The internal parasite Dendrogaster dichotomus, found in starfishes, from here.

Belongs within: Pancrustacea.
Contains: Thoracica.

The Thecostraca is a crustacean clade containing barnacles (Thoracica) and their close relatives. Within the clade, Ascothoracida and Rhizocephala are parasitic lineages, while Acrothoracica are sessile filter-feeders that burrow into the surface of an animal host. Hansenocaris is known only from juvenile specimens; adults are unknown but are perhaps also parasitic. Despite their divergent appearance as adults, members of the Thecostraca are united by characters of the larvae. The Acrothoracica, Rhizocephala and Thoracica are further united in a clade Cirripedia by features including modification of the antennules in the cypris larva for use in exploratory walking while seeking a settlement site, and in permanent cementation using glandular secretions. In contrast, cypris larvae of the Ascothoracida attach to their intended host by means of direct grasping with the antennules.

See also: The secret of Y-larvae; Forcing out the secret.

Synapomorphies (from Grygier 1987): Nauplii lacking post-maxillular limb buds; compound eyes with less than four crystalline cones per ommatidium; strongly developed frontal filaments associated with eyes.

    |  i. s.: Rhamphoverritor LSE13
    |--Hansenocaris [Facetotecta] G87
    |    |--H. acutifrons G87
    |    |--H. hanseni [=Proteolepas hanseni] G87
    |    |--H. pacifica G87
    |    `--H. rostrata G87
    |--Ascothoracida G87
    |    |  i. s.: Ulophysema oeresundense Brattström 1936 BK77, H75
    |    |         Waginella sandersi G87
    |    |         Parascothorax G87
    |    |         Gorgonolaureus muzikae G87
    |    |         Endosacculus Voigt 1959 H75
    |    |           `--*E. moltkiae Voigt 1959 H75
    |    |--Laurida MD01
    |    |    |--Lauridae MD01
    |    |    |--Petrarcidae MD01
    |    |    `--Synagoga Norman 1888 LS02 [Synagogidae MD01]
    |    `--Dendrogastrida MD01
    |         |--Ctenosculum Heath 1910 BR05 [Ctenosculidae MD01]
    |         |--Ascothorax BK77 [Ascothoracidae MD01]
    |         |    `--A. ophioctenis BK77
    |         `--Dendrogaster BK77 [Dendrogastridae MD01]
    |              |--D. astericola BK77
    |              |--D. dichotomus BK77
    |              |--D. dogieli BK77
    |              |--D. murmanensis [=Myriocladus murmanensis] BK77
    |              `--D. rimskykorsakowi BK77
    `--Cirripedia G87
         |  i. s.: Mitella spinosa O81
         |         Epopella plicata HS01
         |         Notobalanus vestitus HS01
         |         Notomegabalanus decorus HS01
         |         Lepadites Blumenbach 1803 TMNZ64
         |         Pentalasmis vitrea H04
         |         ‘Amalthea’ coxi Sowerby 1908 H08
         |--Thoracica LS02
         |--Acrothoracica LS02
         |    |--Trypetesa Norman 1903 H75 [Apygophora, Trypetesidae MD01]
         |    `--Pygophora MD01
         |         |--Cryptophialidae MD01
         |         `--Lithoglyptidae MD01
         `--Rhizocephala LS02
              |  i. s.: Boschmaella japonica GLT03
              |--Akentrogonida GLT03
              |    |--Clistosaccidae [Sylidae, Sylonidae] MD01
              |    |--Duplorbidae MD01
              |    |--Mycetomorphidae MD01
              |    |--Polysaccidae MD01
              |    |--Chthamalophilidae MD01
              |    `--Thompsoniidae MD01
              `--Kentrogonida GLT03
                   |  i. s.: Peltogasterella GLT03
                   |--Peltogastridae MD01
                   |--Lernaeodiscus G87 [Lernaeodiscidae MD01]
                   |    `--L. porcellanae G87
                   `--Sacculinidae GLT03
                        |--+--Loxothylacus GLT03
                        |  |    |--L. panopaei GLT03
                        |  |    `--L. texanus RS10
                        |  `--+--Heterosaccus GLT03
                        |     |    |--H. californicus GLT03
                        |     |    `--H. dollfusi GLT03
                        |     `--Sacculina GLT03
                        |          |--*S. carcini GLT03
                        |          |--S. anceps B02
                        |          `--S. pinnotherae GLT03
                        `--+--+--‘Sacculina’ sinensis GLT03
                           |  `--+--‘Sacculina’ leptodiae GLT03
                           |     `--+--‘Sacculina’ confragosa GLT03
                           |        `--‘Sacculina’ oblonga GLT03
                           `--Polyascus Glenner, Lützen & Takahashi 2003 GLT03
                                |  i. s.: ‘Sacculina’ bourdoni GLT03
                                |         ‘Sacculina’ gibba GLT03
                                |         ‘Sacculina’ imberbis GLT03
                                |         ‘Sacculina’ insueta GLT03
                                |         ‘Sacculina’ nigra GLT03
                                |         ‘Sacculina’ robusta GLT03
                                |         ‘Sacculina’ schmitti GLT03
                                |--P. gregaria [=Sacculina gregaria] GLT03
                                `--+--*P. polygenea (Lützen & Takahashi 1997) [=Sacculina polygenea] GLT03
                                   `--P. plana [=Sacculina plana] GLT03

Boring: Trypetesa caveata Tomlinson 1963 H75

*Type species of generic name indicated


[BK77] Barel, C. D. N., & P. G. N. Kramers. 1977. A survey of the echinoderm associates of the north-east Atlantic area. Zoologische Verhandelingen 156: 1–159.

[BR05] Bouchet, P., & J.-P. Rocroi. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1–2): 1–397.

[B02] Boyko, C. B. 2002. A worldwide revision of the recent and fossil sand crabs of the Albuneidae Stimpson and Blepharipodidae, new family (Crustacea: Decapoda: Anomura: Hippoidea). Bulletin of the American Museum of Natural History 272: 1–396.

[GLT03] Glenner, H., J. Lützen & T. Takahashi. 2003. Molecular and morphological evidence for a monophyletic clade of asexually reproducing Rhizocephala: Polyascus, new genus (Cirripedia). Journal of Crustacean Biology 23: 548–557.

[G87] Grygier, M. J. 1987. New records, external and internal anatomy, and systematic position of Hansen’s y-larvae (Crustacea: Maxillopoda: Facetotecta). Sarsia 72: 261–278.

[H04] Haeckel, E. 1899–1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig und Wien.

[H75] Häntzschel, W. 1975. Treatise on Invertebrate Paleontology pt W. Miscellanea Suppl. 1. Trace Fossils and Problematica 2nd ed. The Geological Society of America: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[H08] Hedley, C. 1908. Studies on Australian Mollusca. Part X. Proceedings of the Linnean Society of New South Wales 33: 456–489, pls 7–10.

[HS01] Hayward, B. W., A. B. Stephenson, M. S. Morley, W. M. Blom, H. R. Grenfell, F. J. Brook, J. L. Riley, F. Thompson & J. J. Hayward. 2001. Marine biota of Parengarenga Harbour, Northland, New Zealand. Records of the Auckland Museum 37: 45–80.

[LS02] Lange, S., & F. R. Schram. 2002. Possible lattice organs in Cretaceous Thylacocephala. Contributions to Zoology 71 (4): 159–169.

[LSE13] Legg, D. A., M. D. Sutton & G. D. Edgecombe. 2013. Arthropod fossil data increase congruence of morphological and molecular phylogenies. Nature Communications 4 (2485): 1–7.

[MD01] Martin, J. W., & G. E. Davis. 2001. An updated classification of the Recent Crustacea. Natural History Museum Los Angeles County, Science Series 39: 1–124.

[O81] O'Brien, C. O. 1981. A. A. Book of New Zealand Wildlife: A guide to the native and introduced animals of New Zealand. Lansdowne Press: Auckland.

[RS10] Regier, J. C., J. W. Shultz, A. Zwick, A. Hussey, B. Ball, R. Wetzer, J. W. Martin & C. W. Cunningham. 2010. Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences. Nature 463: 1079–1083.

[TMNZ64] Teichert, C., R. C. Moore & D. E. Nodine Zeller. 1964. Rhyncholites. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt K. Mollusca 3. Cephalopoda—General Features—Endoceratoidea—Actinoceratoidea—Nautiloidea—Bactritoidea pp. K467–K484. The Geological Society of America and the University of Kansas Press.

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