A new species of Tomlinsonia Turquier, 1985 (Crustacea, Cirripedia, Trypetesidae) in hermit crab shells from the Philippines, and a new parasite species of Hemioniscus Buchholz, 1866 (Crustacea, Isopoda, Hemioniscidae)

Les femelles de T. mclaughlinae n. sp. atteignent des tailles dépassant 8 mm et forment, sur la columelle, un terrier qui s’étend vers l’apex de la coquille. Les mâles sont petits (0,4-0,7 mm), en forme de chaussure, et se trouvent attachés à la femelle sous la lèvre du manteau. L’espèce peut être distinguée de T. asymetrica de Madagascar en se basant sur les proportions des segments des cirri terminaux, la forme du labrum et la morphologie des pièces buccales.

Parmi les 31 spécimens de T. mclaughlinae n. sp. examinés, trois étaient parasités par des mâles au nombre de deux à six et/ou des femelles juvéniles d’une espèce nouvelle d’un isopode cryptonicien, décrit comme Hemioniscus pagurophilus n. sp. Les mâles de cette espèce peuvent être distingués de ceux d’ Hemioniscus balani balani Buchholz, 1866 en se basant sur la dentition de la plaque coxale et la forme du lobe médian ventral se trouvant entre les premiers pléopodes.

La description du nouvel isopode parasite implique la modification des diagnoses du genre Hemioniscus et de la famille Hemioniscidae; les neuf espèces d’épicarides, réparties dans trois familles, qui parasitent les balanes, sont passées en revue. C’est la première fois que des mâles du genre Tomlinsonia sont examinés et c’est également la première fois que des balanes acrothoraciques, parasités par des isopodes cryptoniciens, sont observés.

MOTS CLÉS Crustacea, Cirripedia, Tomlinsonia, Isopoda, Hemioniscus, balanes, bernard-l’ermite, symbiontes, parasites, espèces nouvelles. INTRODUCTION In the central Philippines, we recently discovered a species of burrowing trypetesid barnacle of the genus Tomlinsonia Turquier, 1985 in shells occupied by three species of Calcinus Dana, 1851 hermit crabs from the shallow subtidal zone of coral reef habitats. These specimens can clearly be placed in Tomlinsonia, rather than Trypetesa Norman, 1903 (the only other genus in this family), as they have protuberant “cushions” on the distal inner margin of all three pairs of terminal cirri, rather than only on the first two pairs as in Trypetesa (see Turquier & Carton 1976).

They also bear distinctly asymmetrical opercular bars (apertural lips), as opposed to the subequal opercular bars of Trypetesa spp. These specimens differ in several aspects from Tomlinsonia asymetrica (Turquier & Carton, 1976) from Madagascar, the only previously known species of the genus, and are described herein as a new species. Five of the Philippine specimens have associated dwarf males and this is the first report of males for Tomlinsonia.

Three female specimens of this new Tomlinsonia have the mantle cavity containing two to six cryptoniscoid isopods. Although the first report of cryptoniscoid isopods parasitizing acrothoracican barnacles was given by Turquier (1987, on Lithoglyptes stirni Turquier, 1987), those specimens were then only tentatively identified as perhaps belonging to a new genus near Hemioniscus Buchholz, 1866 or Scalpelloniscus Grygier, 1981, and have never been subsequently fully identified or described.

Identification of isopods that parasitize other crustaceans (known either as Epicaridea or Bopyroidea) can be a challenge as older descriptions are often lacking in key morphological details and many type specimens have been lost. These problems are particularly apparent when dealing with those epicarideans that parasitize barnacles, as most of the key morphological characters used to delimit species (and even genera and families) are found in the neotenous males that are externally indistinguishable from the cryptoniscid larvae.

Historically, however, authors have focused on describing the highly reduced, sac-like females and only superficially describing the males. Only relatively recently has there been a concerted effort to describe males at the level of detail needed to identify species and attempt to define genera on morphological characters rather than on an artificial framework of host specificity (e.g., Nielsen & Strömberg 1965, 1973a, b).

Identification of the Philippine cryptoniscoid parasites required a review of the nine species of epicarideans that parasitize barnacles distributed among three families: Hemioniscidae (six species on pedunculate and sessile Thoracica), Crinoniscidae (one species on sessile Thoracica), and Cryptoniscidae (two species of Liriopsis on Rhizocephala and two species of Scalpelloniscus on scalpellid Thoracica), as well as the monotypic genus Gorgoniscus Grygier, 1981 (family incertae sedis) from ascothoracicans.

Based on this review, we conclude that the Philippine cryptoniscoids from Tomlinsonia belong to an undescribed species of the genus Hemioniscus, but that both Hemioniscus and Hemioniscidae require some modification in diagnoses to accommodate the new species. METHODS Hermit crabs inhabiting gastropod shells were collected shallow subtidally (<5 m) in Aklan, Bataan, and Oriental Mindoro provinces of the Philippines from June to August 1997 and January to April 1999 (Williams 2002: fig. 1).

Hermit crabs were removed from shells after cracking with a mortar and pestle constructed of galvanized steel pipe (60 mm in diameter) and the shield length (SL) of host hermit crabs was measured using a vernier caliper or stage micrometer to the nearest 0.1 mm. Isopod size is given as total body length (anterior margin of head to posterior margin of pleotelson). Maximal length and width of complete barnacles were measured.

For SEM, fixed specimens were dehydrated in an ascending ethanol series followed by four changes of 100% ethanol. Drying was completed with a Samdri 795 Critical Point Drier. Dried specimens were mounted on an aluminum stub, coated with gold (EMS-550 Sputter coater), and viewed with a Hitachi S-2460N SEM.

Type specimens are deposited in the Zoological Reference Collection of the Raffles Museum of Biodiversity Research, Singapore (ZRC) and the National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA (USNM). Higher level classification follows Martin & Davis (2001). The simple, bifid and multifid projections on the inner and outer surfaces of the opercular bars have been variously referred to as spines (Turquier 1978), denticules (Watling 1989), scales (Kolbasov 1999) and teeth (Smyth 1986).

It is not clear if these structures are all modified setae with individual sockets or non-articulated cuticular extensions (homologous with spines or scales as defined by Watling 1989). However, they are definitely not “teeth” in any sense and we use the terminology of Watling (1989) to describe them. In the text we use the term “male” to refer to any cryptoniscid isopod not clearly in the process of metamorphosis into the definitive female phase.

It is not possible to distinguish larvae from males or even immature females at early stages of development and it is possible that at least one individual in each batch will become a female, but we cannot demonstrate this point through external examination of specimens. SYSTEMATICS Infraclass CIRRIPEDIA Burmeister, 1834 Superorder ACROTHORACICA Gruvel, 1905 Order APYGOPHORA Berndt, 1907 Family TRYPETESIDAE Stebbing, 1910 Genus Tomlinsonia Turquier, 1985