the auricles (between the first cardinal tooth and the periauricular apertures) is different: in S. morrisoni they are less numerous (7/12), liltle raised and very sparse, almost absent in the left valve. ln S. fauroti they are more tight and numerous (15/18), clear-cut in both valves.
ln S. fauroti, the median lines of the lunulae, indicating the growth of ligament furrows (resilifer), are always completely open, while in the new species they are totally closed. Again in S. fauroti the lunula on the left valve is more developed in height and it is more inclined. Cardinal teeth of the right valve are always brown. From cardinal teeth, the color contjnues in the lunula by making two radial greysh/brown str¡pes, wide descending, marking the developmental phases of the shell. ln this species, cardinal teeth of the right valve are bigger, squat and less oblique, and the indents are more deep and accentuated. Moreover, the denticle on the left of the cardinal dimples is less pronounced and protruding.
On the other hand, in S. morrisoni, on the right valve, peculiar brown-ocher blothces are visible on the tip of cardinal teeth, which are withe for the remaining part, while the lunula is always withish with only some darker nuances on the edges. According to these data and considerations, I may conclude this is a new species. By careful analyzing its features, l highlighted some structural shared characteristics that may also define a new subgenus, which I will analyze in detail in a following article.
ETYMOLOGY
The species name is dedicated to Hugh Morrison, who first discovered lhis Spondylus.» PIERO DAMARCO, 2015
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