l—h SIX IM Number 492 15 April 2002 Contributions IN Science Phylogenetic Systematics of Reticulidia Brunckhorst, 1990 (Mollusca, Nudibranchia) with the Description OF A New Species from the Tropical Indo-Pacific Angel Valdes and David W. Behrens OF Los Angeles County Natural History Museum Serial Publications OL THE Natural History Museum ol Los Angeles County Scientific Publications Committee John Heyning, Deputy Director for Research and Collections John M. Harris, Committee Chairman Brian V. Brown Gordon Hendler Ines Horovitz Joel W. Martin K. Victoria Brown, Managing Editor The scientific publications of the Natural History Museum of Los Angeles County have been issued at irregular in- tervals in three major series; the issues in each series are numbered individually, and numbers run consecutively, re- gardless of the subject matter. # Contributions in Science, a miscellaneous series of tech- nical papers describing original research in the life and earth sciences. # Science Bulletin, a miscellaneous series of monographs describing original research in the life and earth sci- ences. This series was discontinued in 1978 with the issue of Numbers 29 and 30; monographs are now published by the Museum in Contributions in Science. # Science Series, long articles and collections of papers on natural history topics. Copies of the publications in these series are sold through the Museum Book Shop. A catalog is available on request. The Museum also publishes Technical Reports, a miscel- laneous series containing information relative to scholarly inquiry and collections but not reporting the results of original research. Issue is authorized by the Museum’s Sci- entific Publications Committee; however, manuscripts do not receive anonymous peer review. Individual Technical Reports may be obtained from the relevant Section of the Museum. Natural History Museum OF Los Angeles County 900 Exposition Boulevard Los Angeles, California 90007 Printed at Allen Press, Inc., Lawrence, Kansas ISSN 0459-8113 Phylogenetic Systematics oe Reticulidia Brunckhorst, 1990 (Mollusca, Nudibranchia), with the Description oe a New Species erom the Tropicae Indo-Pacieic / Angel Valdes^ and David W. Behrens^ ABSTRACT. The genus Reticulidia includes three previously described species, R. halgerda and R. fungia from the tropical Indo-Pacific, and R. gofasi from the Atlantic. A new species, R. suzanneae, is described on the basis of specimens collected from the Indian Ocean coast of Thailand. This species is distinguishable from the other species by having an orange external coloration with circular black spots and the bursa copulatrix smaller than the seminal receptacle. A phylogenetic analysis of Reticulidia shows that R. gofasi is the sister taxon to the Indo-Pacific species, and a vicariant event probably produced this pattern. Reticulidia suzanneae is a derived species within Reticulidia and is the sister taxon to R. fungia. Reticulidia is a monophyletic group supported by three synapomorphies related to the shape of the buccal bulb, the oral glands, and the esophageal connection. The dorsal ridges, which were used by other authors to define this genus, are absent in R. gofasi and therefore their presence is a synapomorphy of the Indo-Pacific clade. INTRODUCTION The genus Reticulidia was described by Brunck- horst (1990) to include a single described species of Indo-Pacific Phyllidiidae, R. halgerda Brunckhorst and Burn, 1990. This species is characterized by having smooth reticulate ridges on the dorsum and radially arranged glandular discs within the pha- ryngeal or bucal bulb on the buccal mass. A second species of the genus, R. fungia, was subsequently introduced by Brunckhorst and Gosliner (in Brunckhorst, 1993), also from the tropical Indo- Pacific. Separation of these two species was justified on the basis of differences in the external coloration (Brunckhorst, 1993). Later, Valdes and Ortea (1996) described a third species of this genus, coL lected from western Atlantic seamounts, between 76 and 340 m depth. This new species, R. gofasi Valdes and Ortea, 1996, is remarkably different from the two Indo-Pacific members of the genus in having dorsal conical tubercles, rather than dorsal ridges. The two Indo-Pacific species are sympatric, whereas R. gofasi is isolated by continental land masses. Valdes and Gosliner (1999), based on a phylo- genetic analysis of the radula-less dorids, found Re- 1. Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007. E-mail: avaldes@nhm.org. 2. California Academy of Sciences, Department of Inver- tebrate Zoology and Geology, Golden Gate Park, San Fran- cisco, California 94118. E-mail: dave@seachallengers.com. Contributions in Science, Number 492, pp. 1-10 Natural History Museum of Los Angeles County, 2002 ticulidia to be a monophyletic group, supported by a single synapomorphy, the presence of radially ar- ranged glandular discs on the buccal mass. How- ever, these authors did not propose a hypothesis of the phylogenetic relationships within Reticulidia. The present paper examines the phylogenetic re- lationships of members of Reticulidia and describes a new species collected from the Andaman Sea, Thailand. Previously described species are studied here again in order to describe characters used in the phylogenetic analysis. Additionally, the phylo- genetic hypothesis is used to further understand the biogeography of the genus Reticulidia and the most likely speciation patterns within this group. MATERIALS AND METHODS The material examined is deposited in the Natural History Museum of Los Angeles County (LACM), the Department of Invertebrate Zoology and Geology of the Galifornia Academy of Sciences (GASIZ), and the Museum National d’Histoire Naturelle, Paris, France (MNHN). Specimens were dissected by dorsal incision. Their in- ternal features were examined and drawn under a dissect- ing microscope by using a camera lucida. Special attention was paid to the morphology of the reproductive and di- gestive systems. Features of living animals were recorded from photographs or from notes of collectors. To calculate the most parsimonious phylogenetic tree, data were analyzed with Phylogenetic analysis using par- simony (PAUP), Version 4.0b8 (Swofford, 2001) by using the exhaustive algorithm. Characters were polarized by using the outgroup selection of the genera Phyllidia Cu- vier, 1797 [Phyllidia varicosa Lamarck, 1801) and Phyl- 2 ■ Contributions in Science, Number 492 Valdes and Behrens: Phylogeny of Reticulidia Contributions in Science, Number 492 lidiella Bergh, 1869 {Phyilidieila pustulosa [Cuvier, 1804]), and subsequent analysis with PAUP. This out- group selection was made on the basis of the study by Valdes and Gosliner (1999), where the clade containing Phyllidia and Phyilidieila was hypothesized to be the sister taxon to Reticulidia, which is a monophyletic group. In- formation on Phyllidia and Phyilidieila was obtained from the literature (Brunckhorst, 1993; Valdes and Gosliner, 1999) and newly examined specimens (Table 1). A Bremer support analysis (Bremer, 1994) was carried out to esti- mate branch support. See Kitching et al. (1998) for a thor- ough explanation of the advantages of Bremer’s method in morphological data analyses. Synapomorphies were identified by the character trace option in MacClade, Ver- sion 4.0 (Maddison and Maddison, 2000). SYSTEMATICS Genus Reticulidia Brunckhorst Reticulidia Brunckhorst, 1990:567-568. Type spe- cies: Reticulidia halgerda Brunckhorst and Burn, 1990, by original designation. DIAGNOSIS. Medium-sized phyllidiid nudi- branchs with the dorsum normally covered with ir- regular ridges or exceptionally conical tubercles. Buccal mass with several radially arranged glan- 4ular discs (synapomorphy). Esophagus connecting into the dorsal surface of the rounded buccal bulb (synapomorphies). Reproductive system similar to that of other phyllidiid nudibranchs. Reticulidia halgerda Brunckhorst and Burn, 1990 Figures lA, 2A-C Reticulidia halgerda Brunckhorst and Burn in Brunckhorst, 1990:570-575, figs. 2A-C, 3-7. MATERIAL EXAMINED. North side of Rasch Passage, near Madang, Papua New Guinea, depth 38 m, 17 June 1992, 1 specimen 34 mm preserved length, collected by T.M. Gosliner (CASIZ 086401). EXTERNAL MORPHOLOGY. The external dorsal morphology of this species was described in detail by Brunckhorst (1993), and a description is not repeated here. A specimen from Madang, Pap- ua New Guinea, is illustrated (Fig. lA) to confirm the identity of the material examined. Ventrally, the mantle margin is narrow (about one-fourth the foot width). Spots of different sizes are irregularly dis- tributed in one or two rows. Some of them are lo- bate and some are circular. The oral tentacles are separated from each other and have a lateral lon- gitudinal groove. The respiratory leaves show al- ternation in size (Fig. 2B). INTERNAL MORPHOLOGY. The reproductive system is triaulic (Fig. 2A). The ampulla is oval. Valdes and Behrens: Phyiogeny of Reticulidia ■ 3 almost rounded. From its distal portion emerges the postampulary duct, which divides into the prostate and a long oviduct. The prostate is wide, long, and convoluted, distally narrowing and expanding again into the long muscular ejaculatory portion. The distal portion of the deferent duct opens into a short, common atrium with the vaginal duct. The penial hooks have a long and robust pointed cusp and a narrow base (Fig. 2C). They are about 70 [xm long. The vaginal duct opens into the bursa copulatrix. The bursa copulatrix is oval and con- nects to the seminal receptacle by a short duct. Near the seminal receptacle this duct is joined by the uterine duct, which enters the female gland mass. The bursa copulatrix is about five times as large as the oval seminal receptacle. GEOGRAPHIC RANGE. This species is known from the central and western Pacific Ocean (includ- ing Fiji and the Marshall Islands), from eastern Australia to Taiwan (Brunckhorst, 1993). REMARKS. The anatomy of this species has been studied by Brunckhorst (1993) and Valdes and Gosliner (1999). The reproductive system of the specimen examined here is very similar to those de- scriptions and no substantial differences have been found. According to Brunckhorst (1993), this species differs from R. fungia in lacking a bluish back- ground coloration and having narrower ridges. An- atomical differences found in this study include a shorter atrium and the presence of two ducts, in- stead of one, connecting to the bursa copulatrix of R. halgerda. In addition, the penial hooks of R. halgerda are very large, about 70 |xm long, with a robust cusp and a short base, whereas those of R. fungia are smaller and have a more delicate, curved cusp and a more elongate base. Reticulidia fungia Brunckhorst and Gosliner, 1993 Figures IB, 2D-F Reticulidia fungia Brunckhorst and Gosliner in Brunckhorst, 1993:78-79, fig. 31D, pi. 9H. MATERIAL EXAMINED. Ima Anchorage, north coast of Tagula Island, Calvados Chain, Lou- isiade Archipelago, Solomon Sea, Papua New Guinea, depth 10 m, 3 June 1998, 1 specimen 36 mm preserved length, collected by G. Williams (CASIZ 113687). EXTERNAL MORPHOLOGY. The external dorsal morphology of this species was described in detail by Brunckhorst (1993), and a description is not repeated here. A specimen from Anilao, Phil- ippines, is illustrated (Fig. IB). Ventrally, the mantle margin is wide (about one-half the foot width). Figure 1 Living animals. A, Reticulidia halgerda, specimen from Madang, Papua New Guinea, photograph by T. Gosliner. 1^, Reticulidia fungia, specimen from Anilao, Batangas, Philippines, photograph by A. Valdes. C, Reticulia siizanneae sp. i|ov., holotype (LACM 2897), photograph by M. Strickland. 4 ■ Contributions in Science, Number 492 Valdes and Behrens: Phylogeny of Reticulidia Table 1. Additional specimens of phyllidiids examined for the phylogenetic analysis, including locality, depth, collection date, collector, and museum registration number. Species Locality and depth Date Collector Registration number Phyllidia varicosa Dawapia Rocks, Simpson Harbor, Bismarck Arch., 0-12m 24 August 1981 A.J. Ferreira LACM 1981-27.1 Pelangi and Putri Islets, Pulau-Pulau Seribu Is., Java, 10-30 m 16-18 May 1986 J.H. McLean LACM 1986-163.7 Phyllidiella pustulosa South of Suva Pt., Viti Levu, Fiji, 0-1 m 16-17 May 1979 J.H. McLean LACM 1979-40.7 Low Isles, off Port Douglas, Queens- land, Australia, 0-1 m 13 August 1981 A.J. Ferreira LACM 1981-20.1 with a few elongate spots arranged in a single row around the mantle margin. Spots are shorter, al- most circular, near the anterior and posterior ends of the foot. The oral tentacles are separated from each other and have a lateral longitudinal groove. The respiratory leaves do not alternate in size (Fig. 2E). INTERNAL MORPHOLOGY. The reproductive system is triaulic (Fig. 2D). The ampulla is oval, almost rounded. From its distal portion emerge the Figure 2 Anatomy of Reticulidia. A, Reticulidia halgerda (CASIZ 086401), reproductive system; scale bar = 1 mm. B, Same specimen, ventral respiratory leaves; scale bar = 1 mm. C, Same specimen, penial hook; scale bar = 2 |xm. D, Reticulidia fungia (CASIZ 113687), reproductive system; scale bar = 1 mm. E, Same specimen, ventral respiratory leaves; scale bar = 1 mm. F, Same specimen, penial hooks; scale bar = 2 |xm. Abbreviations: am, ampulla; be, bursa copulatrix; dd, deferent duct; fg, female gland; pr, prostate; sr, seminal receptacle; v, vagina Contributions in Science, Number 492 Valdes and Behrens: Phylogeny of Reticulidia ■ 5 prostate and a long oviduct. The prostate is wide, long, and convoluted, distally narrowing and ex- panding again into the long muscular ejaculatory portion. The distal portion of the deferent duct opens into a very long, common atrium with the vaginal duct. The penial hooks have a curved and delicate cusp and an elongate base. They are about 40 |JLm long (Fig. 2F). The vaginal duct opens into the bursa copulatrix. The bursa copulatrix is oval. From the vaginal duct, near the bursa copulatrix, leads a duct. This duct connects to the seminal re- ceptacle and to the short uterine duct, which opens into the female glands. The bursa copulatrix is about three times as large as the rounded seminal receptacle. GEOGRAPHIC RANGE. This species occurs sympatrically with R. halgerda, but it is also known from Christmas Island, in the eastern Indian Ocean (Brunckhorst, 1993). Reticulidia gofasi Valdes and Ortea, 1996 Reticulidia gofasi Valdes and Ortea, 1 996:7-8, figs. IF, 4C, 8. MATERIAL EXAMINED. Lusitanian sea- mounts, Josephine Bank (36°40.02'N, 14°16.00'W: Seamount I Expedition station DW61), depth 200- 205 m, 7 October 1987, 1 specimen 11 mm preserved length, Holotype (MNHN). Meteor Group seamounts, Atlantis Bank (34°06.20'N, 30°16.00'W: Seamount II Expedition station DW256), 340 m depth, 2 February 1993, 1 speci- men 9 mm preserved length, Paratype (MNHN). EXTERNAL MORPHOLOGY. The external dorsal and ventral morphology of this species was described in detail and figured by Valdes and Ortea (1996: fig. IF), and another description is not in- cluded here. INTERNAL MORPHOLOGY. Anatomical de- scriptions are based on the illustrations by Valdes and Ortea (1996:fig. 8B). The reproductive system is triaulic. The ampulla is oval. From its distal por- tion emerge the prostate and a long oviduct. The prostate is narrow, long, and convoluted, distally narrowing and expanding again into the long mus- cular ejaculatory portion. The distal portion of the deferent duct opens into a very short, common atri- um with the vaginal duct. The vaginal duct opens into the bursa copulatrix. The bursa copulatrix is oval. From the vaginal duct, near the bursa copu- latrix, leads another duct that connects to the sem- inal receptacle and the short uterine duct, which opens into the female glands. The bursa copulatrix is approximately 10 times as large as the pyriform seminal receptacle. GEOGRAPHIC RANGE. Reticulidia gofasi is only known from the Atlantic Ocean (Valdes and Ortea, 1996), in the Meteor Group seamounts (At- lantis Bank), Lusitanian seamounts (Josephine Bank), and the Azores (slope of Terceira). REMARKS. This is the only species of the genus that lacks dorsal ridges. It was placed in the genus Reticulidia by Valdes and Ortea (1996) on the basis of the morphology of the buccal bulb, with several glandular discs, which is characteristic of this ge- nus. Reticulidia suzanneae, new species Figures 1C, 3 Reticulidia halgerda (Brunckhorst and Burn): De- behus, 1999:277. Reticulidia sp. 1 Rudman, 2000: http://www. seaslugforum.net/retispl .htm. MATERIAL EXAMINED. Similan Island, An- daman Sea, Thailand, depth 21 m, February 2001, 1 specimen 37 mm preserved length, collected by M. Strickland on coral rubble, Holotype (LACM 2897). ETYMOLOGY. Reticulidia suzanneae is named in recognition of Suzanne Forman, Phuket, Thai- land, who was the first to bring this species to our attention and was instrumental in collecting the ho- lotype. EXTERNAL MORPHOLOGY. The living ani- mals are 40-70 mm in length. The body is oval and high, and the notal surface is covered with a series of sharp ridges that form a reticulate pattern (Fig. 1C). The ridges, which are irregular and serrated, delimit pits of various shapes from square to pen- tagonal and triangular. The anus is positioned dor- soventrally. The perfoliate rhinophores have 18 la- mellae. The background color of the body is bright yellow and the crests of the ridges are white. One or more large black spots are found at the bottom of each pit. The rhinophores are uniformly orange. Ventrally, the mantle margin is approximately as wide as the foot, with several oval spots arranged in two rows around the mantle margin. The spots of the inner row are larger and fewer than those of the outer row. The oral tentacles are separated from each other (Fig. 3D). The respiratory leaves show alternation in size (Fig. 3E). INTERNAL MORPHOLOGY. The reproductive system is triaulic (Fig. 3A). The ampulla is oval, almost rounded. From its distal portion emerge the prostate and a long oviduct. The prostate is narrow, long, and convoluted, distally narrowing and ex- panding again into the short muscular ejaculatory portion. The distal portion of the deferent duct opens into a long, common atrium with the vaginal duct. The penial hooks have a wide base and a long, strong, and pointed cusp. They are about 50 jam in length (Fig. 3B). The vaginal duct opens into the bursa copulatrix. The bursa copulatrix is rounded and connects with the seminal receptacle by a long and wide duct. Near the seminal recep- tacle, this duct is joined by the uterine duct, which enters the female gland mass. The pyriform seminal receptacle is about twice as large as the bursa co- pulatrix. The buccal mass is composed of an oval to rounded buccal bulb and the oral tube (Fig. 3C). The buccal bulb is covered with several radially ar- 6 ■ Contributions in Science, Number 492 Valdes and Behrens: Phylogeny of Reticulidia Figure 3 Anatomy of Reticulidia suzanneae sp. nov., holotype (LACM 2897). A, Reproductive system; scale bar = 1 mm. B, Penial hook; scale bar = 2 |xm. C, Buccal mass; scale bar = 1 mm. D, Mouth area; scale bar = 1 mm. E, Ventral respiratory leaves; scale bar = 1 mm. Abbreviations: am, ampulla; be, bursa copulatrix; dd, deferent duct; es, esophagus; fg, female gland; m, retractor muscle; o, oral tube; og, oral gland; ot, oral tentacle; pr, prostate; sr, seminal receptacle; v, vagina ranged glandular discs. The esophagus opens on the dorsal side of the buccal mass, where two large re- tractor muscles attach. GEOGRAPHIC RANGE. This species is known only from several localities in the Phuket Province, Andaman Sea, Thailand. REMARKS. Reticulidia suzanneae is clearly dis- tinguishable from other members of the genus. The external coloration resembles that of R. fungia by having orange pigment with black spots, but R. suzanneae lacks the bluish background pigment present in the latter. Also, the black spots of R. suzanneae are always rounded, whereas in R. fun- gia they are irregular in shape. In addition, the ven- tral side of R. suzanneae has two rows of black spots, whereas R. fungia has only one. The descrip- tion of R. suzanneae is not based only on the ex- amination of a single specimen, but also on several unpublished (by M. Strickland) and published pho- tos (Debelius, 1999; Rudman, 2000). The four specimens photographed show a very similar and distinct color pattern, and no significant variation has been observed. The reproductive system of R. suzanneae is dis- tinctive in having the bursa copulatrix clearly smaller than the seminal receptacle. Also, the sem- inal receptacle is pear-shaped, whereas it is oval or rounded in the other species of the genus. The atri- um of this species is very elongate, similar to that of R. fungia. PHYLOGENETIC ANALYSIS TAXA For a phylogenetic analysis, six taxa have been in- cluded. They are all four species of Reticulidia and two outgroups, Phyllidia varicosa Lamarck, 1801, and Rhyllidiella pustulosa (Cuvier, 1804). CHARACTERS The eight characters of external and internal mor- phology used to resolve the phylogeny of Reticuli- dia are listed below. All characters are coded as binary. The character states are indicated with numbers, 0: plesiomorphic condition, 1: apo- morphic condition. The polarities discussed below have not been obtained a priori, but rather as the result of outgroup comparison in the phylogenetic analysis. The distribution of plesiomorphic and apomorphic character states is found in Table 2. 1. Dorsal morphology. Species of Phyllidia and Phyllidiella have the dorsum covered with tu- bercles, which can be simple or compound, and Contributions in Science, Number 492 Valdes and Behrens: Phylogeny of Reticulidia ■ 7 Table 2. Data matrix of character states in the taxa involved in the phylogenetic analysis. Data code: 0 = plesiomorphic condition, 1 = apomorphic condition. 1 2 3 4 5 6 7 8 Phyllidia varicosa 0 0 0 0 0 0 0 0 Phyllidiella pustulosa 0 0 0 0 0 0 0 0 Reticulidia halgerda 1 1 1 1 1 1 0 0 Reticulidia fungia 1 1 0 1 1 1 1 1 Reticulidia gofasi 0 0 1 1 1 1 1 0 Reticulidia suzanneae 1 1 1 1 1 1 0 1 are supported by integumentary spicules [0]. In most species of Reticulidia, there are no dorsal tubercles, but rather ridges that are not sup- ported by spicules [1], except for R. gofasi, which has simple, conical tubercles [0]. 2. Body texture. Most phyllidiid nudibranchs, in- cluding Phyllidia varicosa, Phyllidiella pustulo- sa, and Reticulidia gofasi have a very dense net- work of calcareous spicules in the body [0], which gives the body a rigid texture. In other members of Reticulidia, the network of spicules is not so dense and the body texture is softer and more flexible [1]. 3. Ventral respiratory leaves. The respiratory leaves of Phyllidia varicosa, Phyllidiella pustulosa, and Reticulidia fungia are all similar in size or change size gradually [0], whereas in the other species of Reticulidia they show an alternation of larger and smaller ones [1]. 4. Buccal bulb shape. In the genera Phyllidia and Phyllidiella the buccal bulb is oval to elongate [0], whereas in Reticulidia it is more circular [1]. 5. Oral gland shape. In species of Phyllidia and Phyllidiella the oral glands are stalked protuber- ances [0], more densely arranged on the poste- rior and dorsal sides of the buccal mass. How- ever, in the genus Reticulidia the oral glands are radially arranged glandular discs [1]. 6. Esophageal connection. In all species of Reticu- lidia the esophagus connects to the buccal bulb through its dorsal surface 11], whereas in Phyl- lidia and Phyllidiella it connects to the posterior end of the buccal mass [0]. 7. Bursa copulatrix. The bursa copulatrix of Phyl- lidia varicosa, Phyllidiella pustulosa, Reticulidia halgerda, and R. suzanneae has two ducts lead- ing from it 10]. One of them connects to the seminal receptacle and the uterine duct and the other one becomes the vaginal duct. In Reticu- lidia fungia and R. gofasi, there is a single duct leading from the bursa copulatrix that splits into two distally 11]. 8. Genital atrium. This is the duct formed by the fusion of the deferent duct and the vagina near the reproductive opening. In all species exam- ined here, the atrium is a short structure [0]. However, in two species, Reticulidia fungia and R. suzanneae, the atrium is very elongate [1]. RESULTS Figure 4 Most parsimonious tree of the phylogenetic re- lationships of Reticulidia, with the Bremer support values in terms of steps on the left side of the each branch (in bold), and character evolution on the right side of each branch. Numbers on the right refer to characters listed in the text. Characters printed in bold and italic face pre- sented one instance of reversal From the analysis of the data matrix a single most parsimonious tree, 10 steps long, was obtained (Fig. 4). This tree has a consistency index of 0.800 and a retention index of 0.818. The tree is fully resolved and shows that R. fungia and R. suzan- neae are sister taxa, and the sister group to R. hal- gerda. Reticulidia gofasi is the most basal member of Reticulidia, which is a monophyletic group. The Bremer support analysis shows that the Reticulidia clade is well supported (with a value of 3). The genus Reticulidia is sustained by three synapomor- phies: buccal bulb oval to elongate [4], disc-shaped oral glands [5], and esophagus connected dorsally to the buccal mass [6]. Only one character [3] showed one instance of reversal in R. fungia. 8 ■ Contributions in Science, Number 492 Valdes and Behrens: Phylogeny of Reticulidia DISCUSSION The evidence from this phylogenetic hypothesis supports Reticulidia as a monophyletic group, sus- tained by three synapomorphies and supported by a high value in the Bremer analysis. This confirms Brunckhorst’s (1993) perceptions, which were later sustained in a phylogenetic hypothesis by Valdes and Gosliner (1999). Reticulidia suzanneae is the sister taxon to R. fungia. Resemblances between these two species in- clude the presence of black spots and the small size and similar shape of the penial hooks. These two characters were not included in the phylogenetic analysis, but corroborate the hypothesis proposed. However, as mentioned above, both species are clearly distinguishable in other regards. BIOGEOGRAPHY The development of a phylogenetic hypothesis for the genus Reticulidia allows further investigation of the biogeography of the group. Reticulidia gofasi, which is the only Atlantic member of this clade, is the sister taxon to the other species of the genus. A vicariant event, most likely the closure of the east- west communication in the Suez area during the Oligocene-Miocene transaction (23 Ma), produced the split of the original range of the ancestor of the Reticulidia clade and subsequent speciation. Dis- persal of Indo-Pacific Reticulidia into the Atlantic or vice versa seems to be very unlikely, because of the presence of large land barriers separating both basins. Valdes (2001) hypothesized that the vicari- ant event derived from the separation of the Indo- Pacific and Atlantic basins explains the presence of a distinct clade of Atlantic and eastern Pacific spe- cies in the genus Phyllidiopsis Bergh, 1875, which is the sister taxon to some other Indo-Pacific spe- cies. Acceptance of this hypothesis implies that the genus Reticulidia appeared before the closure of the east-west communication (during the Oligocene or earlier). The absence of species of Reticulidia from most of the Indian Ocean and the Mediterranean could be due to subsequent extinction in these ar- eas. The higher stability of the deep sea could ac- count for the survival of a species of Reticulidia in the Atlantic Ocean, despite documented environ- mental changes in shallow areas. Again, Valdes (2001) proposed a similar line of thinking to ex- plain the presence of several deep-water Atlantic species of Phyllidiopsis. Within the tropical Indo-Pacific clade, R. halger- da is the sister taxon to the clade containing the other two species, jR. fungia and R. suzanneae. Re- ticulidia halgerda and R. fungia are sympatric for the most part, and widespread throughout the cen- tral to western Pacific (including Fiji and Micro- nesia), from eastern Australia to Taiwan. The range of R. fungia is the larger of the two species, includ- ing populations reaching the eastern Indian Ocean (Ghristmas Islands). Reticulidia suzanneae appears to be endemic to the Indian Ocean coast of Thai- land (Andaman Sea); it has never been recorded from other localities in the Indo-Pacific. The ranges of the sister pair R. fungia-R. suzanneae do not overlap, and a vicariant event could also be in- volved in the speciation of these taxa. In this case, their populations are separated by Sumatra and the Malaysian Peninsula. However, given the small number of specimens of R. suzanneae collected to date, not much can be said about the geographic range of this taxon. ACKNOWLEDGMENTS We thank Mark Strickland and Suzanne Foreman for col- lection of type material. We also thank Narongpon Sitti- thaweepat and Erwin Kohler for additional information on the geographic range of the new species. Additional specimens examined were collected by Terrence Gosliner, James McLean, Gary Williams, and Antonio Ferreira. This paper has been supported by the National Science Foundation through the PEET grant DEB-9978155 Phy- logenetic systematics of dorid nudibranchs to Terrence M. Gosliner and the senior author. LITERATURE CITED Bremer, K. 1994. Branch support and tree stability. Cla- distics 10:295-304. Brunckhorst, D.J. 1990. Description of a new genus and species belonging to the family Phyllidiidae (Nudi- branchia: P)ondo\de2i). Journal of Molluscan Studies 56:567-576. . 1993. 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Gosliner. 1999. Phylogeny of the radula-less dorids (Mollusca, Nudibranchia) with the description of a new genus and a new family. Zoologica Scripta 28:315-360. Valdes, A., and J. Ortea. 1996. Review of the family Phyl- lidiidae in the Atlantic Ocean (Nudibranchia, Dori- doidea). American Malacological Bulletin 13:1-9. Received 18 January 2001; accepted 5 October 2001. SMITHSONIAN INSTITUTION LIBRARIES 3 9088 01402 9615 Natural History Museum Los Angeles County 900 Exposition Boulevard Los Angeles, California 90007