an overview of muricid taxonomy above generic level

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Tropical Marine Mollusc Programme (TMMP)

AN OVERVIEW OF MURICID TAXONOMY ABOVE GENERIC LEVEL by Anuwat Nateewathana and Jorgen Hylleberg Phuket marine Biological Center, P. O. Box 60, Phuket 83000, Thailand.

INTRODUCTION Muricids belong to one of the most abundant taxa of molluscs. More than 800 species of the Muricidae have been named (Ponder and Vokes,1988). Even if muricids have long been one of the most popular groups among the shell collectors, little attempt has been made to review them in this century. Revisions of the Muricidae have been made by Radwin and D' Attilio (1976). Recently, Ponder and Vokes (1988) revised the Indo-West Pacific fossil and recent species of two genera of the Muricidae. The Muricidae is a complex family and it is difficult to identify not only to genera or species level, but also subfamilies may create problems. Classification of muricids is still strongly debated among the conchologists. In order to get a general baseline for further studies within the TMMP, the present report will deal with the broader aspects of taxonomy of the muricids. The topics discussed include the general background and some problems concerning muricid taxonomy. Since revisions of the Muricidae are rare, the present review is mainly based on Radwin and D'Attilio (1976).

CLASSIFICATION OF MURICIDS A diagram of the muricid classification based on Radwin and D'Attilio (1976) is shown in Fig.l. Short definitions at different taxonomic levels will be given.

tIe, which secretes calcareous spicules, plates or shell. Respiration is generally by ctenidia, a type of gill characteristics of the molluscs. The anterior part of the digestive tract has cuticularized tooth plates or a complex band of teeth, the radula apparatus. CLASS: The phylum Mollusca is generally divided into six classes: Monoplacophora, Polyplacophora, Bivalvia (Pelecypoda), Gastropoda, Scaphopoda and Cephalopoda (Maybe one more class can be added, Aplacophora, see Scheltema,1978) Class Gastropoda: Gastropods have a single, generally coiled shell (a few groups lack the shell), a flat sole-like foot, a well-developed radula feeding apparatus. The life cycle is generally contracted, with the loss of the trochophore (the primitive molluscan larval stage) and the advent of the veliger (a second larval stage). SUBCLASS: The Gastropoda are traditionally divided into three subclasses distinguished primarily on the basis of type and position of respiratory organs. The Prosobranchia are characterized by a torsion-produced anterior mantle cavity and gills, the Pulmonata by an anterior, vascularized pulmonary chamber, the gills having disappeared in the course of evolution, and the Opisthobranchia by a posterior mantle cavity brought about by a detorsional phenomenon.

ORDER: 'The Prosobranchia are generally PHYLUM:Muricids belong to phylum MOLLUSCA. Molluscs are coelomate invertebrates. The body is divided into a distinct head region with sensory structures, a propulsive foot used for creeping or digging, and a visceral mass enveloped by a fold of the body called the man-

divided into three orders: the more primitive Archaeogastropoda, including those prosobranchs with noncopulatory reproduction, all or part of the left gill and kidney persisting, and the rake- or comblike (docoglossate or rhipidoglossate) radula types; the Mesogastropoda, with

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Phuket mar. bioi. Cent. Spec. Publ. no.9 (1991)

Phylum Mollusca Class

Monoplacophora

Scaphopoda

I

Prosobranchia

Subclass Order

Bivalvia

Pulmonata

Archaeogastropoda

Family

Buccinacea

Muricacea Thaididae

I

Neogastropoda Toxoglossa

Stenoglossa I

Superfamily

Volutacea I

Rapanidae

Cephalopoda

Opisthobranchia

Mesogastropoda I

Suborder

I Gastropoda

Polyplacophora

Columbariidae

Muricidae

Coralliophildae

i

Subfamily

Ocenebrinae

Muricopiinae

Typhinae

Muricinae

Tropininae

Figure 1 Diagram showing the classificatiort of muricids (adapted from Radwin and D'Attilio, 1976).

copulatory reproduction,the progressive loss (from primitive to advanced forms) of the left gill and kidney as a result of shell impingement, and the moderately reduced taenioglossate radula type; and the Neogastropoda, supposedly the most advanced group, with copulatory reproduction (at times in conjunction with well-developed reproductive behavior), the uniform loss of the . right gill and kidney, and the reduced stenoglossate or toxoglossate radula types.

terized by an intricate and elaborate sculpture of spinose, frondose, or lamellose varices of the shell. Ponder (1973) has discussed the evolution of the neogastropods and recognized three superfamilies: Cancellariacea, Conacea and Muricacea. The distinguishing features are mainly due to the internal structures, such as proboscis, radula, esophagus, valve of Leiblien, etc . However, from both separations, the Muricacea is clearly separated from other superfamilies.

SUBORDER: The neogastropod suborders Stenoglossa and Toxoglossa are separated on the basis of their radula distinctions: the toxoglossate forms have extremely reduced radulae consisting generally of packets of darts (in some cases, these have completely disappeared); the stenoglossate forms have a radula with one or three longitudinal rows of teeth.

FAMILY: Radwin and D' Attilio (1976) divided the Muricacea into five families, the Muricidae, Rapanidae, Thaididae, Columbariidae and Coralliophilidae (Fig. 1). They are distinguished from one another on the basis of radula details and shell forms. Ponder (1973) mentioned that the Muricacea contains several groups of closely related families and he also noted that the Buccinidae, Nassariidae, Fasciolariidae and Galeodidae (=Melongenidae) may usually be differentiated on shell and/or radula features but lack anatomical characters that will consistently separate them. Features of the muricacean families given by Ponder (1973). The family Rapanidae and Thaididae is not included in his classification.

SUPERFAMILY: It has been accepted that the muricids are in suborder Stenoglossa. However, it is still debated how to separate this suborder at the superfamily level. Radwin and D' Attilio (1976) recognized three stenoglossan superfamilies, the Muricacea the Buccinea, and the Volutacea (Fi~.I). They mentioned that these three superfamllies can be distinguished by radula differences and conspicuous shell characters. The shells of the muricacean group are charac-

Characteristics of family Muricidae: Neogastropods with varicate shells, radula con-

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Tropical Marine Mollusc Programme (IMMP) .

sisting of a central tooth and a pair of hook-like marginal teeth in each row. An anal gland, a pedal accessory boring organ, accessory salivary glands and a large, triangular gland of Leiblein usually present. The anatomical features of the Muricidae can be summarized as follow: 1. A well developed, bipectinate osphradium. 2. A moderately long, pleurembolic proboscis much like those in other carnivorous gastropod groups. 3. A moderately long radula, or rasping organ, with a rachiglossate radula dentition of several hundred similar transverse rows, three teeth per row (a rachidian tooth and two lateral teeth). 4. An accessory boring organ (ABO) widespread in the Muricidae and clearly associated with the shell-boring habit of the group. 5. Two pairs of buccal or salivary glands that emit a mucoid substance or other kind of lubricant. 6. The gland of Leiblein (found throughout the Muricacea), a large, solid mass of tissue lying behind the anterior nerve ring. This gland has been shown to produce powerful amylolytic enzymes. 7. The valve of Leiblein, consisting of two flaps projecting backward into the lumen of the pharynx, their free surfaces fringed with long cilia. 8. A true anal gland, in the form of a caecal outgrowth of the rectum in the anal region.

9. A hypobranchial gland having several apparent functions, one better known than the others. As in other stenoglossan groups, this gland produces a mucoid or slimy substance that cements extraneous particles together as they leave the mantle cavity. The result is a viscous conveyor belt that is moved by beating cilia. The gland also emits a clear fluid that becomes the Tyrian purple dye of antiquity, a characteristic unique to the Muricacea. 10. As in other stenoglossan groups, a ventral pedal gland, which receives the eggs from the capsule gland enveloped in a soft capsule, hardens and molds the capsule, and expels it. SUBFAMILY: The family Muricidae have been subdivided into five subfamilies, Muricinae, Ocenebrinae, Muricopsinae, Trophoninae, and Typhinae. Ponder(l973) and Radwin & D'Attilio (1976) have suggested that there is little support for this separation. There is substantial disagreement concerning the precise limits of the subfamilies of Muricids. However, recent works on muricids, for practical reasons, have still used these separations, for instance, Vokes (1978) and Ponder & Vokes (1988). Characteristics of the five subfamilies have been given by Radwin & D' Attilio (1976). At the next workshop we hope to be able to deal with the generic and species levels when more is known about the muricids in our study areas.

REFERENCES Ponder, W.P. 1973. The origin and evolution of the Neogastropoda. Malacologia. 11: 295~342 Ponder, W.P. and E.H. Vokes. 1988. A revision of the Indo-West Pacific fossil and recent species of Murex s.s. and Haustellum (Mollusca:Gastropoda: Muricidae). Rec. Aust. Mus. Suppl. 8:1160 Radwin, G.E. and A.D'Attilio. 1976. Murex shells of the world: An illustrated guide to the Muricidae. Stanford University Press, Stanford. 284 pp. Scheltema, A. 1978. Position of the class Aplacophora in the phylum Mollusca. Malacologia. 17:99109 Vokes,E.H. 1978. Muricidae (Mollusca:Gastropoda) from the eastern coast of Africa. Ann.Natal Mus. 23(2):375-418