Decaphyllus
A genus of small Indo-Pacific hermit crabs related to Catapaguroides.
Decaphyllus is a genus of small hermit crabs belonging to the family Paguridae, distributed across the Indo-Pacific region. These crabs are considered closely related to the genus *Catapaguroides*, from which they are set apart by a specific set of physical traits: the structure of their walking legs, the form of the fourth pereopods, and the shape of the telson.
The genus was first described by Michèle de Saint Laurent in 1968, with *Decaphyllus spinicornis* designated as the type species. Originally, the genus contained three species, but subsequent taxonomic work has expanded this to eleven recognized species. The initial three were *D. spinicornis* from Japan, *D. similis* from Indonesia, and *D. janquai* from New Guinea and Indonesia. Later revisions included two Indonesian species added by Patsy Ann McLaughlin in 1997—*D. barunajaya* and *D. maci*—and a further six species described by Komai and Rahayu in 2013.
Morphologically, *Decaphyllus* species are small pagurids. They typically have eight to ten pairs of phyllobranchiate gills, with no pleurobranch above the fourth pereopod. The shield is well calcified or partly decalcified down the middle, with strongly convex sides, while the rear part of the carapace is weakly calcified or membranous. The crista dentata on the third maxilliped is reduced and lacks an accessory tooth. Key diagnostic features separating them from *Catapaguroides* include unarmed but setose dactyli on the walking legs, non-chelate fourth pereopods, and a telson without a transverse suture, which usually has strongly asymmetrical rear lobes bearing two to four spines. The dactylus of the fourth pereopod is covered in dense setae that hide the terminal claw. The fourth pereopods are simple rather than semichelate, and the sternite of the fifth pereopods is entire, not split into two lobes. Other traits include dorsal or dorsomesial rows of long setal tufts on the ocular peduncles, no long dorsolateral plumose setae on the ultimate segment of the antennular peduncle, and spiniform armature or protuberances on the meri and ischia of the chelipeds. The right cheliped is usually slightly longer and stouter than the left, though both are similar in shape.
Sexual characteristics differ between males and females.
Quick Facts
- Taxon
- Decaphyllus
- Type Species
- Decaphyllus spinicornis
- Type Species Authority
- de Saint Laurent, 1968
Facts from the source article.
Lore & Background
The genus Decaphyllus was erected by Michèle de Saint Laurent in 1968, with Decaphyllus spinicornis as its type species. The original treatment established three Indo-Pacific species and regarded the genus as closely related to Catapaguroides. Patsy Ann McLaughlin later emended the generic diagnosis and added two Indonesian species, Decaphyllus barunajaya and Decaphyllus maci. In 2013, Komai and Rahayu described a further six species, bringing the total number of recognised species to eleven.
Morphologically, Decaphyllus is characterised by eight to ten pairs of phyllobranchiate gills, with the pleurobranch above the fourth pereopod absent. The shield is well calcified or partly decalcified medially, with strongly convex lateral margins, while the posterior carapace is weakly calcified or membranous. The crista dentata of the third maxilliped is reduced and lacks an accessory tooth. The genus is distinguished from Catapaguroides by the unarmed but setose dactyli of the ambulatory legs, the non-chelate fourth pereopods, and the form of the telson. The telson lacks a transverse suture and usually has strongly asymmetrical posterior lobes armed with two to four spines.
Variation occurs within the genus in the development of the arthrobranchs of the third maxilliped, which may be small, vestigial, or absent. McLaughlin noted that this character is too variable to define the genus on its own and must be considered together with other morphological features. In males, the right sexual tube is very long, directed from right to left beneath the thorax and recurved anteriorly, while the left sexual tube is shorter and directed in the opposite direction. Females have a single gonopore on the left side.
Reader's Guide
Decaphyllus holds significance as a genus that illustrates the complexity of morphological variation within the Paguridae. The taxonomic history, from de Saint Laurent's original three species to the current eleven recognised species, shows how careful revision and the addition of new material can expand understanding of a group. The genus is notable for the debate over the taxonomic weight of the arthrobranchs on the third maxilliped, which McLaughlin found to be too variable to justify generic separation on its own. This underscores the importance of considering a broad suite of characters in crustacean taxonomy. Ecologically, Decaphyllus species occupy a range of marine benthic habitats from shallow coral reefs to deeper sublittoral bottoms, with most species known from depths greater than 50 m. The genus was first recorded from the Philippines in the 2013 revision. No detailed behavioural synthesis has yet been published, and most ecological information comes from collection data associated with taxonomic studies. The genus continues to be a subject of taxonomic interest, particularly in relation to its close relative Catapaguroides.
Did You Know?
- Decaphyllus spinicornis is the type species of the genus.
- The genus originally comprised three species but now includes eleven recognised species.
- Decaphyllus litoralis is unusual in inhabiting shallow coral reefs at depths of 4–18 m.
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