BIOLOGICAL INVESTIGATIONS OF THE DEEP SEA. 34. A NEW STARFISH HOST AND AN EXTENSION OF RANGE FOR THE COMMENSAL CRAB, MINYOCERUS ANGUSTUS (DANA, 1852) (CRUSTACEA: PORCELLANIDAE)l ROBERT H. GORE AND JOHN B. SHOUP Institute of Marine Sciences, University of Miami ABSTRACT Minyocerus angustus, a porcellanid crab commensal on the sea star, Luidia clathrata (Say), is here reported occurring on a new host, the nine- armed sea star, Luidia senegalensis (Lamarck). Specimens of the crabs are compared with descriptions given in the literature. The color of the crab in life and observations of its habit are described. The known range for M. angustus is extended from Isla Cubagua, Venezuela, 1300 miles (ca. 2000 km) north and west to Trujillo Harbor, Honduras. INTRODUCTION Members of the porcellanid genus Minyocerus live commensally on sea stars of the genus Luidia (Glassell, 1938; Haig, 1956). The occurrence of the western American species Minyocerus kirki on the serpent stars Amphipholis platydisca, Ophiothrix spiculata, and Ophiolepis grisea, as well as on Luidia columbia, L. phragma, and L. foliolata, has been noted by Haig (1960) in her work on eastern Pacific Porcellanidae. The eastern American species, M. angustus, has until now been found only on Luidia clathrata (Haig, 1956, 1962). Minyocerus angustus has been previously reported from Brazil (Haig. 1956, 1962, 1966), Venezuela (Haig, 1956), Surinam (Holthuis, 1959), and Limon Bay, Panama (Boone, 1930). Haig (1956) considered Boone's Porcellana rosamondae from Panama as probably identical with Minyo- cerus angustus but left the Panama record in question at that time. The present paper is a report of 6 specimens of Minyocerus angustus which were found living commensally on a new host, the nine-armed sea star Luidia senegalensis (Lamarck). Observations of the crab on its host are noted. In addition, a northwestern extension of the range for this crab is reported. We wish to thank Drs. Anthony J. Provenzano, Jr., Lowell P. Thomas, and Donald R. Moore, all of whom critically read the manuscript and made many helpful suggestions. Our thanks are also extended to Mr. Jerald A. Halpern who confirmed our identification of Luidia senegalensis. 1Contribution No. 870 from the Institute of Marine Sciences, University of Miami. This work was supported in part by Research Grant No. GN-l1244 from the Institute of General Medical Science. U. S. Department of Health, Education and Welfare; National Geographic Society-University of Miami Deep Sea Biological Program; and National Science Foundation Grant No. GB-3BOBin support of ship time. 1968] Gore & Shoup: Commensal Crab, Minyocerus angustus 241 COLLECTION DATA Two pairs of crabs, a large male and large female, and a small male and female, were found living on a single Luidia senegalensis (UMML 40. 182). The sea star, which measured 20 em from arm tip to center of disc, was collected by one of us (JBS) on 21 July, 1966, in 3 m of water in the harbor of Trujillo, Honduras, during a diving trip. The crabs were seen on the ventral surface of the sea star when it was excavated from the bottom of the harbor. The third pair of crabs was collected from a 15-cm (arm tip to center of disc) Luidia senegalensis (UMML 40.181) while the first author was participating on a cruise of the Institute of Marine Sciences' research vessel, JOHN ELLIOT PILLSBURY. These crabs were taken in a 10-foot otter trawl in 24 m of water, just offshore and west of Colon, Panama~ This location is only 15 km west of Limon Bay, Panama. It would confirm Boone's record of location if her species is indeed M. angustus as Haig (1956, 1966) suggested. Genus Minyocerus Stimpson, 1858 Minyocerus angustus (Dana), 1852 For previous records and synonymy, see Haig, 1956: 30; 1960: 193; 1962: 184; 1966: 354. All crustacean measurements refer to carapace length obtained with an ocular micrometer. Material Examined.-l ~, 5.3 mm; 1 lj>, 5.0 mm, ovigerous; commensal on Luidia senegalensis. Cruise P 6608, Station P-432, 9° 18.2N, 80° 03.3'W, 20 July, 1966; 24 meters; UMML 32.3357. 1 ~, 5.6 mm; 1 'i?, 5.6 mm, non-ovigerous; 1 i5, 2.77 mm; 1 'i?, 2.3 mm, non-ovigerous, all commensal on Luidia senegalensis. Trujillo Har- bor, Honduras, sand bottom, 21 July, 1966; 3 meters. Collected by John B. Shoup. UMML 32.3358. Remarks.-The specimens from Honduras and Panama are similar to each other. All have 3 frontal teeth, the median tooth being equal or very slightly longer than its neighbors. Rathbun's specimen (1900) was two- toothed frontally, the left tooth being much shorter than the right and with only a shallow lobe where the median tooth should be. Rathbun (loc. cit.) thought it possible that both median and left tooth had been broken prior to the last molt in her specimen and had not been renewed. Haig's (1956) specimens agreed with Dana's (1852) description and with Rathbun's specimen. Our specimens agree with both Dana's and Rathbun's descrip- tion, but do not completely agree with Boone's description. In Boone's specimens the carapace is wider posteriorly than anteriorly, and the median 242 Bulletin of Marine Science [18(1) ....: ]968] Gore & Shoup: Commensal Crab, Minyocerus angustus 243 frontal tooth is shorter relative to the two pre-orbital teeth. In her figure (I930, plate 21) she depicted two suprahepatic spines directly behind the eyes. We consider these to represent the left and right postorbital teeth respectively, which occur in all of our specimens and are located above the eyes but in the same plane of curvature as the median and pre-orbital teeth (Figs. 1 and 2). If the spines pictured by Boone are truly supra- hepatic, there is no mention of it in her description. As Haig (I 956) pointed out, the differences in width of carapace and lack of median frontal tooth are the only characters which separate Porcellana rosamondae from Minyocerus angustus. Thus, we concur with her suggestion that Boone's P. rosamondae is the same species as Minyocerus angustus. Haig, in a later paper (1966) classified P. rosamondae in the synonymy of M. angustus. Our specimens differ from all descriptions in one minor respect. The merus of the cheliped in both our Honduran and Panamanian crabs not only has a spine on the inner, upper, distal angle, but all of our specimens have a smaller, second spine or series of spinules on the dorsomedial margin of the merus (Figs. 1 and 2, A-B). The presence in our adult specimens of three more-or-less-equal spines located distally on the inner lateral margin of the carpus is apparently within the range of variation allowed for this species (Haig, ]960: 196). In our specimens, the outer surface of the chelipeds, the fingers, and the inner surface of the carpus were liberally covered with hair. The remaining appendages and the abdominal segments were less densely pubescent. The carapace is lightly covered with setae, especially the anterior, lateral, and posterior margins. This pubescence, while perhaps implied by other authors, was mentioned in earlier description only by Dana. Only minor variation was observed in color patterns (see Figs. 1, 2, and 3). The female from Panama molted aboard ship on July 21, and died on July 26. Both the molt and dead female were preserved in 70 per cent ethanol on board ship. The molt was later transferred to 10 per cent non-buffered formalin when the specimens reached the Institute. The preserved female (Fig. 2, B) has lost most of the reticulate pattern, becoming pale pinkish-tan with diffuse orange on both hepatic regions. The molt (Fig. 3, A), however, retains the reticulation which is similar to that seen in all other specimens examined. The color of the preserved molt which, as might be expected, differs from the color seen in life, is the same as described by Rathbun (loc. cit.) for the animals she examined. Presumably she was looking at alcohol- or formalin-preserved specimens. Haig's animals had only "a faint trace of color (remaining)," and these were also preserved specimens. Thus, while the true color may be lost, the reticulate pattern, for the most part, remains for some time. 244 Bulletin of Marine Science [18 (1) L968] Gore & Shoup: Commensal Crab, Minyocerus angustus 245 Color in Life.-The following color notes were made on the living crabs collected from Panama. The live crabs were strikingly colored. The overall hue was an ochreous yellow-grey with dark brown reticulations on the dorsal surface of the carapace, chelipeds, and walking legs. On both the chelipeds and walking legs, the dark brown reticulation ( = "marbling," [Rathbun, lac. cit.]) was more irregular, being less distinct than that on the carapace. The dactyls were a lighter, translucent grey. The antennules were a brilliant blue with bright yellow flagella. The extremely extensible eyestalks were the same ochreous yellow-grey. Chelae were a more or less uniform grey, less translucent than the dactyls of the walking legs. Examination under the microscope showed that the major reticulate pattern was further broken up into smaller, thinner, and less distinct reticulations over the entire dorsal area of the carapace. In the figures, the major pattern is shown darker than the more irregular reticulation. The entire pattern appears to be a disruptive one which blends well with the dark grey, tuberculous background of the sea star. It may function as protective coloration for the crabs if they move onto the dorsal area of the sea star. OBSERVATIONS OF THE CRAB ON ITS HOST The sea star collected by the PILLSBURY was the only one of several specimens of L.