The Doridacea (Opisthobranchia; Mollusca) of the Hawaiian Islands! E. ALISON KAy2 and DAVID K. YOUNG3 THE DORIDACEA form a conspicuous element of Gould (1852) from the visit of the U. S. Ex­ the shallow-water molluscan fauna along both ploring Expedition to the Islands; the remaining tropic and temperate shores. The 50 species de­ twenty-two species were recorded by William scribed here from the Hawaiian Islands comprise Harper Pease, a naturalist resident in the approximately 5 per cent of the marine mol­ Hawaiian Islands (Pease, 1860). In recent years luscan fauna of the Islands and 25 per cent of only Edmondson (1933, 1946) and Ostergaard the opisthobranch fauna. (1950, 1955) have discussed Hawaiian dorids, The hallmark of most dorids is a middorsal the former quoting some of Pease's descriptions, tuft of branchiae; the branchial tuft is lacking the latter augmenting several of Pease's descrip­ only in such minute (2 to 3 mm long) forms tions and describing three more species. as Okadaia elegans. Dorids are recognized also This study consists of a systematic account of by their dorsoventrally compressed, oval or the Hawaiian dorids and reports on their syn­ elongate, soft bodies, although a few are limaci­ onymy, anatomy, habits, and abundance. All of form (Goniodorididae, Polyceridae), and some the previously recorded species are accounted for have rather crisp mantles (Platydoris). In other either as validly occurring species or as syn­ respects the dorids exhibit a variety of features: onyms of validly occurring species, an additional they range in length from 2 or 3 mm to 200 mm fifteen are recorded, and eight are described as (Archidoris nttbilosa); they may be brightly new. colored (Hexabranchtts, Ch,'omodoris, H ypselo­ doris) or cryptic (Al'chidoris nttbilosa, Trippa SYSTEMATIC TREATMENT scabriuscttla); and the mantle may be smooth (Chromodoris, H ypselodoris, Hexabranchus) or The Doridacea, like other nudibranchs, are variously sculptured with tentacular processes notoriously difficult animals to deal with from (Archidoris nttbilosa) , pustules (Aste1'Onotus the standpoint of systematics. Early workers cespitoStts), spicules (Trippa echinata, Jortt11na (Pease, 1860; Kelaart, 1859; and others) de­ tomentosa) , granules (Doriopsis granulosa, scribed species on the basis of external characters Platydoris) , or ridges (Halgerda). only, and from these descriptions it is often Dorids were among the first mollusks to be impossible to identify the animals involved. recognized in the Hawaiian Islands, with twenty­ Other workers, among them Bergh and Eliot, seven species described between 1852 and 1860. utilized various internal characters but were in­ Two species were described by Eydoux and consistent in their use of these features both in Souleyet (1852) from specimens collected dur­ describing species and in ascribing species to ing the voyage of the "Bonite," and three by genera and higher taxonomic categories. The difficulties inherent in the early studies are com­ ! Contribution No. 319, Hawaii Institute of Marine pounded by the incomplete nature of collections Biology. Manuscript received May 30, 1968. of dorids in the Indo-West-Pacific. 2 Department of General Science, University of With a collection of several hundred speci­ Hawaii, Honolulu, Hawaii 96822. This research was mens at hand, representing 50 species of dorids supported by National Science Foundation Grant GB from a single locality, we have found the cus­ 1346. 3 Woods Hole Oceanographic Institution, Woods tomary taxonomic approach to the dorids both Hole, Mass. 02543. This paper is part of a disserta­ awkward and unsatisfactory. We have, there­ tion submitted to the Graduate Division of the Uni­ fore, diverged from the usual treatment of the versity of Hawaii in partial fulfillment of the require­ group (Taylor and Sohl, 1962; Marcus and ments for the Ph.D. degree in Zoology. The research was supported by a Bureau of Commercial Fisheries Burch, 1965; Marcus, 1965) and recognize the Marine Science Graduate Fellowship. Doridacea as a superfamily divisible into families 172 Hawaiian Doridacea-KAY AND YOUNG 173 and subfamilies. Although familiar dorid group­ localities, which may have prIOrIty, because of ings, such as the suborder Doridoidea and the the vague descriptions which accompany them. infra-order Cryptobranchia, disappear in this Although the descriptions of Hawaiian dorids treatment, our approach has the advantage not by Eydoux and Souleyet (1852), Gould (1852), only of being an arrangement which incorporates and Pease (1860) are manifestly incomplete, both ecological and anatomical similarities, but it has been possible, with living animals avail­ of conforming to current practice wherein not able in the type locality, to determine all the only the Prosobranchia among the gastropods species described by those authors from the but the Bivalvia are treated as superfamilies and Hawaiian Islands. Synonymies are limited to families. those pertinent to the Islands, and suggestions The seven families into which the Hawaiian are made as to other names which may be ap­ dorids are subdivided are recognized primarily propriate in the sections termed "Remarks." on the basis of feeding types (i.e., rasping sponge-feeders, sucking sponge-feeders, opistho­ HABITATS branch-feeders, polychaete-feeders) and by con­ comitant differences in the musculature of the The data were accumulated over a four-year buccal apparatus as well as differences in the period from monthly collections made in the genitalia. At a lower taxonomic level such littoral zone at four stations on the island of features as the presence or absence of buccal Oahu and collections every two months from armature, penial stylets, etc., are utilized to dis­ three stations on the island of Kauai. The few tinguish subfamilies, while genera are distin­ records included of animals occurring at depths guished by combinations of characters such as of more than 10 meters were obtained from mantle sculpture, type of branchiae, and radular SCUBA divers and from the dredging activities differences. The theoretical basis and anatomical of a privately owned cabin cruiser, the "Pele." details of this approach, with special reference In the littoral (= intertidal) zone, dorids to the feeding types, will appear in a paper by are found most frequently under and in chunks Young (in press). of dead coral which occur in shallow water In assigning species, the following characters shoreward of fringing reefs, as at Kewalo and have been utilized: shape, skin texture, color, Nanakuli, Oahu, or on a reef platform such as branchiae, rhinophores, oral tentacles, radula, the one at Ala Moana, Oahu. The coral, per­ jaws and buccal armature, genital mass, and egg forated with worm tubes and molluscan borers, masses and larvae. To eliminate some subjec­ is heavy with dense growths of marine inverte­ tivity from color descriptions the standard color brates, presenting numerous niches occupied by guide issued by Stanley Gibbons, London, for the encrusting sponges upon which many of the stamp collectors was used; this guide has the Hawaiian dorids feed. The shallow water areas advantage of being more accessible and less are protected from wave action and sediment expensive than other standard color guides, such deposition, but a fair amount of water exchange as those of Ridgeway. Patterns are described occurs at all tidal periods. with the prevailing lightest color used as the The majority of dorids for which we have background color on which darker pigment records of only one or two specimens were en­ forms patterns. Radular tooth counts are based countered at the shoreward edges of fringing on that row which is maximally developed reefs, or high on a dead reef platform east of (which usually occurs about one-third of the the reef at Ala Moana, Oahu, both areas which distance proximally from the distal tip of the border considerable depths of water. It would radular membrane); row counts are maximal, appear that these animals are inhabitants of deep including all those radular rows which are dis­ off-shore waters, and the collections of only one tinguishable. or two specimens may represent spawners. We have utilized as many of the species names Although represented by many species, the attributed to the Hawaiian Islands as was feasi­ Hawaiian dorids with few exceptions are not ble, avoiding in several instances names intro­ numerous, and the numbers which we have col­ duced for species in other Indo-West-Pacific lected are so small that they do not lend them- 174 PACIFIC SCIENCE, Vol. XXIII, April 1969 selves to statistical treatment. In order to give Doriopsis granulosa Pease, 1860 some indication of numbers and seasonal occur­ Fig. 1 rence, we have summarized the collection data Doriopsis granulosa Pease, 1860:32-33. in Table 1. Sandwich Islands [Hawaiian Islands]; Pruvot-Fol, 1947:109. DORIDACEA Doriopsilla granulosa (Pease) Bergh, 1905:147. The superfamily Doridacea is here recognized as encompassing that group of nudibranchs with DESCRIPTION: length, 4 to 11 mm; width, a middorsal anus which is usually encircled en­ 1 to 4 mm. The animal is oblong-ovate, rather tirely or partially by secondary branchiae. The rigid, convex above, and the margins of the group includes at least five feeding types in mantle are thin and discrete. The mantle is pale Hawaiian waters: rasping sponge-feeders, suck­ yellow to buff, occasionally with green spots ing sponge-feeders, opisthobranch-feeders, poly­ and/or a blue tinge middorsally; it is orna­ chaete-feeders, and forms which are usually mented with minute, irregular spicular granules. associated with ascidians. We have excluded The rhinophores are short, widely spaced, with from the Doridacea the genera Marionia, Bor­ 8 to 10 pale yellow lamellae. There are 8 or 9 nella, and Phyllidia, all of which diverge so far simply pinnate branchiae arranged in a semi­ from the characteristic dorid pattern in the circle; the branchiae, like the rhinophores, are anatomy of the digestive and reproductive sys­ pale yellow. The foot is pale yellow and non­ tems and in ecology that they are best considered bilabiate.