Posted: Mar 23 2013

Morums of Caribbean - Are they the same?

After I had finished preparing this presentation, I reviewed the helpful communications I had received supporting this effort, and revisited an email from Franck Frydman pointing out the work of Philippe Bouchet (2002)* supporting the distinction of M. lamarckii (M. lamarckii = M. purpureum) as a valid species separate from  M. oniscus. Bouchet first discussed and concluded that the protoconchs of Morums can be discerned as either planktotrophic or non-planktotrophic and that this would be useful in distinguishing species, since planktotrophic and non-planktotrophic taxa are by nature separate species.

Bouchet noted that the mode of

development has been observed in

only one Morum; namely, M. oniscus

(Linnaeus, 1767), which was

non-planktotrophic hatching as a

crawling snail. The protoconch is

paucispiral (with few turns). In the

absence of any hard observations of

development in other Morums that

were planktotrophic, by comparison

with known data for Harpa, Bouchet

inferred that those species of Morum

with multispiral type protoconchs

similar to planktotrophic Harpa

multispiral type protoconchs also have

planktotrophic larval development.

He illustrated the two types of

protoconchs in Figure 4.

Bouchet concluded that the non-planktotrophic type of Morum protoconch was paucispiral, consisting of 1.1-1.2 smooth whorls, has a diameter of 1150-3360 pm, and the protoconch/teleoconch transition is often sharp. He concluded that the majority of Morums had paucispiral; non-planktotrophic protoconchs, and noted that M. oniscus and M. dennisoni (Reeve, 1842) had paucispiral type protoconchs.

Bouchet described the planktotrophic type of Morum protoconch as multispiral, consisting of 1.8-2.8 whorls, smooth or finely papillose, and the protoconch/teleoconch transition is sharp with a slight raised varix. Specifically regarding M. oniscus and M. lamarckii, Bouchet commented:

“Incidentally, the Caribbean Morum lamarckii (Deshayes, 1844), often treated as a synonym of M. oniscus, differs from it by multispiral, rather than paucispiral, protoconch. This difference was first noticed by Kaicher (1983: cards 3752, 3760), who treated M. oniscus and M. lamarckii as distinct species, but regrettably she illustrated the wrong protoconchs with the corresponding adults.” “The difference between the protoconchs of M. oniscus and M. lamarckii reflects non-planktotrophic … vs. inferred planktotrophic development respectively.”

*Bouchet, P. 2002. Protoconchs, Dispersal, and Tectonic Plates Biogeography: New Pacific Species of Morum (Gastropoda: Harpidae). Journal of Conchology 37(5): 533-549.

---------------------------------------------------------------------------------

Following is some of the communications resulting in the above and below rewritten presentations.

3/23/13 Marlo Posted on Conch-L:

"I am not persuaded that M. oniscus, purpureum and strombiforme are anything more than subspecies or forms of the same species. To investigate this issue I have prepared this presentation and am asking for loans of specimens to expand my efforts into a community project and present a broad base of samples for us to draw conclusions."

Comments:


Harry Lee (3/21/13 upon previewing slide 16): "It's got some of the color in the parietal shield, but the protoconch is of the oniscus-strombiforme sort.

For the purposes of maintaining the trichotomy, I'd say that M. strombiforme and M. oniscus are more closely akin than either is to M. purpureum.

Clearly there are strictly ontogenetic factors (developmental processes over the lifespan of an organism that determine its physical shape) such as the accretion of callus on the parietal shield and labrum (the latter including an increase in the number of labral denticles) that add to the complexity.

I think the best course of action is to look at more material with the same care and fine technique as you've established thus far."


Franck Frydman: "Then here is the abstract of a 2002 article by Philippe Bouchet (Protoconchs, dispersal, and tectonic plates biogeography: new Pacific species of Morum (Gastropoda: Harpidae). Journal of Conchology 37(5): 533-549.):

'Morum clatratum n. sp. and Morum roseum n. sp. are described from depths of 100-200 m in the Marquesas Islands. Mode of development inferred from protoconch morphology and comparison with the protoconchs of Harpa with teleplanic larvae suggests that the new species have planktotrophic larval development, and that they are expected to range widely outside the Marquesas. In addition, Morum kurzi, M. macdonaldi, and M. teramachii, with inferred planktotrophic development, and M. watanabei, with inferred non-planktotrophic development, are newly recorded from South Pacific localities. The distribution of individual species of Morum appears to reflect dispersal during the planktonic phase, rather than movement of the lithospheric plates on the geological scale. The Caribbean Morum oniscus and M. lamarckii, respectively with inferred non-planktotrophic and planktotrophic development, are treated as separate valid species.'

Otherwise as far as M. strombiforme is concerned I think that it is nothing but a variation of M. oniscus."


Marlo: Based upon Franck’s recommendation I reviewed Bouchet’s article as it pertains to our discussion and found that he concluded that M. oniscus and M. lamarckii/purpureum were separate species because planktotrophic and non-planktotrophic taxon are by nature separate species, the protoconchs of Morums can be discerned as either planktotrophic or non-planktotrophic, and the protoconch of M. lamarckii/purpureum is planktotrophic, while the protoconch of M. oniscus is non-planktotrophic.

Harry:

"Dear Franck,

It's nice to see that Dr. Bouchet ... agreed with the protoconch analysis of the two western Atlantic Morum s.s. species under consideration and credited Kaicher with the discovery of the salient (transposition of inset images notwithstanding). I sometimes feel that Sally's work is greatly under credited.

You may have noticed that Marlo makes little mention of Morum lamarckii (Deshayes, 1844) in his (old) presentation. There are two reasons: (1) We believe M. purpureum Röding, 1798 is a senior synonym, and (2) Emily Vokes (1998: 15) pointed out the unavailability of Oniscia lamarckii Deshayes, 1844 [non Lesson, 1840*].

* The senior homonym, Cassidaria (Oniscia) lamarkii Lesson, 1840 is apparently an overlooked nomen dubium, allegedly from Australia. Aside from being unfigured, its description imprecise (except for the thin labrum, it might even be a mislocalized M. oniscus). Certainly there is no mention of pink/purple, the columella being described as griseous, so I doubt there was any collusion/confusion involving Lesson and Deshayes, and Vokes' treatment of the homonymy, during the hegemony of the third edition of the Code, is final pending a petition.

Lesson, R.P., 1840. Molluscorum novae. Espèce nouvelle de mollusque du genre Cassidaire. Revue Zoologique (Société Cuvierienne) 3: 212.

Vokes, E.H., 1998. Neogene paleontology in the northern Dominican Republic 18. The superfamily Volutacea (in part) (Mollusca: Gastropoda). Bulletins of American Paleontology 113(354): (1)-54 + plates 1-10. 20 April."

So, here's my revised presentation in consideration of the above comments.

This site was designed with the
.com
website builder. Create your website today.
Start Now